Which contraction describes movement where the muscle length changes?

• A. Isokinetic
• B. Isometric
• C. Isotonic
• D. Isotoner

Answer: (C)

Isotonic contractions involve movement where the muscle changes length. When you lift or lower a weight, the muscle shortens during the lift (concentric) and may lengthen during the lowering (eccentric), producing actual joint movement. The resistance stays the same while the muscle length changes, which is what defines isotonic action.

Other options don’t fit as neatly: isometric contractions produce force without any change in muscle length (holding a position), so there’s no movement. Isokinetic contractions do involve length change too, but they occur with movement at a constant speed using specialized equipment, which isn’t the general idea of moving with a changing muscle length. The term isotoner isn’t a contraction type at all—it’s a brand name—so it isn’t relevant.