Table 2.

Sample size, correlation, and agreement between Apple Watch and reference methods for heart rate at start (seated rest, HR1), middle (moderate intensity, HR2), and maximal performance level (HR3), and energy expenditure (n=40).

Characteristics	HR1a (bpm)	HR2b (bpm	HR3c (bpm)	Energy expenditure (kcal)
Gold standard measurement, mean (SD)	69.9 (14.5)	94.6 (20.6)	126.5 (30.9)	40.6 (32.4)
Gold standard measurement, standard error	2.30	3.26	4.88	6.49
SDDd, mean (SD)	3.61 (12.4)	0.91 (16.2)	–1.82 (12.0)	30.47 (17.5)
Upper LoAe	27.96	32.63	21.63	64.74
Lower LoA	–20.74	–30.82	–25.27	–3.80
MAEf	6.34	7.55	6.90	30.77
MAPEg (%)	10.69	9.20	6.33	114.72
ICCh (P value)	0.729 (<.001)	0.828 (<.001)	0.958 (<.001)	0.797 (<.001)

^aHR1: heart rate, seated rest.

^bHR2: heart rate, moderate intensity.

^cHR3: heart rate, maximal performance level.

^dSDD: standard deviation of difference.

^eLoA: limits of agreement.

^fMAE: mean absolute error.

^gMAPE: mean absolute percentage error.

^hICC: intraclass correlation coefficient.