TECHNICAL FIELD

[0001] The specification pertains to biological data acquirers of the type which can be worn by a user.

BACKGROUND

[0002] The field of biological data acquisition is quite vast and can include acquisition of multiple types of biosignals, such as electrical signals (EMG - recording of electrical signals stemming from muscle activity otherthan the heart) and electrocardiography (ECG - recording of electrical signals specific to the heart, often including a measure of heart rate), optical signals (e.g. photoplethysmography-PPG which can allow for the determination of oxygen saturation level or arterial pressure for instance), temperature, movement (e.g. using accelerometers, gyroscopes, sometimes referred to as IMU - inertial measurement unit, or other types of sensors), bioimpedance (e.g. the impedance of the biological tissues/skin), amongst a number of other possibilities. Various technologies exist, and their costs in association with acquiring different biosignals with different degrees of precision can vary.

[0003] Some high-end systems have been designed to acquire biosignals in tightly controlled conditions such as a hospital. While they can achieve a relatively high degree of precision, such systems can be ill-adapted for the needs of some consumers such as physical training enthusiasts or even high-end professional athletes, for reasons such as their cost for instance. On another end of the spectrum, consumer products such as smart watches are available to obtain some biosignals such as heart rate, but they typically have limited functionalities and limited accuracy. Moreover, in many cases, biological data acquirers are specialized for a specific use and have limited versatility. While existing technologies were suitable to a certain degree, there always remains room for improvement.

SUMMARY

[0004] Limitations of previously available technologies included versatility either in terms of a limited type of signals, potentially of limited accuracy, which could be acquired with a given device or system, and/or being limited to a specific portion of the body to which the system is operable to be applied. The electronics used to perform some types of biosignal acquisition, such as some EMG, movement or PPG functionalities for example, can be sufficiently costly for it to be dissuasive for potential consumers especially in a context where they have limited versatility.

[0005] In accordance with one aspect, it was found that a system could be adapted to acquire biosignals from more than one portion of the body, such as by being worn on either a limb or a torso of a user, by integrating the electronics in a strip adapted either to be closed upon itself and worn on a limb of a user, or extended with a separable strap for wearing on a torso of a user.

[0006] In accordance with one aspect, there is provided a biosignal acquisition system comprising : a flexible and elongated strip having a first strip end opposite a second strip end, the first strip end being connectable to the second strip end into a direct band wearable around a limb of a user; and a flexible and elongated strap having a first strap end opposite a second strap end, the first strip end being disconnectable from the second strip end and connectable to the first strap end wherein the disconnected second strip end is connectable to the second strap end into an extended band wearable around a torso of the user; the strip further having at least one biosensor operable for acquiring at least one biosignal from the user when worn as the direct band and when worn as the extended band.

[0007] In accordance with one aspect, there is provided a system including a band having a first closed-loop dimension adapted for wearing on a limb such as a leg or arm, and a strap. The band and the strap can each have mating connectors at both opposite ends in a manner that the band can be closed upon itself for wearing around an arm or leg, or connect its ends to respective ends of the strap to increase the available closed-loop dimension and allow wearing it on a significantly larger portion of the body such as the torso or abdomen. Accordingly, biosignal acquisition electronics such as EMG acquisition but potentially other biosignal acquisition modules, can be integrated into the band, and be useful not only on the body portion to which the band is adapted, but also on a significantly larger body portion, such as a torso, without requiring the use of separate systems. Providing a significant degree of elasticity or adjustability to the band can allow to wear the band on either the forearm or torso, for instance, simply based on the band’s elasticity and/or adjustability. The band can be worn on a user’s wrist during everyday activity for instance, and moved to a leg or torso during specific physical training, providing a versatile biosignal acquisition consumer product in some embodiments.

[0008] In accordance with another aspect, it was found that a system could be adapted to acquire biosignals from different limb sizes by providing stretching ability to a strip having the electronics mounted thereon, and by disposing wiring which extends between different components of the system along a stretchable portion in a sinuous configuration, in a manner for the wiring to bend rather than being subjected to the stretching tension and potentially failing.

[0009] Given the subtlety of the EMG signal, EMG acquisition is typically done relatively locally, in the immediate vicinity of a muscle/group of muscles of interest. While in some cases one can benefit from having a plurality of independent EMG signal acquisition points, or channels, a typical EMG recording operation would be interested in grouping the acquisition points around and/or along the target muscle or group of muscles. Accordingly, in an EMG signal acquisition embodiment, electrodes associated to a given biosignal acquisition point would typically be close to one another. In an embodiment with a number of channels, the electrodes of each pair would typically be relatively close to one another and the pairs of electrodes may also be relatively close to one another. Recording an ECG, on the other hand, may benefit from having electrodes more spaced apart from one another than in a typical EMG application.

[0010] It was found that one may more satisfactorily record an ECG from a biological data acquirer worn on a forearm of a user by using a first electrode in contact with the skin of the forearm, and by a second electrode in electrical contact with a user’s other hand (e.g. finger or thumb), for the acquired biosignal to be representative of a difference of potential between one hand and the other forearm, across the torso. This can be achieved with a biological data acquirer having a band worn on a users’ wrist with a first electrode on an inner face, in contact with the user’s wrist, for example, and a second electrode on an outer face, exposed to intentional electrical contact with the user’s other hand. [0011] Following onto such a concept, having a third electrode on the inner face can allow to obtain an EMG signal between the first and the third electrode in addition to providing the capability for an ECG signal between the first and second electrode. In some embodiments, it can be considered suitable to incorporate electronics which allow to automatically record the signal as an ECG when the user’s other hand is in contact with the second electrode, and to otherwise record the signal as an EMG between the first and third electrode. Using the same electrodes for two different functionalities can allow achieving cost reduction, miniaturization, and/or otherwise lead to device simplification.

[0012] In accordance with another aspect, there is provided a biosignal acquisition system comprising : a flexible and elongated strip operable for forming a band wearable around a limb of a user, the strip further having at least one biosensor operable for acquiring at least one biosignal from the user when worn, the at least one biosensor including an ECG acquirer connected to at least two electrodes, including a first electrode on an internal face of the strip and a second electrode on an external face of the strip, the biosignal acquisition system being operable to power up at least one component of the ECG acquirer upon detecting a diminution of impedance between the first electrode and the second electrode.

[0013] Many further features and combinations thereof concerning the present improvements will appearto those skilled in the art following a reading of the instant disclosure.

DESCRIPTION OF THE FIGURES

[0014] In the figures,

[0015] Fig. 1A, 1B and 1C present example embodiments of biosignal acquisition systems;

[0016] Fig. 2 presents a portion of an example biosignal acquisition system featuring a connector;

[0017] Fig. 3 is a diagram schematically representing another embodiment of a biosignal acquisition system;

[0018] Figs. 4A and 4B are example schematics of elements operable for detecting the presence or absence of a contact between an electrode and a user’s skin; [0019] Fig. 5 is another diagram schematically representing yet another embodiment of a biosignal acquisition system;

[0020] Fig. 6A is an oblique view of an example strip with components missing for the purpose of illustration, Fig. 6B presents electronic components thereof, and Fig. 6C is a cross- sectional view taken across a portion thereof;

[0021] Fig. 7 is an oblique view of another example of a strip;

[0022] Figs 8A and 8B are block diagrams of two possible embodiments of electronic arrangements for a strip; and

[0023] Fig. 9A is a block diagram representing an embodiment of a EMG sensor, with Fig. 9B being a graph presenting an example EMG biosignal frequency distribution;

[0024] Fig. 9C is a block diagram representing an embodiment of a ECG sensor;

[0025] Fig. 9D is a block diagram representing an embodiment of a movement sensor.

DETAILED DESCRIPTION

[0026] Fig. 1A shows an example biosignal acquisition system 110 having a flexible and elongated strip 112 which is worn on a forearm of a user. More specifically, the strip 112 forms a closed-loop in Fig. 1A, which will be referred to herein as a direct band which can be worn around a limb 114 of a user 116. The biosignal acquisition system 110 can have one or more biosensors or components thereof such as an EMG sensor, an ECG sensor, a PPG sensor, a movement sensor operable to acquire corresponding biosignals when the strip 112 is worn on the user. It will be noted that in the example embodiment presented in Fig. 1A, the strip 112 has an optional feature of stretchability which can allow it to be stretched in a manner to be worn on limbs having different sizes, such as a leg instead of an arm as schematized in Fig. 1 B, or simply to adapt to users of different sizes. More detail about the stretchability feature will be presented further below in relation with Figs. 5, 7A-7C and 8. In particular, it will be noted that running an electrical lead (extending, for instance, between an acquirer and an electrode) along a stretchable portion can represent a challenge which can be overcome by disposing the electrical leads along a sinuous path along the stretchable portion, the sinuous path having sinuosities protruding transversally relative to the longitudinal orientation extending around the closed loop.

[0027] Fig. 1C presents another example embodiment of a biosignal acquisition system 210. The embodiment presented in Fig. 1C also has a strip 212 having similarities to the strip 112 presented in Fig. 1A. However, the strip of Fig. 1C has two opposite ends 220, 222 having connectors. The ends 220, 222 of the strip 212 can be referred to as a first strip end and 220 a second strip end 222 for ease of reference and the connectors can be referred to as a first connector and a second connector. The connectors are operable to either be engaged directly to one another, into a direct band configuration wearable around a limb of a user such as in Fig. 1 A, or disengaged from one another which allows to unwrap the strip 212 such as shown in Fig. 1C. In the example embodiment presented in Fig. 1C, the biosignal acquisition system 210 further has an optional strap 224. The strap 224 has two opposite ends 226, 228 which can be referred to as the first strap end 226 and the second strap end 228 for ease of reference. The strip ends 220, 222, when disconnected from one another, can be connected to corresponding ones of the strap ends 226, 228 (here the expressions first and second do not imply any specific structure and are simply used to provide distinctive labels to different ones of the ends), to form an extended band 230 wearable around a much larger portion of the wearer’s anatomy, such as the torso or abdomen for instance, such as illustrated in Fig. 1B. Such a biosignal acquisition system 210 can allow to use one or more biosensors contained in the strip 212, or partial functionalities or capabilities thereof, on body portions having significantly different sizes. In this manner, a user 116 can leverage the costs associated to one or more biosensors or one or more partial functionalities or capabilities thereof for more than one target body portion, potentially making the investment required to acquire the system more worthwhile.

[0028] In one embodiment, the strap 224 can have an adjustable length for instance to more easily adapt to varying body sizes. The strap 224 can also have connectors at both opposite strap ends 226, 228 which are operable for receiving corresponding ones of the strip connectors 220, 222. For instance, a same male connector can be used at the first strip end 220 and at the second strap end 228, and a same female connector can be used at the second strip 222 end and at the first strap end 226. [0029] Fig. 2 presents the engagement of the first strip end 220 with the second strip end 222 of the strip 212 in greater detail. In this embodiment, the first strip end 220 has a male connector 232 and the second strip end 222 has a female connector 234. The male connector 232 has an elongated, transversally oriented male member and the female connector has an elongated, transversally oriented female member. Both the male member and the female member can have a matching, though respectively positive and negative, and transversally constant cross-section in a manner for the male member to be transversally slidably engageable into the female member until an abutment is reached and the engagement is complete. The male member can be transversally slid out from the female member in a similar manner, but in an opposite direction. Here, “transversal” is used to refer to an orientation which is transversal relatively to the “longitudinal” orientation extending around the closed-loop of the band, wherein both transversal and longitudinal can lie generally within the flat shape of the strip 212. Many other types of connectors can be used in alternate embodiments, such as longitudinally oriented clips, buckles, magnets, etc. It was found, however, that a transversal sliding engagement connector such as the one shown can be advantageous to at least some embodiments, as they can provide a very strong resistance to longitudinal tension, which is the main source of stress acting on the connector during operation, while also offering a relatively small longitudinal footprint in terms of occupied longitudinal space.

[0030] In some embodiments, multiple biosensors can be integrated into the strip. Individual sensors can include sensing elements such as electrodes in the case of an EMG or ECG, and can also include some basic acquisition functionalities which can be implemented by electronics. The biosensors can include one or more of an EMG acquirer, a movement acquirer, a PPG acquirer, an ECG acquirer, etc. More advanced functionalities which will be referred to as “modules” herein can be provided to perform more advanced processing of one or more of such signals. Such more advanced functionalities can require some form of processor and memory, and thus some form of “computer”. Depending on the embodiment, such a computer may be integrated into the strip 212, 112 or may be provided separately, such as will be discussed further below. [0031] Fig. 3 presents an embodiment of a strip 212 in accordance with an example. In this embodiment, the strip 212 has, integrated thereto, two exposed electrodes 240a, 240b on the internal face which are operable to be in contact with the user’s skin when the strip is arranged into a direct band wearable around a limb of the user (hence the expression “internal”). In this embodiment, the two electrodes are spaced apart from one another along the length of the strip and are more specifically disposed here at respective ones of the first strip end and of the second strip end. Accordingly, when the first strip end is disengaged from the second strip end, and connected to the second strap end with the second strip end connected to the first strap end, and worn on the torso of the user, the electrodes can become spaced apart from one another across the user’s torso, which can be particularly useful for recording an ECG. Indeed, acquiring an ECG signal typically benefits from having electrodes further spaced from one another while forming an electrical path therebetween which runs across the chest, including the region of the heart. The ECG acquirer 242, can have an ECG acquisition channel 244a connected to both these electrodes 240a, 240b.

[0032] Still referring to the embodiment presented in Fig. 3, the biosignal acquisition system 210 can further include an EMG acquirer 246, and the EMG acquirer 246 can also have an acquisition channel 248a, 248b, 248c connected to the same, or to different, electrodes 240a, 240b, 240c, 240d, 240e, 240f. In the illustrated embodiment, the same electrodes 240a, 240b are used both for the EMG and for the ECG acquisitions. When both ends of the strip 212 are connected to one another and worn as a direct band 112 around the limb 114 of the user 116, and where an EMG signal is acquired via the electrodes 240a, 240b, the electrodes240a, 240b are close to one another, which can be suitable for EMG acquisition. An embodiment such as presented in Fig. 3 may have rigid or semi-rigid housings housing the electrodes 240a, 240b, 240c, 240d, 240e, 240f and/or other electrical or electronic components, and one or more lengths of flexible material extending therebetween. The one or more lengths of flexible material may be stretchable or not (stretchable implies elastic stretching ability to at least 10% of its initial unstressed length in this specification). Electrical leads made of metal can extend longitudinally along the lengths of flexible material between the housings. [0033] In the embodiment presented in Fig. 3, an intermediary housing 250 can be provided at an intermediary location between the two ends 220, 222. The intermediary housing 250 can have, integrated thereto, electronics associated to one or more of the EMG and ECG acquirers 246, 242 for instance, other biosensors, and perhaps even a computer and/or a user interface for instance. In this embodiment, the intermediary housing 250 has, on its outer face (relative to the closed loop configuration), yet another electrode 240g, which is accessible, when the strip is worn on a first arm of a user, to the hand of the other arm of the user such as by applying a thumb or other finger thereto. This other electrode 240g can form, when the user’s other hand is in contact with it, an electrical path extending across the user’s arms and torso and leading to an electrode 240b which is on the inner face of the strip 212 and in contact with the user’s first arm. As schematized in Fig. 3, the ECG acquirer 246 can have a channel 244b extending between such an externally facing other electrode 240g and an internally facing electrode 240b. This channel 244b is a second channel in this example but embodiments are possible where this channel 244b would be the only ECG channel of a given system. This ECG channel 244b can allow a user to use the biosignal acquisition system 210 to acquire an ECG signal while the user 116 is wearing the strip 212 on his arm for instance.

[0034] In some embodiments, such the one schematized in Fig. 3, one or more of the inward-facing electrodes 240a, 240b, 240c, 240d, 240e, 240f, can be shared between the ECG acquirer 242 (ECG biosensor) and an EMG acquirer 246 (EMG biosensor) to achieve a hardware economy, and/or one or more of electronic elements associated to the ECG acquirer 242 and EMG acquirer 246 can be shared. In such embodiments, or other embodiments, it can be considered relevant to allow for automatic detection of whether a user’s hand is applied to the outward facing electrode or not, as this can be interpreted as a signal indicating whether or not ECG acquisition should proceed through channel 244b of the ECG acquirer 242, particularly if limited resources, such as energy or memory, are required for ECG acquisition. In an alternate embodiment to the one presented in Fig. 3, the ECG acquirer can also use a reference electrode. From the point of view of hardware efficiency, it can be preferred to use the same reference electrode both for the EMG acquirer and for the ECG acquirer but in some embodiments it may nonetheless be preferred to use distinct reference electrodes for distinct biosensors. [0035] Fig. 4A and 4B schematize two example embodiments operable to provide an indication of whether or not a user’s finger 260 is being applied to the outward facing electrode 240g. In both embodiments, an inward facing electrode 240b can be maintained in contact with the user’s skin 262 on a first arm by the strip 212, and the outward facing electrode 240g can be exposed to selective, intentional contact with a finger 260 of the user’s other arm. An ECG amplifier 264 can be used between the two electrodes 240b, 240g, and can be connected to an analog to digital converter (ADC) for digital processing, storing into memory and/or transmission for instance. Components such as the ECG amplifier 264 and the analog to digital converter (ADC) can be operated by a microcontroller for instance. In the embodiment presented in Fig. 4A, a positive power supply 266 can be applied to the electrical lead 268 of the outward facing electrode 240g through a high-impedance pull-up resistor 268, and the outward facing electrode 240g can also be connected to a low gain amplifier 270 with the reference voltage Vref. A high impedance detector can then detect, based on a so-called “pull-up” configuration, whether high impedance associated to the presence of the user’s finger on the outward facing electrode 240g is present or not, and a comparator 272 can be used to send a first signal, e.g. 1 , if the finger 260 is detected on the electrode and another signal, e.g. 0, if the finger 260 is detected to be absent, this latter signal can be sent to the microcontroller for instance which can determine whether or not to power any electric or electronic component associated to ECG signal acquisition based on the signal.

[0036] The embodiment presented in Fig. 4B can perform a similar function, but simply by measuring a bioimpedance between the two electrodes at a bioimpedance measurement circuit 280. If the bioimpedance measurement circuit 280 is saturated, a controller such as a microcontroller or computer module determines that a finger 260 is not present on the electrode 240g and controls the biosensor accordingly, whereas if the bioimpedance measurement circuit 280 is not saturated, the controller determines that a finger 260 is present and that ECG is to be acquired, for example.

[0037] Figs. 4A and 4B are but two of numerous possible examples of how such an auxiliary ECG functionality can selectively be activated or de-activated by the user performing nothing additional to putting his/her finger on the electrode, a motion which is to be effected for the ECG recording to take place and which can be very intuitive. [0038] Turning now to Fig. 5, yet another example embodiment of a strip 312 is schematically depicted. In this embodiment, multiple EMG acquisition channels 348a, 348b, 348c are provided for and the EMG acquirer 346 can be operable for simultaneously acquiring an EMG biosignal from each ones of the channels 348a, 348b, 348c. More specifically, each channel 348a, 348b, 348c is associated to a corresponding pair of electrodes 390a, 390b, 390c to which the EMG acquirer 346 is connected by a corresponding pair of electrical leads. Each pair of electrodes 390a, 390b, 390c includes two electrodes, which can be referred to as a positive and a negative electrode by convention, which are relatively close to one another. In this embodiment, each pair of electrodes 390a, 390b, 390c is provided on an inner face of a corresponding housing 392a, 392b, 392c, and the electrodes of each pair are transversally spaced apart from one another. The pairs of electrodes 390a, 390b, 390c are longitudinally spaced apart from one another along the length of the strip 312, i.e. along the orientation of the closed loop when the ends 320, 322 are secured to one another. It was found that such a configuration could be particularly interesting as it can obtain EMGs from a number of acquisition points circumferentially interspaced from one another around the limb of the user when the direct band formed by the strip 312 is worn. Indeed, if worn on the forearm of a user 116 for instance, one or some of the acquisition points can detect the extensor carpi flexion activity, which can be very active when the wrist is raised for instance, whereas acquisition points on a lower side of the forearm can detect the flexor carpi activity, obtaining a significant degree of information about the solicitation of more than one muscle or muscle area. Similarly, an embodiment having a plurality of acquisition points circumscribing a limb during use can be useful in an embodiment where it is desired to detect symmetry of a movement, for instance. In an alternate embodiment, the second electrode of each pair of electrodes can be connected to a single electrode acting as a reference voltage Vref instead of using a separate, additional electrode connected to Vref, to name one possible variation.

[0039] As evoked above, there are several embodiments in which elastic stretchability, within the elastic deformation domain, of the strip 112, 212, 312, and more specifically of the direct band which can be formed by the strip 112, 212, 312, may be beneficial. An example embodiment of a strip which can include multiple-point EMG acquisition sensing such as schematized in Fig. 5, combined with ECG acquisition sensing over two channels such as schematized in Fig. 3, and further offering stretch-ability is presented in Figs. 6A-6C. Indeed, in this embodiment, the strip 212 includes a plurality of housings 290 disposed adjacent to one another along the length of the strip 212. The housings 290 are interconnected to one another by pairs of transversally opposed flexures 292a, 292b. The flexures 292a, 292b are operable to provide elastic stretchability when pulling the housings 290 away from one another along the length of the strip 212. In Fig. 6A, a cover of one of the housings 290 is removed, revealing otherwise hidden portions of the flexures 292a, 292b, perhaps even better understood with reference to the cross-sectional view of Fig. 6C, and one of the housings 290 is entirely absent to show more details. In this embodiment, all the housings 290 are identical, each having two openings 294a, 294b on the internal face as shown in Fig. 6A, where corresponding electrodes can be exposed for contact with the user’s skin, except for a central housing 290’ which is provided with two additional openings : a third opening 294c on the internal face for the electrode which is connected in a manner for applying a reference voltage to the user’s skin, and a fourth opening 294d on the outerface forthe dedicated ECG electrode which is exposed to contact with the user’s finger 260. The housings 290 can all house rigid PCB elements 296 having corresponding electrodes 240a, 240b integrated thereto. The rigid PCB elements 296 can be interconnected to one another by thin, flexible PCB elements 298 which can be inserted into corresponding slots 300 formed within the flexures 292a, 292b and then loosely trapped therein for physical protection. The central housing 290’ can have all the electronics such as acquirers and controller electronics, thus allowing to free the PCBs of the other housings to have a reduced amount of, or no electronics other than electrodes and electrical leads, which can allow to further take advantage of any hardware efficiency available based on the used of shared hardware usage between different functionalities. In yet another embodiment, electronics can be more equally shared between housings, for instance. Since the electrical leads, provided here in the form of flexible PCB elements 298, follow the transversally-oriented U-shape of one or both flexures 292a, 292b of a given flexure pair as they interconnect one housing 290 to another, they can be said to form a sinuous path having sinuosities extending transversally to the length of the strip 212. When two housings 290 are stretched longitudinally apart from one another, the two legs of each of the two flexures which interconnect them become splayed, slightly bending the electrical leads while not significantly pulling them in any form of substantial tension which could otherwise lead to breaking the leads. Accordingly, while the strip 212 can be stretched elastically by more than 10% along its length, the electrical leads can be subjected to only slight elastic bending and no significant stretching. [0040] Fig. 7 shows an alternate embodiment of a strip 412 which has only a single rigid housing 490 which houses all electronic functionalities. The strip 412 has, however, a plurality of electrodes wherein the electrodes are regularly interspaced from one another along the length of the strip 412. As seen in Fig. 7, the electrical leads connecting the electronics within the housing to different ones of the electrodes extends along portions of elastic fabric. Along the portions of elastic fabric, the electrical leads 468 follow a sinuous path which, while generally extending along the length of the strip, includes a plurality of sinuosities of alternating transversal orientations. Accordingly, when the elastic fabric portions of the strip is stretched, the sinuosities in the electrical leads bend, avoiding the electrical leads to be subjected to significant tension which could otherwise lead to breaking the leads.

[0041] On another note, the alternate embodiment presented in Fig. 7 has an adjustable length which is adapted for wrapping around the torso of a user. It can nonetheless, in some cases, be also used for wrapping around a limb of a user, simply by wrapping the strip multiple times around the limb of the user and adjusting the length of the strip to accommodate any excess.

[0042] In an embodiment where the strip is adapted to perform advanced functions such as determining EMG median frequency and comparing it to a threshold for instance, in real time, it can be convenient to incorporate the computer as part of the strip, in which case the computer, and some form of user interface, can be incorporated to the strip such as illustrated in Fig. 8A. The computer can be connected to the one or more sensors in a wired manner, for instance, in which case it can also be convenient to integrate a user interface to the strip. Alternately, it can be preferred to incorporate only the sensors and possibly some basic acquisition electronics in the strip, such as in the embodiment of Fig. 8B. In such a latter scenario, a transmitter can be incorporated in the strip to transmit the pre-processed signals in real time in a wireless manner. In such a scenario, the modules can take the form of applications running on the computer integrated into a smartphone orsmartwatch for instance, which can also serve the functionality of a user interface. In still another example embodiment (not shown), a computer memory can be integrated to the strip, and the acquired data can simply be stored into the memory incorporated in a manner to later be accessed by a computer at other premises for detailed analysis. [0043] In the case of electrical biosignals such as EMG and ECG, various technologies exist. EMG in particular, often referred to as sEMG when acquired externally, across a user’s skin - we will use the expression EMG in this text for simplicity, works with a sometimes particularly subtle electrical signal, and can require monitoring in a number of points and more advanced signal processing (e.g. median frequency calculation over successive time windows, potentially over multiple channels, etc) in order to provide a useful indication than ECG, especially compared to scenarios where ECG is solely directed to measuring heartbeat rate, a metric which is relatively easy to acquire.

[0044] The interest in EMG has risen in recent years for various reasons. Indeed, it was found that a reduction in median EMG frequency is an indicator of muscle fatigue, and that there can be a link between muscle fatigue and risk of injury. Measuring the evolution of median EMG frequency overtime during training, for instance, can thus allow to adjust training vs. rest time in a manner to optimize the training efficiency while limiting risk of injury. Moreover, in other scenarios, such as bodybuilding and powerlifting, symmetrical muscle contraction during training can be a key factor in optimizing training efficiency and reducing risk of injury, especially in situations where an athlete is recovering from a previous injury, for instance, and where the body tends to over-utilize the uninjured limb and under-utilize the previously injured limb. Symmetricity of muscle contraction can be measured using an EMG acquirer.

[0045] As evoked above, muscle fatigue can entrain variations in the muscle force or agility of muscle recruitment. Muscle fatigue can also entrain variations detectable by a noticeable change in movement. From a wearable sensor point of view, different signals can be used as a basis of forming an objective indication of muscle fatigue. Such signals can include electromyography (EMG - and more specifically here surface electromyography), and movement monitoring. Indeed, muscle fatigue can entrain reduction of the median frequency of EMG. Accordingly, monitoring the median frequency, and determining whether it has reduced in excess of a given threshold, can form the basis of one indicator of muscle fatigue. EMG can alternately be monitored to ascertain symmetry of muscle solicitation, for instance. Comparably, muscle fatigue typically entrains an effect in the movement of the user. In a static posture, such as holding a heavy object with one hand and the arm oriented horizontally for instance, muscle fatigue typically entrains a weakening of the solicited muscle(s), and eventually causes lowering of the arm in the latter example. In a repeated dynamic movement, muscle fatigue can also frequently entrain some change in the movement over time, and measuring this variation, or even monitoring a variability of the movement over time, and determining if it has exceeded a given threshold, can form the basis of another indicator of muscle fatigue.

[0046] It was found that while such indicators of muscle fatigue can be relevant in and of themselves, their individual limitations could be alleviated to a certain extent by using them in combination. Moreover, since EMG signals and ECG signals can both be acquired using electrodes, hardware efficiencies may be available by using some or all of the same electrodes for ECG and for EMG. In other words, providing additional ECG acquisition capability to a given biosignal acquisition system may not represent much more hardware costs than simply providing EMG acquisition capability. Some of acquisition electronics and/or computer processing capabilities for higher functionalities may also be shared.

[0047] As schematized in Fig. 9A, EMG, to begin, is typically acquired by applying electrodes 12, 14 into contact with the skin covering muscle tissue. The EMG signal is a relatively subtle, low amplitude, electrical signal which causes a change in electric potential between two of the electrodes. This change in electric potential is measured by electronics which we will refer to herein as an EMG acquirer 16 for simplicity, which is connected to the electrodes by corresponding electrical leads 18, 20. The electrodes 12, 14 can take various forms, such as off-the-shelf electrodes, for instance, or be permanently integrated into a rigid, semi-rigid, or flexible housing. Due to the subtleness of the EMG signal the EMG acquirer 16 typically involves some form of amplification. Moreover, the electric potential of the body is a priori unknown and can vary over time, and to avoid biasing the measurement of the EMG signal by the electrical potential of the body, a third electrode 22 can be used, also connected to the EMG acquirer 16 by a corresponding electrical lead 24, and driven by the EMG acquirer 16 to impart a known, reference potential to the body. The electrical leads 18, 20, 24 can connect the EMG acquirer 16 directly, or via one or more connectors, for instance.

[0048] The amplitude of the EMG signal is typically distributed over a frequency range of 10Hz to 500Hz, such as shown in Fig. 9B, with most of the amplitude being within the range of roughly between 10 and 350Hz, and even 15 and 250Hz, for instance, as shown. The EMG acquirer 16 can operate over the entire bandwidth of 10-500Hz, but in some embodiments, a suitable signal may be obtained over only one continuous, or discontinuous portion of this bandwidth. This can be the case if it is a portion of the bandwidth which represents the frequencies of highest amplitude of the EMG signal, for instance.

[0049] As presented above, obtaining a useful indication from an EMG signal typically involves some form of signal processing, such as determining a median frequency of the EMG signal over one or more successive time windows. Returning to Fig. 9A, a median frequency calculator module 26, such as a function operated by a computer, or other electronics, connected in a wired or wireless manner to the sEMG acquirer 16, or otherwise integrated thereto, can be used to determine the median frequency of the sEMG signal. In a static posture the median frequency can be repeatedly calculated in real time for instance. In a dynamic, repeated movement scenario, software can be used to determine windows of time w1 , w2, w3, wn... associated to each one of the repeated movements, and a median frequency of the sEMG signal can be calculated for each one of these windows. In an embodiment where it is sought to advise a user of a situation of muscle fatigue, one or more deviation threshold 28 can be defined, such as by including the corresponding value as data in the memory of the computer for instance, and shifting of the median frequency overtime can be measured, and compared to the threshold by an indicator generator module 30, such as a function operated by a computer, or other electronics, connected in a wired or wireless manner to the median frequency calculator module 26, or otherwise integrated thereto. An indication of muscle fatigue can be triggered based on the shifting of the median frequency, such as contingent upon the measured median frequency exceeding the threshold 28, for instance.

[0050] The threshold(s) can be predetermined, or defined in real time. For instance, if one wishes to monitor fatigue by EMG median frequency monitoring, the threshold can be defined in the form of a shift from an earlier measured value of EMG median frequency associated to a given user in a given context of use, or from an average of earlier measured values, for instance, and the indication of muscle fatigue can be triggered, or increased, when the detected value exceeds the defined shift threshold or otherwise experiences an increasing shift relative to earlier measured values. [0051] Achieving a good signal to noise ratio can be a concern for EMG. One technique which can be used with this in mind is to use three electrodes positioned in a manner that equal, but opposite differences of potentials are obtained between each of two electrodes with the third one, for one EMG measurement. Much of the noise (n) generated by the electronics would thus be equally applied to both signals. The second signal, essentially -sEMG +n, is subtracted from the first signal, essentially sEMG + n, yielding 2sEMG, which was found to be a suitable and relatively low-cost solution at least in some embodiments.

[0052] It is also possible to obtain an indication of muscle fatigue using EMG on a user subjected to static muscle contraction (i.e. maintained posture). This can be performed, for instance, by measuring the power spectrums and median frequencies of EMG signals acquired for given time intervals (e.g. 1 second). This has been successfully measured on users wearing electrodes on the shoulder muscles, and holding the arm at 90 degrees for as long as they could.

[0053] Higher functionality modules associated with EMG acquisition can collectively be referred to as EMG modules.

[0054] As schematized in Fig. 9C, ECG can also be acquired by applying electrodes 12, 14 into contact with the skin covering muscle tissue. The ECG signal is also an electrical signal which causes a change in electric potential between two of the electrodes. This change in electric potential is measured by electronics which we will refer to herein as a ECG acquirer 16 for simplicity, which is connected to the electrodes by corresponding electrical leads 18, 20. The electrodes 12, 14 can take various forms, such as off-the-shelf electrodes, for instance, or be permanently integrated into a rigid, semi-rigid, or flexible housing. ECG may be less subtle of a signal to acquire than EMG, for practical purposes, and while amplifying the signal with an amplifier integrated to the ECG acquirer, or applying a known reference potential to the body by a third electrode may be helpful in some embodiments, it may also be omitted. The electrical leads 18, 20, 24 can connect the ECG acquirer 16 directly, or via one or more connectors, for instance.

[0055] Either one of the embodiments evoked above can include a group of elements which can be said to form an EMG biosensor, or be referred to collectively as an EMG acquirer, and whose functionality can be summarized as to extract an electronically useable EMG signal from the wearer. Either one of the embodiments evoked above can also include a group of elements which can be said to form an ECG biosensor, or be referred to collectively as an ECG acquirer, and whose functionality can be summarized as to extract an electronically useable ECG signal from the wearer. Some of the elements of the EMG biosensor and of the ECG biosensor can be shared to achieve hardware efficiencies. Some higher functionalities associated to ECG acquisition, such as calculating the heartbeat rate for instance, may benefit from being performed by some form of computer. Any and all higher functionality modules associated to ECG acquisition can collectively be referred to as ECG module(s). Such a system can also include a group of elements which can be referred to collectively as a movement acquirer, and whose functionality can be summarized as to extract an electronically useable movement signal from the sensor.

[0056] Movement can be monitored in various ways, some more elaborate than others. Ways of obtaining an indication of movement which can be used in some embodiments can include sensors (e.g. an IMU) associated with one or more articulation of the user, configured in a mannerforthe articulations to be activated, the extent of which is sensed by the sensor(s), when the user exhibits a movement of interest. In a signal acquired during a static posture, while a user holds a weight statically with his/her hand while the arm is statically held horizontally, over time, when muscle fatigue occurs, the arm begins to lower and thereby cause a measurable change in the movement signal occurs. In signal acquired during a dynamic, repeated movement, with the hand and weight moving regularly up and down, a relatively cyclic signal of motion can be acquired.

[0057] Fig. 9D shows a simplified block diagram showing a movement signal acquirer 42, communicating a or partially processed signal to one or more modules or functions provided as part of a computer, or other electronics, connected in a wired or wireless manner to the movement acquirer, or otherwise integrated thereto and to one another, can be used to process the movement signal and to generate an additional, and possibly two additional indications of muscle fatigue. Such higher functionalities associated to movement acquisition may benefit from being performed by some form of computer. Any and all such higher functionality modules associated to movement acquisition can collectively be referred to as movement module(s), and similarly for PPG modules if a PPG biosensor is present in a particular embodiment of the device.

[0058] A process of generating an indication of muscle fatigue based on a movement signal can work on the basis of a comparison of portions of the signal to a given reference, or template, a process referred to herein as “template matching”. More specifically, the process can compare a portion of the signal within a time window to the template and determine a correlation coefficient indicative of the degree of similitude therebetween. The template can have a given tolerance, such that certain variations can all be considered to be within the tolerance, and in which case the coefficient of correlation can be of 1, for instance, and the more of the signal portion exceeds the tolerance, the closer the coefficient of correlation can be to 0, for instance. The module or function responsible for performing the template matching function can be referred to herein as the coefficient of correlation generator 52.

[0059] Indeed, when individuals make repetitive movements such as gait, movement kinematics are stereotyped. While the exact movement features vary across individuals, they can be very identifying for a given person and form a sort of ‘movement signature’ (coefficient of variation <=10%). The low variability of movement signatures can be used to detect the gradual development of muscle fatigue using a technique called ‘template matching’. First, a reference template (TREF) can be created by averaging a series of initial movement, this can be the first 10-20 movements performed by a user, or to factor in changes in user movement that can occur overtime, such as due to a change of weight or a change in muscle force, or long-term learning, it can be reset periodically, such as by taking the first 10-20 movements every day for instance. Considering the low variability of repetitive movements, TREF represents the non-fatigued standard of reference. In the context where it is created each day for each participant, TREF can be highly individually tailored. Muscle fatigue is known to modify movement kinematics, and in particular, to cause a reduction in movement speed and an increase in movement variability.

[0060] One difference in which the way the process works between the static and dynamic scenarios is the way the portion of the signal, which will be referred to as the time window, is defined. In the case of a static scenario, the time window can be regularly predefined, such as a sequence of X second time windows for instance (where the number X can be selected in a suitable manner in view of a specific embodiment), and the main focus can be to see whether, for example, a movement is detected over time. In the dynamic scenario, the time windows can be actively defined using a module or function which can be referred to herein as the time window definer 54, which recognizes the presence of a repeated movement, and can then separate the signal timespan into windows w1 , w2, w3, wn... corresponding to individual ones of the movements. Two separate indications of muscle fatigue can be obtained from this general process. The module or function responsible for generating the indication(s) of muscle fatigue can be referred to herein as the indication generator 56.

[0061] An additional module or function can be responsible for monitoring a variability of the coefficient of correlator over time. The indication generator 56 can include one or more thresholds and be adapted to generate an indication when either the coefficient of correlation exceeds a given threshold, or the variability exceeds a given threshold, for instance. The thresholds can be predetermined, set in real time based on acquired data, and combinations of these two avenues are also possible, such as a pre-set threshold which is actively modified based on acquired data.

[0062] Returning to Fig. 9A, a median frequency calculator module 26, such as a function operated by a computer, or other electronics, connected in a wired or wireless manner to the EMG acquirer 16, or otherwise integrated thereto, can be used to determine the median frequency of the sEMG signal.

[0063] Returning to Fig. 9D, one or more movement modules provided as part of a computer, or other electronics, connected in a wired or wireless manner to the movement acquirer, or otherwise integrated thereto and to one another, can be used to process the movement signal and to generate one or more additional indications of muscle fatigue.

[0064] In alternate embodiments, the EMG acquirer and/or the movement acquirer 42 can be used for other purposes than obtaining an indication of muscle fatigue, one or more additional biosignal acquirer can be included in a same device, and/or one or the other of the EMG acquirer and the movement acquirer 42 can be absent from the device. [0065] In some embodiments, higher functionalities can be performed by a computer. Such higher functionalities can include sEMG modules or functions such as a median frequency calculator, an sEMG median frequency comparator, and an sEMG muscle fatigue indication generator. Such higher functionalities can also include movement modules or functions, such as a template matching coefficient generator, a coefficient comparator, a first order muscle fatigue indication generator, a variability determinator, a variability comparator, and a second order muscle fatigue indication generator. Some of the modules or functions can be shared between sEMG and movement. For instance, in an embodiment adapted fordynamic repeated movement scenarios, such higher functionalities can also include module or function which operates to recognize a pattern of repeated movement, and separates the signal in time windows associated to individual ones of the movements of the pattern, and which can be referred to as a window determinator, for instance. Such higher functionalities can also include a composite muscle fatigue indicator generator operable to generate a composite indication of muscle fatigue based on two or more of the individual indications of muscle fatigue referred to above.

[0066] The example system can also include a user interface operable to allow interaction with the user. In a simple example case, where the computer is also incorporated to the apparel or otherwise worn by the user, for instance, the user interface can be a visual or audible alarm which can be triggered based on the composite indication of muscle fatigue. In a more elaborate example case, the computer can be provided remotely, and signals or associated data can be communicated to the computer in any suitable way, such as via the Internet for instance, and the computer can be provided with elaborate software allowing more in-depth analysis, for instance.

[0067] In all embodiments, the sensor will be worn by a wearer during the process of signal acquisition. In some embodiments, one or more biosensors can be housed in a preferably relatively small, one or more, electronics housing(s) which can also be worn by the user. In some embodiments, for instance, it can be preferred to provide the system with connectors, for easily connecting and disconnecting the electronics housing from the electrical leads of the sensor. [0068] Some, or all, of the aforementioned higher functionalities can also be integrated into such one or more electronics housing(s) operable to be supported by the strip, or by a separate computer, and the exact choice of which can be left to the designer in view of the specifics of corresponding embodiments. For instance, in some embodiments, a transmitter can be integrated to an electronics housing supported by the apparel, and operable to transmit relevant data to a computer. In a relatively simple example, the transmitter can transmit the raw signals of the acquirers, or processed data if one or more higher functionalities are incorporated to the electronics housing, to a smartphone, smartwatch, or other computer, worn or held separately from the apparel by the user. Such a smartphone or smartwatch can have a software application operable to perform one or more of the higher functionalities and interact with the user via the user interface, for instance, and can further be operable to communicate some relevant data to another computer over the Internet or other network. In a more elaborate example, the transmitter can transmit the raw signals of the acquirers, or processed data if one or more higher functionalities are incorporated to the apparel, directly over the Internet, for access by a healthcare professional or trainer, for instance. The transmitter, and/or a memory can be controlled by a microcontroller (MCU) which receives the signals from the sEMG acquirer and the movement acquirer, for instance.

[0069] It will be understood that the expression “computer” as used herein is not to be interpreted in a limiting manner. It is rather used in a broad sense to generally refer to the combination of some form of one or more processing units and some form of memory system accessible by the processing unit(s). The memory system can be of the non-transitory type. The use of the expression “computer” in its singular form as used herein includes within its scope the combination of a two or more computers working collaboratively to perform a given function. Moreover, the expression “computer” as used herein includes within its scope the use of partial capabilities of a given processing unit. Example computers include desktop, laptop, smartphone, smartwatch, less elaborated controller devices such as a microcontroller MCU, etc.

[0070] A processing unit can be embodied in the form of a general-purpose micro-processor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, a programmable read-only memory (PROM), to name a few examples.

[0071] The memory system can include a suitable combination of any suitable type of computer-readable memory located either internally, externally, and accessible by the processor in a wired or wireless manner, either directly or over a network such as the Internet. A computer-readable memory can be embodied in the form of random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM)to name a few examples.

[0072] A computer can have one or more input/output (I/O) interface(s) to allow for communication with a human user and/or with another computer via an associated input, output, or input/output device such as a keyboard, a mouse, a touchscreen, an antenna, a port, etc. Each I/O interface can enable the computer to communicate and/or exchange data with other components, to access and connect to network resources, to serve applications, and/or perform other computing applications by connecting to a network (or multiple networks) capable of carrying data including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fiber optics, satellite, mobile, wireless (e.g. Wi-Fi, Bluetooth, Bluetooth low-energy, WiMAX), SS7 signaling network, fixed line, local area network, wide area network, to name a few examples.

[0073] It will be understood that a computer can perform functions or processes via hardware ora combination of both hardware and software. For example, hardware can include logic gates included as part of a silicon chip ofa processor. Software (e.g. application, process) can be in the form of data such as computer-readable instructions stored in a non-transitory computer-readable memory accessible by one or more processing units. Wth respect to a computer or a processing unit, the expression “operable to” relates to the presence of hardware or a combination of hardware and software which is operable to perform the associated functions. Different elements of a computer, such as processor and/or memory, can be local, or in part or in whole remote and/or distributed and/or virtual. [0074] As can be understood, the examples described above and illustrated are intended to be exemplary only. The scope is indicated by the appended claims.