What term refers to the determined amount of fat cells in comparison to the amount of lean cells within a person's body mass?

The term that specifically refers to the determined amount of fat cells in comparison to the amount of lean cells within a person's body mass is body composition. Body composition provides insight into the proportion of fat and lean tissue in the body, which is critical for assessing overall health and fitness. Understanding body composition can help individuals set fitness goals, track changes in body fat or muscle mass, and evaluate the effectiveness of diet and exercise programs.

The other terms listed relate to different aspects of physical fitness. Cardiovascular efficiency refers to how well the heart and lungs supply oxygenated blood to the working muscles during physical activity. Muscular endurance is the ability of a muscle or group of muscles to sustain repeated contractions over a period. Flexibility involves the range of motion in a joint or group of joints, which is not directly related to the ratio of fat to lean mass in the body.