Define isotonic and isometric contractions.

• A. Isotonic contractions generate force without changing muscle length; isometric involve shortening.
• B. Isotonic contractions change muscle length with movement; isometric generate force without changing length.
• C. Isotonic contractions involve lengthening without movement; isometric contractions cause movement.
• D. Isometric contractions occur only in smooth muscle.

Answer: (B)

The main idea being tested is how muscle length changes during contraction and whether movement occurs. Isotonic contractions produce force while the muscle changes length, leading to movement of a body part (including both shortening when lifting and lengthening during controlled lowering). Isometric contractions generate force without changing the muscle’s length, so there’s no movement at the joint even though the muscle is tensing. That’s why the best description is that isotonic contractions change muscle length with movement, while isometric contractions generate force without changing length. For clarity, a bicep curl is a common example of an isotonic contraction, whereas holding a steady position (like pushing against an immovable object) is an isometric contraction. The other statements mix up length change, movement, or muscle type, which is why they aren’t correct.