Abstract

We use time-resolved near-infrared diffusing-wave spectroscopy (DWS) to non-invasively measure the contraction of skeletal muscle in humans. The evolution of the muscle strain Γ (t) is determined by analyzing the autocorrelation functiong⁽¹⁾ (τ,t) of the multiply scattered light field with the analytical solution of the correlation-diffusion equation for a semi-infinite, homogeneous medium whose dynamics is a mixture of diffusion and shear deformation. The temporal resolution of 6 ms allows to follow the build-up of contraction at time scales comparable to the ones of EMG. We observe that the diffusion coefficient increases practically immediately after stimulation; in contrast, the shear deformation is delayed by about 10 ms. Our data indicates that the strain signal arises from the velocity gradient associated with axial contraction and radial dilation of the muscle fiber. Our method could provide a painless alternative to fine-wire EMG for assessment of muscle function in sports medicine and clinical applications.

© 2010 Optical Society of America