What type of contraction maintains muscle length without changing it?

The correct option is isometric contraction because this type of contraction occurs when a muscle generates force without changing its length. During isometric contractions, the muscle remains under tension while its fibers do not shorten or lengthen, allowing for stabilization. This is commonly seen in exercises where you hold a position, such as planking or wall sits, where the muscle is actively engaged but the joint angle remains constant.

In contrast, concentric contraction involves the muscle shortening as it generates force, such as when lifting a weight. Eccentric contraction occurs when a muscle lengthens under tension, as seen when lowering a weight back down. Isotonic contraction, on the other hand, is a broader term that includes both concentric and eccentric movements, which involve a change in muscle length. Therefore, the unique characteristic of maintaining muscle length while generating tension specifically defines isometric contractions.