ExRx.net : Biceps Brachii (original) (raw)

Comments

The biceps brachii is a stronger elbow flexor when the radioulnar joint (forearm) is supinated. The biceps brachii is a stronger forearm supinator when the elbow is flexed.

During elbow flexion, motor units in the lateral portion of the long head of the biceps are preferentially activated, whereas during forearm rotation, motor units in the medial portion are preferentially activated (ter Haar Romeny 1984).

During a dynamic elbow flexion, the biceps is more readily activated than the brachialis. Alternatively, the brachialis becomes more readily activated during isometric elbow flexion (Tax 1989).

The biceps brachii enhances dynamic stability of the shoulder joint through initial range of motion of shoulder flexion although its moment arm is relatively small (Landin 2017).

The triarticulate biceps brachii muscles, particularly the short head [2 ] enters passive insufficiency through the completion of elbow extension when the shoulders are more extended or through the completion of shoulder extension when the elbows are more extended. The triarticulate biceps brachii muscles, particularly the short head [2 ] enters active insufficiency through the completion of elbow flexion when the shoulders are more flexed (brachialis becomes more active) or through the completion of shoulder flexion when the elbows are more flexed.

References

Landin D, Thompson M, Jackson MR (2017). Actions of the Biceps Brachii at the Shoulder: A Review. J Clin Med Res. 9(8): 667-670.

Tax AA, van der Gon JJ, Gielen CC, van den Tempel CM (1989). Differences in the activation of m. biceps brachii in the control of slow isotonic movements and isometric contractions. Exp Brain Res. 76, 55–63.

ter Haar Romeny BM, van der Gon JJ, Gielen CC (1984). Relation between location of a motor unit in the human biceps brachii and its critical firing levels for different tasks. Exp Neurol. 85(3): 631-50.