Which term describes a contraction with no change in speed?

The term that accurately describes a contraction with no change in speed is "Isometric." In isometric contractions, the muscle generates force without changing its length, meaning that while the muscle is activated and contracting, the angle at the joint remains constant. This type of contraction occurs, for example, when one holds a position, like a plank, without moving.

In contrast, an isokinetic contraction refers to a contraction that occurs at a constant speed throughout the range of motion, which is often facilitated by specialized equipment. Concentric and eccentric contractions involve changes in muscle length; concentric contractions shorten the muscle while producing movement, and eccentric contractions lengthen the muscle while it is under tension. Therefore, while the isokinetic contraction maintains a constant speed, it doesn’t correspond to "no change in speed" as isometric does, making isometric the correct choice in this context.