Methods and apparatus for power expenditure and technique determination during bipedal motion

A system for measuring motion of a user during physical activity, the system comprising:

• a housing configured to be attachable to a shoe of a user, the housing including a sensor platform disposed therein, the sensor platform comprising:
• an inertial measurement unit (IMU), disposed within the housing, to acquire multi-axis motion data, the multi-axis motion representing motion of the system;
• and
• an orientation sensor, disposed within the housing, to acquire orientation data at a sampling rate, the orientation data representing an orientation of the sensor;
• a barometer to acquire air pressure data while the user is engaging in the physical activity;
• a processor, operably coupled to the IMU, the barometer, and the orientation sensor;
• and
• at least one memory, operably coupled to the processor, to store the multi-axis motion data and the orientation data, the at least one memory storing instructions that when executed by the processor cause the system to perform operations comprising:
• calculating at least one of a velocity or a change in velocity of the sensor platform based on at least the multi-axis motion data;
• and
• generating, based on the acquired air pressure data, a body forward-facing surface area of the user and a drag coefficient, an estimate of wind resistance experienced by the user during the physical activity;
• generating an estimate of power expended by the user, based on the estimate of wind resistance and at least one of the velocity of the sensor platform or the change in velocity of the sensor platform.