Fig. 4

A Arousal levels. The data at each intensity (y-axis) are plotted against %\({\dot{V}}_{{\text{O}}_{\text{2peak}}}\). (x-axis). The plots, from left to right, show rest, very-light, light, moderate, vigorous, and near maximal/maximal intervals. Data are presented as mean. The gray band represents 95% CI. The horizontal error bars (95% CI) cannot be visualized as all were smaller than 1.0%\({\dot{V}}_{{\text{O}}_{\text{2peak}}}\). B Association between Δ pupil diameter (very-light–rest) and Δ arousal (very-light–rest). The black line represents linear regression and gray band represents 95% CI