Exercise, isotonic: Exercise when a contracting muscle shortens against a constant load, as when lifting a weight. Isometric exercise is one method of muscular exercise. In contrast, isotonic exercise is when muscular contractions occur without movement of the involved parts of the body.

Isotonic comes from the Greek "iso-", equal + "tonos", tone = maintaining equal (muscle) tone. The muscle maintains equal tone while shortening in isotonic exercise.