Identifying poor cardiorespiratory fitness using sensors of wearable devices

A method comprising:

• determining, with at least one processor, confidence-weighted historical sensor observations and confidence-weighted maximal oxygen consumption estimates based on heart rate data, mechanical work rate data, input sensor quality, validity of a work rate model for generating the mechanical work rate data and a measure of observation consistency;
• determining, with the at least one processor, a first joint confidence based on the confidence-weighted historical sensor observations;
• determining, with the at least one processor, a second joint confidence based on the confidence-weighted maximal oxygen consumption estimates, historical maximal oxygen consumption estimates and context data;
• and
• determining, with the at least one processor, a cardiorespiratory fitness of the user by evaluating the first and second joint confidences using at least one criteria.