How does the muscular system produce movement and what are concentric and eccentric contractions with examples?

• A. Concentric contractions lengthen the muscle; eccentric contractions shorten the muscle while moving.
• B. Concentric contractions occur when lowering a weight; eccentric contractions occur when lifting.
• C. Eccentric contractions shorten the muscle under tension; concentric contractions lengthen to produce movement.
• D. Concentric contractions shorten the muscle to produce movement; eccentric contractions lengthen the muscle while controlling movement.

Answer: (D)

Movement is produced when a muscle changes length under tension: it shortens to bring a limb through a joint (concentric contraction) and lengthens under tension while controlling or slowing movement (eccentric contraction).

In a concentric contraction, the muscle fibers actively shorten to move a part of the body. For example, during a bicep curl, the biceps brachii shortens to flex the elbow and raise the dumbbell toward the shoulder, producing the upward movement.

In an eccentric contraction, the muscle lengthens while still producing tension, often to control or slow movement. Lowering the dumbbell slowly in a bicep curl is eccentric work—the biceps lengthen as the elbow extends while the weight is being resisted, acting to decelerate the motion.

The correct description matches this pattern: concentric contractions shorten the muscle to produce movement, while eccentric contractions lengthen the muscle while controlling movement. The other options mix up which way the muscle changes length or when each type occurs.