Which fitness component focuses on the proportion of fat to lean tissue in the body?

Body composition is the correct answer because it specifically refers to the ratio of fat to lean tissue in the body, which includes muscles, bones, and organs. Understanding body composition is crucial in assessing an individual's overall health and fitness level. It provides insight into how much of a person's weight comes from fat compared to the amount that comes from lean mass. This information is valuable for setting fitness goals, as a healthier body composition is often associated with reduced risks of many diseases and improved overall physical performance.

The other fitness components, while important, do not specifically address the ratio of fat to lean tissue. Muscular endurance is focused on the ability of muscles to perform repeated contractions over time. Flexibility refers to the range of motion in joints and muscles, while cardiorespiratory endurance measures the efficiency of the heart and lungs during physical activity. Each of these components plays a significant role in overall fitness, but they do not directly relate to the proportion of fat in the body as body composition does.