Page 68 - ASOP ROT Study Guide

10 . 4 Type of Movement

Under the action of muscle, the elbow joint is able to carry out the following movements:

Flexion - the forearm is bent upwards.
Extension - the forearm moves backwards to be in line with the humerus.
Supination - this is the position the forearm adopts when the radius and ulna lie parallel to each
other and the palm is turned face up.
Pronation - this is the position achieved when the radius has rotated round the ulna. The palm is
turned face down.

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10 . 5 Muscles

The muscles which control the elbow joint originate on either the scapula or the humerus.

Flexors - the most prominent group of muscles in the arm are the flexors. The biceps brachii
muscle is easily seen at the front of the upper arm when you "flex your muscles". It comes from
two origins on the scapula and inserts into the proximal radius. Its action is therefore to flex the
forearm but because it is sited on the medial side of the radius, it also acts as a prime mover of
supination for external rotation of the forearm. The brachialis muscle rises on the shaft of the
humerus and inserts into the ulna and is the most powerful flexor of the elbow.

Extensors - the triceps brachii is the extensor of the elbow. It has one origin from the scapula and
one from the proximal humerus. It occupies the entire back of the arm and inserts into the
olecranon process of the ulna.

Pronators - the pronator teres is an example. This muscle arising from the medial side of the
distal humerus can pull the radius over the ulna thus rotating it along its long axis into pronation.
This action is the reverse of the supinating action of biceps.

Supinators - as mentioned before, biceps brachii acts as a supinator of the forearm. A second
muscle, called supinator, wraps around the back of the radius to achieve this action as well.