Detecting unmeasurable loads using heart rate and work rate

1. A method for determining an energy expenditure of a user with a wearable device, the method comprising:

determining, by a processor circuit of the wearable device, a start of an exercise session for the user;

detecting, by the processor circuit, an exercise type associated with the exercise session wherein the exercise type is walking or running;

measuring, by a heart rate sensing module of the wearable device, heart rate data of the user, wherein the heart rate sensing module comprises a photoplethysmogram (PPG) sensor and the PPG sensor is configured to be worn adjacent to the user's skin;

applying, by the processor circuit, a first time stamp to the measured heart rate data;

collecting, by one or more work rate sensing modules of the wearable device, work rate data of the user;

applying, by the processor circuit, a second time stamp to the collected work rate data;

calculating, by the processor circuit, a heart rate-based energy expenditure based on the heart rate data measured at the first time stamp;

calculating, by the processor circuit, a work rate-based energy expenditure based on the work rate data collected at the second time stamp;

determining, by the processor circuit, an energy expenditure of the user based on the calculated heart rate-based energy expenditure and the calculated work rate-based energy expenditure; and

outputting the energy expenditure of the user.

2. The method of claim 1 , wherein calculating the heart rate-based energy expenditure comprises:

measuring, by the heart rate sensing module, a maximum heart rate and a resting heart rate;

determining, by the processor circuit, a heart rate confidence parameter based on the measured heart rate data;

calculating, by the processor circuit, a fraction of heart rate reserve (FHR) based on the measured heart rate data, the maximum heart rate, and the resting heart rate; and

calculating, by the processor circuit, the heart rate-based energy expenditure based on the FHR.

3. The method of claim 2 , wherein determining the energy expenditure of the user comprises:

determining the energy expenditure of the user as the calculated work rate-based energy expenditure when:

the determined heart rate confidence parameter is less than a pre-defined heart rate confidence threshold,

the detected exercise type is running and the calculated fraction of heart rate reserve is greater than a pre-defined fraction of heart rate reserve threshold, or

the detected exercise type is walking and a heart rate-based metabolic equivalents of task is greater than a pre-defined metabolic equivalents of task threshold; and

determining the energy expenditure of the user as the greater of the calculated heart rate-based energy expenditure and the calculated work rate-based energy expenditure when:

the determined heart rate confidence parameter is greater than or equal to a pre-defined heart rate confidence threshold,

the detected exercise type is running and the calculated fraction of heart rate reserve is less than or equal to a pre-defined fraction of heart rate reserve threshold, or

the detected exercise type is walking and a heart rate-based metabolic equivalents of task is less than or equal to a pre-defined metabolic equivalents of task threshold.

4. The method of claim 3 , wherein the pre-defined metabolic equivalents of task threshold is between 0 and 50.

5. The method of claim 1 , wherein determining the start of the exercise session comprises determining the start of the exercise session in response to receiving an input from the user.

6. The method of claim 1 , wherein the one or more work rate sensing modules comprises a motion sensing module.

7. The method of claim 6 , wherein the motion sensing module comprises at least one of an accelerometer, a gyroscope, a magnetometer, an altimeter, a barometer, or a GPS sensor.

8. A system for determining an energy expenditure of a user with a wearable device, the system comprising:

a heart rate sensing module configured to measure heart rate data of the user, wherein the heart rate sensing module comprises a photoplethysmogram (PPG) sensor and the PPG sensor is configured to be worn adjacent to the user's skin;

one or more work rate sensing modules configured to collect work rate data of the user; and

a processor circuit in communication with the heart rate sensing module and the one or more work rate sensing modules and configured to execute instructions causing the processor circuit to:

determine a start of an exercise session for the user;

detect an exercise type associated with the exercise session, wherein the exercise type is walking or running;

apply a first time stamp to the measured heart rate data;

apple a second time stamp to the collected work rate data;

calculate a heart rate-based energy expenditure based on the heart rate data measured at the first time stamp;

calculate a work rate-based energy expenditure based on the work rate data collected at the second time stamp;

determine an energy expenditure of the user based on the calculated heart rate-based energy expenditure and the calculated work rate-based energy expenditure; and

output the energy expenditure of the user.

9. The system of claim 8 , wherein the heart rate sensing module is configured to measure a maximum heart rate and a resting heart rate, and the instructions further cause the processor circuit to:

determine a heart rate confidence parameter based on the collected heart rate data;

calculate a fraction of heart rate reserve (FHR) based on the collected heart rate data, the maximum heart rate, and the resting heart rate; and

calculate a heart rate-based energy expenditure based on the FHR.

10. The system of claim 8 , wherein the instructions further cause the processor circuit to:

determine the energy expenditure of the user as the calculated work rate-based energy expenditure when:

the determined heart rate confidence parameter is less than a pre-defined heart rate confidence threshold,

the detected exercise type is running and the calculated fraction of heart rate reserve is greater than a pre-defined fraction of heart rate reserve, or

the detected exercise type is walking and a heart rate-based metabolic equivalents of task is greater than a pre-defined metabolic equivalents of task threshold; and

determine the energy expenditure of the user as the greater of the calculated heart rate-based energy expenditure and the calculated work rate-based energy expenditure when:

the determined heart rate confidence parameter is greater than or equal to a pre-defined heart rate confidence threshold,

the detected exercise type is running and the calculated fraction of heart rate reserve is less than or equal to a pre-defined fraction of heart rate reserve, or

the detected exercise type is walking and a heart rate-based metabolic equivalents of task is less than or equal to a pre-defined metabolic equivalents of task threshold.

11. The system of claim 10 , wherein the pre-defined metabolic equivalents of task threshold is between 0 and 50.

12. The system of claim 8 , wherein the one or more work rate sensing modules comprises a motion sensing module.

13. The system of claim 12 , wherein the motion sensing module comprises at least one of an accelerometer, a gyroscope, a magnetometer, an altimeter, a barometer, or a GPS sensor.

14. A mobile device comprising:

a wearable case;

a heart rate sensing module disposed in the wearable case and configured to measure heart rate data of the user, wherein the heart rate sensing module comprises a photoplethysmogram (PPG) sensor and the PPG sensor is configured to be worn adjacent to the user's skin;

one or more work rate sensing modules configured to collect work rate data of the user; and

a processor circuit in communication with the heart rate sensing module and the one or more work rate sensing modules and configured to execute instructions causing the processor circuit to:

determine a start of an exercise session for the user;

detect an exercise type associated with the exercise session, wherein the exercise type is walking or running;

apply a first time stamp to the measured heart rate data;

apple a second time stamp to the collected work rate data;

calculate a heart rate-based energy expenditure based on the heart rate data measured at the first time stamp;

calculate a work rate-based energy expenditure based on the work rate data collected at the second time stamp;

determine an energy expenditure of the user based on the calculated heart rate-based energy expenditure and the calculated work rate-based energy expenditure; and

output the energy expenditure of the user.