The three energy systems work as follow. The ATP/PC system last for around 10 secs and requires no oxygen. This system is when the phosphate from phosphocreatine (PC) is broken away and joins with Adenosine Diphosphate (ADP) to form Adenosine Triphosphate (ATP). The ATP/PC produces no waste product which is a benefit. The Anaerobic Glycolysis/Lactic Acid System takes over once the alactic threshold is reached. The lactic acid system relies on glycolysis which is the break down of carbohydrates into glucose. Glycolysis occurs without oxygen and produces 2 ATP molecules. It unfortunately produces lactic acid as a waste product which has to be cleared to avoid muscle fatigue. After roughly 4 minutes the Aerobic system takes full effect of energy production. This system use proteins, carbohydrates and fats to resynthesize ATP molecules. The difference between this cycle and the Lactic acid system is because oxygen is required to complete the break down of glucose, with no lactic acid production, instead carbon dioxide and water are produced which are much easier to remove. This system can be used continuously for extended periods of time and yields at total 38 molecules of ATP pre glucose molecule.
ATP/CP system ATP Re-synthesis
Lactic Acid System Aerobic System
With these three energy systems providing the drive for your body it is important to be able to train them, specialize for your sport. For example, a marathon runner would receive minimal gain in competition if he or she trained their ATP/CP system to a high level because this system only provides energy to the body for roughly 10 seconds. A marathon runner would receive a much better gain in competition if the aerobic energy system was trained to a higher level. Because a marathon takes longer than 2-3 minutes the event primarily uses the aerobic system. At the beginning of the event the ATP/CP would begin before switching to the aerobic system quickly. The lactic acid system would come in when the athlete bursts to pass an opponent or to sprint home in the final stages. Therefore a marathon runner would be much better suited to train his/hers aerobic system to achieve the best result. A runner of any long distance would benefit from this and can train the aerobic system in multiple ways. To improve all systems it is best to undergo progressive overload to keep the body improving. To train your aerobic system the body should be working at 70-80% of maximum HR for a prolonged period of time (more than 30 minutes). In most average people their heart rate will be between 142-162 bpm, however in elite athletes their resting heart rate will be lower and maximal heart rate will be higher, so in their case they would have to work at a higher rate and have a higher heart rate to achieve results.
The best type of training for the aerobic system is continuous training. This training must go for at least 15 minutes and can last up to an hour. The aim is to reach the zone for inducing cardiovascular effect which is between 70-80% of max heart rate. The...