Which of the following BEST explains how a muscle cell exerts force?

• A. When the Muscle Cell Contracts It Exerts A Pulling Force On Whatever Is Attached, And When It Relaxes It Exerts A Pushing Force Against The Same Objects.
• B. The Muscle Cell Folds Itself In Half And Exerts A Pulling Force On Whatever Is Attached To The End That Was Folded Over.
• C. The Muscle Cell Shortens Or Contracts And Exerts A Pulling Force On Whatever Is Attached To Both Ends.
• D. The Muscle Cell Expands And Exerts A Pushing Force Against Whatever Is Attached To It.

Answer: (C)

When a muscle generates force, it does so by contracting and becoming shorter. This contraction pulls on the tendinous attachments at each end, creating tension that pulls both ends toward each other. Muscles can only pull; they don’t push. So the best explanation is that the muscle shortens or contracts and exerts a pulling force on whatever is attached to both ends.

The other ideas aren’t accurate because muscles do not push during relaxation, they don’t fold to produce force, and they don’t expand to push on attachments. The pulling action from a shortening muscle is what moves bones and other connected structures through the tendons.