Abstract
A method for determining the quality of running of a test subject includes: measuring at least two orthogonal acceleration values a.sub.c and a.sub.c of the test subject each at a plurality of times t.sub.i, wherein a.sub.c and a.sub.c are each one differently selected from the group of: acceleration a.sub.z of the test subject in the down-up direction, acceleration a.sub.y of the test subject in the right-left direction, and the acceleration a.sub.x of the test subject in the backward-forward direction; wherein the down-up direction, the left-right direction and the backward-forward direction form a Cartesian coordinate system for the test subject; determining the area A.sub.i defined by the origin (0,0) and the points (a.sub.c(t.sub.i),a.sub.c(t.sub.i)) and (a.sub.c(t.sub.i1), a.sub.c(t.sub.i1)); and calculating the accumulated area A (t.sub.N)=.sub.i=1.sup.N A.sub.i by adding the areas A.sub.i until a point in time t.sub.N.
Claims
1. A method for determining the quality of running of a test subject comprising the following steps: measuring at least two orthogonal acceleration values a.sub.c and a.sub.c of the test subject each at a plurality of times t.sub.i, wherein a.sub.c and a.sub.c are each one differently selected of the group of: acceleration a.sub.z of the test subject in the down-up direction, acceleration a.sub.y of the test subject in the right-left direction, and the acceleration a.sub.x of the test subject in the backward-forward direction; wherein the down-up direction, the left-right direction and the backward-forward direction form a Cartesian coordinate system for the test subject; determining the area A.sub.i defined by the origin (0,0) and the points (a.sub.c(t.sub.i),a.sub.c(t.sub.i)) and (a.sub.c(t.sub.i1), a.sub.c(t.sub.i1)); and calculating the accumulated area A(t.sub.N)=.sub.i=1.sup.N A.sub.i by adding the areas A.sub.i until a point in time t.sub.N.
2. The method of claim 1, wherein the method further comprises a step of evaluating A(t.sub.N) for obtaining the quality of running of the test subject, wherein the step of evaluating A(t.sub.N) further comprises: obtaining a sliding mean value for A(t.sub.N) for a time interval t.sub.N-t.sub.N to t.sub.N; and comparing A for different times t.sub.N and t.sub.N, wherein a lower value of A indicates a better quality of running, wherein equal values of A indicate the same quality of running, wherein a higher value of A indicates a worse quality of running, and wherein the different times t.sub.N and t.sub.N form part of the same measurement series or of different measurement series, and/or comparing A with a predetermined threshold value, wherein a value of A lower than or equal to the predetermined threshold value indicates a good quality of running, and wherein value of A higher than the predetermined threshold value indicates a bad quality of running
3. The method of claim 1, wherein the sliding mean value for A(t.sub.N) is a weighted sliding mean value.
4. The method of claim 2, wherein the sliding mean value for A(t.sub.N) is determined per time unit, and wherein t.sub.N is a constant time interval t equal to the time unit.
5. The method of claim 2, further comprising determining steps of the test subject; wherein the sliding mean value for A(t.sub.N) is determined per n steps, wherein n is a positive integer, and wherein t.sub.N is a time interval corresponding to n steps of the test subject.
6. The method of claim 2, further comprising determining the speed of the test subject; wherein the sliding mean value for A(t.sub.N) is determined per distance unit, and wherein t.sub.N is a time interval corresponding to the distance unit passed by the test subject.
7. The method of claim 1, wherein A(t.sub.N) is given by the following formula: wherein (t.sub.i) is the angle between the vectors (a.sub.c(t.sub.i1),a.sub.c(t.sub.i1)) and (a.sub.c(t.sub.i),a.sub.c(t.sub.i)).
8. The method of claim 1, wherein the acceleration values a.sub.c and a.sub.c of the test subject are each measured with a frequency of 100 Hz.
9. The method of claim 1, wherein the selected orthogonal acceleration values a.sub.c and a.sub.c are a.sub.x and a.sub.z.
10. The method of claim 1, further comprising displaying the measured acceleration values a.sub.c(t) and a.sub.c(t) for subsequent times t.sub.i in a two-dimensional Cartesian coordinate system with the abscissa being the a.sub.c axis and the ordinate being the a.sub.c axis.
11. A non-transitory machine-readable medium comprising a plurality of machine-readable instructions which when executed by one or more processors of a computer are adapted to cause the computer to perform a method for determining the quality of running of a test subject comprising: receiving at least two orthogonal acceleration values a.sub.c and a.sub.c of the test subject each at a plurality of times t.sub.i, wherein a.sub.c and a.sub.c are each one differently selected of the group of: acceleration a.sub.z of the test subject in the down-up direction, acceleration a.sub.y of the test subject in the right-left direction, and the acceleration a.sub.x of the test subject in the backward-forward direction; wherein the down-up direction, the left-right direction and the backward-forward direction form a Cartesian coordinate system for the test subject; determining the area A.sub.i defined by the origin (0,0) and the points (a.sub.c(t.sub.i),a.sub.c(t.sub.i)) and (a.sub.c(t.sub.i1), a.sub.c(t.sub.i1)); and calculating the accumulated area A (t.sub.N)=.sub.i=1.sup.N A.sub.i by adding the areas A.sub.i until a point in time t.sub.N.
12. A system for determining the quality of running of a test subject comprising: an accelerometer measuring at least two orthogonal acceleration values a.sub.c and a.sub.c of the test subject each at a plurality of times t.sub.i, wherein a.sub.c and a.sub.c are each one differently selected of the group of: acceleration a.sub.z of the test subject in the down-up direction, acceleration a.sub.y of the test subject in the right-left direction, and the acceleration a.sub.x of the test subject in the backward-forward direction; wherein the down-up direction, the left-right direction and the backward-forward direction form a Cartesian coordinate system for the test subject; and a processor for determining the area A.sub.i defined by the origin (0,0) and the points (a.sub.c(t.sub.i),a.sub.c(t.sub.i)) and (a.sub.c(t.sub.i1), a.sub.c(t.sub.i1)), wherein the processor calculates the accumulated area A(t.sub.N)=.sub.i=1.sup.N A.sub.i by adding the areas A.sub.i until a point in time t.sub.N.
13. The system of claim 12, wherein the processor is comprised of a smartphone.
14. The system of claim 12, wherein the accelerometer is worn by the test subject in or on a belt around the waist of the test subject.
15. The system of claim 12, wherein the accelerometer is positioned at the center front portion of the test subject's waist.
16. The system of claim 12, wherein the accelerometer is positioned at the center rear portion of the test subject's waist.
17. The system of claim 12, wherein the accelerometer transmits its measured acceleration values to the processor using wireless technology standard for exchanging data over short distances, such as Bluetooth.
18. A method for determining the quality of a cyclic locomotion of a test subject comprising the following steps: measuring at least two orthogonal acceleration values a.sub.c and a.sub.c of the test subject each at a plurality of times t.sub.i, wherein a.sub.c and a.sub.c are each one differently selected of the group of: acceleration a.sub.z of the test subject in the down-up direction, acceleration a.sub.y of the test subject in the right-left direction, and the acceleration a.sub.x of the test subject in the backward-forward direction; wherein the down-up direction, the left-right direction and the backward-forward direction form a Cartesian coordinate system for the test subject; and determining the area of the closed trajectory of the acceleration values a.sub.c and a.sub.c of the test subject in the a.sub.c and a.sub.c coordinate system for at least one cycle.
19. The method according to claim 18, wherein the locomotion is selected of the group of: walking, skipping, running and crawling.
20. The method according to claim 18, wherein the locomotion is selected of the group of: bipedal and quadrupedal locomotion.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] In the drawings show:
[0034] FIG. 1 a schematic diagram showing the components and the set-up of the system according to an exemplary embodiment of the invention;
[0035] FIG. 2 a schematic diagram for explaining the determination of a quality measurement parameter or quality measure for a runner;
[0036] FIG. 3A in its upper portion acceleration values a.sub.x and a.sub.z for a runner in a first phase of a running step cycle which is a flying phase with no contact to the floor, in its lower left portion the actual current position of the legs of a runner in this phase, and in its lower right portion the measured values of a.sub.x and a.sub.z depicted in a diagram with a.sub.x in the x-direction and a.sub.z in the negative z-direction, wherein the dot indicates the currently measured value for a.sub.x and a.sub.z;
[0037] FIG. 3B in its upper portion acceleration values a.sub.x and a.sub.z for a runner in a second phase of a running step cycle which is the phase of maximum a.sub.x when the braking through contact to the floor sets in, in its lower left portion the actual current position of the legs of a runner in this phase, and in its lower right portion the measured values of a.sub.x and a.sub.z depicted in a diagram with a.sub.x in the x-direction and a.sub.z in the negative z-direction, wherein the dot indicates the currently measured value for a.sub.x and a.sub.z;
[0038] FIG. 3C in its upper portion acceleration values a.sub.x and a.sub.z for a runner in a third phase of a running step cycle which is the phase of the beginning of the positive acceleration for a.sub.z corresponding to push off, in its lower left portion the actual current position of the legs of a runner in this phase, and in its lower right portion the measured values of a.sub.x and a.sub.z depicted in a diagram with a.sub.x in the x-direction and a.sub.z in the negative z-direction, wherein the dot indicates the currently measured value for a.sub.x and a.sub.z;
[0039] FIG. 3D in its upper portion acceleration values a.sub.x and a.sub.z for a runner in a fourth phase of a running step cycle which is the phase just before the first (flying) phase shown in FIG. 3A, in its lower left portion the actual current position of the legs of a runner in this phase, and in its lower right portion the measured values of a.sub.x and a.sub.z depicted in a diagram with a.sub.x in the x-direction and a.sub.z in the negative z-direction, wherein the dot indicates the currently measured value for a.sub.x and a.sub.z;
[0040] FIG. 4A and FIG. 4B the accumulated area sum parameter A for three different runners with various running styles, wherein the top curve depicts A for a heel-strike runner, the middle curve depicts A for a fore-foot runner with overstriding and the bottom curve depicts A for a fore-foot runner; the time scale being much wider in FIG. 4B than in FIG. 4A;
[0041] FIG. 5 a bar graph of the accumulated area sum parameter A per step for five different runners with various running styles; and
[0042] FIG. 6 a bar graph of the accumulated area sum parameter A per step for a single runner during various stages of a marathon with variable running speed in each stage.
DETAILED DESCRIPTION
[0043] The present inventive concept is best described through certain embodiments thereof, which are described in detail herein with reference to the accompanying drawings, wherein like reference numerals refer to like features throughout. It is to be understood that the term invention, when used herein, is intended to connote the inventive concept underlying the embodiments described below and not merely the embodiments themselves. It is to be understood further that the general inventive concept is not limited to the illustrative embodiments described below and the following descriptions should be read in such light.
[0044] Additionally, the word exemplary is used herein to mean, serving as an example, instance or illustration. Any embodiment of construction, process, design, technique, etc., designated herein as exemplary is not necessarily to be construed as preferred or advantageous over other such embodiments. Particular quality or fitness of the examples indicated herein as exemplary is neither intended nor should be inferred.
[0045] Referring now to FIG. 1 an exemplary embodiment of the system embodying the present invention will be described. The system 100 comprises a three-dimensional accelerometer comprising an acceleration sensor 10 such as the actibelt accelerometer described in the background section of the present specification. The acceleration sensor 10 is mounted behind a buckle (not shown) on a belt 11 which is worn around the waist of a test subject. This positioning allows for a reproducible positioning of the acceleration sensor 10 simply because people are used to properly buckling their belt with the buckle being oriented and aligned in a typical manner (front-centered). This arrangement also has the advantage that the three-dimensional acceleration sensor 10 is mounted in a symmetric location on the individual's body, i.e. located on the symmetry axis of the individual, and at a position close to the center of mass of the test subject so that the various sensed accelerations are largely independent. The sensor position is also fixed relative to the body which makes it actually more preferred than the actual center of mass position which would change by moving of the extremities such as arms and legs, thereby changing the moment of inertia. Generally, the acceleration sensor 10 could also be mounted at a different position of the test subject such as centered on its back, simply by wearing the actibelt the other way round. The acceleration sensor 10 measures the accelerations in the x, y and z directions wherein these directions are shown in FIG. 1. As a convention in this application (other conventions could be used) the x direction corresponds to the forward direction and the z direction corresponds to the upward direction. In order that the three directions from a Cartesian coordinate system the y direction points into the paper plane of FIG. 1, i.e. goes from right to left of the test subject moving to the right in the representation of FIG. 1. The accelerations are a.sub.x, a.sub.y and a.sub.z are measured simultaneously with a frequency of 100 Hertz and are transmitted via Bluetooth in real time to smartphone 20 which is exemplarily attached at the wrist of the test subject. In the smartphone 20 there is a mobile app processing the data received from the acceleration sensor 10 according to the inventive method. On a display screen of the smartphone 20 the results of the inventive processing can be displayed. Furthermore, other functionalities of smartphone 20 can be used in an advantageous manner in the context of the present invention. For instance, acoustic alarm signals could be generated and outputted via the loudspeaker of smartphone 20 to alert the individual when the quality of his or her running is considered to be bad or when there is a decrease in quality.
[0046] As is obvious for a skilled person there are many other ways for implementation of the system of the invention. For instance, the smartphone 20 might comprise the acceleration sensor 10 or the acceleration sensor 10 might be plugged directly on the Smartphone so as making a Bluetooth connection and attachment means for the second of two different components unnecessary. Alternative to smartphone 20 any other device which allows for processing the acceleration data may be used, particularly, a specially dedicated device to this purpose. In another embodiment without use of smartphone 20 the acceleration data could also be transmitted directly from the acceleration sensor 10 via the air interface, e.g. using 3G or 4G telecommunication techniques, which essentially means that a mobile telephone is integrated in the acceleration sensor. The acceleration data can be transmitted from the acceleration sensor 10 to a remote processing device such as another smartphone, e.g. of a coach of the individual runner. Alternatively, the acceleration data could also be stored within the acceleration sensor 10 itself and later be read out or transferred to a processing device such as a personal computer.
[0047] Turning now to FIG. 2 in connection with which the inventive method will be described. Although, the three-dimensional acceleration sensor 10 (FIG. 1) provides acceleration data in all three spatial directions it is preferred to use only two orthogonal accelerations in connection with the inventive method for analyzing the quality of running If all three acceleration values would be used then the results would be not so meaningful as will be explained below. Preferably, the acceleration values in the x and z directions, i.e. a.sub.x and a.sub.z, will be used. They characterize the acceleration of the test subject in the down-up and the backward-forward directions, respectively. In FIG. 2, the acceleration values a.sub.x(t.sub.i) and a.sub.z(t.sub.i) at time t.sub.i are shown for various times (t.sub.i+1, t.sub.i, t.sub.i+1, t.sub.i2, t.sub.i3) in a coordinate system with the abscissa being the acceleration a.sub.x in the x direction and the ordinate being the acceleration a.sub.z in the z direction. Because of the gravitational acceleration of the earth it can clearly be seen that the acceleration values a.sub.z in the z direction are all negative except at a point (0, 0), i.e. the origin of the coordinate system, which corresponds to the flight phase where the acceleration a.sub.z in the z direction becomes 0 since the runner has left the ground with both feet. In this phase the runner experiences free fall. The subsequent values of (a.sub.x, a.sub.z) for various times t.sub.i provide points in the a.sub.x, a.sub.z coordinate system which move along a balloon-like curve. Although the acceleration measurements are taken at regular time intervals with a frequency of 100 Hertz, the resultant points in the graphical illustration of FIG. 2 are not equidistant. Most measured points will lie in the area around of the origin since within a step the flight phase is the longest. Therefore, most part of this diagram describes the critical phases of landing of a foot or pushing off which are believed to be most crucial for evaluating the quality of running. In other words, the landing and pushing off phases are blown up due to the nature of the diagram and the nature of running. Since running itself is a quasi-period process, the term quasi is used in order to indicate that not every step is identical, the measured point (a.sub.x(t.sub.i), a(t.sub.i)) in this diagram will move around the balloon-like curve a plurality of times in the clockwise direction. For an ideal runner the center of mass should follow a trajectory of a straight line, i.e. it should be so to speak elf-like so that limb movement, rotation of the spinal cord/trunk during running should be zero even in response to different shoes/surfaces etc. Therefore, the quality of running should be the best, if the area enclosed by this curve is as small as possible. In other words, an ideal runner should be in a permanent flight phase. Therefore, it is preferred that the combination of two orthogonal acceleration values is for evaluating the quality of running Although generally possible, taking into account a third acceleration value would cancel out important information when looking at the size of the area which is generated in the acceleration space.
[0048] FIG. 2 shows how to calculate the area A.sub.i between the origin and two subsequent measurement points (a.sub.x(t.sub.i), a.sub.z(t.sub.i)) and (a.sub.x(t.sub.i1), a.sub.z(t.sub.i1)) which have been obtained at the times t.sub.i and t.sub.i1, respectively. This area A, can be obtained through the following formula using trigonometry
[00002]
wherein the angle (t.sub.i) between the lines defined by the origin and (a.sub.x(t.sub.i), a.sub.z(t.sub.i)) and (a.sub.x(t.sub.i1), a.sub.z(t.sub.i1)), respectively, can be obtained by the law of cosines to yield
[00003]
[0049] According to the present invention these partial areas A.sub.i can be summed up to yield a quality parameter for running
[00004]
[0050] The unit of this accumulated sum area A(t.sub.N) is
[00005]
since it is an area in a space defined by two accelerations. The accumulated area can be taken as a sliding mean value, wherein this sliding mean value can also be a weighted sliding mean value, wherein, for instance, various stages of the curve shown in FIG. 2 can be weighted differently. The accumulated sum area sliding mean value A(t.sub.N) can be taken over a constant time interval t, a constant number of steps t.sub.N, in particular, one step, or over a certain distance t.sub.N. In case it is taken over a constant number of steps, of course, the steps have to be detected wherein it is clear from FIG. 2 that a step can be defined as the trajectory of the measured acceleration values going through the origin. Of course, alternatively, a pedometer or step counter could be used for step detection. When the sliding mean of the accumulated sum is taken over certain distance then the speed has to be measured externally, for instance, with additional GPS data, e.g. obtained through the smartphone 20. Due to the finite resolution of the measurement of the acceleration values the accumulated sum area A(t.sub.N) is an approximation of the curve enclosed by the trajectory formed by the acceleration values in the acceleration coordinate space/system, with the approximation becoming better when the resolution is increased.
[0051] Referring now to FIGS. 3A to 3D four different phases of a running cycle (recorded for a runner on a treadmill) are schematically illustrated. The upper portion of each of these Figures shows the acceleration a.sub.x into the x direction, whereas the lower curve of the upper portion shows the acceleration a.sub.z in the z direction. One can clearly see the double peaks of the lower a.sub.z acceleration curve which show that there is a double peak caused by the heel of the foot striking first the ground followed by the remainder of the foot. Further, one can see that the range of occurring acceleration values is larger for a.sub.z than for a.sub.x so that in the diagram of the lower right portion FIGS. 3A to 3D showing a.sub.x on the abscissa and a.sub.z on the ordinate (into which the acceleration values of the upper portion of each Figure have been plotted) the vertical extension of the resulting curve is larger than in the horizontal direction. In the lower left portion of the respective FIGS. 3A to 3D the actual position of the legs of the runner are shown for the current time which is also indicated by a dot in the trajectory shown in the lower right portion of the respective FIG. 3A to 3D.
[0052] One can clearly see that during running in the coordinate space defined by the a.sub.x and a.sub.z accelerations a somewhat balloon-shaped trajectory is passed in the clockwise direction. In each flight phase corresponding to the origin (0, 0) the trajectory returns to its upper left extension. FIG. 3A shows a first phase of a running step cycle which is the flying phase with the runner's feet making no contact to the ground and which is the calibration point for the measurement. FIG. 3B shows a second phase of a running step cycle which is the phase of maximum forward acceleration a.sub.x when the braking through contact to the floor sets in and slows down the forward acceleration. FIG. 3C shows a third phase of the running step cycle in which the positive acceleration against the gravitational acceleration for a.sub.z just started corresponding to a push off of the runner's foot on the ground. FIG. 3D shows a fourth phase of a running step cycle which is the phase just before the first (flying phase) shown in FIG. 3A.
[0053] For each measured position (only four such measurements are shown in FIGS. 3A to 3D) the area of the curve is determined, in particular, calculated as has been described above in connection with the schematic diagram shown in FIG. 2. Then, accumulated sums are calculated as has been described above.
[0054] In FIG. 4A and 4B the accumulated area sum A(t.sub.N) is shown for three different running styles. The diagrams of 4A and 4B show the same measurements, with FIG. 4A essentially showing the first second of the running process, whereas FIG. 4B shows the first 60 seconds, i.e. at a much smaller scale. The upper curve shows a heel-strike running style (heel-strike: the runner sets first the heel onto the ground during the landing phase). The middle curve shows a fore-foot running style with overstriding (overstride: the foot comes into contact with the ground well ahead of the hips or ahead of the center of gravity) and the bottom curve shows a fore-foot running style (forefoot-strike: the runner sets first the fore-foot onto the ground during the landing phase). The steps shown in the curves of FIG. 4A correspond to respective flight phase, i.e. indicate real steps of the runner. It has been recognized by the present inventor that a low value of the accumulated area sum A(t.sub.N) corresponds to a better running style or quality. This is in line with the experimental results shown in 4A and 4B inasmuch as the best running style is generally considered to be the fore-foot running style, followed by the heel-strike running style. The type of running style shown in the middle curve (fore-foot running style with overstriding) can be recognized as being of a running quality in between the forefoot striker and the heel-striker.
[0055] FIG. 5 shows experimentally obtained values for the accumulated area sum A per step (with some normalization). The experimental data shown in FIG. 5 were taken on a treadmill with a uniform speed and which, of course, comprises a damping. One can clearly see the different values obtained on the top of the bar graph diagram showing that the forefoot-strike runner has the lowest A value of 0.83. This is followed by an A of 1.09 by the heel-strike runner wherein heel-strike running is generally considered as being of worse quality (e.g. more likely to cause injuries) than fore-foot running The extreme heel-strike runner has an A value of 1.19 which is, of course, considered a worse running style than the heel-strike running The heel-strike runner with overstride, i.e. the runner sets the foot onto the ground before the center of mass, which is also considered a very bad quality of running yields an A value of 1.33. Really bad is a running style with fore-foot strike with overstride which again yields a bad A value of 1.34.
[0056] The experimental data shown in FIG. 6 were taken outdoors during a marathon. The various A values indicated in the bar diagram of FIG. 6 show A per step at the start of the marathon, after 5 kilometers, after 10 kilometers, at half-time, after 30 kilometers and at the end. One can clearly see that different A values are obtained when the runner runs in realistic conditions, i.e. without the damping of a treadmill, with different speeds, the effects of fatigue etc. The overall result of this bar graph diagram is that the running style was believed to be optimum between 10 to 30 kilometers during the marathon.
[0057] Having described preferred embodiments of new and improved method and system for determining the quality of running, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the spirit and scope of the present invention as defined by the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Various publications are cited herein, the disclosures of which are incorporated by reference in their entireties.
