Impact of central adiposity on the heart rate and calorie estimation accuracy of diverse smartwatches and the resulting subjective exercise experience.

INTRODUCTION: In light of the growing global trend toward health awareness, wearable technologies like smartwatches have become essential for monitoring physiological indicators such as heart rate (HR). However, their utility faces two critical challenges: a technical disparity between premium and affordable devices and a conceptual gap where objective HR may fail to capture the true subjective strain experienced by diverse populations. Consequently, this study has a dual objective: to evaluate the HR accuracy of four commercially available watches and examine how measurement variations propagate through a standardized HR-derived energy expenditure model; and to investigate the dissociation between objective HR and subjective perceived exertion (RPE) in individuals with elevated central adiposity.

METHODS: Forty healthy adults ( n = 40 ) participated in a 45 min multi-stage exercise protocol consisting of stretching, cycling, and running. Participants were stratified into two groups based on their waist-to-height ratio (WHtR): normal ( ≤ 0.5) and elevated (>0.5). Data were synchronized using a temporal alignment procedure, and calorie expenditure was calculated through a standardized heart-rate-based regression model to ensure fair comparisons across all devices.

RESULTS: Premium smartwatches, specifically the Apple Watch and Garmin, demonstrated superior HR precision across all activity phases, maintaining high correlations ( r ≥ 0.98 ) with the clinical reference. While the low-cost Xiaomi and ThaiSook watches exhibited higher HR errors during motion-intensive activities, their derived calorie expenditure estimates remained remarkably stable and consistent with the reference standard. Notably, individuals with elevated WHtR reported significantly higher Ratings of Perceived Exertion (RPE) during running and recovery phases ( p < 0.05 ), despite showing no significant difference in heart rate responsiveness compared to leaner participants.

CONCLUSION: This study confirms that while higher-end sensors offer greater heart rate precision, affordable wearables can provide sufficient HR data to yield consistent energy expenditure estimates when using a standardized mathematical model, supporting their potential utility in large-scale health monitoring. The divergence between objective heart rate and subjective exertion in participants with central adiposity indicates that heart rate alone is an insufficient gauge of exercise intensity. Consequently, personalized weight-management programs should integrate wearable-derived metrics with perceived effort to better account for the unique physiological and psychological strain associated with higher body mass.