The primary purpose of aerobic exercise in a fitness regimen is to improve cardiovascular endurance. It enhances the efficiency of the heart and lungs, enabling the body to use oxygen more effectively during prolonged activities. Regular aerobic workouts, such as running, swimming, or cycling, help to maintain a healthy weight, lower blood pressure, and reduce the risk of chronic diseases. Additionally, they boost overall stamina, energy levels, and promote mental well-being by releasing endorphins, often referred to as "feel-good" hormones.