ADENOSINE TRIPHOSPHATE – THE BASICS
- Adenosine triphosphate (ATP) is a high-energy molecule that is the source of energy for muscle contraction. However, the muscle only contains enough ATP to expand energy at maximal rate for one second. For muscle contraction to continue, additional ATP must be supplied. The faster you want your muscles to contract, the more rapidly you must replenish ATP.
- The purpose of the 3 energy systems (ATP- CP / Lactic acid / Oxygen) is to supply additional ATP; however the rate at which they can supply ATP varies.
- The manner in which ATP in produced is dependent on the duration and intensity of the exercise. If the muscle is required to work at maximum intensity, it can draw on the small amounts of ATP stored in the muscles.
- To release energy, one molecule of phosphate splits from the Adenosine Tri –Phosphate to leave Adenosine Di-Phosphate).
- If ATP is required for longer than one second, the broken down ADP molecules can be reformed through the arrival of Creatine Phosphate.
- Creatine Phosphate contains a spare phosphate molecule which bonds onto ADP, re-synthesising ADP back into ATP, which it can do for around 5 seconds of intense physical activity.
- Creatine Phosphate is produced naturally by the body, and is available in small quantities in the muscles.
- To continue exercising for longer than 5 seconds requires the breakdown of Glycogen (stored carbohydrate) in our muscles, re-synthesising the ATP and releasing more energy.
- Under aerobic conditions (using oxygen at a lower intensity, such as running or cycling), molecules of glucose can yield their full store of 38 ATP molecules, allowing you to continue exercising.
- However, under anaerobic conditions (without oxygen at a high intensity EXAMPLE), molecules of glucose only yield 2 ATP molecules. The remaining 36 ATP units essentially becoming wasted converting to pyruvic acid, and then finally lactic acid. When this lactic acid accumulates in the muscle, it causes fatigue.
ATP-CP (O → 5 SECONDS OF ACTIVITY) – ANAEROBIC SYSTEM
- The ATP-CP energy system consists of Adenosine Tri-Phosphate and Creatine Phosphate. ATP is the immediate source of energy for muscle contraction, releasing energy very rapidly; however ATP is in very limited supply in our muscles.
- Creatine Phosphate also breaks down and releases energy very rapidly; however this energy cannot be used directly for muscle contraction.
- Creatine Phosphate supply is also limited in our muscles and may only be able to re-synthesise ATP for an additional 5 seconds, the ability to use ATP and CP rapidly is a primary characteristic of the white fast-twitch muscle fibres.
LACTIC ACID (5 → 90 SECONDS) – ANAEROBIC SYSTEM
- The Lactic Acid Energy System uses CARBOHYDRATES as fuel, primarily in the form of GLYCOGEN stored in our muscles.
- The breakdown of glycogen leads to a process called GLYCOLYSIS in which ATP can be produced rapidly, although not as rapidly as compared to the breakdown of CP. As we begin to exercise, the rate of Glycolysis increases to meet our demand for additional ATP.
- As we pick up your speed, we eventually reach a point where aerobic glycolysis is inadequate to support energy production. Through a series of chemical reactions in the muscle cell, the formation of lactic acid allows anaerobic glycolysis to continue. Unfortunately the accumulation of excess Lactic Acid leads to fatigue within the muscle cell, limiting this energy system to 90 seconds.
OXYGEN SYSTEM (90 SECONDS +)
- The aerobic breakdown of oxygen is the long term and fundamental energy system for endurance activity. Oxygen is the key substance to maintain aerobic performance for long periods.
- Insufficient oxygen forces the body to exercise anaerobically, resulting in the body experiencing premature fatigue.
- The oxygen energy system needs an adequate supply of oxygen delivered to the muscle to release the chemical energy stored in carbohydrates and fats.
- Although the oxygen system produces ATP more slowly than the two anaerobic systems, it is capable of producing greater quantities over sustained periods.