What does long duration depolarization primarily result in?

Long duration depolarization primarily results in fatigue in muscle response because it leads to a sustained activation of muscle fibers. When a muscle is stimulated for an extended period, it often cannot maintain its force due to a depletion of energy sources and the accumulation of metabolic byproducts, such as lactic acid. This prolonged activation causes the muscle to become less responsive and can lead to a decrease in the efficiency of muscle contractions, resulting in fatigue.

The other options do not accurately describe the primary outcome of long-duration depolarization. Quick muscle twitch refers to short, rapid contractions, which are not the result of prolonged stimulation. Prolonged pain sensation may occur in different contexts but is not directly linked to the effects of long-duration depolarization. Muscle relaxation typically results from cessation of stimulation, rather than from prolonged depolarization, making fatigue the most fitting outcome.