Muscle fatigue of the deltoid and the biceps brachii muscles during arm flexion were detected electromygraphically to evaluate the role of each muscle as a flexor of the shoulder. This study was performed on 11 healthy men (21.1±2.2yrs. ). The anterior portion of the deltoid and both heads of the biceps were examined. The subjects performed the maximum strength (MVC) measurements at 45° of flexion and 30° of external rotation of the shoulder with the forearm neutrally rotated and the elbow extended. The peak torque was measured and electromyographic signals were recorded by surface electrodes simultaneously. Then 30% of the peak torque was applied to the upper arm until reaching the limit of patience. An integrated EMG was used to estimate the muscle activity. The maximum amplitude, the mean. power frequency and the turns count (threshold level>0.05mV) were used as estimates of the muscle fatigue. These data were detected at the time of the MVC, pre and post-fatigue. The mean power frequency decreased in all the muscles examined. The decreasing ratio of the deltoid was higher than those of the biceps muscles. The turns count decreased almost equally in all muscles. The IEMG and the amplitude increased in the biceps groups, especially in the long head. The deltoid muscle was harder to fatigue than the biceps muscles. The long head was remakably increased its activity with the fatigue phenomenon. This may be one of the causes of muscular disorders of the LHB.
