This action, which is aided by the supinator muscle, requires the humeroulnar joint of the elbow to be at least partially flexed. If the  humeroulnar joint, is fully extended, supination is then primarily carried out by the supinator muscle. The biceps is a particularly powerful supinator of the forearm due to the distal attachment of the muscle at the radial tuberosity, on the opposite side of the bone from the supinator muscle. When flexed, the biceps effectively pulls the radius back into its neutral supinated position in concert with the supinator muscle. : 346–347 
Humeroulnar joint of the elbow – The biceps brachii also functions as an important flexor of the forearm, particularly when the forearm is supinated. Functionally, this action is performed when lifting an object, such as a bag of groceries or when performing a biceps curl. When the forearm is in pronation (the palm faces the ground), the brachialis, brachioradialis, and supinator function to flex the forearm, with minimal contribution from the biceps brachii. It is also important to note that regardless of forearm position, (supinated, pronated, or neutral) the force exerted by the biceps brachii remains the same; however, the brachioradialis has a much greater change in exertion depending on position than the biceps during concentric contractions. That is, the biceps can only exert so much force, and as forearm position changes, other muscles must compensate. Glenohumeral joint (shoulder joint) – Several weaker functions occur at the glenohumeral joint.
The biceps brachii weakly assists in forward flexion of the shoulder joint (bringing the arm forward and upwards). It may also contribute to abduction (bringing the arm out to the side) when the arm is externally (or laterally) rotated. The short head of the biceps brachii also assists with horizontal adduction (bringing the arm across the body) when the arm is internally (or medially) rotated. Finally, the short head of the biceps brachii, due to its attachment to the scapula (or shoulder blade), assists with stabilization of the shoulder joint when a heavy weight is carried in the arm. The tendon of the long head of the biceps also assists in holding the head of the humerus in the glenoid cavity. : 295 
Motor units in the lateral portion of the long head of the biceps are preferentially activated during elbow flexion, while motor units in the medial portion are preferentially activated during forearm supination.The biceps are usually attributed as representative of strength within a variety of worldwide cultures. Clinical significance
The proximal tendons of the biceps brachii are commonly involved in pathological processes and are a frequent cause of anterior shoulder pain. Disorders of the distal biceps brachii tendon include insertional tendonitis and partial or complete tears of the tendon. Partial tears are usually characterized by pain and enlargement and abnormal contour of the tendon.