Muscles can only pull; what is the action they do not do?

• A. Pull
• B. Relax
• C. Stretch
• D. Push

Answer: (D)

Muscles generate force only when they contract, which means they pull on tendons attached to bones. That pulling shortens the muscle and moves the bones toward each other across a joint. Because the muscle’s action is to shorten and pull, it cannot actively push a bone away. Movement in the body is achieved by opposing muscle groups working as pairs, where one pulls to bring a bone in one direction while the other controls the opposite direction. For example, bending the elbow happens when the flexor contracts to pull the forearm toward the upper arm while the opposite muscle relaxes; straightening occurs when the opposing muscle contracts to pull in the opposite direction. Since contraction always produces a pulling effect, the action muscles do not perform is pushing.