Validity of the Polar H10 for heart rate variability and cardiac autonomic reflex tests

We tested the validity of the Polar H10 chest strap against criterion electrocardiography (ECG) for heart rate variability (HRV) and cardiac autonomic reflex assessment in young adults and examined associations between supine HRV and other cardiovagal markers. Forty-three healthy adults (18-39 years, 44% male) completed an 8-min protocol: 3 min supine rest (HRV assessed in minute 2 after 1-min stabilization), 1 min paced deep breathing (minute 4; 0.1 Hz), 1 min supine washout, and 3 min active standing (30:15 ratio assessed post-transition; HRV assessed in minute 6 after 1-min post-transition stabilization). Simultaneous RR intervals were recorded via ECG and H10. Agreement was evaluated for time-domain HRV (mean RR interval, root-mean square of successive differences [RMSSD], and standard deviation of normal RR intervals) and reflex tests (deep breathing expiratory [E] to inspiratory [I] ratio, E - I difference, heart rate response; orthostatic 30:15 ratio). Excellent agreement was observed between devices for all metrics (concordance correlation ≥0.99; mean absolute percentage error < 1%; and narrow 95% limits of agreement (widest = -1.5 to 1.7 ms). Supine RMSSD shared 39-53% of variance with deep breathing outcomes, 34% with standing RMSSD, and < 1% with the 30:15 ratio. The H10 provides measurements effectively interchangeable with laboratory ECG for time-domain HRV and standard cardiovagal reflex tests in healthy young adults. Supine RMSSD shares approximately half or less of the variance with other cardiovagal markers, reinforcing the importance of incorporating complementary reflex and orthostatic tests for comprehensive cardiac autonomic assessment.