We have previously reported an optical response in human subjects occurring at 100 ms following electrical stimulation of peripheral nerves. In the present study, an animal model has been created to directly investigate the myogenic components of the signal. In addition, experiments have been performed in human subjects to investigate the signal's neuroanatomical specificity, sensitivity to muscle motion, and spatial and spectral features. The results of this work suggest that the observed optical signal derives from stimulus-induced motion associated with muscle contraction and likely contains myological information of clinical value.