What is the difference between isotonic and isometric contractions?

Isotonic contractions occur when a muscle changes length while generating force, resulting in movement. This type of contraction can be further divided into concentric contractions, where the muscle shortens, and eccentric contractions, where the muscle lengthens while under tension. This movement leads to joint motion and is typically what one envisions when thinking of muscle actions, such as lifting a weight.

In contrast, isometric contractions involve tension in the muscles without any visible movement or change in length of the muscle fibers. While the muscles are exerting force, the joint angle remains the same, meaning there is no movement produced. An example of an isometric contraction is holding a weight in a fixed position, like maintaining a squat without moving up or down.

The other choices misinterpret the nature of these contractions. They fail to accurately represent the fundamental characteristics that differentiate isotonic from isometric contractions. Specifically, one suggests that isotonic contractions involve no movement, which contradicts the very definition of the term. Another incorrectly implies a speed comparison where speed is not inherently part of the definition of either contraction type. Lastly, associating isometric contractions solely with aerobic exercise overlooks their true nature, as both contraction types can play roles in various forms of exercise.