Muscle: Biceps brachii, short head
Origin: At the tip of the coracoid process of the scapula.
Insertion: At the radial tuberosity
Function: Flexor of the elbow, strong superinator and has a weak flexion effect on the shoulder (because it is biarticular- crosses both the should and elbow joints).
Muscle: Biceps brachii, long head
Origin: At the supraglenoid tubercle of the scapula
Insertion: At the radial tuberosity
Function: Flexor of the elbow, strong superinator and has a weak flexion effect on the shoulder (because it is biarticular- crosses both the shoulder and elbow joints).
Muscle: Brachialis
Origin: At the anterior lower half of the humerus
Insertion: At the ulnar tuberosity
Function: Flexor of the elbow (uniarticular), regardless of whether the arm is superinated or pronated (since the ulna does not rotate)
Indications of Weakness
Biceps weakness is indicated when the arm hangs excessively straight or is hyperextended. This weakness may also make it difficult to supinate the forearm when the arm is moving into flexion. Brachialis or biceps that have shortened will make full arm extension or superination difficult. This will impair strength and muscular development. Triceps strength can also decrease if the biceps has shortened and is hypertonic because of the against antagonist relationship.