Statistical heart rate monitoring for estimating calorie expenditure

A method of calibrating a fitness tracking device for calorie estimation for a specific exercise session, the method comprising:

• determining, by a wearable computing device, a start of an exercise session associated with a user of the wearable computing device, the wearable computing device including a processor, a memory, a heart rate sensor, and at least one of a motion sensing module, a display module, and an interface module;
• in response to determining the start of the exercise session, measuring, by the heart rate sensor of the wearable computing device, heart rate data (HR) for a first period of time, the first period of time following the start of the exercise session;
• determining, by the processor of the wearable computing device, an onset heart rate value of the user based on the measured heart rate data, the onset heart rate value associated with a lowest valid heart rate measured during the first period of time, the onset heart rate value being different from a calibrated resting heart rate (RHR) for the user stored in the memory;
• associating, by the processor of the wearable computing device, an RHR parameter of a calorimetry model to the onset heart rate value to calibrate the wearable computing device for the exercise session;
• and
• estimating, by the processor of the wearable computing device, energy expenditure of the user during a second period of time based on the calorimetry model and a plurality of heart rate measurements (HR) obtained by the wearable computing device during the second period of time, the second period of time associated with a portion of time after the first period of time and prior to an end of the exercise session.