TABLE 3.

Heart rate variability accuracy.

Statistic	Garmin Fenix 6	Oura Gen 3	Oura Gen 4	Polar Grit X Pro	WHOOP 4.0
N (number of nights)	150	470	139	206	289
Mean bias (ms)	−1.84 ± 6.86	−2.50 ± 4.56	−0.96 ± 5.52	−4.65 ± 9.67	−0.78 ± 5.98
Limits of agreement (ms)	−15.218, 11.60	−11.43, 6.43	−11.78, 9.85	−14.30, 23.60	−12.50, 10.94
Mean absolute error (ms)	5.29 ± 4.72 b , d	3.91 ± 3.40 a , c	3.93 ± 3.98 d	7.27 ± 7.88 a , b , c , d	4.17 ± 4.33 d
Pearson's R correlation	0.96	0.97	0.99	0.86	0.96
MAPE (%)	10.52 ± 8.63 b , c , d	7.15 ± 5.48 a , d	5.96 ± 5.12 a , d	16.32 ± 24.39 a , b , c , e	8.17 ± 10.49 d
CCC	0.87	0.97	0.99	0.82	0.94

^a Significantly different from Garmin Fenix 6.

^b Significantly different than Oura Gen 3.

^c Significantly different from Oura Gen 4.

^d Significantly different from Polar Grit X Pro.

^e Significantly different from WHOOP 4.0.