Final answer:
An isotonic contraction is when the muscle changes length while maintaining tension, either shortening during a concentric contraction or lengthening during an eccentric contraction as it moves a load.
Step-by-step explanation:
In which type of contraction does the muscle change length while maintaining tension? The correct answer is a. Isotonic Contraction. In isotonic contractions, the tension in the muscle stays constant while a load is moved as the muscle changes length. There are two subtypes of isotonic contractions, concentric and eccentric. A concentric contraction is when the muscle shortens to move a load, such as lifting a weight with the biceps. Conversely, an eccentric contraction is when the muscle lengthens while controlling the lowering of a load.
An example of concentric contraction would be the biceps brachii contracting to lift a hand weight, thereby decreasing the angle of the elbow joint. During eccentric contraction, the same muscle controls the lowering of the weight, increasing the elbow joint's angle as the muscle lengthens and the amount of activated cross-bridges decreases.
Understanding these types of contractions is essential for movement, balance, and various physical activities. Isometric contraction, where the muscle tension changes but the muscle length remains constant, differs from isotonic as it usually occurs when a muscle cannot overcome a given resistance, and is crucial in maintaining posture and joint stability.