A program aimed at increasing muscular endurance is most likely to improve which aspect?

A program focused on increasing muscular endurance primarily enhances strength, particularly muscular endurance strength, which refers to the muscle's ability to sustain repeated contractions over a period of time.

Muscular endurance training involves performing a higher number of repetitions at lower weights, which emphasizes the muscle's capacity to perform activities without fatigue. This training enhances the efficiency of muscle fibers and improves the ability of muscles to work over longer durations, which contributes to overall strength.

The development of endurance leads to improved performance in various activities by allowing an individual to exert strength consistently over extended periods. This is why activities that involve repeated lifting or sustained physical activities often see gains in muscular endurance directly translating to increased strength performance in those specific contexts.

The other options pertain to different physical attributes: flexibility relates to the range of motion in joints, power represents the ability to exert force rapidly, and speed concerns the rate of movement. While there can be overlaps, particularly between strength and endurance, the direct enhancement from a program aimed at muscular endurance aligns most closely with improving strength capabilities.