The biceps brachii is a bi-articular muscle, this means that it helps control the motion of two different joints, the shoulder and the elbow. The biceps brachii has 3 functions, flexes the elbow, shoulder flexion and the supination of the forearm. The biceps are a prime mover when you flex your arm. The muscle pulls on the radius which then flexes the elbow pulling the forearm towards the head of the humerus. The synergists in this movement are the brachialis and the brachioradialis, these two muscle help assist the bicep in flexing the arm, the stabiliser is the rotator cuff. The biceps are also act as a synergist when the forearm supinates a when the shoulder flexes. The reason the biceps help with the supination of the forearm is because
