What fitness component is best measured by the number of sit-ups an adolescent can perform?

The component of fitness best measured by the number of sit-ups an adolescent can perform is muscular strength. Sit-ups primarily target the abdominal muscles, assessing their strength and endurance. When performing sit-ups, individuals engage their core muscles to lift their upper body off the ground, which requires strength in those muscle groups.

While sit-ups may also contribute to muscular endurance—since they assess how many repetitions a person can perform until fatigue—this specific question focuses on the overall strength of the muscles involved. The strength of the core muscles is essential for many physical activities and overall stability.

In terms of the other fitness components, cardiovascular endurance relates to the efficiency of the heart and lungs during sustained physical activity, which is not directly assessed by sit-ups. Flexibility pertains to the range of motion in the joints and muscles, and body composition looks at the proportion of fat to lean mass in the body. Neither flexibility nor body composition is measured through sit-up performance, making muscular strength the most appropriate choice in this context.