Which contraction describes a muscle length that shortens during contraction?

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

Answer: (C)

Muscle length changes during contraction reveal the type of contraction. When a muscle shortens as it contracts, it is performing a concentric contraction. This occurs when the muscle’s force is greater than the resistance, pulling the bone toward the body and producing movement—think of curling a dumbbell up during a bicep curl. In contrast, an eccentric contraction happens when the muscle produces force while lengthening as it slows or controls the lowering of a weight, and an isometric contraction involves generating force without any change in length. Isotonic contractions describe movements with a change in length under a constant load and include both concentric and eccentric phases. Since the scenario describes shortening of the muscle, the appropriate type is concentric.