Final answer:
An isotonic contraction is when a muscle maintains constant tension as it changes length, with concentric and eccentric being the two types.
Step-by-step explanation:
The type of muscle contraction that maintains constant tension in the muscle as the length changes is termed an isotonic contraction. There are two forms of isotonic contractions: concentric and eccentric. Concentric contractions shorten the muscle, while eccentric contractions involve the muscle lengthening while still under tension. During a concentric contraction, the muscle shortens as it acts against a force, like when lifting a weight with the biceps brachii muscle. The muscle fibers contract, sarcomeres shorten, and cross-bridges cyclically form as actin is pulled by myosin. In contrast, during an eccentric contraction, the muscle lengthens while maintaining tension, such as when lowering the same weight in a controlled manner. This type of contraction is critical for movements and providing balance to the body. In a concentric contraction, the muscle shortens as it moves a load, while in an eccentric contraction, the muscle lengthens as the tension diminishes.
Both types of contractions are used for movement and balance in the body.