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To evaluate the activated muscles by surface electrode functional electric stimulation (S-FES) using magnetic resonance imaging (MRI), and to know the usefulness of MRI for evaluating the muscle activation by S-FES in clinic. Twelve young neuromuscularly normal healthy subjects with an average age of 23.3 (range : 22-27) years. Muscle activation was evaluated in the surface and deep layers of quadriceps and hamstring muscles. MRI was obtained resting, and after voluntary knee isometric extension exercise (VIE) and S-FES. VIE was performed with 10 seconds maximal extension and 10 seconds rest repeated for 20 minutes. S-FES was performed for 20 minutes in a gait cycle pattern. Activated muscles by VIE and S-FES were evaluated using percent increase of T2 value (%IT2). Regions of interests were picked out in surface and deep layers of muscles for evaluation. T2 value in activated muscles increased both after VIE and S-FES. After VIE, %IT2 value was 40.23% in the superficial and 34.09% in the deep layer of the rectus muscle. After SFES, it was 20.23% and 13.8% respectively. There was no significant difference between superficial and deep layers of muscles both after VIE and S-FES. %IT2 of S-FES was significantly smaller than that of VIE in rectus, vastus lateralis, and vastus medialis (p<0.05). S-FES activated muscles can be evaluated using %IT2 of MRI. The muscles, part of which locates on the surface, can the activated using surface electrode MRI is clinically useful in evaluating the activated and inactivated muscles by S-FES, and to determine the indication and limitation of S-FES.
