Final answer:
In isotonic contractions, muscle length changes to move a load while tension remains constant. This includes concentric contractions where muscles shorten and eccentric contractions where muscles lengthen.
Step-by-step explanation:
In isotonic contractions, the muscle length changes to move a load, while the tension within the muscle remains relatively constant. There are two subtypes of isotonic contractions: concentric contractions and eccentric contractions. During a concentric contraction, the muscle shortens, such as when the biceps brachii contracts to lift a hand weight. Conversely, during an eccentric contraction, the muscle lengthens while controlling the lowering of the load as seen when the same muscle gradually lowers the weight. The load is the object being moved by the muscle contraction, and it can vary in weight. In both types, although muscle length changes, the overall muscle tension generated is maintained to lift or lower the load effectively.