What is Aerobic Exercise?
Aerobic Exercise is prolonged moderate intensity exercise that uses up oxygen at a rate at or below the level that the cardio-respiratory system can replenish it. Examples are running, walking, cycling, and swimming. This type of exercise relies primarily on slow-twitch muscle fibers which have high numbers of mitochondria meaning they can produce ATP through aerobic respiration, in which ATP is formed through oxidative phosphorylation. This type of respiration can be sustained for very long periods of time, depending on the intensity of the activity and so is sometimes called endurance exercise or continuous exercise. The term aerobic means with oxygen.
For muscle building and body-building, aerobic training, sometimes called ‘cardio,’ develops cardio-respiratory fitness and is used to burn fat to achieve maximum definition, but can be highly catabolic if done in excess.
What is Anaerobic Exercise?
Anaerobic Exercise is higher intensity exercise than aerobic exercise and uses up oxygen more quickly than it can be replenished in the muscles. Resistance training such as strength training and bodybuilding is anaerobic exercise, which primarily relies on fast-twitch muscle fibers. These muscle fibers do not possess many mitochondria and so must create energy without oxygen. The primary means of producing this energy is the process of glycolysis which, although it produces only about 5 percent as ATP per glucose molecule as aerobic respiration, is much more rapid.
Anaerobic training, in the strictest sense, is training that relies primarily on the phosphagen system and glycolysis, which are energy transfer processes that operate in the absence of oxygen, thus the term AN-aerobic wherein the AN means not or without.
Anaerobic metabolism operates during activities which require an immediate and rapid supply of energy to the working muscles. Any all-out activity, within the first two minutes or so, would use anaerobic energy.
Muscles cells also have a small amount of stored ATP, estimated to be able to fuel a 2 to 5-second burst of muscle contraction, upon which time stored creatine phosphate can be used to rapidly regenerate ATP for up to 15 seconds.
Aerobic and Anaerobic Metabolism are Not Mutually Exclusive
Many people have been lead to believe that aerobic metabolism switches off when anaerobic metabolism takes over, or vice versa. In reality these metabolic pathwyas are not mutually exclusive and during most exercise, they do work concurrently together to provide energy to working muscles. When we discuss ‘aerobic exercise’ or ‘anaerobic exercise’ we are usually discussing which energy system is dominant.