What is the primary feature of isotonic contractions?

The primary feature of isotonic contractions is that the muscle length changes while remaining under tension. During an isotonic contraction, the muscle fibers actively generate force, leading to a visible shortening or lengthening of the muscle without a change in the tension produced. This type of contraction is commonly seen in exercises like lifting weights, where the muscle fibers need to contract and shorten to lift the load or lengthen as they lower it while still producing a consistent level of tension.

In contrast, other types of contractions, such as isometric contractions, involve muscle tension without any change in muscle length, meaning the muscle does not visibly shorten or lengthen despite generating force. High-speed contractions are not a defining feature of isotonic contractions, as they can occur at various speeds depending on the load and the type of exercise. Additionally, muscle tension does not drop during isotonic contractions; rather, it can vary as the muscle changes length while still maintaining some level of tension throughout the movement.