What best describes aerobic exercise?

Aerobic exercise is correctly defined as movement of large muscle groups that increases the body's use of oxygen. The word aerobic literally means 'with oxygen,' and aerobic activities — such as walking, jogging, swimming, and cycling — rely on the aerobic energy system, which uses oxygen to metabolize carbohydrates and fats to produce sustained energy in the form of ATP. This type of exercise strengthens the cardiovascular and respiratory systems, improves endurance, and supports weight management. The other options describe different types of physical activity. Exercise in which muscles work against resistance describes resistance or strength training, a form of anaerobic exercise that builds muscle mass and bone density. Lengthening of muscles through slow, controlled movements describes stretching or flexibility exercise, such as yoga or static stretching routines. Any activity not related to a person's occupation is an imprecise lay definition of leisure-time physical activity but does not define aerobic exercise. Students should remember that the hallmark of aerobic exercise is sustained, rhythmic engagement of large muscle groups with increased oxygen demand, distinguishing it from both resistance training and flexibility work.