The biceps brachii muscle, being a two-joint muscle, has multiple functions, and at the shoulder joint, its two heads contribute different actions.
Essentially, the biceps' role at the shoulder is less prominent than its function at the elbow. However, it plays a part in arm movement and stability. Because of the two different heads, these movements somewhat oppose each other.
Here's a breakdown:
-
Long Head:
- Abduction: Assists in pulling the arm away from the body's midline (raising the arm laterally).
- Internal (Inward) Rotation: Contributes to rotating the arm inwards, towards the body.
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Short Head:
- Adduction: Assists in pulling the arm towards the body's midline.
It is important to note that the biceps' contribution to shoulder joint movements is secondary to muscles like the deltoid and rotator cuff muscles, which are specifically designed for shoulder function. The biceps' primary function is flexion and supination of the forearm at the elbow joint.
