During an examination of elbow strength using manual muscle testing, the patient supinates the forearm when attempting elbow flexion. Which muscle is MOST likely doing the major part of the work?

During an examination of elbow strength using manual muscle testing, the patient supinates the forearm when attempting elbow flexion. Which muscle is MOST likely doing the major part of the work?

• A. Brachialis
• B. Supinator
• C. Biceps brachii
• D. Brachioradialis

Answer: (C)

When the forearm is in a supinated position during elbow flexion, the biceps brachii becomes the primary elbow flexor. This muscle crosses both the elbow and radioulnar joints and not only flexes the elbow but also supinates the forearm. In a supinated forearm, the biceps has a favorable angle and active role, so it contributes most to the elbow flexion torque. The brachialis does flex the elbow regardless of forearm position but does not cause or rely on forearm rotation, so it wouldn’t be the main contributor when supination is observed. The supinator only rotates the forearm and does not contribute to elbow flexion. The brachioradialis flexes the elbow most effectively in a neutral ( midway between pronation and supination) position, not in full supination. Thus, the muscle doing the major work in this scenario is the biceps brachii.

When the forearm is in a supinated position during elbow flexion, the biceps brachii becomes the primary elbow flexor. This muscle crosses both the elbow and radioulnar joints and not only flexes the elbow but also supinates the forearm. In a supinated forearm, the biceps has a favorable angle and active role, so it contributes most to the elbow flexion torque.

The brachialis does flex the elbow regardless of forearm position but does not cause or rely on forearm rotation, so it wouldn’t be the main contributor when supination is observed. The supinator only rotates the forearm and does not contribute to elbow flexion. The brachioradialis flexes the elbow most effectively in a neutral ( midway between pronation and supination) position, not in full supination.

Thus, the muscle doing the major work in this scenario is the biceps brachii.