Fig. 2

Prediction error of VO₂ on the free-living walks for the treadmill- and track-based calibration methods. Figure 2 shows the relationship between mean prediction error for VO₂ (ml · kg⁻¹ · min⁻¹) and actual walking speed (km · h⁻¹) on the free-living walks for the treadmill- (left) and track-based (right) calibration methods. Dashed lines are 95 % confidence intervals