Energy systems
Creatine Phosphate System
The creatine phosphate system is an anaerobic system. Creatine phosphate is available in muscle cells and rapidly produces ATP. CP is only available in short supply in the muscles, so it can only provide limited amounts of ATP to the muscle so that it will keep contracting; lasting up to 10 seconds and taking 1-2 minutes to fully recover when stationary [2]. |
Lactic Acid System
The second anaerobic system is the lactic acid system and it takes over when CP stores are exhausted. This is a slightly more complex method of producing ATP. It uses glycogen, stored forms of carbohydrates, as the energy source and involves 10-12 chemical reactions. Lactic acid is the by-product of the anaerobic metabolism of glucose in muscle. Lactic acid levels in the muscles increase when high-intensity exercise continues for more than 10 seconds and can last for up to 3 minutes [2]. |
Aerobic System
The aerobic system is the most complex of the three energy systems because it has many more reactions. It uses carbohydrates and fats as the primary fuels in the presence of oxygen, which explains why it is called the aerobic system. This energy system is slow to start, due to the time it takes to provide the increased amount of oxygen, it produces an abundant supply of ATP and no fatiguing by-products as long as the fuel and oxygen supplies remain adequate. The fuel used depends on the duration and intensity of the exercise. During exercise such as running, swimming and intense team sports, carbohydrates are the primary fuel [2]. |
All three energy systems can operate at the same time within
the muscle cell. Which method is used
depends on whether our muscles are resting or active and on the intensity and
duration of the activity [3]. The aerobic
system is predominant when maximum heart rate is less than 85% and this depends
on the duration and intensity of the activity.
The aerobic system is used after the first few minutes of exercise for
low to moderate intensity and long duration.
It offers a high energy yield, allowing activity to be maintained for
long periods [6].