The present invention relates to a method for measuring muscular power, and to an apparatus thereof.

More specifically, the invention relates to a method carried out by an apparatus that can be worn by a user that can measure muscular power following a motion activity.

As it is well known, at present, during execution of motion activity (running, jumping, etc.), it is possible evaluating power by different systems.

A first system exploits the stereophotogrammetry technique (video cameras) and it is based on the use of digital cameras for measuring trajectory of reflecting spheres (markers) placed on the user body. Said systems can be used within a laboratory or studio, but they require a difficult setup. Moreover, this kind of system cannot be transported.

Another approach concerns the use of a dynamometric platform, mainly comprising a scale, resting on the grounds, for measuring constraint reactions exchanged between its surface and the body surface in contact with the same (e.g. feet). However, these instruments are heavy and bulky, cannot be easily transported and require a computer for operating.

Always according to known technique, it is possible employing different switches (contact detecting mats and light emission bars), that can substantially detect contact/flying times, these systems can employ transportable and cheap instruments, but they have remarkable drawbacks with respect to the information that they provide and that are connected with movement. The latter thus require integration with hypothesis concerning phenomenon evolution and math models making muscular power evaluation not accurate. Furthermore, in function of distance that one wishes covering, it is necessary installing in series a high number of optical bars or contact detecting mats. It linearly increases costs of the instrument, at the same time reducing its transportability. Therefore, for example, the above instrument cannot be used for reduced distances (even 20 meters), since it would require mounting switches all along the path. Finally, a further method according to the known technique employs inertial sensors (accelerometers or gyroscopes), magnetic sensors (magnetometers) and miniaturised GPS. Interpretation of signals measured by said sensors (linear accelerators, angular speed, local magnetic field and geodesic coordinates) during execution of a set motion task is not immediate, but it requires processing comprising the transformation process of the information measured by sensor into variables and indexes easily usable by clinic personnel and trainers in order to interpret movements.

According to this solution, inertial sensors are known containing accelerometers, gyroscopes and magnetometers, but they are used as measuring instrument and not finalised to evaluation of muscular power. Furthermore, inertial sensors are known finalised to evaluation of muscular power but containing inside only accelerometers. The latter permit such an evaluation only if the body within which the sensor is positioned makes a purely translatory motion.

It is well evident that the above systems are expensive and not adapt to different uses.

In view of the above, it is therefore object of the present invention that of suggesting a method for measuring muscular power and the relevant apparatus for detecting translatory and rotatory movements.

It is also object of the present invention that said apparatus can be a portable apparatus.

It is therefore specific object of the present invention a method for measuring muscular power of a user by an apparatus attachable to the body of said user, comprising the following steps:

(a) detection of a starting status of the acquisition, in which said user is in a substantially static posture, thereby obtaining a first offset initial acceleration constant of linear acceleration a nd a second offset initial angular speed (ω) constant;

(b) acquisition of one or more signals of cinematic variables during the execution of a movement by said user;

(c) detection of an end status of the acquisition, in which said user is in a substantially static posture; and

(d) calculation of at least one parameter related to the muscular power of said user as in function of the acquired signals of said cinematic variables. Always according to the invention, signals of said cinematic variables can comprise the acceleration (ace) and the angular speed (ω) and said step (b) comprises the following steps:

(b1) acquisition of a detected sampled vector acceleration signal (acc-r) and of a sampled vector angular speed signal (ω);

(b2) filtration of said detected acceleration signal (acc-r) and of said angular speed signal (ω);

(b3) transformation of the detected acceleration signal (acc-r) in an acceleration signal (ace) to a global reference system;

(b4) determination of the movement or exercise number cycle performed by the user; and

(b5) segmentation of said acceleration signal (ace) in order to distinguish the different condition of a movement, in particular related to the flight and/or transition phases.

Still according to the invention, said step (b3) can comprise the calculation of the rotating matrix from a local reference system to a global one at any sampling time, by numerical integration of said angular speed signal (ω), and correction of an offset error.

Furthermore, according to the invention, said step (b3) can comprise the following steps:

- reading said detected acceleration signal (accr), subtraction of said first offset initial acceleration constant from said detected acceleration signal (acc-r), filtration by means of a low-pass filter, calculation of the arccosine thereby obtaining a first roll and pitch signal vector, calculation of the initial rotation matrix (Gi) with respect to a global reference system;

- reading said angular speed signal (ω), subtraction of said second offset initial angular speed (ω) constant from said angular speed signal (ω), filtration by means of a high-pass filter, integration of said vector signal and multiplication of said vector signal by said initial rotation matrix (Gi), thereby obtaining a second roll and pitch signal vector and a yaw signal vector;

- subtraction of said first roll and pitch signal vector and said second roll and pitch signal vector, thereby obtaining an error signal vector;

- correction of said second roll and pitch signal vector by means of said detection error signal vector, thereby obtaining a final roll and pitch signal vector; -obtaining a final rotating matrix (Gf) for transforming a local reference system to a global one by said final roll and pitch signal vector;

- multiplication of said final rotating matrix (Gf) by said detected acceleration signal (acc-r), in order to obtain a transformed acceleration signal (ace).

Advantageously, according to the invention, said step (b4) can comprise the following steps:

- replacing the negative values of said acceleration signal (ace) with a normalized logic negative constant value -1 and the positive ones with a normalized logic positive constant value +1 thereby obtaining a square wave curve;

- calculation of the derivative with respect to the time of said square wave, thereby obtaining a peak curve; and

- detection of cycles related to a specific exercise.

Always according to the invention, said step (b5) can comprise the following steps:

- calculation of the average value of the values of the samples of the curve portion between a sequence of one or more negative peaks and a sequence of one or more positive peaks;

- if said average value is below a preset threshold, said preset threshold being preferably the gravitational acceleration constant (g), then a flight and/or transition phase is detected and the calculation o f the estimate of the values of said vector displacement signal (s) in said flight and/or transition phases is performed.

Still according to the invention, calculation of the estimate of said values of said sampled displacement signal (s) in said flight and/or transition phases is carried out according the to the following algorithm:

- integration of said acceleration signal (ace) in order to obtain a sampled vector speed signal (v);

- integration of said speed signal (v) in order to obtain said sampled vector displacement signal (s);

- detection of the final value of the speed (vθ) and of the displacement (sθ) of each transition phase precedent to each flight phase; and

- calculation of the displacement in a flight and/or transition phase according to the formula s = s0 + vθ_t + 0,5_g_t2, in which g is the gravitational acceleration constant. Furthermore, according to the invention, said step (d) can comprise the following steps:

- calculation of a sampled vector speed signal (v), as the integration of said acceleration signal (ace), preferably as v = 1/6 * [acc(i- 1) + 4* acc(i) + acc(i+1)] ^* dt, in which dt is the time interval between two consecutive samples and i is the numbering index of the samples; and

- calculation of the sampled vector displacement signal (s), as the integration of said speed signal (v), preferably as s= 1/6 * [v(i-1) + 4 ^* v(i) ⁺ v(i+1)] ^* dt; in order to carry out the calculation of at least one parameter related to the muscular power of said user, selected among the following:

- power (P), calculated as P = m ace v, with m being the body mass of said user;

- mechanical energy (E), calculated as E = K + U, with K is the cinematic energy and U potential energy, with K = 0,5 ^* V2 e U = s_vert ^* g, in which s vert being the vertical component of said displacement signal

(S).

Always according to the invention, integration operations can be carried out on one or more of said cycles related to a specific exercise, preferably three cycles.

Still according to the invention, said step (b2) can provide the filtration by means of one or more low-pass filters, with a cut off frequency of said low-pass filters is about 20 Hz.

Advantageously, according to the invention, said steps (a) and (c) can comprise the following steps:

- acquisition of said detected acceleration signal (acc-r) and of said angular speed signal (ω);

- calculation of the average and the standard deviation of the samples of each of said signals; and

- comparison of the measures of said standard deviations to respective preset thresholds; if said measures of the standard deviations are higher than the respective preset threshold, then continue said step (a) or (c), else end of the acquisition, so determining respectively the start and the end of the acquisition, said first offset initial acceleration constant and said second offset initial angular speed (ω) constant of said step (a) being proportional respectively to said average value of said signals. It is further object of the present invention an apparatus for measuring the muscular power of a user, said apparatus being attachable to the body of said user, comprising at least one three dimensional accelerometer, suitable to detect a sampled detected vector acceleration signal (acc-r) of the body of said user on which said apparatus is placed, at least one three dimensional gyroscope, suitable to detect a sampled vector angular speed (ω) on which said apparatus is placed, and a processing unit connected to said at least one accelerometer and to said at least one gyroscope, characterized in that said processing unit is suitable to run the method for measuring the muscular power as defined in the above, by processing said detected acceleration signal (acc-r) and said angular speed signal (ω), in order to determine the normalized muscular power calculated with respect to the body mass (m) of said user.

Always according to the invention, said at least one gyroscope can be made by a first and a second bi-dimensional gyroscope, arranged in such way that they have an axis aligned.

Still, according to the invention, said apparatus can comprise a magnetometer suitable to detect the earth's magnetic field, in order to permit a more precise correction of jaw of the same apparatus.

Furthermore, according to the invention, it can comprise: a GPS receiver for detecting the position; means for interacting with said user, such as an organic light emitting diode display and/or a keyboard and/or a LED (Light Emitting Diode) and/or a buzzer; a wireless transceiver unit, preferably of Bluetooth type, suitable to transmit and/or receive data to/from an external data processor; a memory, preferably of microSD type, for storing and viewing the results of the measures; and a rechargeable battery and an input for charging said rechargeable battery.

Advantageously, according to the invention, said apparatus can comprise an elastic band fastenable to said user, said elastic band comprising a pocket in which said apparatus is placeable.

The present invention will be now described for illustrative but not limitative purposes with reference to its preferred embodiments, making particular reference to the figures of the enclosed drawings, wherein: figure 1 shows a block diagram of an apparatus for measuring muscular power according to the present invention; figure 2 shows an embodiment of apparatus of figure 1 ; figure 3 shows a flow chart of part of the operation method of apparatus for measuring muscular power according to the present invention; figure 3 shows an algorithm that can combine signals of an accelerometer and of a gyroscope for evaluating orientation of apparatus according to the invention; figures 5a - 5c show a processing procedure for an accelerometer and a gyroscope signals for determining the number of cycles of a movement; and figure 6 shows a flow chart of the data processing according to the present invention.

In the different figures, similar parts will be indicated by the same reference numbers.

Making reference to figure 1 , it is possible observing a functional block diagram of apparatus 1 for measuring muscular power according to the present invention.

Said apparatus 1 comprises a processing unit 2, such as a programmable microprocessor, a tri-dimensional accelerometer 3 and a tri-dimensional gyroscope 4. Said tri-dimensional gyroscope 4 is made up by a first and a second bi-dimensional gyroscope 4 ¹ and 4", placed in such a way that axis of first gyroscope 4 ¹ is aligned with axis of the second bi- dimensional gyroscope 4". Said tri-dimensional gyroscope 4 is suitable to measure angular speed of segment on which apparatus 1 is positioned, by segment being meant the body portion of a user (not shown in the figures) to which it is fixed the apparatus 1.

Said accelerometer 3 and said gyroscope 4 are connected with an analogue-digital converter 5, connected by a bus with said processing unit 2.

Apparatus 1 also provides a microSD memory 6 and a light emission organic diode display 7, respectively for storing and displaying results of measurements.

Furthermore, apparatus 1 comprises, besides light emission organic diode display 7, also further means for interaction with the user, such as a keyboard 8, a LED (Light Emitting Diode) 9 and a buzzer 10. Apparatus 1 also comprises a rechargeable battery 11 and an inlet for charging said battery 11. Apparatus 1 further comprises a wireless transceiving unit 13, e.g. of the Bluetooth type, for transmitting and receiving data to/from an outer processor. Obviously, it is also possible transceiving data by wire, according to USB protocols. Data received are then stored within memory 6.

Thus, said apparatus can mainly have:

- an autonomous operation, carrying out acquisitions and calculations without needing the use of an outer station (processor);

- an operation by wire or wireless data transmission, wherein apparatus 1 is used along with an outer station (laptop, PDA, cellular phone, ecα), wherein a dedicated software is installed for acquiring said data and making calculations, with which it is connected also by said wireless transceiving unit 13.

Preferably, apparatus 1 can also comprise a GPS (Global Positioning System, not shown in the figures) receiver, for recording position of the used during an exercise.

Finally, in a preferred embodiment, said apparatus 1 comprises a magnetometer (not shown in the figures), suitable to detect the earth magnetic field, in order to permit a more precise determination of apparatus 1 jaw during execution of a physical exercise by a user.

Figure 2 shows an apparatus 1 , wherein it can be easily observed light emission organic diode display 7, LED 9 and keyboard 8.

The operation of apparatus 1 will be described in the following, using the following references: acc-r = acceleration vector detected by said accelerometer 3; ace = acceleration vector transformed by a local reference system into a global one; v = speed vector; s = position vector; m = body mass;

P = power;

K = kinetic energy;

U = potential energy; g = gravity acceleration constant.

Apparatus 1 is usually worn and provided on the user trunk, placing it inside a pocket of a suitable elastic strap. Said strap is usually tightened so as to make it fully adhering to the body of said user. Thanks to the accelerometer 3 and to said gyroscope 4, positioning of apparatus 1 can be an arbitrary positioning, since its orientation is automatically detected by apparatus 1 , as it will be described in the following.

Method for measuring muscular power of a user by said apparatus 1 , mainly comprises the following steps:

(a) detection of a starting status of the acquisition, in which said user is in a substantially static posture, thereby obtaining a first offset initial acceleration constant of linear acceleration a nd a second offset initial angular speed (ω) constant;

(b) acquisition of one or more signals of cinematic variables during the execution of a movement by said user;

(c) detection of an end status of the acquisition, in which said user is in a substantially static posture; and

(d) calculation of at least one parameter related to the muscular power of said user as in function of the acquired signals of said cinematic variables.

Calculation procedure can, therefore, being divided into two main parts:

- a first part (steps (a) - (c) of data acquisition and processing, mainly suitable to detection and control of signal quality; and

- a second part (step (d) carried out after the end of the signal acquisition, comprising different calculation algorithms in order to obtain the wished results indicating mechanical energy and muscular power, which are then displayed on display 7.

At the beginning and at the end of each data acquisition (i.e. every physical exercise), steps (a) to (c) are carried out, wherein the static posture is determined. By static posture it is meant a condition during which acceleration signal (analysed within a short time window, about 1 - 1.5 seconds) varies very few. Therefore, the used is stationery, until when he/she hears an acoustic signal from apparatus 1 , indicating the ending of an acquisition starting condition detection step, for calibrating the initial orientation of apparatus 1.

During each one of said static posture detection steps (a) and (c), an acc-r acceleration vectorial signal is acquired, detected by said accelerometer 3, as well as an angular speed vectorial signal ώ, proportional to their average values within said time interval during which standard deviation is lower than said set threshold.

Making now reference to figure 3, it is possible observing sub steps of said step (b) that will be described in the following.

Detection step (b1), during a detected sampled vectorial acceleration signal acc-r is obtained in real time by said accelerometer 3, and a sampled vectorial angular speed signal ώ is detected in real time by said gyroscope 4.

Low-pass filtering step (b2), carried out on signals detected by said accelerometer 3 and by said gyroscope 4, with cut-off frequency depending on the type of movement carried out (typically at 20 Hz).

Transformation step (b3) of the detected acceleration signal acc-r into an acceleration signal ace within a global reference system. Taking into consideration that during the movement, the body segment on which apparatus 1 has been fixed can deviate from its initial orientation, it is necessary transforming accelerations measured by a reference system integral with apparatus 1 into a global inertial system.

In order to carry out said operation, it is calculated the rotation matrix from a local reference system into a global one each time of the sampling time. Typically, orientation of said body segment is determined by numeric integration of vectorial angular speed signal ώ of gyroscope 4 fixed on said user.

However, a relatively small offset error due to the temperature effect or to noise on gyroscope 4 signal will introduce large errors into the numeric integration, said errors growing quickly. Accelerometer 3 can correct calculation of orientation thanks to its capability of providing a measure of inclination along horizontal plane about medium - lateral axis (pitching) and front - rear axis (rolling) of the reference system integral with apparatus 1 body.

Block diagram of figure 1 is an example of an algorithm permitting combining detected acceleration signal acc-r and angular speed ώ, respectively detected by accelerometer 3 and by gyroscope 4, for a more precise and stable evaluation of apparatus 1 orientation. On the basis of said algorithm, the following operations are carried out on the detected acceleration signal acc-r and on said angular speed signal ώ:

- reading of said detected acceleration signal (acc-r), subtraction of said first offset initial acceleration constant from said detected acceleration signal, filtering by a low-pass filter, calculation of the cosine-arc obtaining a first rolling and pitching signal vector, calculation of the initial rotation matrix Gi with respect to a global reference system;

- reading of said angular speed signal ώ, subtraction of said second offset initial vectorial angular speed constant from said angular speed signal, filtering by high-pass filter, integration of said vectorial signal and multiplication of said vectorial signal obtained by said initial rotation matrix Gi, obtaining a second rolling and pitching signal vector and an jaw signal vector;

- subtraction of said first rolling and pitching signal vector and of said second rolling and pitching signal vector, thus obtaining an error signal vector;

- correction of said second rolling and pitching signal vector by said detection error signal vector, thus obtaining a final rolling and pitching signal vector;

- obtaining a final rotation matrix for transformation of a local reference system into a global one by said final rolling Gf and pitching signal vector; and

- multiplication of said final rotation matrix Gf with said detected acceleration signal acc-r, so as to obtain a transformed acceleration signal.

Then, a possible step (b4) for determining the number of cycles of a motion or exercise carried out by said user is carried out.

Since movements carried out during some kind of exercises can consist in movements repeated for more than one cycle, it is first determined if more than one movement cycle exists. In the positive, it is determined the stationary regime of the movement on time windows, preferably, but not limited to, three cycles.

Moreover, apparatus 1 can be programmed in such a way to select detection of cycles of a specific exercise or movement (programmed within processing unit 2 for specific exercises).

Said step (b4) has the following sub steps that can be observed in figures 5a - 5c. Particularly, starting from an acceleration signal ace of a typical movement of jumping (figure 5a), negative values of said acceleration signal are replaced with a normalised logic negative constant value -1 and positive values are replaced with a normalised logic positive constant value +1 , thus obtaining a square wave as shown in figure 5b. Then, derivative is calculated with respect to the time of said square wave, thus obtaining a peak curve, as shown in figure 5c.

Finally, a detection of cycles relevant to a specific exercise is carried out, on the basis of a set algorithm, selected on apparatus 1.

Then, an automatic segmentation step (b5) of signals is provided, during which estimate of signal being detected (ace and thus v or s) during particular steps of a motion is carried out starting from the acceleration signal ace.

For example, during a vertical jumping, 4 different steps can be distinguished: a first eccentric step, a second concentric step, a third flying step and a fourth landing step. Therefore, typically, an automatic determination occurs (i) of a flying step, i.e. a step during which no contact occurs between ground and user; or (ii) a transition step (e.g. vertical speed = 0 while going to the higher point of the body trajectory).

In order to recognise these conditions during particular types of exercises, used criteria is that on signal obtained as in figure 5c the part of the curve between a sequence of one or more negative peaks and a sequence of one or more positive peaks as average value under a threshold (typically the gravitational acceleration constant g), represents a flying step.

Then, a hybrid calculation algorithm can be applied to the possible flying steps to evaluate displacement s (information useful for calculating mechanical energy) or speed v.

Said hybrid algorithm uses speed and displacement calculated at the last contact time as data replacing the ballistic motion equation, so that, starting from acceleration ace, it is integrated acceleration signal ace in order to calculate speed v, it is integrated speed signal v in order to calculate displacement s, it is obtained final value of v (vθ) and s (sθ) of the transition step before each flying step, that are then used in the following equation

S = s0 + sOt + 0.5gt ² ,

Thus obtaining displacement during flying.

Finally, during calculation step (d), interesting variables are obtained. Power is calculated as:

P = m ace v and mechanical energy is calculated as:

E = K + U In order to calculate both energy and muscular power, it is necessary calculating both linear speed v and displacement s all along exercise, starting from accelerometer 3 signal acc-r transformed into acceleration signal ace with respect to a global reference system.

Linear speed v is calculated numerically integrating acceleration signal ace: v = 1/6 ^* [acc ^* (i-1) + 4 ^* acc(i) + acc(i+1)] ^* dt wherein dt is time interval between two consecutive samples.

Displacement is calculated numerically integrating speed signal: s= 1/6 ^* [v(i-1) + 4 ^* v(0 + v(i+1)] ^* dt, wherein dt is time interval between two consecutive samples.

As already said, mechanical energy E is calculated normalised with respect to body mass as sum of potential energy U and kinetic energy K:

E = K + U

Wherein K = 0.5*v ² and U = S_vert ^* g and s_vert is s vertical component.

Muscular power is calculated normalised with respect to body mass:

P = v*acc.

Figure 6 schematically shows method of different processing steps of acceleration signals ace and of angular speed signal (ώ).

As it can be observed, in this case it is also provided evaluation of position by GPS (Global Positioning System) receiver.

Present invention has been described for illustrative, but not limitative, purposes, according to its preferred embodiments, but it is to be understood that variations and/or modifications can be introduced by those skilled in the art without departing from the relevant scope, as defined in the enclosed claims.