Cardiovascular

Beats per minute measured at rest or during activity

Heart rate measured during periods of rest

Variation in time between heartbeats (RMSSD)

VO2 max represents maximal oxygen uptake—the maximum rate at which the body can consume oxygen during intense exercise. Expressed in mL/kg/min, it is the gold-standard measure of cardiorespiratory fitness. Average values are 35-40 mL/kg/min for men and 27-31 for women, declining with age. Elite endurance athletes may exceed 70-85 mL/kg/min. Higher VO2 max correlates strongly with reduced all-cause mortality and cardiovascular disease risk. Wearables estimate VO2 max using heart rate response during submaximal exercise, age, and sometimes running pace—accuracy is ±10-15% compared to laboratory testing. Improvements of 10-20% are achievable with consistent aerobic training. Clinical applications include assessing cardiac rehabilitation progress and surgical risk stratification.