Abstract
Heart rate (HR) and heart rate variability (HRV) can be monitored with wearable devices throughout the day. Resting HRV in particular, reflecting cardiac parasympathetic activity, has been proposed to be a useful marker in the monitoring of health and recovery from training. This study examined the validity of the wrist-based photoplethysmography (PPG) method to measure HR and HRV at rest. Recreationally endurance-trained participants recorded pulse-to-pulse (PP) and RR intervals simultaneously with a PPG-based watch and reference heart rate sensor (HRS) at a laboratory in a supine position (n = 39; 5-min recording) and at home during sleep (n = 29; 4-h recording). In addition, analyses were performed from pooled laboratory data (n = 11344 PP and RR intervals). Differences and correlations were analyzed between the HRS- and PPG-derived HR and LnRMSSD (the natural logarithm of the root mean square of successive differences). A very good agreement was found between pooled PP and RR intervals with a mean bias of 0.17 ms and a correlation coefficient of 0.993 (p < 0.001). In the laboratory, HR did not differ between the devices (mean bias 0.0 bpm), but PPG slightly underestimated the nocturnal recordings (mean bias −0.7 bpm, p < 0.001). PPG overestimated LnRMSSD both in the laboratory (mean bias 0.20 ms, p < 0.001) and nocturnal recordings (mean bias 0.17 ms, p < 0.001). However, very strong intraclass correlations in the nocturnal recordings were found between the devices (HR: 0.998, p < 0.001; LnRMSSD: 0.931, p < 0.001). In conclusion, PPG was able to measure HR and HRV with adequate accuracy in recreational athletes. However, when strict absolute values are of importance, systematic overestimation, which seemed to especially concern participants with low LnRMSSD, should be acknowledged.
Highlights
Wearable technology has been ranked in the top three fitness trends in the ACSM annual survey for fitness professionals since 2016 [1]
HR and heart rate variability (HRV) provides information on autonomic nervous system (ANS) regulation, and HRV could be used as an indirect marker of cardiac parasympathetic nervous system activity [4]
While HR and HRV could be monitored with an increasing number of wearables, it
Summary
Wearable technology has been ranked in the top three fitness trends in the ACSM annual survey for fitness professionals since 2016 [1]. HR and heart rate variability (HRV) provides information on autonomic nervous system (ANS) regulation, and HRV could be used as an indirect marker of cardiac parasympathetic nervous system activity [4]. Altini and Plews [5] illustrated how resting HRV may provide additional insights compared to HR only on responses to different types of stressors. Monitoring of resting HR [6] or heart rate variability (HRV) [7,8] could be beneficial for predicting the risk of cardiovascular events, such as acute coronary syndromes or strokes. Daily resting HRV recordings have been used in the endurance training prescription of untrained [9], recreationally trained [10], and well-trained [11] participants, inducing greater improvements in endurance performance compared to predefined training. While there are more wearables available that claim to measure meaningful results, their validity should be critically studied [2,12] and sources of inaccuracies acknowledged [13,14]
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