Antagonistic Muscle Pair for Elbow Flexion

Steps:

• Determine the elbow movement shown: flexion (bending the arm).
• Identify muscles: X as biceps (flexor), Y as triceps (extensor).
• For flexion, the flexor contracts to pull bones closer.
• The extensor relaxes to allow the movement without opposition.

Why C is correct:

• Antagonistic muscles operate oppositely; contraction of flexor X bends the elbow while extensor Y relaxes, per reciprocal inhibition in muscle physiology.

Why the others are wrong:

• A: Both contracting causes no net movement or strain.
• B: Y contracting extends the elbow, opposing flexion.
• D: Both relaxing produces no movement.

Final answer: C