Although the two types of exercise--anaerobic and aerobic--sound similar, they are actually quite different--and the controversy over which type of exercise is best continues. “Aerobic” literally means in the presence of oxygen. In general, any activity that allows oxygen to release energy through metabolism and that is performed at a low to moderate intensity for more than 90 seconds is usually considered to be an aerobic activity. Because aerobic exercise increases your need for oxygen and requires your heart and lungs to work harder, the benefits of aerobic activity include increased cardiovascular capability and a decrease in body fat. The disadvantages of aerobic activity include a decrease in muscle mass, strength, power, speed and anaerobic capacity. Aerobic exercise is typically longer in duration than anaerobic exercise and involves such activities as running, walking, swimming and cycling. On the other hand, “anaerobic” means in the absence of oxygen--any activity where energy is produced without oxygen and is performed at a medium to high intensity level for less than two minutes, is usually called an anaerobic activity. Anaerobic exercise is exercise that has a lower impact on your cardiovascular system and generally lasts for shorter periods of time than aerobic exercise. Although anaerobic activity requires an aerobic foundation, it provides the benefits of a decrease in body fat, an increase in muscle mass as well as improved strength, power and speed. Examples of anaerobic exercise include such activities as weight lifting and sprints. So, which type of exercise is best? The answer is that to achieve optimum physical fitness, you must train to improve your performance in both aerobic and anaerobic abilities and not focus your performance on one type of exercise at the expense of all others. In other words, fitness is a compromise. However, many people fail to realize that by focusing exclusively on prolonged aerobic or anaerobic training that they may be actually decreasing their overall fitness level. The best solution is to combine both types of training at varying levels of intensity and duration. For example, you can periodically switch from high intensity, short duration to medium intensity, medium duration and low intensity, long duration workouts. The truth is that unless you are training to be an endurance athlete, there is no need to train like one and that most activities encountered in sport, work and life are a combination of aerobic and anaerobic movements flowing in a seamless continuum.