Method for determining an instant velocity of a user and for improving estimation of heart rate

1. Method for determining an instant velocity of a user using a sensing device destined to be worn on an arm of the user and comprising a motion sensor for measuring and delivering a motion signal representative of the user's movements when the sensing device is worn; the method comprising:

measuring the motion signal;

identifying when the user is performing a rhythmical activity and estimating a fundamental movement frequency of the user from the measured motion signal;

identifying when the user is walking or running by calculating an activity level of the user using the measured motion signal and the fundamental movement frequency;

when the user is walking or running, providing a relationship between the measured motion signal and corresponding features of the user's motion which are indicative of a propulsive impulsion of a user's step, by using a bio-mechanical model of human locomotion comprising an active damper model wherein the user's arms act as an active damper of torque produced by a propulsive phase of the user's legs;

estimating a frequency of the user's step and estimating a user-relative step length of the user's step using the motion features;

determining a user-relative instant velocity by combining the estimated user's step frequency and the estimated user-relative step length; and

determining the instant velocity from the user-relative instant velocity using a calibration factor.

2. Method according to claim 1 , wherein the calibration factor is determined using one of: cumulated 25 distance when the user is walking or running, average velocity of the user when walking or running, or a morphological parameter of the user.

3. Method according to claim 1 , wherein said estimating a step frequency comprises identifying a time of impact of the user's foot using the motion features.

4. Method according to claim 1 , wherein said estimating a step length further comprises using a calibration measurement taken at the determined instantaneous velocity or at an estimated traveled distance by the user.

5. Method according to claim 1 , wherein combining the estimated step frequency and the estimated step length comprised multiplying the estimated step frequency with the estimated step length.

6. Method according to claim 1 , further comprising multiplying the estimated user-relative step length by a user-specific calibration factor.

7. Method according to claim 5 , wherein the calibration factor is obtained by measuring an average velocity or a distance traveled by the user when the user is walking or running.

8. Method according to claim 5 , wherein the calibration factor is estimated by using morphological parameters of the user in combination with an empirically determined model.

9. Method according to claim 1 , further comprising estimating an a priori heart rate of the user by using the determined instant velocity and a model relating a heart rate value with the instant velocity.

10. Method according to claim 9 , wherein the model comprises a linear or a nonlinear relationship between the determined instants velocity and said heart rate value.

11. Method according to claim 9 , wherein the model comprises a physiological model including one of age, gender, weight or height of the user.

12. Method according to claim 9 , wherein the sensing device further comprises a heart rate sensor adapted to measure a heart rate signal when the sensing device is worn; and wherein the method further comprises measuring the heart rate signal and estimating a measured heart rate from the measured heart rate signal.

13. Method according to claim 12 , wherein said estimating a measured heart rate comprises determining a reliability of the measured heart rate; and wherein the a priori heart rate is used in combination with the measured heart rate when the measured heart rate is unreliable.

14. Method according to claim 13 , further comprising user-specifically adapting the model by using the measured hear rate when the measured heart rate is reliable.

15. Method according to claim 1 , further comprising estimating a distance traveled by the user by using the integration of the determined instant velocity.

16. Method according to claim 1 , further comprising calculating an energy expenditure of the user by using the determined instant velocity.