Which statement best differentiates isotonic from isometric exercise?

• A. Isometric involves movement with length change.
• B. Isotonic involves movement with length change; isometric involves tension without shortening.
• C. Both involve holding a position without movement.
• D. Isotonic uses static stretching only.

Answer: (B)

The key idea is whether the muscle changes length during contraction. In isotonic exercise the joint moves and the muscle changes length—shortening during lifting (concentric) and lengthening during lowering (eccentric). In isometric exercise the muscle tenses but does not shorten, so the joint angle stays the same (holding a position like a plank). So describing isotonic as movement with length change and isometric as tension without shortening best captures the difference. The other statements misstate this: isometric does not involve length change, isotonic is not just a static hold, and static stretching is not what isotonic training entails.