Which statement correctly describes how skeletal muscles work in pairs?

• A. Both contract at the same time
• B. Both relax
• C. One contracts while the other relaxes
• D. Neither relaxes

Answer: (C)

Skeletal muscles move joints by acting in antagonistic pairs: when one muscle shortens and contracts, its partner on the opposite side lengthens and relaxes. This setup lets a joint bend or straighten smoothly because the pulling muscle drives the movement while the opposing muscle yields. For example, bending the elbow happens when the biceps contracts and the triceps relaxes; straightening uses the reverse—the triceps contracts while the biceps relaxes. If both muscles contracted at the same time, the joint would be blocked, and if both relaxed, the joint would sag without control.