The Energy Systems
Topic Review
1. Energy for all movements/activity comes from the breakdown of adenosine triphosphate
(ATP), which is stored at the muscles. Once ATP is broken down, it cannot be used again
until it is recharged.
2. The foods we eat are digested, stored and then broken down to release energy, which allows
ATP to be recharged. Phosphocreatine is a chemical fuel stored at the muscles that can
readily be broken down to release energy and recharge ATP.
3. The foods we eat are made up of a variety of nutrients. Our food intake consists of three
basic nutrients – carbohydrates, fats and protein – which are broken down, releasing energy
to rebuild ATP.
4. Food is stored at various sites in the human body. Carbohydrates are the body’s preferred
fuel during exercise because they break down easily and require less oxygen in the process.
5. There are three energy systems or pathways – two of which are anaerobic and the other
aerobic
6. The three energy systems are ATP-PC, anaerobic glycolysis and aerobic.
7. Virtually all physical activities derive some energy from each of the three energy systems.
Each system is best suited to supply energy for specific types of events/activities.
8. The three systems work together (interplay) in supplying energy for movement, but
generally one system provides the bulk of the energy required to recharge ATP at any one
time. The percentage contribution from each system is essentially determined by the
intensity and duration of the activity. Other factors such as fatigue and recovery also need to
be taken into consideration when determining which system is the major energy provider.
9. The ATPPC and anaerobic glycolysis systems are capable of responding immediately to the
energy demands of exercise and are suited to short, high-intensity bursts of activity.
10. The ATPPC system provides energy for explosive actions, but not for very long. Highintensity actions can be sustained by the anaerobic glycolysis system, but this is limited by
the accumulation of lactic acid. The aerobic system is the slowest to contribute towards ATP
resynthesis, but is capable of producing the most energy. It can provide 40 to 50 times more
energy than both of the anaerobic energy systems combined.
11. The ATPPC system uses PC stored at the muscles for immediate energy release. This
system is limited by the amount of PC stored at the muscles – the more intense the activity,
the quicker this is used to produce ATP. After 10 to 15 seconds, all of the PC is depleted and
once this occurs this system can no longer contribute to energy production (ATP recharge)
until the athlete rests. It takes about three minutes of total rest to fully replenish the
ATPPC system. After approximately five seconds of maximal activity, the PC stores are 40
to 50 per cent depleted and the anaerobic glycolysis system becomes the major producer of
ATP.
12. The anaerobic glycolysis system involves more complex recharge reactions than the
ATPPC system, and during maximal efforts takes over at the five to 10 second mark as the
major contributor to energy supply. Peak power from this system is usually reached
between five and 15 seconds and will continue to contribute to ATP production until it
fatigues (two to three minutes) due to lactic acid accumulation. This system is able to
provide twice as much energy as the ATPPC system.
13. The aerobic system responds quickly to the demands of intense exercise but cannot meet
energy demands during the first 10 seconds of activity. It does not, however, take two to
three minutes (as previously thought) for it to become the major energy contributor. Recent
studies have revealed that it can provide ATP for activities above 85 per cent maximum
heart rate as early as one minute into the activity. Depending on training levels, oxygen
uptake can be as high as 90 per cent of an athlete’s maximum within 60 seconds.
14. The difference between aerobic and anaerobic glycolysis is the availability of oxygen.
Glycolysis deals with the breakdown of glycogen. With moderate-intensity exercise, the
glycogen is broken down completely to release energy and non-fatiguing by-products such
as carbon dioxide and water. Increased ATP demand sees glycogen being broken down to
release energy and the fatiguing by-product, lactic acid. The anaerobic glycolysis system is
hence also known as the alactic acid system system.