Fitness enthusiasts talk a lot about aerobic and anaerobic exercise, and everyone else wants to know what’s the difference and which one is better. It's kind of like asking if using a home rowing machine is better than a home elliptical machine. Essentially, these two are types of exercises meant to train the cardiovascular system and burn calories. What separates them is the intensity and the corresponding physiological effects. Your body responds differently to varying exercise intensity.
What is aerobic exercise?
On face value, aerobic exercise is a moderate-pace exercise, and as its name implies, it relies solely on the aerobic metabolic pathway for energy. That means it just requires the metabolic process that relies on the presence of enough oxygen. The aerobic energy-generating mechanism sustains most of our daily activities and sustains moderate levels of physical activity (e.g. walking, jogging, or cycling). At moderate pace, the lungs and heart are able to pump enough oxygen for the muscles.
However, the ability of the aerobic metabolic mechanism to generate energy reaches a ceiling. As you increase the intensity of an exercise, say you shift from jogging to running, your body responds by increasing your breathing and heart rate to compensate for more massive demands for oxygen and fuel (glucose). At a certain point, even such compensation falls short of the demand. This is evident when you exert more effort, for instance, when you break into a sprint. Your muscles will have to rely on another type of mechanism for energy.
What is anaerobic exercise?
When working at extreme intensity, your body’s fuel and oxygen demands exceed what aerobic energy generating mechanisms can supply. To compensate for additional energy requirements, your body, your muscles in particular, resort to anaerobic metabolism. Any type of exercise intense enough to prompt the body to switch to anaerobic metabolism is considered anaerobic exercise. In fact, aerobic exercise done intense enough can become anaerobic exercise.
You don’t realize anaerobic mechanisms happening, but you recognize the effect--muscle fatigue. Muscles cannot sustain anaerobic (high intensity) exercise too long because lactic acid builds up fast as a result of rapid breakdown of glucose. Lactic acid retards muscle function and should be cleared by the body before muscle function resumes to previous level. The accumulation of lactic acid adds to the soreness you feel after an intense exercise. Note that the intense exercise itself tears muscle fibers, causing the feeling of soreness as well.
So which is better?
One isn’t necessarily better than the other. Aerobic and anaerobic exercise both have their own uses. Some people are better off doing aerobic exercises, while others should try anaerobic exercises.
Beginners and those recovering from injury should be on aerobic exercise, because it is less demanding and puts less stress on muscles, tendons, and joints. Aerobic exercise has its place in fitness, especially in cardiovascular training. However, your body adapts to this type of training and soon it becomes less effective for weight loss, supposing you’re doing it to burn fat.
This is why advanced fitness enthusiasts add anaerobic exercise to their programs. High intensity interval training, circuit training, and weight training are examples of exercises that require anaerobic energy generation. They are more effective at burning fat, building muscle, building more robust cardiovascular system, and improving your overall fitness. However, they are quite physically demanding and must be performed properly to avoid injuries.