Fatigue-induced Continuous Changes in Muscle Pennation Angle during Isometric Contraction

Muscle fatigue is an exercise-induced reduction in the maximal capacity of muscle to produce force or power output. The continuous changes of brachialis pennation angles during the fatiguing isometric contraction was investigated in this study. The muscle torque, surface electromyography (SEMG) and ultrasound image of brachialis were continuously recorded during the process of isometric contraction. The mean brachialis pennation angles of four subjects increased from 19.75 +/- 2.57 degrees of pre-fatigue to 23.10 +/- 2.85 degrees of post-fatigue. The results demonstrated that the muscle fatigue would result in the dramatic increase of pennation angle during the submaximal sustained isometric contraction.