Examination of extrinsic foot muscles during running using mfMRI and EMG

Over-pronation has been cited as a key contributor to many types of running injuries. However, the roles of the extrinsic foot muscles during running have not been adequately identified. The purpose of this study was to examine the muscle functional (mf) MRI and EMG responses to perturbations of the foot by running in varus, neutral and valgus wedged shoes. Ten males ran at 3.6 m/s in specially constructed shoes for 5 min with T2-weighted mfMRI collected before and after each run. The change in T2 from before to after each run characterized the level of metabolic activity in each of muscle. Kinematic and EMG data were also collected while subjects ran on a treadmill. There were no T2 differences across the three shoe conditions. In contrast, there was significantly less EMG activity in the tibialis anterior and soleus while wearing the neutral shoe. Overall, the results did not support the theory that muscle activity would increase as the degree of eversion increased. It also appears that surface EMG was more sensitive to differences between conditions than mfMRI. However, this study illustrated that mfMRI may be a useful tool for quantifying muscle activity in cases where surface EMG is inadequate.