ACSM Personal Trainer Certification Practice Exam

Which muscle is responsible for flexion at the elbow joint?

1. Biceps brachii

2. Triceps brachii

3. Rhomboids

4. Supinator

The correct answer is: Biceps brachii

The biceps brachii is primarily responsible for flexion at the elbow joint. This muscle is located in the upper arm and has two heads that originate from the shoulder blade. When the biceps brachii contracts, it pulls on the radius bone of the forearm, resulting in flexion of the elbow. This movement is commonly demonstrated in activities such as lifting, curling weights, or performing a bicep curl exercise. The triceps brachii, while also located in the upper arm, has the opposite function; it is responsible for extension at the elbow joint. The rhomboids, situated in the upper back, primarily play a role in scapular retraction and are not involved in elbow movement. The supinator muscle assists in supinating the forearm (turning the palm upward), but it does not contribute to flexion at the elbow. Thus, the biceps brachii is clearly identified as the muscle responsible for flexion at the elbow joint.