The efficacy of physical therapy for a patient with impaired hair-washing motion due to dysfunction of the inferior fibers of the trapezius was assessed. Surface electromyography was performed to investigate the clinical implications, and to elucidate the relationship between changes in the speed of elbow joint flexion-extension during simulated hair-washing motion and the corresponding activities of the superior, intermediate, and inferior fibers of the trapezius and of the caput longum of triceps brachii. In a sitting position, the subject moved the shoulder joint approximately 110 degrees in flexion and the elbow joint approximately 45 degrees horizontally on the measured side, and performed flexion-extension of the elbow joint in which the middle finger on the measured side reciprocated between the torus occipitalis and vertex in a hair-washing motion-simulating task. The motion speed was set at 40, 80, 120, and 160 motions per minute using a metronome and electromyograms of the superior, intermediate, and inferior fibers of the trapezius and the caput longum of triceps brachii were measured for 10 seconds 3 times during each task. Electromyogram waveforms of these fibers at each speed and the influence of changes in the elbow joint flexion-extension speed on the relative integrated electromyogram value were investigated. In the caput longum of triceps brachii, the amplitude of the electromyogram waveform in a single elbow joint flexion-extension motion was compared among the tasks at different speeds. The waveform amplitude increased and the relative integral value tended to increase as the elbow joint flexion-extension speed increased only in the inferior fibers of the trapezius. These findings suggest that to evaluate and improve hair-washing motion in patients with impairment of the scapulothoracic joint, the arm should be maintained in an elevated position during this motion. Furthermore, attention should be paid to the activity of the inferior fibers of the trapezius, which are assumed to be involved in stabilization of the scapula during the elbow joint flexion-extension motion, in this posture.
