Which contraction shortens the muscle to produce movement?

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

Answer: (A)

Understanding how muscle contractions produce movement. When a muscle contracts and its fibers shorten, the muscle pulls on the bones to bring about joint motion — that is a concentric contraction. Isometric contractions generate force without changing the muscle length, so no movement occurs. Isokinetic contractions are movement at a constant speed, usually with specialized equipment, and describe the speed rather than the direction of shortening. Isotonic contractions involve a muscle applying a constant load as it changes length; this includes both shortening (concentric) and lengthening (eccentric) phases. Therefore, the contraction that shortens the muscle to produce movement is concentric.