Validity of Wearable Technology Assessments of Heart Rate and Energy Expenditure Under Exercise Conditions
Wearable Electronic Devices , Oxygen Consumption , Spirometry
Apple Watches are just one popular form of tracking fitness metrics including heart rate and caloric expenditure. We tested Apple Watches against gold standard technologies for measuring heart and energy expenditure during light steady-state exercise. We recruited 9 subjects (6F; 3M; Age=20±0.78; Height=171±8.53cm; Weight=184±63.21lbs; Percent body fat=29±8.69%; Predicted VO2max= 38±6.73ml/kg/min) who owned Apple Watches with the most current operating software to participate in this study. Each subject completed 3 5-minute bouts of steady-state exercise on a rower, treadmill, and cycle ergometer in a randomized order. Subjects were allowed to select their own pace with instructions to achieve a “fairly light” intensity. Oxygen consumption was measured via open-circuit spirometry and heart rate was monitored via a three-lead electrocardiogram (ECG). Apple Watch estimates of caloric expenditure and average exercise heart rate were compared with values gathered from oxygen consumption and ECG, respectively. Pearson product-moment correlations were used to compare electrocardiogram and caloric expenditure values between Apple Watch and gold standard measures across the 3 exercise conditions. Correlations for caloric expenditure between the two devices were as follows: treadmill=0.88, bike=0.54, rower=0.87. For heart rate, the correlations were the following: treadmill=0.99, bike=0.96, rower=0.85. These data indicate strong correlations between Apple Watch and ECG with lower correlations between Apple Watch and oxygen consumption, particularly in the cycling condition. Apple Watch appears to accurately measure heart rate; however, it appears to overestimate caloric expenditure.