What are the actions of the biceps brachii?

The biceps brachii muscle primarily functions to facilitate elbow flexion and supination of the forearm. When the biceps contracts, it draws the forearm upward towards the shoulder while also allowing the forearm to rotate outward, resulting in supination. This muscle plays a crucial role during activities that involve lifting and turning the palm upward, such as when performing a bicep curl or twisting a corkscrew.

Elbow flexion occurs when the biceps brachii shortens, bringing the forearm closer to the upper arm, while supination involves the lateral rotation of the forearm so that the palm faces upward. This dual capability makes the biceps an essential muscle for upper limb movements that require both bending of the elbow and manipulation of the hand's orientation.

Understanding these actions helps in numerous clinical scenarios, such as rehabilitation and designing effective orthotic devices to support or enhance arm function, particularly in patients who may have suffered injuries affecting muscle strength or coordination.