Effect of Joint Angle and Forearm Posture on the Elbow Flexor and Extensor Muscles During Isometric Contraction

Abstract

The effects of elbow joint angle, forearm posture and different force levels on the activation level of the long head and short head of biceps brachii, the brachioradialis, and the triceps brachii during isometric contractions were investigated. The muscle activation levels are simultaneously acquired by linear surface electrode arrays placed on the muscles. The results suggest that each muscle’s contribution to elbow joint torque is affected by changing joint angle and forearm posture, which are muscle, and even subject dependent. At least one of the biceps brachii muscles is sensitive to changes in joint angle, from 60° to 90°, in supination. In the neutral posture, the sensitivity of the biceps muscles and the brachioradialis to joint angle was subject dependent. The short head of biceps brachii is sensitive to forearm posture at 60° but not at 90° joint angle. At 90°, the brachioradialis was significantly affected by forearm posture.