Cadence detection based on inertial harmonics
The method and apparatus disclosed herein determine a user cadence from the output of an inertial sensor mounted to or proximate the user's body. In general, the disclosed cadence measurement system determines the user cadence based on frequency measurements acquired from an inertial signal output by the inertial sensor. More particularly, a cadence measurement system determines a user cadence from an inertial signal generated by an inertial sensor, where the inertial signal comprises one or more frequency components. The cadence measurement system determines a peak frequency of the inertial signal, where the peak frequency corresponds to the frequency component of the inertial signal having the largest amplitude. After applying the peak frequency to one or more frequency threshold comparisons, the cadence measurement system determines the user cadence based on the peak frequency and the frequency threshold comparison(s).
1. A device configured to be worn by a subject, the device comprising:
an inertial sensor configured to generate an inertial signal responsive to body motion of the subject, the inertial signal comprising a plurality of frequency components;
an optical emitter configured to emit light onto at least some portion of skin of the subject;
an optical detector configured to detect light scattered from or through the skin of the subject responsive to the light emitted by the optical emitter to generate a first output signal;
at least one processor circuit operatively connected to the inertial sensor and the optical detector, the at least one processor circuit configured to:
determine a spectral signal based on a frequency transform of the inertial signal;
determine a peak spectral signal from the spectral signal having a peak frequency and a peak magnitude, said peak frequency corresponding to a frequency component of the inertial signal having a largest magnitude;
determine at least one frequency threshold for one or more frequency threshold comparisons responsive to a previous cadence of the subject;
compare the peak frequency to at least one of the at least one frequency threshold determined for the one or more frequency threshold comparisons; and
determine a cadence of the subject responsive to the comparison; and
a noise circuit configured to:
attenuate motion artifact noise from the first output signal responsive to the determined cadence of the subject to generate a second output signal; and
output the second output signal to an output circuit.
2. The device of claim 1 wherein the at least one processor circuit determines the cadence of the subject responsive to the comparison by calculating the cadence using the peak frequency and the previous cadence when the peak frequency exceeds the at least one of the at least one frequency threshold determined for the one or more frequency threshold comparisons.
3. The device of claim 1 wherein the at least one processor circuit determines the cadence of the subject responsive to the comparison by setting the cadence of the subject equal to the peak frequency divided by a harmonic factor when the peak frequency is less than the at least one of the at least one frequency threshold determined for the one or more frequency threshold comparisons.
4. The device of claim 1 wherein the at least one processor circuit is further configured to:
determine a power of the inertial signal, said power of the inertial signal encompassing the plurality of frequency components of the inertial signal; and
compare the power of the inertial signal to a power threshold; and
determine the cadence of the subject responsive to the comparison of the peak frequency to the at least one of the at least one frequency threshold determined for the one or more frequency threshold comparisons and responsive to the comparison between the power of the inertial signal to the power threshold.
5. The device of claim 1 wherein the at least one processor circuit is further configured to determine a subject activity parameter responsive to input from the subject, and wherein the at least one processor circuit determines the cadence of the subject by determining the cadence of the subject responsive to the subject activity parameter and responsive to the comparison of the peak frequency to the at least one of the at least one frequency threshold determined for the one or more frequency threshold comparisons.
6. The device of claim 1 wherein the device is configured to be worn on or proximate a limb of the subject.
7. The device of claim 1 wherein the device is configured to be worn on or proximate an ear of the subject.
8. The device of claim 1 wherein the device is configured to be worn on or proximate a wrist of the subject.
9. The device of claim 1 wherein the device is configured to be worn on or proximate one or more phalanges of the subject.
10. A device configured to be worn by a subject, the device comprising:
an inertial sensor configured to generate an inertial signal responsive to body motion of the subject, the inertial signal comprising a plurality of frequency components;
an optical emitter configured to emit light onto at least some portion of skin of the subject;
an optical detector configured to detect light scattered from or through the skin of the subject responsive to the light emitted by the optical emitter to generate a first output signal;
at least one processor circuit operatively connected to the inertial sensor and the optical detector, the at least one processor circuit configured to:
determine at least one frequency threshold for one or more frequency threshold comparisons responsive to a previous cadence of the subject;
compare a peak frequency to at least one of the at least one frequency threshold determined for the one or more frequency threshold comparisons, said peak frequency corresponding to a frequency component of the inertial signal having a largest magnitude; and
determine, responsive to the comparison of the peak frequency and responsive to the inertial signal and an inertial power threshold, a cadence of the subject based on a comparison between a power of the inertial signal and the inertial power threshold; and
a noise circuit configured to:
attenuate motion artifact noise from the first output signal responsive to the determined cadence of the subject to generate a second output signal; and
output the second output signal to an output circuit.
11. The device of claim 10 wherein the at least one processor circuit is further configured to determine a subject activity parameter responsive to input from the subject, and wherein the at least one processor circuit determines the cadence of the subject by determining the cadence of the subject responsive to the subject activity parameter and responsive to the inertial signal and the inertial power threshold.
12. The device of claim 10 wherein the at least one processor circuit determines the cadence of the subject responsive to a comparison between the inertial signal and the inertial power threshold.
13. The device of claim 10 wherein the device is configured to be worn on or proximate a limb of the subject.
14. The device of claim 10 wherein the device is configured to be worn on or proximate an ear of the subject.
15. The device of claim 10 wherein the device is configured to be worn on or proximate a wrist of the subject.
16. The device of claim 10 wherein the device is configured to be worn on or proximate one or more phalanges of the subject.