The ATP-PC system has the ability to provide a brief but intense amount of energy for times when the body must do a large amount of work over a small period of time. Glycolysis is not involved in this. This only provides energy for short periods of time which are usually eight to ten seconds long. It can be used many times but it will eventually run out and ‘get tired’ even with the help of other molecules. The Creatine Phosphate molecule sort of recycles and rebuilds the ATP molecules which doubles the time someone can use this energy system and also doubles the amount of times they can use it. The system can/should be trained by doing short maximum intervals with a recovery of three times the work load time. This helps to strengthen it. When rebuilding the supply of the ATP system it takes from 24-48 hours to fully rebuild it. The first half hour following the ride or period of exercise is crucial, this is where the most of the ATP molecules are rebuilt and this can be sped up by a high glycaemic sports drink or a decent level of protein.
After 10 seconds your body relies on the glycolysis energy system which is capable for high intensity for up to 4 minutes. The glycolysis energy system prevents the body from removing waste products. It works without the use of oxygen so there is not enough oxygen to help get rid of the waste products produced. Lactic acid builds up which causes fatigue which slows the athlete down. The more intense the activity the higher the amount of lactic acid builds up and removing it is a much longer process than that of replenishing your ATP-PC system. It can take over an hour to fully return the levels of lactic acid to pre exercise levels. Doing a warm down at the end of a session will help to speed up the removal of lactic acid. The first ten minutes get rid of the most amount of lactic acid. When the glycolysis energy system starts to struggle to keep up and maintain the energy requirements the aerobic system is introduced and takes over.
The aerobic energy system requires oxygen, which re-synthesizes ATP to create the energy required. It is used in lower-intensity exercises and provides the energy for most human activity during our lives. It is also important in the recovery from exercise of all intensities.
The aerobic energy system is very efficient and resists fatigue because there is enough oxygen to allow the waste products to be removed. This means the heart and lungs, which help move oxygen around your body are very important when doing physical activity.
It takes longer to overload the aerobic energy than it does to overload both the anaerobic energy system so an aerobic training session must last longer than 20 mins. During longer, low-moderate intensity periods of exercise such as long-distance running, the energy supplied comes from this system.