Technical Field

This invention relates to an in-line exercise measurement device for measuring physical movements of a user, particularly though not exclusively for use with fitness equipment such as strength training equipment including but not limited to cable machines resistance bands, free weights, and body weights.

Background Art

In recent years, the health and fitness industry has exploded in popularity. In 2019, it was estimated that the global fitness industry was valued at approximately $1 billion US dollars. Membership to health and fitness centres such as gyms as well as sports clubs increases every year. In the wake of the COVID-19 pandemic, the public are increasingly aware of the importance of physical fitness.

Physical exercise can also be incredibly important for medical purposes, particularly in the field of physical rehabilitation. Many people sustain significant physical injuries by virtue of their work or lifestyle, including athletes and professional sportspersons or those that acquire injuries in the line of duty such as police officers, fire fighters, service personnel and military veterans.

As well as an increase in interest in carrying out physical exercise, there has also been an ever-increasing interest in fitness tracking devices, both for leisure and medical purposes. Many people wear commercially available fitness trackers such as an Apple Watch® or FitBit® (or any other similar devices) when performing exercise - and potentially throughout their daily lives - that generate insights on their activities using various sensors within that device. For example, such devices might provide information on the user's heart rate, oxygen levels, calories burnt, step count, and so on.

Such devices are typically best suited for cardiovascular activities such as running, rowing, cycling, and swimming. However, these devices are often not well suited for generating insights in strength-based exercises, in particular the types of physical activities in which a user makes use of fitness equipment like cable machines in which a user applies a force, such as a pulling force, to a handle attached to a cable that is affixed to a weighted load, often via one or more pulleys. Exercises that make use of resistance bands (i.e. a large elasticated strap or band) may also be difficult to characterise using conventional fitness trackers.

The Applicant has appreciated that it would be beneficial to have a device that can measure the force a user is applying when carrying out exercises using such equipment, and potentially other metrics in addition to the force. In particular, it would be beneficial to have a device that could be retrofitted to fitness equipment that can provide an accurate measurement of force (e.g. an in-line tensile force) to aid in the quantification and subsequent assessment of a person's movements. It would be particularly advantageous for such a device to be lightweight, low cost, sufficiently robust to withstand relatively large loads, and that does not significantly alter the user's interaction with the fitness equipment.

While there are in-line tensile force measurement devices that are known in the art perse, there are a number of disadvantages associated with such known devices. Many devices make use of the extension of a spring and make a measurement using Hooke's law to determine the tensile force being applied by the user based on the extension of the spring. However, the use of such springs negatively impacts a user's movements, as there is an additional component in line that is extending and/or contracting, impacting the effective responsiveness of the fitness equipment to the user's movements due to the reduction in stiffness in the system. Such a device may also lead to unwanted changes to the user's movement, e.g. by allowing a user's wrist to bend or flex when it should have been held straight while performing a particular exercise.

Other devices, known in the art perse, can be physically very large and/or heavy, reducing their portability. In other arrangements, the device could be built into the equipment itself, which means that each individual apparatus would need its own device if measurements from that device are required, which increases the cost and complexity of such devices and restricting the number of devices available to the user if they need to track their strength movements.

The Applicant has appreciated that having a small, lightweight device that generally can be retrofitted to any suitable fitness equipment would advantageously permit the device to easily be carried to a facility with the fitness equipment. For example, a user may keep the device in their sports bag that they take with them to the gym; a physiotherapist can take the device with them between different sites that they treat clients at; or a coach of a sports team may be able to carry a number of such devices to a team training session. Similarly, such a device can be moved between different types of equipment, e.g. between one cable machine used for a bicep workout and another cable machine used for a calf workout.

Such a device may be used when carrying out a wide range of different physical exercises. However, while measuring the tensile force being applied by a user (e.g. with a cable machine or resistance band) is beneficial for characterising certain movements or exercises carried out by the user, this may not be suitable for the characterisation of all movements or exercises. In particular, some exercises involve forces that are not necessarily proportional to linear displacement, i.e. that don't follow Hooke's law.

The Applicant has appreciated that it would be highly beneficial to have a device that can characterise a wider range of physical exercise movements than conventional devices that are known in the art perse.

Summary of the Invention

When viewed from a first aspect, embodiments of the present invention provide an in-line exercise measurement device for use with fitness equipment, the device comprising: first and second coupling portions onto which fitness equipment is detachably couplable, the first and second coupling portions being aligned along a first axis; a connecting portion extending along a second axis parallel to said first axis, the connecting portion being rigidly connected at a first end thereof to the first coupling portion, and rigidly connected at a second end thereof to the second coupling portion; a thin film strain gauge mechanically coupled to the connecting portion, said thin film strain gauge being arranged to deform in response to an externally applied in-line tensile force along the second axis, wherein the strain gauge is further arranged to generate a first signal dependent on the deformation of said strain gauge; an ancillary sensor arrangement arranged to generate a second signal dependent on at least one of: an externally applied acceleration being applied to the device; an externally applied angular rate being applied to the device; and an altitude of the device; and a wireless communications module configured to transmit the first and second signals to an external electronic device.

The first aspect of the invention extends to a fitness equipment system comprising first and second fitness equipment; and the device of the first aspect of the invention. Thus, the first aspect of the invention extends to a fitness equipment system comprising: first and second fitness equipment; and an in-line exercise measurement device for use with fitness equipment, the device comprising: first and second coupling portions aligned along a first axis; a connecting portion extending along a second axis parallel to said first axis, the connecting portion being rigidly connected at a first end thereof to the first coupling portion, and rigidly connected at a second end thereof to the second coupling portion; a thin film strain gauge mechanically coupled to the connecting portion, said thin film strain gauge being arranged to deform in response to an externally applied in-line tensile force along the second axis, wherein the strain gauge is further arranged to generate a first signal dependent on the deformation of said strain gauge; an ancillary sensor arrangement arranged to generate a second signal dependent on at least one of: an externally applied acceleration being applied to the device; an externally applied angular rate being applied to the device; and an altitude of the device; and a wireless communications module configured to transmit the first and second signals to an external electronic device; wherein the first and second fitness equipment are detachably couplable to the first and second coupling portions of the device.

The first aspect of the invention also extends to a method of monitoring a physical movement applied to fitness equipment by a user using the device of the first aspect of the invention, the method comprising: receiving the first and second signals; determining metrics corresponding to the in-line tensile force and the at least one of: an externally applied acceleration being applied to the device; an externally applied angular rate being applied to the device; and an altitude of the device; and using said metrics to generate a measurement result corresponding to the physical movement.

The first aspect of the invention further extends to a non-transitory computer-readable medium comprising instructions that, when executed by a processor, cause the processor to carry out a method of monitoring a physical movement applied to fitness equipment by a user using the device of the first aspect of the invention, the method comprising: receiving the first and second signals; determining metrics corresponding to the in-line tensile force and the at least one of: an externally applied acceleration being applied to the device; an externally applied angular rate being applied to the device; and an altitude of the device; and using said metrics to generate a measurement result corresponding to the physical movement.

The first aspect of the invention yet further extends to a computer software product comprising instructions that, when executed by a processor, cause the processor to carry out a method of monitoring a physical movement applied to fitness equipment by a user using the device of the first aspect of the invention, the method comprising: receiving the first and second signals; determining metrics corresponding to the in-line tensile force and the at least one of: an externally applied acceleration being applied to the device; an externally applied angular rate being applied to the device; and an altitude of the device; and using said metrics to generate a measurement result corresponding to the physical movement.

The method may comprise receiving the first and second signals from the wireless communications module.

Thus it will be appreciated that, in accordance with the first aspect of the invention, there is provided a device that can be fitted 'in-line' on fitness equipment that sense both an inline tensile force and at least one of an externally applied acceleration, an externally applied angular rate; and an altitude of the device - as outlined in further detail below, the device may sense multiple of these. Where multiple such parameters are measured by the ancillary senor arrangement, the second signal may be a composite signal dependent on each (e.g. the signal may be a data signal comprising information about each) or there may be multiple second signals, each dependent on at least one of these parameters.

Advantageously, the ancillary sensor arrangement provides for 'sensor fusion', in which the measurements acquired from the sensor(s) of the ancillary sensor arrangement can be used to enhance the measurement from the thin-film strain gauge. The resulting characterisations of the user's movements may be more accurate than would be possible with using only one of the sensors individually.

Embodiments of the present invention provide a device that can be positioned in-line with fitness equipment, which can be used to measure forces applied by a user during exercise. For example, the device may measure the forces associated with a user's movement during an exercise, e.g. a repetition (commonly referred to more simply as a 'rep') of a given exercise on a cable machine or other fitness equipment. Multiple reps may be carried out one after another in a 'set' before the fitness equipment is returned to a resting position (during which time the user may also rest or carry out a set of reps of a different exercise). The specific configuration of this device enables for a lightweight, low-cost solution that is robust enough to be used with relatively large loads (e.g. when lifting weights). As is outlined in further detail below, a device in accordance with embodiments of the first aspect of the invention is capable of measuring the performance of a wider variety of exercises than conventional devices that are known in the art perse.

In addition to the strain gauge(s), the ancillary sensor arrangement contains one or more additional sensors that may generate respective signals, which may be transmitted to the external electronic device by the wireless communications module.

In some embodiments, the ancillary sensor arrangement comprises one or more accelerometers arranged to generate respective acceleration signals corresponding to an applied acceleration. Typically each accelerometer measures acceleration in a single linear direction, and so three accelerometers may be used to determine acceleration components in three dimensions.

The acceleration signal(s) may typically contain a component attributable to the acceleration due to gravity. By using the acceleration signals, this component can be removed such that the force of gravity can be removed from the measured forces being exerted on the device. This may advantageously simplify characterisations of the user's movements.

In some potentially overlapping embodiments, the ancillary sensor arrangement comprises one or more gyroscopes arranged to generate respective angular rate signals corresponding to an applied angular rate (i.e. rotational speed). Typically each gyroscope measures an angular rate in a single rotational direction, and so three gyroscopes may be used to determine angular rate components in three dimensions.

The angular rate signal(s) from the gyroscopes may be used to determine an orientation of the device. If the starting orientation is known, then tracking the angular rate allows the orientation of the device to be known.

Additionally, or alternatively, the device may comprise a magnetometer arranged to generate a magnetic field signal corresponding to a magnetic field. It will be appreciated that the magnetic field of the Earth can be used to determine orientation. Typically, the absolute orientation of the device may be determine through the use of both accelerometers and either gyroscopes and/or a magnetometer. The accelerometers can be used to determine which way is 'down' by determining the direction of acceleration due to gravity. When the direction of gravity is known (which may be determined ahead of time but need not be), a magnetometer can be used to determine the yaw around that axis, and/or gyroscopes can be used to determine changes in angular orientation over time from a known starting orientation, as outlined above. The direction of gravity may be determined first, however in practice it is possible to take the accelerometer and magnetometer readings simultaneously and use that to determine the reference orientation, and then combine that noisy-but-drift-free reference orientation with the noise-free-but drift-prone gyroscope values to form an estimate of the orientation.

Where accelerometers and gyroscopes are provided - e.g. in an inertial measurement unit (IMU) package as outlined below - the orientation of the device may be determined from the acceleration signals and angular rate signals using a Kalman filter, quaternion integration and gradient descent, or other similar methods that are known in the art per se.

Where provided, the accelerometer(s) and/or gyroscope(s) may be individual components or modules, however the ancillary sensor arrangement may comprise an inertial measurement unit (IMU). It will be appreciated that an IMU is a package which contains a combination of accelerometers and/or gyroscopes. In a particular set of embodiments, the IMU comprises a three-axis accelerometer arrangement and a three-axis gyroscope arrangement.

In some further potentially overlapping embodiments, the ancillary sensor arrangement comprises one or more barometers arranged to generate respective signals corresponding to a measured air pressure. This measured air pressure may be used to determine the device's altitude, i.e. vertical position. Thus in a preferred set of embodiments, the ancillary sensor arrangement is arranged to generate a second signal dependent on at least an altitude of the device. It will be appreciated that the signal produced by a barometer is dependent on the altitude of the device because it is dependent on the air pressure, which is in turn dependent on the altitude - i.e. it provides a proxy measure of altitude as outlined elsewhere herein.

The respective signal(s) provided by such accelerometers, gyroscopes, and/or barometers (as appropriate) may be used in conjunction with the tensile force measurement provided by the strain gauge(s) to enhance the characterisation of a given movement by the user, by providing 'spatial quantification ¹ of that movement. For example, strain gauge measurements may provide an indication of the tensile force being applied by a user, whereas the accelerometer, gyroscope, and/or barometer measurements may provide indications of a change of direction within a rep, a duration of a rep, a speed or velocity of a rep, etc. Combining this spatial quantification with the measured tensile load may advantageously allow for a more accurate assessment.

The Applicant has appreciated that it is highly beneficial to be able to count the number of reps (i.e. cycles) of various exercises performed using the device. A single rep may be characterised as a displacement from a starting position, optionally a hold at the fully displaced position, and finally a controlled return to the initial position. Different types of exercise may, however, have different profiles of force against displacement. To achieve this, the Applicant has appreciated that it is useful to obtain measurements of more than just the in-line tensile force for measuring certain types of exercises, where the additional measurements that are particularly useful depend on the particular physical movement being carried out and/or the equipment which the device is being used with.

The device may be operated in different modes of operation corresponding to different types of exercise.

In some embodiments, when operated in a first mode, the device may be used during some exercises in which the force applied by the user is proportional to displacement. This is true for fitness equipment that follows Hooke's law. For example, where the device is being used with a resistance band, the applied force is directly proportional to the extension of the resistance band (because it is elastic). With an elastic load, the displacement can therefore be calculated directly from the measurement of force, which can be obtained from the thin-film strain gauge. Any equipment that obeys Hooke's law - meaning it is elastic, like a spring or resistance band - will have a linear relationship between force and distance, meaning the reps appear as clear peaks in the first signal.

In order to measure reps in this first 'elastic' scenario, the first signal generated by the thin- film strain gauge may, in a set of embodiments, be passed through a first processing stage.

The first processing stage may, in some embodiments, comprise a low pass filter to generate a filtered first signal. The (filtered) first signal may then be passed to a peak detector which is configured to generate a peak signal indicative of peaks in an amplitude or power of the signal, i.e. the points at which the force is maximal - this corresponds to the 'top' of the rep being measured. The (filtered) first signal may also - e.g. in parallel - be passed to a threshold detector which is configured to generate a fall signal indicative of when an amplitude or power of the (filtered) first signal falls below a threshold value - this is to ensure force falls to around zero, which is the 'bottom' of the rep being measured.

In some embodiments, a repetition counter is configured to receive a peak signal from the peak detector and/or a fall signal from the threshold detector, and to increment a repetition count value upon determining from said peak and/or fall signals that a repetition has been completed by the user. In some embodiments, the repetition counter may be configured to increment the repetition counter based on the fall signal alone, however in preferred embodiments the peak signal is also used by the repetition counter (i.e. the force must reach a peak value and return to the specified 'floor' level for a rep to be counted).

Thus the first processing stage may comprise the low pass filter, the peak detector, the threshold detector, and/or the repetition counter. In some embodiments, the first processing stage may be included within the device. If so, any of the resultant signals (i.e. the intermediate processed signals from these components or the final output from the repetition counter) may be communicated to the external electronic device via the wireless communications module in addition to, or instead of, the 'raw' first signal, potentially with further processing carried out on the external electronic device or some further device or system. In a set of potentially overlapping embodiments, the work done during a repetition may be obtained from the first signal. In a particular set of embodiments, a second processing stage is configured to: obtain a tensile force value from the first signal; divide the tensile force value by a stiffness value to obtain an extension signal; differentiate the extension signal to obtain an extension delta signal; when the extension delta signal is greater than zero, integrate a product of said extension delta signal and the tensile force value to obtain a work done value. The second processing stage may, in some embodiments, be included within the device. However, embodiments are envisaged in which the tensile force value, the extension signal, and/or the extension delta signal are transmitted to the external electronic device via the wireless communications module, with the rest of the process being conducted on the external electronic device or some other device or system.

In some embodiments, when operated in a second mode, the device may be used during some other exercises, such as exercises that use free weights, body weights, and/or cable machines, that may have a force profile that is proportional to acceleration. The Applicant has appreciated that if the fitness equipment (e.g. a free weight) is not put down during a set, then the force does not fall to zero because a force is required to hold the weight above the ground. This means the force applied mainly stays in the vicinity of the weight of the object being lifted but has peaks when the object is accelerating and troughs where the object is decelerating. In the case of a slow, controlled rep, there typically will be only a small variation in the force exerted (force due to inertia, as the mass accelerates or decelerates at the beginning or the end of a rep). In the case where an exercise is being performed at a high speed, these inertial forces may be more significant. Such a profile changes significantly with the speed at which the exercise is performed.

The user may put the weight entirely down, meaning that the measured force falls to zero, or the user may cycle between two different heights, meaning that the force does not fall to zero. In the scenario of weightlifting, measurement of the altitude of the device provides a measurement by which the change in height of the device can be estimated, and therefore the vertical displacement can be estimated. This altitude measurement may be obtained directly, however in some embodiments the ancillary sensor arrangement comprises a barometer arranged to generate an air pressure signal dependent on the altitude of the device. The Applicant has appreciated that a barometer (i.e. an atmospheric pressure sensor) can therefore be used to provide a proxy measurement of the altitude of the device, and therefore its vertical displacement. When operating in this second mode, the device may determine the work done from the estimate of the weight (obtained from the thin-film strain gauge) and the estimate of the vertical displacement - the change in height - of the device, specifically the work done in this scenario is equal to the product of the force (weight) and vertical displacement (change in height).

The force measurement used for determining work done in this second mode may be obtained directly from the thin-film strain gauge. However, in a particular set of embodiments, a low pass filter may be used to obtain a filtered first signal by filtering the output of the thin-film strain gauge, as outlined previously in respect of a set of embodiments having the first processing stage. This may be a different low pass filter that produces an independent filtered first signal to the low pass filter associated with the first processing stage discussed previously.

The air pressure signal from the barometer may be input to a third processing stage configured to determine an altitude value from the air pressure signal. This may be achieved using barometric equations, in a manner known in the art per se. The altitude value therefore provides an estimate of the height of the device. The Applicant has appreciated that this estimate of the height is typically drift -free but potentially noisy - these potential drawbacks are overcome in certain embodiments outlined below.

The third processing stage may, in some embodiments, also receive one or more correction signals, which may, in some such embodiments, comprise a temperature signal from a temperature sensor and/or a humidity signal from a humidity sensor. Where these sensors are provided, the ancillary sensor arrangement may comprise the temperature sensor and/or humidity sensor. The third processing stage may use the temperature and/or humidity signals (as appropriate) to correct for variations in the air pressure due to temperature and/or humidity as appropriate (which might otherwise cause inaccuracies in the determined altitude).

A fourth processing stage may be configured to receive acceleration signal(s) from the accelerometer(s) and a signal indicative of the orientation of the device. The signal indicative of the orientation of the device may be acquired from gyroscope(s) or magnetometer(s) within the device, e.g. within the ancillary sensor arrangement, as appropriate. The fourth processing stage may use the acceleration and orientation signals to determine a vertical linear acceleration value. In other words, the measured acceleration and orientation of the device are used to determine the device's linear velocity in the vertical direction (i.e. the rate at which it is changing height or altitude).

The vertical linear acceleration value may then be subjected to a double integration process - which may be carried out by an integrator - in order to obtain a second altitude value. This second altitude value provides an additional estimate of the height of the device, where this second estimate is lower in noise but more prone to drift than the estimate from the barometer.

The vertical linear acceleration value may be subjected to integration and linear regression to determine velocity values. These values can help optimise rep counting and be combined with force (the multiplicative product of mass and acceleration) values for power readings. A further integration may then generate a second altitude value. By applying linear regression, which may be reactive to particular modes of repetitions (e.g. frequency, speed, etc.), the velocity profile can be corrected to provide more accurate outputs against time. By implementing iterative coefficients and machine learning, further correction of the velocities may be achieved.

While the work done may be obtained by multiplying the tensile force measurement (from the thin-film strain gauge) and altitude value, in a particular set of embodiments the altitude value (potentially corrected for temperature and/or humidity variation as above) and the second altitude value (obtain from the vertical linear acceleration value) may be combined, e.g. by a combination unit or processor, in order to generate a refined altitude value. The refined altitude value may provide an improved estimate of the height by combining the low noise but drift-prone acceleration-based estimate with the noisy but drift-free barometer-based estimate. The refined altitude value may be multiplied by the force value obtained from the (filtered) first signal from the thin-film strain gauge to obtain the work done when the device is operated in this second mode.

The means that produces the refined altitude value, which may be a combination unit or processor, may provide feedback on the velocity and/or position of the device to the integrator that performs the double integration process.

The first and second altitude values may otherwise be used independently of one another.

In order to obtain a repetition count in this second mode, the estimate of the height may be used to determine the top and bottom of each rep, where these can be counted (e.g. by incrementing a repetition count value after each cycle in height). By comparing the (refined) estimate of the height to suitable upper and lower threshold values, the completion of each rep may be detected. The selection of these upper and lower threshold values may be obtained experimentally or set during a calibration process.

In some embodiments, the device may be operated in a third mode, in which the device may be used with exercises that may involve more complex force profiles. Fitness equipment such as rowing machines have a more complex force profile that does not have a simple relationship to displacement, velocity, or acceleration, however the majority exercises have periods of higher force alternating with periods of lower force meaning that the number of reps can be counted without knowing the relationship between force and displacement, velocity, and/or acceleration. The Applicant has appreciated that a barometer may provide a particularly accurate indicator of change in direction under such circumstances as it may detect movements having a slight incline or decline (i.e. leading to a change in height of the device). If a movement is purely horizontal, then an IMU may be needed to characterise the movement instead.

If the movement is repetitive and involves changes in orientation, it may be determined that the device is moving between two different orientations, and that can be used to count reps. In a slow, purely horizontal, linear movement, with a constant force, detection of reps may be more difficult. In this case, the user may be prompted to mount the device on the relevant fitness equipment (e.g. a cable) above the weight but before the pivot point of the machine so that the device travels vertically, and therefore the motion can be captured, e.g. by the barometer.

Alternatively Fourier analysis may be used to look for signals within an expected range (e.g. if a repetition is performed over the course of 2 seconds, a peak would be expected in the overall magnitude of acceleration at around 0.5 Hz.

The Applicant has appreciated that the device may also be used for measuring exercises that do not involve tensile forces. For example, a user may hold the device or attach it to a limb while performing certain body weight exercises, and the outputs from the ancillary sensor arrangement may be used alone to count the number of reps performed while the tensile force applied is negligible or zero.

As outlined above, the different modes of operation available to the device may be useful for particular types of exercise being carried out. The mode of operation in use at any given time may be set by a user, for example they may select the mode using an interface on the device itself or on the external electronic device (which may communicate this to the device where the signal processing is carried out on the device, rather than the external electronic device) such that the appropriate signal processing method is used. However, in a particular set of embodiments, the signal(s) provided by the ancillary sensor arrangement may be used to determine the mode in which the device operates. In other words motion data from the ancillary sensor arrangement may allow automatic detection of what type of exercise is being performed, and therefore allow selection of the best signal processing method to use. Additionally, the motion data from ancillary sensor arrangement (e.g. from an IMU) may provide additional detail and/or an enhanced resolution, thereby allowing repetitions to be counted more accurately.

It will be appreciated that the terms 'processor' and 'processing stage(s)' referred to herein may refer to discrete processing units defined by their function, or these may be functions carried out by a suitable processing means such as a processor, microprocessor, microcontroller, central processing unit (CPU), graphical processing unit (GPU), integrated circuit (IC), application specific integrated circuit (ASIC), field-programmable gate array (FPGA), reduced instruction set computer (RISC), digital signal processor (DSP), or any other suitable type of processor, known in the art perse. The various functions may be carried out such that each function has its own dedicated processing means, or one or more (and potentially all) such functions may be carried out within one or more general or generic processing means, i.e. functions may be shared or distributed across one or more processing means, as appropriate.

It will be appreciated that the 'coupling portions' provide a means onto which the fitness equipment can be connected or coupled via e.g. straps such as those on a cable machine or a resistance band can be fitted. Thus these coupling portions provide a 'universal connector' onto which cable machines, suspension trainers, hand loops, foot straps, resistance bands, dumbbells, pull up bar/Olympic rings, sprint harnesses, sled pulls, free weights, direct pull-on straps, and many other types of fitness equipment can be fitted.

The device may also be used with body weight and isometric hold exercises.

In some embodiments, the first axis and second axis are the same. In such embodiments, the connecting portion is in-line with the coupling portions (e.g. hooks).

However, in other embodiments the second axis is offset from the first axis. In other words, the tensile force may be measured offset from the central line of tensile force because the second axis runs parallel to the first axis (i.e. the primary axis of applied force).

It will be appreciated that the term 'mechanically coupled to' means that the thin film strain gauge is arranged in such a way that when the connecting portion is subject to a mechanical deformation, so is the strain gauge. There are a number of ways in which this may be achieved, e.g. via a suitable adhesive or bonding agent. In some embodiments, the strain gauge is bonded to the connecting portion. In other embodiments, the strain gauge may be embedded within the connecting portion. In other words, the strain gauge may be located within the connecting portion itself, for example within a cavity or formed integrally within that connecting portion. Where multiple strain gauges are provided, a suitable method of mechanical coupling may be selected for each, though typically they may all be mechanically coupled to the respective connecting portion as appropriate.

The thin film strain gauge may, in a set of potentially overlapping embodiments, be arranged to deform along a direction parallel to the second axis. In other words, the strain gauge may be aligned along the direction of the tensile force, rather than perpendicular (i.e. transverse) to it. In accordance with such embodiments, the strain gauge is aligned such that it deforms along the principal direction of the tensile force, i.e. the connecting portion and the strain gauge mechanically coupled to it extend and contract along the principal direction of force. The Applicant has contemplated alternative arrangements in which a strain gauge is positioned transverse to the axis along which the tensile force is applied. In such arrangements, the 'transverse surface ¹ (i.e. the surface perpendicular to the tensile force axis) bends - i.e. it bevels - as the tensile force is applied, and a strain gauge may be used to determine the extent of such bending. The Applicant has appreciated, however, that relying on a bending or a torsional force to provide a measure of the applied in-line tensional force may be less accurate and may also lead to an increased need to perform calibration of the device to maintain accuracy, e.g. after the device has undergone many cycles of the relevant transverse surfaces being bent. By applying the sensor(s) to a surface that undergoes less deflection, this may protect those sensors. Additionally, this may advantageously reduce the amount of material needed to reduce these transverse plane deflections, leading to a lighter and more affordable device.

During normal use, the device may generally be subject to a range of forces typically applied by a user during physical exercises using fitness equipment. In general, this may vary somewhat depending on the specific user, their strength, and the types of exercise being performed, however the device may typically be subject to forces up to 7,000 N (corresponding to a mass of approximately 700 kg). In other words, the device may be rated for forces between approximately 0 N to 7,000 N. During normal use, typical forces applied to the device may be between approximately 100 N and 400 N (corresponding to masses of approximately 10 kg to 40 kg respectively).

The connecting portion may, in some embodiments, be made from metal. The Applicant has appreciated that with the forces that are typically exerted on the device, a metal connecting portion subject to the resultant strain would typically be in its elastic deformation region. The metal connecting portion may, at least in some such embodiments, comprise stainless steel or aluminium. The Applicant has appreciated that stainless steel and aluminium both have excellent properties for use with an in-line thin film strain gauge across the operating range of the device, i.e. with the forces typically applied by a user during physical exercises using the fitness equipment in normal use. Where multiple connecting portions are provided (as per certain embodiments of the claimed invention) some and potentially all of these may be made from metal.

In a set of such embodiments, the device may be asymmetric, with a single connecting portion on one side. However, in a particular set of such embodiments, the device further comprises a second connecting portion extending along a third axis parallel to said first axis, wherein the third axis is different to the first and second axes, the second connecting portion being rigidly connected at a first end thereof to the first coupling portion, and rigidly connected at a second end thereof to the second coupling portion. Thus there may be a connecting portion on each side of the device. The second and third axes may be equidistant from the first axis (i.e. such that a plane between the second and third axes is bisected by the first axis).

In embodiments where multiple connecting portions are provided at the sides of the device (e.g. with multiple strain gauges), the ancillary sensor arrangement and potentially other electronics (e.g. a power source such as a battery) may be positioned in a cavity located between the connecting portions.

In some embodiments, the device further comprises a second thin film strain gauge mechanically coupled to the second connecting portion, said second thin film strain gauge being arranged to deform in response to an externally applied in-line tensile force along the third axis, wherein the second strain gauge is further generates a third signal dependent on the deformation of said second strain gauge.

The second thin film strain gauge may, at least in a set of embodiments, be arranged to deform along a direction parallel to the third axis. The wireless communications module may be configured to transmit the third signal from the second thin film strain gauge to the external electronic device.

One or more further connecting portions may be connected between the coupling portions, each of which may be oriented along a respective axis parallel to the first axis, and may each have a respective strain gauge for measuring tensile force along that axis.

One or both of the coupling portions may be 'open ¹ , such that there is a gap in the coupling portion for receiving the external fitness equipment (e.g. a cable or handle). In some embodiments, the first and/or second coupling portions each comprise a hook. It will be appreciated that the term 'hook' as used herein means a portion having an angled, and typically curved, construction suitable for holding or hanging onto another object. Typically the hook is formed such that the outermost point of the curve of the hook lies along the first axis, such that the fitness equipment (e.g. handle, cable, or resistance band) sits centrally on the device when in use.

Alternatively one or more of the coupling portions may be of carabiner form, i.e. in which the coupling portions (e.g. hooks) have a coupling/gate mechanism to retain the fitness equipment (e.g. cable, handle, strap, etc.) in use. Such an arrangement may be advantageous in preventing the fitness equipment from inadvertently disengaging from the device.

Further alternatively, one or both of the coupling portions may be 'closed ¹ , such that there is no gap in the coupling portion. Such a closed construction may advantageously improve the strength of the device, provide for uniform distribution of force, and/or reduce the size of the device in line of force. In some such embodiments, the first and/or second coupling portions each comprise a ring. It will be appreciated that the term 'ring' does not necessarily imply that the coupling portions are substantially circular in shape, though they may be - however, any other shape may be used as appropriate. With such a configuration, fitness equipment may be connected or coupled to the device via suitable means - for example a cable, strap loop, or band may be passed through an aperture or hole enclosed by the coupling portion(s). Additionally, or alternatively, the fitness equipment may be provided with a carabiner, clip, hook, clamp, or such like that can be attached to the coupling portion.

In some embodiments, the coupling portions are substantially equal in size.

The device may be of any suitable size, however it is preferably small enough to be easily carried by a user, for example in a pocket or gym bag. In some embodiments, the device has a length of between 100 mm and 200 mm, preferably between 120 mm and 180 mm, more preferably between 140 mm, and 160 mm, further preferably approximately 150 mm, and in certain embodiments the device has a length of 150 mm.

In some potentially overlapping embodiments, the device has a width of between 40 mm and 90 mm, preferably between 50 mm and 80 mm, more preferably between 60 mm, and 70 mm, further preferably approximately 65 mm, and in certain embodiments the device has a width of 65 mm.

In some potentially overlapping embodiments, the device has a thickness of between 5 mm and 15 mm, preferably between 8 mm and 12 mm, more preferably between 9 mm, and 11 mm, further preferably approximately 10 mm, and in certain embodiments the device has a thickness of 10 mm.

The shapes of the first and second coupling portions may be substantially the same, though they may be 'mirror images' of one another. For example, where the coupling portions comprise hooks or have a carabiner-like form, one coupling portion may have the 'open part' or carabiner 'gate' to the left of the device while the other coupling portion may have the 'open part' or carabiner 'gate' to the right of the device. It will appreciated that the terms 'left' and 'right' when used in this context mean that, looking at the device face on, with the first axis running vertically.

The device may, in some embodiments, be arranged such that respective ends of the first and second coupling portions face one another with a receiving gap between said ends. It will be appreciated that in such embodiments, the device may have a clip construction, and may have a form alike to a C clip, snap ring, clip ring, spring clip, retaining ring, circlip, or other such device known in the art perse. It will be appreciated that the first and second coupling portions and connecting portion may together form a substantially continuous shape, and may have a curved construction, for example a 'C-shaped' curve - however other shapes could be used (e.g. a more angular shape such as rectangular or square). In other words, the first and second coupling portions may - at least in certain embodiments - form a pair of jaws.

In such embodiments, the receiving gap between the two coupling portions provides an aperture through which external equipment may be fed - for example fitness equipment (e.g. cables, resistance bands, ropes, carabiners, or strap loops) can be pushed through the receiving gap such that such fitness equipment then abuts against the first and second coupling portions for in-line tensile force applications. The receiving gap may also be used to receive other types of fitness equipment such as free weights - for example the device can clamp on to the bar of a barbell or dumbbell.

In some such embodiments, the first coupling portion and/or the second coupling portion may comprise a flexible material. By allowing one or both coupling portions to 'flex' in response to an applied force, the device can be pushed on to fitness equipment, with the receiving gap extending to receive fitness equipment and then the coupling portion(s) can return to their normal position, with the fitness equipment being securely retained by the device. Those skilled in the art will appreciate that this provides a 'sprung gate' construction. The flexible material may be used for a part of or the whole of the or both coupling portion(s) as appropriate. Where the flexible material is only used for part of the coupling portion(s), the flexible material may be used for the end of the coupling portion(s) associated with the receiving gap. The flexible material may, in some embodiments, comprise a rubber material.

The connecting portion may also comprise the (or a further) flexible material, and so in a particular subset of such embodiments the coupling portions and the connecting portion are all made of a flexible material, and may be of integral construction. However, in other embodiments, the connecting portion may comprise an inflexible or robust material, and may in some such embodiments comprise metal, as outlined previously. The use of such a material (e.g. metal) allows strain to distribute uniformly to the strain gauge(s) located along the connecting portion.

In some embodiments, a housing surrounds the connecting portion and internal electronics including the strain gauge, ancillary sensor arrangement, and wireless communications module, with the coupling portions extending from either side of the housing. This housing may therefore provide a 'case' around the electronics.

In an alternative set of embodiments, a detachable housing surrounds the ancillary sensor arrangement and wireless communication module, said detachable housing being detachable from the first and second coupling portions and the connecting portion(s). In other words, a 'case' containing the ancillary (non-strain gauge) sensors can be detachable from the rest of the device. This may, in some embodiments, be achieved via a simple docking 'push-click' system. The strain gauges on the device may have a simple way of reestablishing connection to the other electronic circuits (i.e. the components within the detachable housing) on docking. This is deemed desirable by the Applicant as it means the in-line tension measurement - relevant to strain gauges and coupling portions - is the only configuration where the entire device is required. When detached, the detachable housing, may be more easily integrated into other exercises (such as affixed to free weights, body parts or parts of an exercise machine) due to its reduced size and weight. This attachment may be through material, elastic or other push-click docking arrangements. This may allow users to conveniently track their exercises via the ancillary sensors. It may also allow for tensile loads to be left attached to coupling devices allowing for swift and easy transitions between exercise types, for example the main 'body ¹ of the device (the coupling portions, connecting portion, and strain gauge) can be 'left behind' connected to a cable machine, while the detachable housing can be removed and used as a standalone device in another exercise, before the user then returns to the cable machine and 'click' the detachable housing back into place.

The detachable housing may, in some embodiments, comprise an attachment means for connecting the detachable housing to the device and/or to other objects (e.g. a free weight). The attachment means of the housing may comprise one or more of: a magnet arrangement (where magnets may, for example, be situated via location moulding, or other means), a hook and loop (e.g. Velcro®) arrangement, a push clip arrangement (which may be of single- or multi-part construction), a spring catch arrangement, and/or a rubberised push grip arrangement. It will be appreciated that the detachable housing may be provided with one or more of these arrangements (and/or other such arrangements) to provide the function of the attachment means. Different arrangements may be advantageous for different objects to which the detachable housing is to be fitted, for example the Applicant has appreciated that a rubberised push grip arrangement is particularly well suited for attaching the detachable housing to a barbell or dumbbell, as it can be pushed on to the bar to 'clamp' on to it.

The detachable housing may, in some embodiments, comprise an interface button for receiving a user input. This interface button may be used to turn the electronics within the detachable housing on and off. The interface button may, additionally or alternatively, be used to turn electronics in the device on and off (e.g. the strain gauge and associated electronics). Additionally, or alternatively, the interface button may be used to enable one or more other functions of the detachable housing, such as those functions set out herein.

In some embodiments, the detachable housing may comprise a near field communication (NFC) module. The NFC module may be usable to enable a further mode of communication, e.g. to enable communication via the wireless communication module.

A power source for the device may, in some embodiments, be contained within the detachable housing. The Applicant has appreciated that such embodiments may advantageously avoid duplication of electronics across the 'tethered' mode (with the detachable housing connected to the rest of the device) and the 'untethered' mode (where the detachable housing and its components are used as a standalone device. In some such embodiments, a first power coupling is provided on the detachable housing, and a second power coupling is provided on the device, such that power is supplied from the power source to the device (e.g. to the strain gauge and/or other components of the device) when the detachable housing is connected to the first and second coupling portions and the connecting portion(s). The detachable housing may, in some embodiments, comprise charging circuitry for charging the power source. Such an arrangement may allow the power source to be recharged, for example when the device is not in use.

The charging circuitry may comprise a wired charging arrangement. Those skilled in the art will appreciate that a wired charging arrangement may comprise a charging port for receiving a suitable charging cable provided with a connector such as USB-A, USB-B, USB-C, Mini USB, Micro USB, Lightning®, FireWire®, or other standardised or proprietary connector.

Additionally, or alternatively, in some potentially overlapping embodiments the charging circuitry may comprise a wireless charging arrangement. Those skilled in the art will appreciate that a wireless charging arrangement requires no physical connection port on the device, and can instead allow for power to be transferred wirelessly, e.g. using electromagnetic induction. Such a wireless charging arrangement may comply with the Qi® or Qi2® standards, or any other such standard or proprietary wireless charging technology.

The detachable housing may, in some embodiments, have a waterproof construction. This may, in some such embodiments, be achieved by the detachable housing comprising one or more seals arranged to prevent the ingress of water into the housing. The detachable housing may, in a particular set of embodiments, comprise one or more waterproof barometer apertures. Such apertures may allow a barometer positioned within the detachable housing (e.g. as part of the ancillary sensor arrangement) to function while preventing ingress of water.

The detachable housing may have any appropriate size and shape. Furthermore, the detachable housing may be constructed from any suitable material, which may in some embodiments be a plastic material, however other materials may be used instead of, or in addition to, a plastic material.

In general, the strain gauge may comprise a resistive element or resistor, the resistance of which varies in dependence on the tensile force applied along the second axis. The thin film strain gauges may, in some embodiments, comprise a Wheatstone bridge. It will be appreciated that a Wheatstone bridge is an electronic configuration of four resistors arranged in a 'diamond' configuration providing two parallel voltage divider circuits. An input voltage is applied across one pair of opposite nodes and an output voltage is taken across the other pair of opposite nodes. Thus, in some embodiments, the device comprises a Wheatstone bridge circuit comprising first, second, third, and fourth resistors, said resistors being configured such that: a first input node is connected to respective first terminals of the first and fourth resistors; a second input node is connected to respective first terminals of the second and third resistors; a first output terminal is connected to respective second terminals of the first and second resistors; and a second output terminal is connected to respective second terminals of the third and fourth resistors; wherein a respective resistance of one of said resistors is dependent on the applied tensile force along the second axis. In other words, the strain gauge comprises one of the resistors. In a particular set of embodiments, the strain gauge comprises the fourth resistor.

This configuration is typically referred to as a Wheatstone bridge. In such a configuration, the applied tensile force changes the resistance of one of the resistors, which causes the voltage output across the two output nodes to change in dependence on the magnitude of the applied tensile force. The other resistors may be fixed resistors (i.e. resistors that are not subjected to the tensile force).

Where multiple strain gauges are provided, as per certain embodiments of the present invention, a respective resistance of a further one of said resistors may be dependent on the applied tensile force along the second axis. Thus the further thin film strain gauge(s), where provided, may each comprise a respective different one of the first to fourth resistors. It will be appreciated by those skilled in the art that the number of these resistors that are embodied as strain gauges alter the type of Wheatstone bridge configuration. An arrangement with one strain gauge is referred to as a 'quarter' Wheatstone bridge circuit; an arrangement with two strain gauges is referred to as a 'half' Wheatstone bridge circuit; and an arrangement where all four resistors are strain gauges is referred to as a 'full' Wheatstone bridge circuit.

Such a configuration may provide for mutual cancellation of thermal changes. Adjacent strain gauges on the same backing will see identical temperature and therefore eliminate thermal outputs due to differential temperatures across the structure. In a particular set of embodiments in which multiple connecting portions are provided (e.g. symmetrically at either side of the device), a respective thin-film strain gauge may be mechanically coupled to each, and their outputs may respectively be used as different ones of the first to fourth resistors.

The strain gauge may, in some embodiments, comprise a 'T-rosette' (sometimes called a 'Tee-rosette') strain gauge where a first strain gauge coil is positioned to measure tension along the second axis (i.e. along the direction of the tensile force along the first axis, which is parallel to the second axis); and a second strain gauge coil is positioned to measure tension along a further axis at a non-zero angle to the second axis, optionally wherein said angle is approximately 90 degrees, preferably wherein said angle is 90 degrees. Measuring the strains at 90 degrees may advantageously enable calculation of the stresses at the measurement location, which may not otherwise be possible with only a single strain gauge. These T-rosettes are commonly used where tensile or compression material property tests are performed, as they enable calculation of Poisson's ratio as well as Young's modulus. Using a T-rosette for this apparently simple test allows the user to make transverse sensitivity corrections for maximum accuracy of the test results.

It will be appreciated that such a bending moment is, typically, unwanted as it may interfere with the measurement of the in-line tensile force. By measuring the unwanted bending moment, its effect may be compensated for, for example with suitable processing applied by the device itself or by the external electronic device if, as per certain embodiments, the measurement of the bending force is transmitted to the external electronic device via the communications module. For example, in some embodiments, the signal generated by the strain gauge may comprise a respective measurement component for the measurements from each strain gauge coil in such a T-rosette strain gauge. It will be appreciated that the wireless communications module may transmit the signals from the strain gauge and/or ancillary sensor arrangement directly (i.e. the 'raw' output(s) from the respective sensors), however in general the signal from the strain gauge may be subject to some intermediate processing prior to the transmission of the appropriate signal by the wireless communications module. This processing may include the processing steps outlined hereinabove in respect of certain embodiments of the invention. Additionally, or alternatively, the wireless communications protocol may transmit an encoded version of the first and/or second signal(s), where an encoding scheme is used to represent said signal(s) in a particular data format. Such intermediate processing may be carried out by a processor of the device, for example a microprocessor or any other suitable processing means as outlined previously. Such processing may be carried, as appropriate, by one or more structural or functional units, including by any combination of physical and/or logical components.

The determination of the strain or tensile force applied when the device is in use may be conducted externally of the device, for example by the external portable electronic device or a remote server. However, in some embodiments, the device comprises a processor configured to determine a strain measurement or a tensile force measurement from the first signal generated by the strain gauge. In some such embodiments, the signal transmitted by the wireless communications module comprises the determined strain measurement or tensile force measurement.

The communications module may, in some embodiments, use a short-range wireless communications protocol, preferably Bluetooth® or Bluetooth Low Energy®.

The fitness equipment system may comprise a cable machine, wherein the first fitness equipment comprises a cable of said cable machine. In some such embodiments, the cable is mechanically coupled to one or more weights, typically via one or more pulleys.

Additionally, or alternatively, in some embodiments the fitness equipment system comprises a resistance band. The second fitness equipment may, at least in some embodiments, comprise a resistance band. In a particular set of embodiments, the device may be positioned between two resistance bands.

The second fitness equipment may, at least in some embodiments comprises an engagement portion for interaction with by a user, optionally wherein the engagement portion comprises a handle.

In some embodiments, the fitness equipment system comprises the external electronic device.

In some embodiments, the fitness equipment system comprises a remote server communicably coupled to the external electronic device, said remote server being configured to exchange communications from the external electronic device, said communications comprising information associated with the signal dependent on the deformation of the strain gauge.

The Applicant has appreciated that aligning the thin film strain gauge(s) along the direction of the applied in-line tensile force (rather than parallel to it) is novel and inventive in its own right. Thus, in accordance with a second aspect, embodiments of the present invention provide an in-line exercise measurement device for use with fitness equipment, the device comprising: first and second coupling portions onto which fitness equipment is detachably couplable, the first and second coupling portions being aligned along a first axis; a connecting portion extending along a second axis parallel to said first axis, the connecting portion being rigidly connected at a first end thereof to the first coupling portion, and rigidly connected at a second end thereof to the second coupling portion; a thin film strain gauge mechanically coupled to the connecting portion, said thin film strain gauge being arranged to deform along a direction parallel to the second axis in response to an externally applied in-line tensile force along the second axis, wherein the strain gauge is further arranged to generate a signal dependent on the deformation of said strain gauge; and a wireless communications module configured to transmit the signal from the thin film strain gauge to an external electronic device.

The second aspect of the invention extends to a fitness equipment system comprising first and second fitness equipment; and the device of the second aspect of the invention. Thus, the second aspect of the invention extends to a fitness equipment system comprising: first and second fitness equipment; and an in-line exercise measurement device for use with fitness equipment, the device comprising: first and second coupling portions aligned along a first axis; a connecting portion extending along a second axis parallel to said first axis, the connecting portion being rigidly connected at a first end thereof to the first coupling portion, and rigidly connected at a second end thereof to the second coupling portion; a thin film strain gauge mechanically coupled to the connecting portion, said thin film strain gauge being arranged to deform along a direction parallel to the second axis in response to an externally applied in-line tensile force along the second axis, wherein the strain gauge is further arranged to generate a signal dependent on the deformation of said strain gauge; and a wireless communications module configured to transmit a further signal to an external electronic device, said further signal comprising information corresponding to the signal generated by the thin film strain gauge; wherein the first and second fitness equipment are detachably couplable to the first and second coupling portions of the device.

The second aspect of the invention also extends to a method of monitoring a physical movement applied to fitness equipment by a user using the device of the second aspect of the invention, the method comprising: receiving the information corresponding to the signal generated by the thin film strain gauge; and using said information to determine an applied strain or in-line tensile force. The second aspect of the invention further extends to a non-transitory computer-readable medium comprising instructions that, when executed by a processor, cause the processor to carry out a method of monitoring a physical movement applied to fitness equipment by a user using the device of the second aspect of the invention, the method comprising: receiving the information corresponding to the signal generated by the thin film strain gauge; and using said information to determine an applied strain or in-line tensile force.

The second aspect of the invention yet further extends to a computer software product comprising instructions that, when executed by a processor, cause the processor to carry out a method of monitoring a physical movement applied to fitness equipment by a user using the device of the second aspect of the invention, the method comprising: receiving the information corresponding to the signal generated by the thin film strain gauge; and using said information to determine an applied strain or in-line tensile force.

The method may comprise receiving the further signal from the wireless communications module.

In accordance with the second aspect of the invention, the strain gauge is aligned such that it deforms along the principal direction of the tensile force, i.e. the connecting portion and the strain gauge mechanically coupled to it extend and contract along the principal direction of force. The Applicant has contemplated alternative arrangements in which a strain gauge is positioned transverse to the axis along which the tensile force is applied. In such arrangements, the 'transverse surface ¹ (i.e. the surface perpendicular to the tensile force axis) bends - i.e. it bevels - as the tensile force is applied, and a strain gauge may be used to determine the extent of such bending. The Applicant has appreciated, however, that relying on a bending or a torsional force to provide a measure of the applied in-line tensional force may be less accurate and may also lead to an increased need to perform calibration of the device to maintain accuracy, e.g. after the device has undergone many cycles of the relevant transverse surfaces being bent. Conversely, embodiments of the present invention use a different approach, in which the strain gauge deforms along the direction of the tensile force. By arranging the strain gauge in this orientation - i.e. parallel to rather than perpendicular or transverse to the direction of the tensile force - the need for calibration may be significantly reduced. Additionally, by avoiding the need for relatively large transverse surfaces (to accommodate both the degree of bending and the strain gauge in such a transverse orientation), devices in accordance with embodiments of the present invention may be made more compact, allowing the use of a smaller device and/or allowing better use of space within the device.

It will be appreciated, therefore, the strain gauge arrangement used in the present invention measures tensile stress (specifically, the stress on the connecting portion) rather than measuring bending or torsional stress of a part of the housing.

The whole device can therefore be said to be 'uniaxial ¹ , such that substantially all tension applied in use (e.g. as a user performs a rep on a cable machine) is transferred through the device, along that connecting portion, the strain across which is measured by the strain gauge. The resultant signal can then be sent to an external electronic device such as a smartphone which runs an app (or similar) which then uses the signal from the device for various fitness or medical (e.g. physiotherapeutic) purposes.

In accordance with a third aspect, embodiments of the present invention provide an in-line exercise measurement device for use with fitness equipment, the device comprising: first and second coupling portions onto which fitness equipment is detachably couplable, the first and second coupling portions being aligned along a first axis; a connecting portion rigidly connected at a first end thereof to the first coupling portion, and rigidly connected at a second end thereof to the second coupling portion; a thin film strain gauge mechanically coupled to the connecting portion, said thin film strain gauge being arranged to deform in response to an externally applied in-line tensile force along the first axis, wherein the strain gauge is further arranged to generate a signal dependent on the deformation of said strain gauge; and a wireless communications module configured to transmit a further signal to an external electronic device, said further signal comprising information corresponding to the signal generated by the thin film strain gauge. The third aspect of the invention extends to a fitness equipment system comprising first and second fitness equipment; and the device of the third aspect of the invention. Thus, the third aspect of the invention extends to a fitness equipment system comprising: first and second fitness equipment; and an in-line exercise measurement device for use with fitness equipment, the device comprising: first and second coupling portions aligned along a first axis; a connecting portion rigidly connected at a first end thereof to the first coupling portion, and rigidly connected at a second end thereof to the second coupling portion; a thin film strain gauge mechanically coupled to the connecting portion, said thin film strain gauge being arranged to deform in response to an externally applied in-line tensile force along the first axis, wherein the strain gauge is further arranged to generate a signal dependent on the deformation of said strain gauge; and a wireless communications module configured to transmit a further signal to an external electronic device, said further signal comprising information corresponding to the signal generated by the thin film strain gauge; wherein the first and second fitness equipment are detachably couplable to the first and second coupling portions of the device.

The third aspect of the invention also extends to a method of determining an in-line tensile force applied to fitness equipment by a user using the device of the third aspect of the invention, the method comprising: receiving the information corresponding to the signal generated by the thin film strain gauge; and using said information to determine the in-line tensile force.

The third aspect of the invention further extends to a non-transitory computer-readable medium comprising instructions that, when executed by a processor, cause the processor to carry out a method of determining an in-line tensile force applied to fitness equipment by a user using the device of the third aspect of the invention, the method comprising: receiving the information corresponding to the signal generated by the thin film strain gauge; and using said information to determine the in-line tensile force.

The third aspect of the invention further extends to a computer software product comprising instructions that, when executed by a processor, cause the processor to carry out a method of determining an in-line tensile force applied to fitness equipment by a user using the device of the third aspect of the invention, the method comprising: receiving the information corresponding to the signal generated by the thin film strain gauge; and using said information to determine the in-line tensile force.

The connecting portion may, at least in some embodiments of any of the foregoing aspects, be arranged to deform elastically during normal use of the device. In some embodiments, the connecting portion comprises metal. Thus the connecting portion may be a metal connecting portion. The metal connecting portion may comprise aluminium or stainless steel. In a potentially overlapping set of embodiments, the connecting portion comprises a composite material, and optionally comprises a Kevlar composite material. Where multiple connecting portions are provided, they may each comprise the same material or they may comprise different materials.

It will be appreciated that the optional features described hereinabove in respect of embodiments of any aspect of the invention apply equally, where technically appropriate, to the other aspects of the invention.

Where technically appropriate, embodiments of the invention may be combined. Embodiments are described herein as comprising certain features/elements. The disclosure also extends to separate embodiments consisting or consisting essentially of said features/elements.

Technical references such as patents and applications are incorporated herein by reference. Any embodiments specifically and explicitly recited herein may form the basis of a disclaimer either alone or in combination with one or more further embodiments.

In the context of this specification "comprising" is to be interpreted as "including".

Aspects of the invention comprising certain elements are also intended to extend to alternative embodiments "consisting" or "consisting essentially" of the relevant elements.

Brief iption of the

Certain embodiments of the present invention will now be described, by way of nonlimiting example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic diagram of an in-line exercise measurement device in accordance with an embodiment of the present invention;

Fig. 2 is a further schematic diagram of the device of Fig. 1, showing the primary axis along which tensile force is applied;

Fig. 3 is a schematic diagram showing the internal structure within the housing of the device of Fig. 1;

Fig. 4 is a schematic diagram showing the thin-film strain gauge mechanically coupled to the connecting portion;

Fig. 5 is a circuit diagram illustrating a Wheatstone bridge configuration of the thin- film strain gauge;

Fig. 6 is a block diagram illustrating the functional components of the device of

Fig. 1;

Fig. 7 is a schematic diagram illustrating the device of Fig. 1 in use;

Fig. 8 is a block diagram illustrating functional components of a device in accordance with a further embodiment of the claimed invention;

Fig. 9 is a schematic diagram showing the internal structure within the housing of a device in accordance with a further embodiment of the claimed invention;

Fig. 10 is a schematic diagram showing the internal structure within the housing of a device in accordance with another embodiment of the claimed invention;

Fig. 11 is a schematic diagram showing the internal structure within the housing of a device in accordance with a yet further embodiment of the claimed invention; Fig. 12 is a schematic diagram showing a section view of a portion of a device in which the strain gauge is positioned on the flank of the connecting portion;

Fig. 13 is a block diagram illustrating an arrangement in which signal processing is carried out externally;

Fig. 14 is a block diagram illustrating the signal processing on the in-line exercise measurement device when operated in a first mode;

Fig. 15 is a block diagram illustrating the signal processing on the in-line exercise measurement device when operated in a second mode;

Fig. 16 is a graph showing a calibration curve plot of strain as a function of applied tensile force;

Figs. 17A and 17B are schematic diagrams of a detachable housing which may be used as a standalone device;

Fig. 18 is a schematic diagram of an in-line exercise measurement device in accordance with a further embodiment of the claimed invention; and

Fig. 19 is a schematic diagram of an in-line exercise measurement device in accordance with a yet further embodiment of the claimed invention.

Detailed Description

Fig. 1 is a schematic diagram of an in-line exercise measurement device 2 in accordance with an exemplary embodiment of the present invention. The device 2 is arranged to be used with fitness equipment included, but not limited to, cable machines and resistance bands.

The device 2 has a first hook 4a and a second hook 4b extending from a central housing 6 which contains certain electronic components, described in more detail below. These hooks 4a, 4b form 'coupling portions' for fitting on to the desired fitness equipment. For example, a handle (for the user to grip) may be attached to the first hook 4a and a resistance band may be attached to the second hook 4b. Each hook 4a, 4b has a respective opening 8a, 8b into which fitness equipment may be detachably connected or coupled to the device. In this particular example, the hooks 4a, 4b are 'open' such that the fitness equipment can be freely attached and detached, but in other examples, the hooks 4a, 4b may have a carabiner-style form in which a hinged gate is used at the opening 8a, 8b to retain the fitness equipment in place during use.

Referring to Fig. 2, it can be seen that the two hooks 4a, 4b are aligned along an axis 10. This axis 10 is the primary axis along which tensile force is applied to the device 2 when in use. In other words, as a user performs a rep (e.g. lifts a weight via a cable machine or pulls against a resistance band), the resultant tensile force is along the direction of the axis 10.

In particular, the surface of each hook 4a, 4b that comes into contact with the fitness equipment is curved such that the respective outermost point 12a, 12b of each curve (i.e. the position against which the fitness equipment would rest under tension) sits along the axis 10.

Fig. 3 is a schematic diagram showing the internal structure within the housing of the device of Fig. 1. In particular, Fig. 3 shows the device 2 of Fig. 1 with the housing 6 removed from view.

A connecting portion 16, formed as a strut, extends along the axis 10, i.e. the axis along which the connecting portion is aligned is the same as the primary axis of tensile force. However, in other embodiments, which are described below, the connecting portion may be positioned off-centre, such that it is aligned along another axis that runs parallel to the first axis 10. The connecting portion 16 is made of metal as it is optimised for elastic deformation relative to the typical tensile force range the device 10 undergoes in use, which may typically be between 0 N and 1,000 N (corresponding approximately to masses of between 0 kg to 100 kg), though the device may be rated up to some higher maximum force, e.g. 1,500 N or 7,000 N (corresponding approximately to masses of between 150 kg or 700 kg). In this example, the connecting portion 16 is made of metal, and the metal used for the connecting portion may, for example, be stainless steel or aluminium, both of which have excellent properties for use with the strain gauge (discussed in further detail below) across the normal operational range of the device 2, i.e. for forces typical of exercises carried out by the user. It will be appreciated, however, that other suitable metals or non-metal materials may be used instead.

The connecting portion 16 is rigidly connected to the first hook 4a at one end, and is rigidly connected to the second hook 4b at the other end. As can be seen from Fig. 3, the two hooks 4a, 4b are separate pieces which are joined only via the metal connecting portion 16. In effect, within the bounds of the device 2, the connecting portion 16 can be seen as sitting within a cavity 18 between the two hooks 4a, 4b. This cavity 18 is shaped so as to allow relative movement between the hooks 4a, 4b along the direction of the axis 10, with the tensile load being applied along the connecting portion 16.

It can be seen that, in this specific example, there are two optional 'L-shaped' channels 19a, 19b which pass from the cavity 18 to the outside of the device. These channels 19a, 19b are optional, but may advantageously assist with allowing the housing 6 to be mounted to the rest of the device 2 with reduced impact on the tensile loading (i.e. avoiding 'noise' on the tensile load). It can be seen that the part of the second L-shaped channel 19b that connects to the cavity 18 is curved whereas the corresponding part of the first L-shaped channel 19a is not. This curved portion is designed to accommodate one of the through holes 20, outlined below. This asymmetry is not required, however, as the through holes may be positioned elsewhere, or the housing may be attached to the device via means that do not require the presence of these through holes.

The hooks 4a, 4b themselves may be made of a suitable plastic, or may be made from metal such as aluminium or stainless steel. Similarly, the housing 6 may also be made from plastic or from a metal such as aluminium or stainless steel.

A number of through holes 20 are provided on the hooks 4a, 4b which enable it to be secured to the housing 6 during assembly via suitable means, for example a threaded connector such as a nut and bolt, or a screw and suitable thread. Alternatively, however, the hooks 4a, 4b and the housing 6 may all be cut, cast, or pressed from the same material such that no connections between those parts are needed. Fig. 4 is a schematic diagram which illustrates a thin-film strain gauge 22 which is mechanically coupled to the connecting portion 16. The structures of the hooks 4a, 4b are simplified in Fig. 4 for ease of reference.

In this particular exemplary embodiment, the connecting portion is of cuboid form and the strain gauge 22 is shown as being mechanically coupled to the 'front surface ¹ (i.e. the surface shown in the face-on profile view of Fig. 4) of the connecting portion 16, however this is for ease of illustration only and the strain gauge 22 could readily be positioned at another position or surface on or around the connecting portion 16, such as on the underside (i.e. the 'back surface') or at one of the flanks (i.e. the 'sides') of the connecting portion 16.

The thin film strain gauge 22 is mechanically coupled to the connecting portion 16 and is arranged to deform along the axis 10 in response to an externally applied in-line tensile force Ftensiie along that axis 10. Specifically, as the in-line tensile force Ftensiie is applied, the strain gauge 22 undergoes a change in length AL as the connecting portion 16 elastically deforms under tension. In other words, the strain gauge 22 extends or contracts in the same direction as the applied tensile force, and in this case along the same axis 10.

This is different to other strain gauge or load cell arrangements in which the strain gauge is placed transverse (i.e. perpendicular) to the direction of force on a surface that bends as the force is applied, with such a strain gauge bending as a result. Such arrangements may require relatively frequent calibration in order to provide accurate measurements of the tensile force applied.

The strain gauge 22 generates a signal dependent on the deformation of the strain gauge 22, as explained in further detail with reference to Fig. 5, which is a circuit diagram illustrating the electronic configuration of the thin-film strain gauge 22. In this particular embodiment, the strain gauge 22 is configured in a Wheatstone bridge arrangement, constructed from four resistors Ri, R ₂ , R3, and R ₄ , where the strain gauge 22 is arranged as the fourth resistor R ₄ . Those skilled in the art will appreciate, however, that the strain gauge 22 could take the place of any one of (or a combination of) those four resistors Ri to R ₄ . As the strain gauge 22 is subject to an in-line tensile force Ftensiie, it undergoes a change in length AL as outlined previously. This results in a change in resistance of R4. In particular, the resistance of a wire resistor can be expressed as per Equation 1 below: where R is the resistance of the resistor, p is the resistivity of the material, L is the length of the wire, and A is the cross-sectional area of the wire.

The change in the wire's resistance is related to the applied strain by a gauge factor, as defined by Equation 2 below:

AR/R

GF =

AL/L

Equation 2: Gauge factor where GF is the gauge factor which, as can be seen above, is the ratio of percentage (%) changes in the resistance R and length L of the wire. It will be appreciated that the strain e is defined by Equation 3 below: e = AL/L

Equation 3: Strain

Substituting Equation 3 into Equation 2, it can be seen that the strain gauge's resistance changes as a function of strain, as shown in Equation 4 below:

AR = R x GF x e

Equation 4: Strain gauge's resistance as a function of strain

Theoretically, the gain factor GF = 2, independent of the wire material, length, and cross- sectional area. In practice, the gain factor GF = 2 may vary within a variance of several percent. The change in resistance of the strain gauge 22, as a percentage of the nominal resistance of the strain gauge 22, is typically very small. The use of the Wheatstone bridge configuration is advantageous as it allows for a change in a voltage level to be measured, instead of measuring the change in resistance. This is preferred as the voltage level can vary about a zero level, rather than around a substantial offset (as in the case of the resistance level).

In particular, the output voltage V _out of the Wheatstone bridge in Fig. 5 is given by

Equation 5 below: where V _out is the output voltage of the Wheatstone bridge, V _in is the input voltage of the Wheatstone bridge (provided by a suitable supply or reference voltage), and R^ to R ₄ are the resistances of the four resistors.

It will be appreciated, therefore, that changing the resistance of R ₄ , i.e. the resistance of the strain gauge 22, will give rise to a change in the output voltage V _out produced by the Wheatstone bridge circuit.

The applied strain may then be determined from the output voltage V _out of the Wheatstone bridge circuit. In order to simplify the analysis for the purposes of this example, the resistances R ₄ to R ₃ are considered equal, and each of these is also equal the nominal resistance of R ₄ when the device 2 is at rest - referred to as R ₄₀ . When the device 2 is under tension, then the resistance R ₄ of the strain gauge 22 is given by Equation 6 below: Based on the assumption that R^ to R ₃ are equal to the nominal resistance of R _{4 0}

Equation 5 simplifies to Equation 7 below:

Substituting Equation 6 in to Equation 7 yields Equation 8:

As the change in resistance AR is negligible compared to the nominal resistance R _{4 0} component of the denominator, Equation 8 simplifies further to Equation 9 below: the denominator

Rearranging Equation 4, and using R ₄₀ in place of 'R' provides Equation 10 below:

Finally, combining Equations 9 and 10 yields Equation 11 below:

Thus the strain e applied by the user may be determined from the output voltage V _out , providing the input voltage V _in and gauge factor GF are known. Those skilled in the art will appreciate that in order to determine the applied in-line tensile force, the stress applied to the material, as well as the Young's modulus of the material are typically needed. However, the device 2 may be calibrated by applying known forces to it (e.g. a series of known, predetermined weights) to obtain a characteristic calibration curve representing the relationship between measured strain and applied in-line tensile force for the device. This curve can then be used to derive a newly applied unknown in-line tensile force from the known, measured strain from the strain gauge.

An exemplary calibration curve is shown in Fig. 16, which provides plots of strain as a function of applied tensile force. It will be appreciated that Fig. 16 merely provides a model and uses relatively low force values for that model, however the principle when applied to a practical device is the same. To ensure correct calibration across the anticipated range of forces a polynomial equation may be utilised.

In particular, Fig. 16 shows two plots - firstly the actual measured strain as a function of applied tensile force (the circular markers), and secondly a calibrated strain curve (the square markers) which is used to determine an unknown applied tensile force from a measured strain acquired during use of the device. As can be seen from Fig. 16, this particular device is calibrated to closely match the actual strain-force relationship at tensile loads below approximately 70 N. At higher tensile loads, the error between the calibrated and actual strain values diverges. The point at which this divergence occurs may typically be set to a higher value than the rated loads expected during normal operation of the device.

Referring back to Fig. 5, as the stress applied to the material is in the linear elastic region, the change in the output voltage V _out is directly proportional to the force applied, so by applying a coefficient to this voltage drop the in-line tensile force applied can be determined. Thus while the absolute value of the voltage. The relevant coefficient is obtained from the calibration curve discussed previously.

The generation of the calibration curve and/or the derivation of force measurements from a measured strain obtained from that curve may be carried out internally within the device 2 if it has a suitable processor (not shown) or another device, such as on the external portable electronic device with which the device 2 communicates or a yet further device such as a remote server.

Fig. 6 is a block diagram illustrating the functional components of the device 2 of Fig. 1. The device 2 contains the strain gauge 22 which, as discussed above, is mechanically coupled to the connecting portion 6 between the two hooks 4a, 4b. As is shown schematically, the device is in use, connected between a handle 24 and a resistance band 26 (i.e. fitness equipment) connected to a fixed point 28.

As the user pulls the handle 24 during a rep, an in-line tensile force is applied along the axis 10, putting the strain gauge 22 under an in-line strain. This, as discussed above with reference to Fig. 5, causes a change in the resistance R ₄ of the strain gauge 22, which in turn causes a change in the output voltage V _out produced by the Wheatstone bridge circuit.

The output voltage V _out produced by the Wheatstone bridge is fed to a processor 30, which may (by way of example only) be a microprocessor, where any suitable microprocessor may be used. The processor 30 may perform any suitable processing to the output voltage V _out , which may include a sample-and-hold process and/or a quantisation process. It will be appreciated that, in practice, multiple processing units may be provided (e.g. different hardware and/or software components) to provide various processing functions, however for ease of reference and illustration these are treated collectively here as a single processor.

The processor 30 may itself be configured to determine a measure of the applied in-line tensile force from the output voltage V _out produced by the Wheatstone bridge, or it may be configured to pass an intermediate processed version of the output voltage V _out (or even the output voltage V _out itself) suitable for a further device or processor to determine the applied in-line tensile force instead, e.g. in the manner described previously. The output 32 of the processor 30 is supplied to a wireless communications module 34.

The wireless communications module 34 is configured to transmit a signal 36 which contains the information derived from the thin film strain gauge 22 to an external portable electronic device 38 which may, for example, comprise a smartphone or tablet. The wireless communications module 34 may use a suitable wireless communications protocol for communication with the external device 38, for example a short-range radio communications protocol like Bluetooth® or Bluetooth Low-Energy®.

The external device 38 may then use the information contained within the signal 36 received from the device 2 in order to supply information regarding the movement performed by the user. For example, a touchscreen of the device 38 may be used to display the determined in-line tensile force, either directly or via any other suitable form of feedback. In some examples, the device 38 may provide a visual indication of whether the user is meeting a particular exercise goal, such as applying a threshold amount of force, achieving a particular hold time (i.e. holding a weight in place for a particular amount of time), achieving a particular rep speed, and/or a count of the number of reps that have been performed successfully.

The portable electronic device 38 may be for the user's direct use, or it may be in the possession of someone else such as a coach, trainer, or physiotherapist that is overseeing the exercise being performed by the user.

The portable electronic device 38 may optionally be configured to exchange communications 40 with a remote server 42. These communications may be over a long- range network such as the Internet, e.g. with the device 38 making use of Wi-Fi® or a cellular communication network to exchange the communications 40 with the remote server 42.

This remote server 42 may be configured to perform calculations corresponding to the movement and return the result to the device 38. In addition, or in the alternative, the remote server 42 may be configured to collate information relating to the movements performed by the user, and potentially other users. This may enable tracking of physical progress over time, either on an individual basis (so a user can see their progress) or for a group of users (e.g. for a team being managed by a coach, or for a set of clients overseen by a physiotherapist). Fig. 7 is a schematic diagram illustrating the device 2 of Fig. 1 in use. As can be seen in Fig. 7, a user 44 grips a handle 24 which is attached to one hook 4a of the device 2. The other hook 4b of the device 2 is attached to a cable 46 of a cable machine 48, i.e. it is connected in-line on the fitness equipment.

Pulling the handle 24 pulls the cable 46 via the device 2 (which the tensile force being aligned along the axis 10 between the handle 24 and cable 46). This pulls up on a set of weights 50 via a pulley system 52, in manner known in the art perse.

The tensile force Ftensiie causes a change in length AL of the connecting portion 16 and strain gauge 22 in the manner described previously, which results in a signal 36 containing information about the strain and thus the applied tensile force Ftensiie from the movement of the user 44, where that signal 36 is then transmitted to a portable electronic device 38. In this example, the portable device 38 belongs to a physiotherapist 54, who is monitoring the performance of the user 44. The portable electronic device 38 exchanges communications 40 with a remote server 42, which is a cloud-based computing system that provides analysis of the performance of the user 44.

Fig. 8 is a block diagram illustrating functional components of a device in accordance with a further embodiment of the claimed invention. It will be appreciated that elements having reference numerals that are alike to those used previously but appended with a prime symbol (') correspond in structure and function to those elements having the alike reference numerals without the prime symbol as described previously unless technical context dictates otherwise.

In addition to the elements of the device 2 described previously with reference to Fig. 6, the device 2 ¹ of Fig. 8 further includes an ancillary sensor arrangement (ASA) 80, which contains an IMU 81 including accelerometers and gyroscopes and a barometer 83. For example, the IMU 81 may include a three-axis accelerometer arrangement and a three-axis gyroscope arrangement to be able to measure movements with six degrees of freedom. The ASA 80 may be positioned in any suitable location on the device 2', and it may be located proximate to the strain gauge 22'. Where multiple connecting portions are provided at the sides of the device (e.g. with multiple strain gauges), the ASA 80 and potentially other electronics may be positioned in a cavity located between the connecting portions.

The ASA 80 supplies signals 82 to the processor 30', where the signals 82 include measurements of linear accelerations and angular rates from the accelerometers and gyroscopes from the IMU 81 as appropriate, and an air pressure measurement from the barometer 83. The processor 30' may use these signals 82 when characterising the movement (if the processor 30' is arranged to do so), or may pass these signals on with its output 32' to the wireless communications module 34' (potentially after applying some intermediate processing), which supplies them to the external device 38' in the same manner described above. Examples of how these signals 83 are combined with the signal from the strain gauge 22' are outlined in further detail below with respect to Figs. 13 to 15.

Fig. 9 is a schematic diagram showing the internal structure within the housing of a further device 102 in accordance with another embodiment of the present invention. Elements having reference numerals in the format 'lxx' correspond in form and function to those same elements having a corresponding reference numeral 'xx' described with reference to Figs. 1 to 7 unless technical context dictates otherwise.

In general, a housing (not shown) would surround the central part of the device 102 in the same way that the housing 6 surrounds the interior parts of the device 2 of Figs. 1 to 3.

Unlike the device 2 described previously, in this embodiment, device 102 has two metal connecting portions 116a and 116b, each formed as a strut, that each extend along a respective axis Illa, 111b parallel to the primary axis 110 along which the connecting portion is aligned and along which tensile force is applied, as discussed previously.

Each connecting portion 116a, 116b is rigidly connected to the first hook 104a at one end, and is rigidly connected to the second hook 104b at the other end. As can be seen from Fig. 9, the two hooks 104a, 104b are separate pieces which are joined only via the metal connecting portions 116a, 116b. Thus the two connecting portions 116a, 116b sit within a cavity 118 between the two hooks 104a, 104b which is shaped so as to allow relative movement between the hooks 104a, 104b along the direction of the first axis 110. As tensile force is applied, each connecting portion 116a, 116b will be subject to a respective tensile force along the associated axis Illa, 111b. A respective strain gauge 122a, 122b is positioned on each connecting portion 116a, 116b and each strain gauge 122a, 122b is configured to operate in the manner described previously with respect to the strain gauge 22 discussed with reference to Figs. 4 to 8.

It will be appreciated that in other embodiments there may be connecting portions without a strain gauge, e.g. there may be two connecting portions but only one will be supplied with a strain gauge. There may also be more than two connecting portions (and, by extension, more than two strain gauges), each of which may be aligned along a separate respective axis, parallel to the main axis 10, 110 of the device 2, 102.

The hooks 104a, 104b may be made of a suitable plastic, and through holes 120 are provided on the hooks 104a, 104b for securing the hooks 104a, 104b to the housing (not shown) via suitable means, for example a threaded connector such as a nut and bolt, or a screw and suitable thread.

Fig. 10 is a schematic diagram showing the internal structure within the housing of a further device 202 in accordance with another embodiment of the present invention. Elements having reference numerals in the format '2xx' correspond in form and function to those same elements having a corresponding reference numeral 'xx' described with reference to Figs. 1 to 7 unless technical context dictates otherwise.

In general, a housing (not shown) would surround the central part of the device 202 in the same way that the housing 6 surrounds the interior parts of the device 2 of Figs. 1 to 3.

Like the device 102 described previously with reference to Fig. 9, in this embodiment, device 102 has two metal connecting portions 216a and 216b, each formed as a strut, that each extend along a respective axis 211a, 211b parallel to the primary axis 210 along which the connecting portion is aligned and along which tensile force is applied, as discussed previously. However, unlike the device 102 of Fig. 9, the device 202 of Fig. 10 has the connecting portions 216a, 216b at the extreme edges of the device 202, such that the connecting portions 216a, 216b form 'side walls' of the device 202, connecting the two hook portions 204a, 204b to one another.

Each connecting portion 216a, 216b is rigidly connected to the first hook 204a at one end, and is rigidly connected to the second hook 204b at the other end. As can be seen from Fig. 10, the two hooks 204a, 204b are separate pieces which are joined only via the metal connecting portions 216a, 216b. Thus the two connecting portions 216a, 216b and the hooks 204a, 204b define a cavity 218 between them.

As tensile force is applied, each connecting portion 216a, 216b will be subject to a respective tensile force along the associated axis 211a, 211b. A respective strain gauge 222a, 222b is positioned on each connecting portion 216a, 216b and each strain gauge 222a, 222b is configured to operate in the manner described previously with respect to the strain gauge 22 discussed with reference to Figs. 4 to 8.

It will be seen that unlike the devices described previously, in the embodiment of Fig. 10, the strain gauges are mounted on the flanks (i.e. on the 'sides') of the connecting portions 216a, 216b rather than on the face (i.e. on the 'front') of the connecting portions. This is merely to illustrate that the strain gauges may be positioned on any suitable surface of the corresponding connecting portion. The embodiment of Fig. 10 could just as readily have the strain gauges positioned on the front as before, and likewise the earlier embodiments of Figs. 1 to 9 (and Fig. 11 described below) could have their strain gauges positioned on the flanks. Any of these embodiments may also have the strain gauge positioned on any other suitable surface of the connecting portion, such as on its 'back' surface.

In this particular exemplary embodiment, there are no channels connecting the cavity to the outside of the device. As outlined previously, the channels shown in the other embodiments described herein are optional and may be omitted.

As can be seen in Fig. 10, the device 202 further comprises a detachable housing 203 which - in this embodiment - contains an ancillary sensor arrangement and the wireless communication module. This detachable housing 203 can be removably attached to and detached from the rest of the device 203 (as indicated by the large arrow on Fig. 10). This is achieved via a simple docking 'push-click' system, though it will be appreciated that other forms of attachment means could be used, including but not limited to a magnet arrangement (where magnets may, for example, be situated via location moulding, or other means), a hook and loop (e.g. Velcro®) arrangement, a push clip arrangement (which may be of single- or multi-part construction), a spring catch arrangement, and/or a rubberised push grip arrangement. The strain gauges 222a, 222b on the device 203 can be communicatively coupled to the other electronic circuits within the detachable housing 203 when the housing 203 is docked in the cavity 218 located between the two connecting portions 216a, 216b. This may be achieved via exposed electrical contacts on the flanks of the detachable housing 203 which can be aligned with corresponding electrical contacts on the flanks of the device 202 to provide an electrical connection between the strain gauges 222a, 222b and the rest of the electronics, including the wireless communication module. Alternatively, other forms of communication may be used, e.g. an inductive coupling.

This is deemed desirable by the Applicant as it means the in-line tension measurement - relevant to strain gauges and coupling portions - is the only configuration where the entire device is required. When detached, the detachable housing 203 may be more easily integrated into other exercises (such as affixed to free weights, body parts or parts of an exercise machine) due to its reduced size and weight. This attachment may be through material, elastic or other push-click docking arrangements. This may allow users to conveniently track their exercises via the ancillary sensors. It may also allow for tensile loads to be left attached to coupling devices allowing for swift and easy transitions between exercise types, for example the main 'body ¹ of the device (the coupling portions, connecting portion, and strain gauge) can be 'left behind' connected to a cable machine, while the detachable housing can be removed and used as a standalone device in another exercise, before the user then returns to the cable machine and 'click' the detachable housing back into place.

Fig. 11 is a schematic diagram showing the internal structure within the housing of a further device 302 in accordance with another embodiment of the present invention. Elements having reference numerals in the format '3xx' correspond in form and function to those same elements having a corresponding reference numeral 'xx' described with reference to Figs. 1 to 7 unless technical context dictates otherwise. In general, a housing (not shown) would surround the central part of the device 302 in the same way that the housing 6 surrounds the interior parts of the device 2 of Figs. 1 to 3.

In this embodiment, the hooks 304a, 304b are not of an 'open' construction as in the device 2 of Figs. 1 to 7 or the device 102 of Fig. 9, but instead are of a respective carabiner type construction, each having a respective gate 360a, 360b pivotally connected to the respective hook 304a, 304b via a respective hinge 362a, 362b.

As can be seen in Fig. 10, each gate 360a, 360b can 'swing' about its hinge 362a, 362b to selectively provide access to the corresponding opening 308a, 308b. In the arrangement shown in Fig. 10, the gate 360a of the first hook 204a is closed while the gate 360b of the second hook 304b is open. This carabiner-type construction may advantageously help to prevent fitness equipment unintentionally detaching from the device 302 during use.

Fig. 12 is a schematic diagram showing a section view of a portion of a device 402 in which the strain gauge 422 is positioned on the flank of the connecting portion 416, rather than on the face of it (i.e. rather than on the surface shown 'face on' in the previous profile views of Figs. 3, 9, and 11). In this view, the device is shown 'sideways on', such that the hook portions 404a, 404b lie at the left and right of the image, with the connecting portion 416 between them. The positions of the openings 408a, 408b are shown as dashed lines for ease of illustration.

Fig. 13 is a block diagram illustrating an arrangement in which signal processing is carried out externally, e.g. on a mobile app running on an external device such as a smartphone. The in-line exercise device in this exemplary embodiment acquires signals from both a strain gauge and an ancillary sensor arrangement. In this particular example, the device is the in-line exercise measurement device 2' of Fig. 8 which, as outlined above, includes an ancillary sensor arrangement (ASA) 80 including an IMU 81 and a barometer 83. It will be appreciated, however, that other devices in accordance with embodiments of the present invention may be operated in accordance with the modes outlined below. The wireless communications module 34' is configured to transmit a state update message 1302 via a Bluetooth Low Energy signal 36' to the external electronic device 38', which in this example is a smartphone running a mobile app 1304. This state update message 1302 includes information about the measured strain, pressure, orientation, and acceleration as explained in further detail below.

The measured strain output 1306 from the strain gauge 22' - which is amplified by the Wheatstone bridge arrangement as outlined above - is provided to the state update message 1302 directly.

Similarly, the output from the barometer 83 - which provides a measure of atmospheric pressure 1308 - is provided directly to the state update message 1302. In this particular embodiment, the barometer 83 also has temperature and humidity sensors and supplies temperature and humidity measurements alongside the atmospheric air pressure measurement. These temperature and humidity sensor measurements are used to correct for the influence of temperature and humidity on the measured atmospheric pressure, which is used as a proxy measurement of the device's height, i.e. its altitude.

The IMU 81 contains accelerometers and gyroscopes, as outlined previously. The gyroscopes output a measure of angular rate 1310, and the accelerometers output a measure of linear acceleration 1312.

The processor 30' is configured to perform an orientation estimation process 1314, which receives as inputs the angular rate 1310 and acceleration 1312 outputs from the IMU 81. The orientation estimation process 1314 determines the orientation of the device 2', relative to earth, from IMU measurements. This can be performed by integrating the angular rate measurements 1310 with respect to time, and correcting this orientation from measurements of acceleration 1312 (which will be dominated by acceleration due to gravity, in the downwards direction). These techniques are well documented and understood - implementations using a Kalman filter, using quaternion integration and gradient descent, and/or other similar methods, known in the art perse. The estimate orientation 1316 is provided to the state update message 1302, but is also provided to a further process 1318 which removes the acceleration due to gravity from the acceleration measurement 1312. As the orientation is known (or at least estimated) from the orientation estimation process 1314, the direction of gravity is also known and so the acceleration due to gravity (approximately 9.81 m/s ² ) component can be removed from the measurement obtained by the accelerometers of the IMU 81. The resultant linear acceleration output 1320 (with the gravity component removed) is supplied to the state update message 1302.

The state update message 1302 is then sent to the external electronic device 38' via the Bluetooth Low Energy connection 36'. The mobile app 1304 receives the status update message 1302 and uses the strain, pressure, orientation, and linear acceleration information to characterise the movement carried out by the user.

Figs. 14 and 15 are block diagrams illustrating various exemplary modes of operating a device that acquires signals from both a strain gauge and an ancillary sensor arrangement, in accordance with an embodiment of the present invention. In this particular example, the device is the in-line exercise measurement device 2' of Fig. 8 which, as outlined above, includes an ancillary sensor arrangement (ASA) 80 including an IMU 81 and a barometer 83. It will be appreciated, however, that other devices in accordance with embodiments of the present invention may be operated in accordance with the modes outlined below.

The different modes described below may each be useful for specific types of exercise being carried out. The mode of operation in use at any given time may be set by a user, for example they may select the mode using an interface on the device itself via a mobile app. Alternatively, the motion detected by the ASA 80 may be used to automatically select the appropriate mode for a detected exercise type.

Fig. 14 is a block diagram illustrating the signal processing associated with a first mode of operation. This first mode is useful for exercises in which the force applied by the user is proportional to displacement, i.e. fitness equipment that follows Hooke's law such as a resistance band. With an elastic load (such as in the case of a resistance band), the displacement can be calculated directly from the measurement of force, which can be obtained from the thin-film strain gauge 22' via a suitable amplification stage, e.g. a Wheatstone bridge as outlined previously. Any equipment that obeys Hooke's law - meaning it is elastic, like a spring or resistance band - will have a linear relationship between force and distance, meaning the reps appear as clear peaks in the first signal.

A first processing stage 1402 includes a low pass filter 1404 that filters the signal 1406 from the strain gauge 22' to generate a filtered first signal 1408. This filtered signal 1408 is passed, in parallel, to a peak detector 1410 and a threshold detector 1412.

The peak detector 1410 is configured to generate a peak signal 1414 indicative of peaks in an amplitude or power of the signal, i.e. the points at which the force is maximal - this corresponds to the 'top' of the rep being measured.

The threshold detector 1412 is configured to generate a fall signal 1416 indicative of when an amplitude or power of the (filtered) first signal falls below a threshold value - this is to ensure force falls to around zero, which is the 'bottom' of the rep being measured.

A repetition counter 1418 receives the peak signal 1414 from the peak detector 1410 and the fall signal 1416 from the threshold detector 1412. The repetition counter 1418 increments a repetition count value upon determining from the peak and fall signals 1414, 1416 that a repetition has been completed by the user. In this arrangement the force must reach a peak value and return to the specified 'floor' level for a rep to be counted by the repetition counter 1418, however in a simplified version a rep may be counted based on the signal crossing the floor level alone (therefore allowing the peak detector 1410 to be omitted).

The work done during the rep can also be obtained in this first mode, using a second processing stage 1422. The tensile force measurement signal 1406 obtained from the strain gauge 22' is input to a divider 1424 which divides the force by a stiffness value to obtain an extension signal 1426. The extension signal 1426 is input to a differentiator 1428 that differentiates it to obtain an extension delta signal 1430 which represents the change in extension. The extension delta signal 1430 is input to a comparator 1432 which checks whether the change in extension is greater than zero. When the change in extension is greater than zero (i.e. when the output of the comparator 1432 indicates there has been an increase in extension), the extension delta signal - now referred to as the increase in extension signal 1434 - is input to a multiplier 1436 which also receives the tensile force 1406. The multiplier 1436 multiplies the increase in extension 1434 by the tensile 1406, and the result 1438 of that multiplication is input to an integrator 1440. The integrator 1440 integrates the multiplication result 1438 to obtain a work done value 1442.

Fig. 15 is a block diagram illustrating the signal processing associated with a second mode of operation. When operated in this second mode, the device may be used during some other exercises, such as exercises that use free weights and/or cable machines, that may have a force profile that is proportional to acceleration.

If the fitness equipment (e.g. a free weight) is not put down during a set, then the force does not fall to zero because a force is required to hold the weight above the ground. This means the force applied mainly stays in the vicinity of the weight of the object being lifted but has peaks when the object is accelerating and troughs where the object is decelerating.

In the case of a slow, controlled rep, there typically will be only a small variation in the force exerted (force due to inertia, as the mass accelerates or decelerates at the beginning or the end of a rep). In the case where an exercise is being performed at a high speed, these inertial forces may be more significant. Such a profile changes significantly with the speed at which the exercise is performed.

The user may also put the weight entirely down, meaning that the measured force falls to zero, or the user may cycle between two different heights, meaning that the force does not fall to zero. In the scenario of weightlifting, measurement of the altitude of the device provides a measurement by which the change in height of the device can be estimated, and therefore the vertical displacement can be estimated. This altitude measurement may be obtained directly, however in this example the barometer 83, which generates an air pressure signal, is used to provide a proxy measurement of the altitude (i.e. height) of the device.

As outlined in further detail below, when operating in this second mode, the device may determine the work done from the estimate of the weight (obtained from the thin-film strain gauge) and the estimate of the vertical displacement - the change in height - of the device, specifically the work done in this scenario is equal to the product of the force (weight) and vertical displacement (change in height).

The force measurement used for determining work done in this second mode may be obtained directly from the thin-film strain gauge 22', i.e. from its output signal 1502. However, in this example, a low pass filter 1504 is used to obtain a filtered first signal 1506 by filtering the output 1502 of the thin-film strain gauge 22', with the resultant filtered signal 1506 providing an estimate of the weight. This may typically be a different low pass filter to the low pass filter mentioned previously with respect to the first processing stage 1402 described with respect to Fig. 14.

The air pressure signal 1508 from the barometer 83 is input to a third processing stage 1510 which is configured to determine an altitude value 1512 from the air pressure signal 1508. The third processing stage 1510 carries out a process 1514 that makes use of barometric equations, in a manner known in the art per se. The altitude value 1512 provides an estimate of the height of the device. This estimate of the height 1512 is typically drift-free but potentially noisy.

The third processing stage 1510, and thus the barometric equation process 1514 running in that stage 1510, also receives correction signals 1516, which include a temperature, humidity, and any other suitable correction signals 1516 from respective temperature, humidity, or other corrective sensors 85 (which may be part of the same package as the barometer 83 or may be independent components, as appropriate). The third processing stage 1510 uses the correction signals 1516 to correct for variations in the air pressure due to temperature, humidity, etc. that might otherwise cause inaccuracies in the determined altitude of the device. A fourth processing stage 1518 is configured to receive an acceleration signal 1520 from the accelerometers 1522 and an orientation signal 1524 indicative of the orientation of the device. The signal indicative of the orientation of the device may be acquired from gyroscope(s) or magnetometer(s) within the device, but in this case are acquired from the gyroscopes 1523 within the IMU 81.

The fourth processing stage 1518 runs a process 1526 that uses the acceleration signal 1520 and orientation signal 1524 to determine a vertical linear acceleration value 1528. In other words, the measured acceleration and orientation of the device are used to determine the device's linear velocity in the vertical direction (i.e. the rate at which it is changing height or altitude).

The vertical linear acceleration value 1528 is input to an integrator 1530 which carries out a double integration process in order to obtain a second altitude value 1532. This second altitude value 1532 provides an additional estimate of the height of the device, where this second estimate 1532 is lower in noise but more prone to drift than the estimate 1512 from the barometer 83. Corrective linear regression may be added (potentially through the application of machine learning) to remove an error component of the output.

The first altitude value 1512 from the barometer 83 and the second altitude value 1532 obtained from the IMU 81 are combined by a combination unit 1534, which generates a refined altitude value 1536. The refined altitude value 1536 provides an improved estimate of the height by combining the low noise but drift-prone acceleration-based estimate 1532 with the noisy but drift -free barometer-based estimate 1512.

The combination unit 1534 provides a feedback signal 1538 containing information on the velocity and/or position of the device to the integrator 1530 that performs the double integration process.

A further process 1540 multiplies the refined altitude value 1536 by the force value obtained from the filtered signal 1506 from the thin-film strain gauge 22' to obtain the work done when the device is operated in this second mode. This process 1540 also obtains a repetition count by using the refined estimate of the height 1536 to determine the top and bottom of each rep, where these are counted (e.g. by incrementing a repetition count value after each cycle in height). By comparing the (refined) estimate of the height 1536 to suitable upper and lower threshold values, the completion of each rep may be detected. The selection of these upper and lower threshold values may be obtained experimentally or set during a calibration process.

Figs. 17A and 17B are schematic diagrams of a detachable housing 1703 which may be used as a standalone device. The detachable housing 1703 may have similar form and function to the detachable housing 203 previously described with reference to Fig. 10. It will be appreciated that this device may be used in combination with any of the other embodiments described herein, as appropriate.

Fig. 17A shows the front of the detachable housing 1703 and Fig. 17B shows the rear of the detachable housing 1703.

As can be seen in Fig. 17A, the detachable housing 1703 may be provided with an interface button 1705 on the front surface. It will be appreciated that the interface button 1705 could be located elsewhere on the detachable housing 1703. This interface button for receiving a user input. This interface button 1705 can be pressed by a user to turn the device on and off, enabling the electronics at least within the detachable housing 1703 but also potentially within the rest of the device (e.g. the strain gauge and associated electronics) to which it is fitted, via a suitable electrical connection, coupling, or interface between the detachable housing 1703 and the surrounding device (not shown).

The interface button 1703 may, additionally or alternatively, be used to enable one or more other functions of the detachable housing 1703, e.g. to put it in a pairing mode, to enable NFC communications, and/or some other function, as appropriate.

The detachable housing 1703 can include a near field communication (NFC) module which can be used to enable a further mode of communication, e.g. to enable communication via the wireless communication module (which may be located within the detachable housing 1703 itself).

The detachable housing 1703 contains a battery, which in this embodiment acts as a power source for the electronics within the detachable housing 1703. The battery may also, in some embodiments, be used as a power source for the rest of the device to which the detachable housing 1703 is fitted (e.g. the strain gauge and associated electronics) with power being supplied via a suitable electrical connection, coupling, or interface between the detachable housing 1703 and the surrounding device (not shown).

The detachable housing 1703 includes charging circuitry for charging the power source. In this embodiment, a wired charging arrangement is provided via a USB-C port 1707 through which power can be received. Additionally, or alternatively, the detachable housing 1703 could make use of a wireless charging arrangement. The wireless charging arrangement may comply with the Qi® or Qi2® standards, or any other such standard or proprietary wireless charging technology. It will of course be appreciated that the detachable housing 1703 may include both wired and wireless charging options.

The detachable housing 1703 is of a waterproof construction, achieved using a seal that extends around the device (not shown) that prevents the ingress of water into the housing 1703. To allow use of a barometer within the detachable housing 1703 (e.g. as part of an ancillary sensor arrangement) to determine the height of the device during use, a waterproof barometer aperture (not shown) may be provided.

The detachable housing 1703 may have any appropriate size and shape and may differ from what is shown in Figs. 17A and 17B. The detachable housing 1703 may be constructed from any suitable material, including but not limited to plastic.

The detachable housing 1703 may include attachment means for attaching the detachable housing 1703 to fitness equipment. The detachable housing 1703 may be provided with a number of magnets (not shown) situated in the rear of the detachable housing 1703, where these may be external or embedded within the housing material (e.g. embedded within the plastic). Additionally, or alternatively, the detachable housing 1703 could include a hook and loop (e.g. Velcro®) arrangement, a push clip arrangement (which may be of single- or multi-part construction), a spring catch arrangement, and/or a rubberised push grip arrangement. It will be appreciated that the detachable housing may be provided with one or more of these arrangements (and/or other such arrangements) to provide the function of the attachment means.

A number of holes 1709 are provided for connecting the case.

Fig. 18 is a schematic diagram of an in-line exercise measurement device 1802 in accordance with a further embodiment of the claimed invention. In this embodiment, the coupling portions 1804a, 1804b and the connecting portion 1806 together form a substantially C-shaped arrangement. The respective ends 1805a, 1805b of the coupling portions 1804a, 1804b face one another and form a pair of jaws, with a gap 1807 between them.

In this embodiment, the device 1802 is made of a mixture of inflexible and flexible materials. The connecting portion 1806 and the initial parts of the coupling portions 1804a, 1804b connected to that connecting portion 1806 - indicated as those parts to the left of dividing line 1809 shown on Fig. 18 for illustrative purposes only - are made from a robust but inflexible material, which may be metal. The use of such a material (e.g. metal) allows strain to distribute uniformly to the strain gauge(s) located along the connecting portion 1806.

Conversely, the remainder of the coupling portions 1804a, 1804b including the jaws 1805a, 1805b - the parts to the right of the dividing line 1809 on Fig. 18 - are made of a flexible material, particularly a rubberised material (though other flexible materials may be used, as appropriate).

As the ends of the coupling portions 1804a, 1804b can 'flex' in response to an applied force, the device 1802 can be pushed on to fitness equipment, with the gap 1807 extending to receive fitness equipment and then the coupling portions 1804a, 1804b returning to their normal position, with the fitness equipment being securely retained by the device. Those skilled in the art will appreciate that this provides a 'sprung gate ¹ construction.

It can be seen, therefore, that the gap 1807 between the jaws 1805a, 1805b provides an aperture through which external equipment may be fed - for example fitness equipment (e.g. cables, resistance bands, ropes, carabiners, or strap loops) can be pushed through the receiving gap such that such fitness equipment then abuts against the first and second coupling portions for in-line tensile force applications. The receiving gap may also be used to receive other types of fitness equipment such as free weights - for example the device can clamp on to the bar of a barbell or dumbbell.

The aperture and jaws may or may not be shaped to automatically separate and/or fold back the jaws or ends 1805a, 1805b of the coupling portions 1804a, 1804b as fitness equipment is inserted. With this advantageous arrangement, one axis of movement results in clamping or unclamping of the device 1802, making attachment and detachment a simple - and potentially one-handed - operation for the user.

The strain gauge is coupled to (and potentially embedded within) the connecting portion 1806 in the same manner as described previously. The other electronics, such as the ancillary sensor arrangement and wireless communications module could also be embedded within the device 1802, e.g. within the connecting portion 1806. The device 1802 may be thicker around the electronics to provide an enhanced degree of physical protection to those electronics.

The device 1802 may, however, instead be used in combination with a detachable housing arrangement such as those described previously, such that certain electronics such as the ancillary sensor arrangement and wireless communications module (potentially together with a battery and/or any other electronic components) may be situated in a detachable housing (e.g. that shown in Fig. 10 or Figs. 17A and 17B) which can be fixed within the device 1802 via a suitable retention mechanism.

Fig. 19 shows another device 1902 in accordance with a further embodiment. In this particular embodiment, the coupling portions 1904a, 1904b are of a 'closed' construction, and both coupling portions 1904a, 1904b are connected at both ends via respective connecting portions 1906. This construction may advantageously improve the strength of the device, provide for uniform distribution of force, and/or reduce the size of the device 1902 in line of force. It can be seen that the coupling portions 1904a, 1904b are each of a ring-like construction, with a respective hole 1909a, 1909b in the centre, though the actual shape may vary from what is shown in Fig. 19.

In the embodiment shown in Fig. 19, fitness equipment may be connected or coupled to the device 1902 via suitable means - for example a cable, strap loop, or band may be passed through the holes 1909a, 1909b enclosed by respective the coupling portions 1904a, 1904b. Additionally, or alternatively, the fitness equipment may be provided with a carabiner, clip, hook, clamp, or such like that can be attached to the coupling portions 1904a, 1904b.

As in other embodiments, a housing 1903 with an interface button 1905 may be positioned in the centre of the device 1902, where this housing 1903 may contain an ancillary sensor arrangement, wireless communications electronics, and so on as described in more detail previously. This housing 1903 may or may not be detachable, as appropriate, and where it is detachable it may be provided via any suitable means for allowing it to be attached or detached, for example as described in respect of the detachable housings shown in e.g. Figs. 10, 17A, and 17B.

It will be appreciated that embodiments of the present invention provide a device for measuring an in-line tensile force applied during physical movements of a user such as during exercises or physiotherapy. The device may also provide a measure of other activity metrics, including but not limited to power, control, rate of force deployment, consistency, etc.

While specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that the embodiments described in detail are not limiting on the scope of the claimed invention.