Fig. 4.

Bland–Altman meta-analysis for the comparison of wearable-derived VO_2max using resting conditions and exercise tests with the reference VO_2max. The y-axis is the bias between the wearable and reference VO_2max (wearable − reference), with positive values indicating an overestimation and negative values an underestimation by the wearable. The x-axis is the mean VO_2max between the wearable and reference. CI confidence interval, VO_2max maximal oxygen consumption. *Heart rate was measured with chest strap. In the remaining articles not flagged with an asterisk, heart rate was measured using photoplethysmography technology on the wrist