All forms of exercises are not the same and don’t provide the same benefits. Therefore, if your outlook to exercise is “I play tennis”, it may unfortunately, just not be enough. According to Dr. Cooper the father of aerobic exercise (famous for inventing the treadmill test for endurance) exercise can be broken into the following
Isometric exercise where you contract your muscles but do not move your joints for e.g. standing in front of a mirror and flexing your biceps or pulling a chair. Such exercises have long term benefits on your muscles but little effect on your cardiovascular system.
Isotonic exercises which requires contraction of muscles and movement of joints together for e.g. weight lifting. These exercises help you build great muscle strength but do not have sufficient impact on your cardiovascular system.
Isokinetic exercises which makes you perform weight lifting but through a entire range of motions for e.g. using a Nautilus. This form of exercise build both your muscles and also gives you a cardiovascular workout.
Anaerobic exercise which means “without oxygen” which is performed without using the oxygen that you are breathing for e.g. sprinting for one minute. Such exercises cannot be performed for long durations and is usually complemented with some form of aerobic exercise.
Aerobic exercise where you require large quantities of air for prolonged periods and force the body to improve the systems required for transportation of oxygen for e.g. swimming or running. The benefits of this form of exercise is that it increases the volume of blood, the capacity of your lung and make your heart muscles stronger.
It is recommended that you mix your exercise regime to include aerobic, anaerobic and Isotonic exercises to get the full benefit of your effort.