Effect of the Elbow Joint Posture on Elbow Flexor Fatigability and Muscle Strength during Isometric Contraction

Abstract

We examined here the effect of the elbow joint posture on elbow flexor fatigability and strength during isometric contraction. Nine healthy subjects, who gave informed consent, participated in the present study. The subjects were seated in a chair with the shoulder joint at 0°, and the shoulders, pelvis, and thigh were immobilized by straps. The elbow joint posture was positioned at 30, 60, 90 and 120° of elbow flexion. First, subjects produced maximal elbow flexion as a maximum voluntary contraction (MVC) in each elbow joint posture. A myodynamometer was used to measure muscular strength. Secondly, the subjects performed 50% MVC effort for over 60 seconds with visual feedback. The surface electromyograms of the biceps brachii and brachioradialis muscles were recorded. The muscle fatigue was characterized by median power frequency (MDPF) calculated from the power spectrum of surface electromyograms using autoregression models. MDPF were calculated for each section, then 60 seconds was divided into each six sections consisting of 10 seconds. Findings of the present study are: 1) the elbow joint posture requiring the maximum strength is 90°; and 2) MDPF decreased over time in both muscles, and the rate of reduction tended to increase with flexion angle. These findings suggest that the elbow joint posture that demonstrates the maximum muscular strength differs from the one which does not cause muscle fatigue easily. When therapist determines training posture, it is necessary to take this point into consideration.

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