Abnormal EMG muscle activity during gait in patients without neurological disorders.

Abnormal muscle activity in patients with a central neurological disorder is commonly attributed to the underlying condition. This study considered abnormal muscle activity in orthopaedic patients who had no neurological involvement. Thirty-nine patients with a variety of orthopaedic problems underwent gait analysis, which included measurement of passive range of motion at the legs, manual muscle strength testing (MMST), instrumented gait analysis, and surface electromyography (EMG). Abnormal timing and duration of EMG activity was found in 51/77 legs. Muscle weakness was the most important cause of the abnormal EMG activity (p<0.001). However, abnormal muscle activity did not correspond to the joint which was controlled by the weak muscles. The triceps surae muscle, represented by the medial gastrocnemius, was significantly more involved (68.6%). Co-activity of the knee extensors and hamstrings was found in 17% of the affected legs. Three out of the 51 legs showed a continuous activity of the rectus femoris muscle in swing. These findings illustrate mechanisms to compensate for muscle weakness in stance in neurologically intact subjects.