In what type of muscle action does force occur without any change in muscle length?

In isometric muscle actions, the muscle generates force without any change in length. This occurs when the muscle contracts but does not shorten or lengthen, maintaining a stable position against resistance. Isometric exercises, such as holding a plank or wall sit, exemplify this principle where the muscle fibers are activated, but there is no visible movement at the joint level. This type of action is particularly effective for building strength and stability in specific positions and is often utilized in rehabilitation settings.

In contrast, isotonic muscle actions, which include both concentric and eccentric movements, involve changes in muscle length. In concentric actions, the muscle shortens while contracting (e.g., lifting a weight), and in eccentric actions, the muscle lengthens under tension (e.g., lowering a weight). Therefore, these types of muscle actions do not fit the criteria of force generation without a change in muscle length.