To test the hypothesis that pupil diameter, which is innervated by the autonomic nervous system, increases with exercise intensity, we determined pupil diameter during incremental exercise in eight healthy subjects. The subjects performed an incremental ergometer exercise in a room illuminated at 90-100 lx. We continuously measured pupil diameter and heart rate before, during, and after the exercise. Pupil diameter increased significantly with exercise intensity (except at the lowest intensity), peaking at 113±3% (mean±SE) of the diameter during the resting baseline period. The diameter did not differ significantly between the resting baseline and recovery periods. These findings suggest that exercise enlarges pupil diameter and that the magnitude of dilation is related to exercise intensity.
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