Which muscle primarily flexes the elbow without any listed shoulder action?

Which muscle primarily flexes the elbow without any listed shoulder action?

• A. Brachialis
• B. Biceps Brachii
• C. Triceps Brachii
• D. Deltoid

Answer: (A)

The key idea is a pure elbow flexor that does not influence the shoulder. The brachialis attaches from the humerus to the ulna and crosses only the elbow joint, so its contraction bends the elbow without causing any shoulder movement. It’s the primary elbow flexor, especially since it works effectively regardless of forearm position. In contrast, the biceps brachii crosses both the elbow and shoulder joints, so it can flex the elbow but also contributes to shoulder flexion (and forearm rotation), which means it isn’t restricted to elbow action alone. The triceps brachii extends the elbow, not flexes it, and the deltoid is a shoulder muscle that moves the arm at the glenohumeral joint, with no elbow flexion role.

The key idea is a pure elbow flexor that does not influence the shoulder. The brachialis attaches from the humerus to the ulna and crosses only the elbow joint, so its contraction bends the elbow without causing any shoulder movement. It’s the primary elbow flexor, especially since it works effectively regardless of forearm position.

In contrast, the biceps brachii crosses both the elbow and shoulder joints, so it can flex the elbow but also contributes to shoulder flexion (and forearm rotation), which means it isn’t restricted to elbow action alone. The triceps brachii extends the elbow, not flexes it, and the deltoid is a shoulder muscle that moves the arm at the glenohumeral joint, with no elbow flexion role.