The Aerobic Energy System
All humans are aerobic beings, which mean that we require oxygen to sustain life. While being inactive or at rest, the body has a resting oxygen requirement that must be met. This is the minimum amount of oxygen necessary to burn enough fuel in order to create enough energy in order to sustain basic bodily functions.
During rest, the body prefers to burn fat as the main source of fuel, because of its abundance as there is approximately over 80,000 kcals of energy that can be obtained from fat. This process is called aerobic lipolysis.
As the exercise commences there is a greater need to use more oxygen. All systems in the body contribute to the supply and transport of additional oxygen to the working muscle. The muscles are contracting faster and require a greater turnover of ATP. ATP is a chemical reaction that provides energy to the working muscles.
As the exercise intensity increases, the body begins to oxide more carbohydrates than fats. Even though there is over 40 times more fat in the body to metabolize for energy, there is a greater oxygen cost requirement in order to burn just fat. The increased breakdown of carbohydrates and stored carbohydrates during exercise is called aerobic glycolysis. The waste products formed by this process are carbon dioxide and water.
The Lactic Acid Energy System
When a person exceeds their aerobic threshold it becomes impossible to activate the aerobic energy system sufficiently in order to transport all the oxygen required to maintain the exercise intensity. As a result additional energy comes from the breaking down of carbohydrates without oxygen and the waste product of lactic acid is formed. When lactic acid reaches intolerable levels, fatigue in the muscle will result and the exercise will have to be stopped.
The lactic acid system is also used when energy is required at a very fast rate for approximately 60 seconds such as in 100 meter freestyle race or 400 meter track race.
At the completion of an exhaustive lactic acid exercise bout it is really important to cool down thoroughly. This allows the muscle to contract and transport the lactate through the body so that it can quickly be dispersed. Lactic acid can be removed from the working muscle within 45 to 60 minutes.
The ATP-PC System
In intense exercise activities lasting less than 15 seconds, neither the aerobic energy system nor the lactic energy system can supply the energy for the remake of ATP at the rate required.
The preferred energy source used is a high energy compound stored in the muscle called phosphocreatine. During short high intensity bouts of exercise, phosphocreatine is metabolized anaerobically, with large amounts of energy liberated immediately. This supply is completely exhausted between 10-15 seconds and can be replenished almost 100% in about 2 minutes. When phosphocreatine is used as a fuel source, there are no waste products remaining. This system can be used in lifting heavy weights, sprinting 100 metres.
by Serge T (copyright 2007)
