Fatigue-induced changes in longitudinal relaxation time determined by magnetic resonance imaging

Longitudinal relaxation time (T1) determined by 3.0-T magnetic resonance imaging of the tibialis anterior and extensor digitorum longus muscles increased gradually with muscle fatigue caused by three 120-s periods of repeated ankle dorsiflexion separated by 5-min rest periods. T1 values decreased in the recovery period, although they remained higher than the preexercise values. T1 values for the soleus muscle were unchanged throughout the experiment. Results suggest that muscle T1 values increase with increasing muscle fatigue.