Sensor-based athletic activity measurements

1. A method comprising:

receiving a signal generated by a foot-based sensor during athletic activity performed by a user, wherein the signal comprises a plurality of samples;

processing the signal based on a rolling standard deviation;

identifying, from the rolling standard deviation processed signal, a sequence of three samples in the signal that corresponds to a physical foot-step taken by the user, wherein the sequence of three samples includes a first heelstrike sample, a toe-off sample and a second heelstrike sample;

determining a pace of the user based on an elapsed time between at least two of the first heelstrike, toe-off and second heelstrike samples; and

responsive to having received a user request to determine a pace during the athletic activity, providing the determined pace to a user display device.

2. The method of claim 1 , further comprising:

determining a first difference between a value of the second heelstrike sample and a value of the toe-off sample;

determining a second difference between a value of the toe-off sample and the value of the first heelstrike sample;

determining whether the first difference is greater than the second difference; and

in response to determining that the first difference is greater than the second difference, adding the sequence of three samples to a list.

3. The method of claim 2 , further comprising:

adding a plurality of three sample sequences to the list; and

determining a plurality of contact times of the user based on the plurality of three sample sequences in the list.

4. The method of claim 3 , further comprising:

determining a mean contact time of the plurality of contact times;

determining a standard deviation between the plurality of contact times; and

filtering out one or more contact times of the plurality of contact times that exceed a threshold number of standard deviations from the mean contact time.

5. The method of claim 1 , wherein determining the pace of the user based on an elapsed time between at least two of the first heelstrike, toe-off and second heelstrike samples includes:

determining a contact time by determining a difference between the toe-off sample and the first heelstrike sample;

selecting a predefined linear relationship from a plurality of linear relationships, wherein each of the plurality of linear relationships corresponds to a different type of athletic activity; and

applying the predefined linear relationship to the contact time to calculate the pace of the user.

6. The method of claim 1 , wherein identifying the sequence of three samples in the signal that corresponds to a physical foot-step taken by the user includes:

selecting a first sample from the plurality of samples;

determining whether a value of the first sample is at or above a first threshold sample value;

in response to determining that the value of the first sample is not at or above the first threshold sample value, selecting a subsequent sample in the plurality of samples; and

in response to determining that the value of the first sample is at or above the first threshold sample value:

determining a maximum sample value in a first sample window of a predefined size, wherein a lower bound of the first sample window corresponds to the first sample, and

identifying a sample corresponding to the maximum sample value as the first heelstrike sample.

7. The method of claim 6 , wherein in response to determining that the value of the first sample is at or above the first threshold sample value, the method further comprises:

determining a maximum sample value in a second sample window; and

determining whether the maximum sample value of the second sample window is at or above a second threshold sample value; and

in response to determining that the maximum sample value of the second sample window is at or above the second threshold sample value, identifying a sample corresponding to the maximum sample value of the second sample window as the toe-off sample.

8. The method of claim 1 , wherein the rolling standard deviation includes a plurality of standard deviations corresponding to the plurality of samples.

9. The method of claim 1 , wherein the rolling standard deviation is calculated using an equation as follows:

σ

i

=

(

1

N

⁢

∑

i

-

1

i

+

1

⁢

(

x

i

-

x

_

i

)

2

)

wherein N represents a number of samples being considered, i represents a sample number, x represents a raw signal output value, x represents a mean raw signal output of the number of samples being considered.

10. An apparatus comprising:

a foot-based sensor;

at least one processor; and

one or more non-transitory computer readable media coupled to the at least one processor and storing computer readable instructions that, when executed, cause the apparatus to:

receive a signal generated by the foot-based sensor during athletic activity performed by a user, wherein the signal comprises a plurality of samples;

process the signal based on a rolling standard deviation;

identify, from the rolling standard deviation processed signal, a sequence of three samples in the signal that corresponds to a physical foot-step taken by the user, wherein the sequence of three samples includes a first heelstrike sample, a toe-off sample and a second heelstrike sample;

determine a pace of the user based on an elapsed time between at least two of the first heelstrike, toe-off and second heelstrike samples; and

responsive having received a user request to determine a pace during the athletic activity, provide the determined pace to a user display device.

11. The apparatus of claim 10 , wherein the one or more non-transitory computer readable media contains further computer readable instructions that, when executed, cause the apparatus to:

determine a first difference between a value of the second heelstrike sample and a value of the toe-off sample;

determine a second difference between a value of the toe-off sample and the value of the first heelstrike sample;

determine whether the first difference is greater than the second difference; and

in response to determining that the first difference is greater than the second difference, adding the sequence of three samples to a list.

12. The apparatus of claim 11 , wherein the one or more non-transitory computer readable media contains further computer readable instructions that, when executed, cause the apparatus to:

add a plurality of three sample sequences to the list; and

determine a plurality of contact times of the user based on the plurality of three sample sequences in the list.

13. The apparatus of claim 12 , wherein the one or more non-transitory computer readable media contains further computer readable instructions that, when executed, cause the apparatus to:

determine a mean contact time of the plurality of contact times;

determine a standard deviation between the plurality of contact times; and

filter out one or more contact times of the plurality of contact times that exceed a threshold number of standard deviations from the mean contact time.

14. One or more non-transitory computer readable media storing computer readable instructions that, when executed, cause an apparatus to:

receive a signal generated by a foot-based sensor during athletic activity performed by a user, wherein the signal comprises a plurality of samples;

process the signal based on a rolling standard deviation;

identify, from the rolling standard deviation processed signal, a sequence of three samples in the signal that corresponds to a physical foot-step taken by the user, wherein the sequence of three samples includes a first heelstrike sample, a toe-off sample and a second heelstrike sample; and

determine a pace of the user based on an elapsed time between at least two of the first heelstrike, toe-off and second heelstrike samples and

responsive to having received a user request to determine a pace during the athletic activity, provide the determined pace to a user display device.

15. The one or more non-transitory computer readable media of claim 14 , wherein determining the pace of the user based on an elapsed time between at least two of the first heelstrike, toe-off and second-heelstrike samples includes:

determining a contact time by determining a difference between the toe-off sample and the first heelstrike sample;

selecting a predefined linear relationship from a plurality of linear relationships, wherein each of the plurality of linear relationships corresponds to a different type of athletic activity; and

applying the predefined linear relationship to the contact time to calculate the pace of the user.

16. The one or more non-transitory computer readable media of claim 14 , wherein identifying the sequence of three samples in the signal that corresponds a physical foot-step taken by the user includes:

selecting a first sample from the plurality of samples;

determining whether a value of the first sample is at or above a first threshold sample value;

in response to determining that the value of the first sample is not at or above the first threshold sample value, selecting a subsequent sample in the plurality of samples; and

in response to determining that the value of the first sample is at or above the first threshold sample value:

determining a maximum sample value in a first sample window of a predefined size, wherein a lower bound of the first sample window corresponds to the first sample, and

identifying a sample corresponding to the maximum sample value as the first heelstrike sample.

17. The one or more non-transitory computer readable media of claim 14 , further comprising computer readable instructions that, when executed, cause the apparatus to:

determine a first difference between a value of the second heelstrike sample and a value of the toe-off sample;

determine a second difference between a value of the toe-off sample and the value of the first heelstrike sample;

determine whether the first difference is greater than the second difference;

in response to determining that the first difference is greater than the second difference, add the sequence of three samples to a list;

add a plurality of three sample sequences to the list; and

determine a plurality of contact times of the user based on the plurality of three sample sequences in the list.