The effect of exercise on optical properties of the limb is of interest when the optical properties can be related to changes at depth within the limb. Such information may suggest ways in which noninvasive optical methods can be used to monitor exercise. In the present study, a source-detector arrangement was connected to a computer for collection of data at approximately 7-s intervals during sitting, standing, walking, and jogging. Repeatable changes with exercise were observed, and an oxygen index was calculated for subdermal optical data. The data obtained were consistent with a flow-limited system in which exercise had the effect of increasing oxygen availability at the measurement site.<<ETX>>