ACSM Personal Trainer Certification Practice Exam

The supinator muscle performs what action at the wrist joint?

1. Extension

2. Supination

3. Pronation

4. Flexion

The correct answer is: Supination

The supinator muscle is primarily responsible for the action of supination at the forearm and wrist joint. Supination refers to the rotational movement that turns the palm of the hand to face upwards or forward. This action involves the palm facing up, making it essential for various daily activities that require grip or lifting. When the supinator contracts, it effectively rotates the radius over the ulna, allowing the palm to face upward. This muscle works in conjunction with the biceps brachii during supination, particularly when resistance is present or during heavier lifting. In contrast, other options such as extension and flexion refer to movements that increase or decrease the angle at a joint, which are actions related to the elbow and wrist but not specific to the supinator. Pronation is the opposite movement of supination and involves turning the palm downward or backward, which does not involve the action of the supinator muscle. Therefore, the role of the supinator in facilitating supination makes it the correct choice for the action at the wrist joint.