Final answer:
An isotonic contraction refers to a smooth, sustained contraction where the tension in the muscle stays constant and the length of the muscle changes.
Step-by-step explanation:
An isotonic contraction refers to a smooth, sustained contraction where the tension in the muscle stays constant and the length of the muscle changes. There are two types of isotonic contractions: concentric and eccentric. In a concentric contraction, the muscle shortens to move a load, while in an eccentric contraction, the muscle tension diminishes and the muscle lengthens. Therefore, the correct term that refers to a smooth, sustained contraction is A) Isotonic.