What is defined as the fitness of the heart and lungs to deliver oxygen to working muscles?

Aerobic capacity is the term used to define the fitness of the heart and lungs to deliver oxygen to working muscles effectively during sustained physical activity. It reflects the ability of the cardiovascular and respiratory systems to supply oxygen to skeletal muscles, which is crucial for endurance activities such as running, cycling, and swimming. High aerobic capacity indicates that the body is efficient at utilizing oxygen, contributing to improved stamina and overall fitness during prolonged exercise.

On the other hand, muscular endurance refers to the ability of a muscle or group of muscles to perform repetitive contractions over an extended period. Flexibility involves the range of motion in joints and the ability of muscles and tendons to stretch. Body composition pertains to the proportion of fat and non-fat mass in the body, including muscle and bone. These concepts are interconnected in the realm of fitness but do not specifically address the heart and lungs' role in delivering oxygen, making aerobic capacity the most appropriate choice.