Which type of contraction is primarily used to control the speed of a body part's movement?

Eccentric contraction is the type of contraction that primarily controls the speed of a body part's movement. This type of contraction occurs when a muscle lengthens while under tension, which happens during deceleration phases of movement or when one is lowering a load. For instance, when performing a controlled lowering of a limb, the eccentric contraction allows for smooth and graded motions, thus providing more control and stability.

The role of eccentric contractions is crucial in various activities, such as walking down stairs or decelerating during running or jumping, where managing speed and protecting joints from injury is needed. This contrasts with concentric contractions, where muscles shorten to produce force, primarily implicated in initiating movement rather than controlling its speed. Isometric contractions stabilize joints but do not contribute to movement dynamics, while dynamic contraction encompasses both concentric and eccentric actions in general, without specifically isolating the decelerative control aspect provided by eccentric contractions.