Which muscle action indicates an isometric contraction?

An isometric contraction is characterized by tension being generated in a muscle without any change in its length. This means that the muscle is activated and produces force, but it does not shorten or lengthen, maintaining a static position. For example, when holding a plank position, the muscles are engaged but remain at the same length, providing stability without movement.

This characteristic distinguishes isometric contractions from other types of muscle actions, such as concentric contractions, where the muscle shortens, and eccentric contractions, where the muscle lengthens while generating force. The option that describes muscle tension without a change in length directly aligns with the definition of isometric contraction, making it the correct answer.