Which muscle performance characteristic involves maintaining a contraction over an extended period?

The characteristic involving maintaining a contraction over an extended period is endurance. Endurance refers to the muscle's ability to sustain repeated contractions against a resistance for an extended duration or to hold a contraction for a prolonged time without fatigue. This is essential in many physical activities and is a key component of overall fitness.

In contrast, strength pertains to the maximal amount of force a muscle can produce in a single effort, which does not necessarily relate to maintaining a contraction over time. Power involves the ability to exert force rapidly, emphasizing speed and explosiveness rather than sustaining a contraction. Flexibility refers to the range of motion in a joint or a series of joints, which does not relate to the duration of muscle contraction. Thus, endurance stands out as the defining characteristic when the focus is maintaining a contraction over a prolonged period.