The body undergoes multiple adaptations when continuously engaging in aerobic exercise. The heart, lungs, active muscles and circulatory system all undergo changes that are positive to your health. Popular forms of aerobic exercise include running, jogging, swimming, biking and circuit workouts.
As you progress through a regimen of aerobic exercise, your heart starts to function more efficiently. The American College of Sports Medicine reports that your resting heart rate decreases, and your resting stroke volume increases. Your heart becomes more efficient and has a higher functional capacity as it adapts to aerobic training.
During aerobic adaptation, your lungs' efficiency improves as well. Respiratory muscles become stronger and allow for larger amounts of air to be inhaled and exhaled with each breath. The diaphragm muscle adapts so that its endurance and strength improves, which means that the diaphragm can consistently handle continuous forceful breathing patterns while exercising. This allows you to keep a normal breathing pattern for longer durations while performing aerobic exercises. A study performed by the National Strength and Conditioning Association in 2000 found that after a six-month aerobic training program, previously deconditioned people improved their maximal pulmonary ventilation per minute from 123 liters to 142l, as well as decreased their average resting breathing volume from 7l per minute to 6l per minute. Thus, showing that continuous aerobic exercise increases lung efficiency.
The American College of Sports Medicine says aerobic exercise improves your maximum oxygen uptake, which measures how well your body utilizes oxygen at the cellular level. When exercise intensity increases, so does your body's necessary demand for oxygen consumption. As you continue with an aerobic exercise training regimen, your body adapts to the oxygen and energy demands required to function at the increased level of physical exertion. Maximum oxygen uptake is measured in milliliters of oxygen absorbed per kilogram of body weight per minute. The more oxygen absorbed per kilogram per minute, the more efficient the cells of your body are at utilizing the oxygen supply.
Your body begins to have muscular and body composition changes as well. The National Strength and Conditioning Association says muscular changes aren't as significant as they would be if incorporating resistance training, but muscular strength and endurance improve in active muscle, and lean tissue percentage in the body increases as you begin to adapt to aerobic training. For consideration, as your body becomes adapted to your training intensity, you may begin to notice less significant improvements. Continue to increase the intensity of your aerobic exercise -- either in duration, exercise type or rate -- in order to continuously allow for your body to have positive adaptations to aerobic training.