Which of the following opposing muscle pairs is incorrect?

• A. Pronator: Supinator
• B. Deltoid: Pectoralis major
• C. Biceps: Triceps
• D. Brachialis: Carpi

Answer: (D)

The idea being tested is how opposing (antagonist) muscle pairs work across a joint. A true antagonist pair must act on the same joint to produce opposite actions.

The brachialis flexes the elbow, while the flexor carpi muscles act on the wrist. They don’t oppose each other at the same joint—one set controls elbow movement, the other controls wrist movement. So they aren’t a true opposing pair.

In contrast, pronator and supinator oppose each other in forearm rotation around the elbow joint, and the biceps and triceps oppose elbow flexion and extension, respectively. The deltoid and pectoralis major can oppose each other at the shoulder in movements like abduction versus adduction/flexion. Therefore, the pair involving brachialis and wrist flexors is the incorrect opposing pair.