Four commercial smartwatches provided accurate heart rate measurements compared to ECG (r=0.64-0.97) during exercise, but energy expenditure estimates showed weak correlations (r=0.10-0.34).
Cross-Sectional (n=62)
Do commercially available smartwatches accurately measure heart rate and energy expenditure compared to gold-standard methods during endurance and resistance exercise in healthy adult men?
Smartwatches provide accurate heart rate measurements during exercise but fail to accurately estimate energy expenditure, particularly during resistance training.
Smartwatches are widely used to monitor physiological responses during exercise; however, their accuracy in measuring heart rate (HR) and energy expenditure (EE) across different exercise modalities remains insufficiently characterized. This study evaluated the accuracy of HR and EE measurements obtained from four commercially available smartwatches in comparison with gold-standard reference methods. Sixty-two healthy adult men performed standardized endurance and resistance exercise protocols while simultaneously wearing four smartwatches (Apple, Galaxy, Fitbit, and Garmin). HR was measured using electrocardiography (ECG), and EE was determined using indirect calorimetry. Measurement accuracy was assessed using repeated-measures analysis of variance, Pearson’s correlation analysis, intraclass correlation coefficients (ICCs), and Bland–Altman analyses. All smartwatches demonstrated high accuracy in HR measurements during both endurance and resistance exercises. During endurance exercise, HR measurements from all smartwatch brands were comparable to those obtained via ECG, whereas during resistance exercise, only the Apple Watch showed no significant difference from the ECG. HRs showed strong correlations with ECG readings (r = 0.64–0.97), excellent reliability (ICC > 0.94), and narrow limits of agreement (approximately ±10 bpm). In contrast, the EE measurements exhibited limited accuracy across all devices. During endurance exercise, EE was consistently underestimated with wide limits of agreement. EE accuracy further deteriorated during resistance exercise, showing weak correlations with indirect calorimetry (r = 0.10–0.34) and poor reliability (ICC < 0.45). Overall, smartwatches provide accurate HR measurements across endurance and resistance exercise modalities, supporting their use in exercise intensity monitoring and HR-based training. However, smartwatch-derived EE estimates do not accurately reflect the metabolic demands, particularly during resistance exercises. Future research should focus on improving EE estimation algorithms through multimodal biosignal integration and machine-learning approaches, and validating these methods across diverse populations and exercise modalities.
Lee et al. (Sun,) conducted a cross-sectional in Healthy (n=62). Smartwatches (Apple, Galaxy, Fitbit, Garmin) vs. Electrocardiography (ECG) and indirect calorimetry was evaluated on Accuracy of heart rate and energy expenditure measurements. Four commercial smartwatches provided accurate heart rate measurements compared to ECG (r=0.64-0.97) during exercise, but energy expenditure estimates showed weak correlations (r=0.10-0.34).