Fatigue sensation and surface electromyogram during sustained shoulder flexion with spontaneous alternations of...

Sustained contractions were compared between with (AW) and without (NAW) spontaneous alternations of working arm to investigate the fatigue level at which the contraction is felt to be stopped. Subjects maintained an upper limb in the horizontally flexed position at 5%, 10%, 15% and 20% of maximum voluntary contraction strength (MVC). Contractions were continued until they felt exhausted or 45min. had passed. Fatigue level was evaluated with 4 levels of fatigue sensations and surface electromyogram (EMG) of the deltoid. Mean amplitude (AEMG) and relative power in 8-40Hz (RPLF) of EMG were calculated. The following results were obtained. Fatigue level was lower in AW than in NAW for the same amount of work done by one arm. As AEMG often decreased with time, fatigue was estimated by relating AEMG to RPLF. At 20% MVC in AW the alternation interval decreased and the muscle fatigued with repeated contractions though the fatigue level was not severe. Contraction was felt to be stopped when the first fatigue sensation occurred. But it was not necessary to stop the contraction until considerable tiredness or apparent pain occurred.