The document discusses three energy systems - ATP-PCr, glycolytic, and oxidative systems - that the body uses to produce ATP for muscle contraction and energy. The ATP-PCr system uses ATP and phosphocreatine to immediately resynthesize ATP for about 10 seconds of intense exercise. The glycolytic system breaks down glucose to produce energy, mainly through lactic acid production, for 30-45 seconds of activity. The oxidative system uses slow glycolysis, the Krebs cycle, and electron transport chain, along with beta oxidation of fats, to aerobically produce most of the body's energy through oxygen for sustained lower-intensity exercise lasting over 90 seconds.

1. Energy system’s
used in sports and exercise
activities.

2. What is ATP?
Energy is required for all bodily functions including growth and development, repair, the transport of various substances between cells and muscle contraction.
In any type of exercise or activity the skeletal muscle is powered by one compound, adenosine triphosphate or ATP. But can only be stored in small quantities in the
cells, this means it can only be sued for a very short period of time, a few seconds.
The body must resynthesize ATP on an ongoing basis. In order to produce more energy, it is produced through the energy systems.
An ATP molecule consists of adenosine and three phosphate groups. When a molecule of ATP is combined with water in a process called hydrolysis, the last phosphate
group splits away and releases energy. The molecule of adenosine triphosphate now becomes adenosine diphosphate or ADP.
To resynthesize the limited stores of ATP, chemical reactions add a phosphate back to ADP to create ATP. This process is called phosphorylation. If this occurs in the
presence of oxygen it is aerobic metabolism or oxidative phosphorylation. If it occurs without oxygen it is labelled anaerobic metabolism.
(Image 1)

3. ATP-PCr System.
ATP and Phosphocreatine or PCr for short, make up the ATP-PCr system. PCr gets broken down by releasing a phosphate and energy, which is then used to rebuild ATP,
which is energy. The ATP is rebuilt by adding a phosphate to ADP. This is called phosphorylation.
The ATP-PCr energy system can work with or without oxygen but because it doesn't rely on oxygen it’s anaerobic.
During the first 5 seconds of exercise regardless of intensity, the ATP-PCr system is relied on almost exclusively.
ATP stores only last a few seconds with PCr slowing the drop in ATP for another 5-8 seconds.
When combined ATP-PCr system can sustain high intensity exercise for 3-15 seconds and it is during this time that the potential rate for power output is at its greatest.
When exercise continues past this immediate period, the body must rely on another energy system to produce more ATP for energy.
To train this energy system, repetitive exercise activities for 10-15 seconds of maximum intensity activity is required, with approximately two minutes rest between
repeats to allow the system to replenish. The formula to work out the required ret between exercise is ‘work to rest ratio’. For the ATP-PC system the rest ratio is
1 : 10/12. This means that for every second of work you need to allow 10 to 12 seconds for recovery.
Types of sports or activities that would use this system are, weight lifting. When you are lifting heavy weights with 1-3 reps max. Or boxing where your throwing
punches as hard as you can 2-3 times. This energy system is the initial source and is used for quick explosive movements.
(Image 2)

4. Glycolytic System.
Glycolysis means the breakdown of glucose and consists enzymatic reactions. The carbohydrates we eat supply the body with glucose, which can be stored as glycogen
in the muscles or liver for later use.
The end product of glycolysis is pyruvic acid. Pyruvic acid can be processed by either the Krebs cycle or converted into lactic acid. If the end product of the chemical
reaction is lactic acid, the process is called anaerobic glycolysis but if it remains pyruvate the process is called aerobic glycolysis. Oxygen availability determines the end
product but is not required during the actual process of glycolysis.
The fast glycolytic system where the pyruvate becomes lactic acid, can produce energy at a greater rate than slow glycolysis. But because the fast glycolysis produces
lactic acid, it can quickly accumulate and can lead to muscular fatigue.
The fast glycolytic system will begin to take effect rapidly after the initial 10 seconds of exercise. By about 30 seconds of sustained activity the majority of energy
comes from fast glycolysis. At 45 seconds of sustained activity there is a second reduction in power output, the first reduction being after about 10 seconds. Activity
beyond this point has a greater reliance on the Oxidative system.
This system needs 2 ATP to fuel glycolysis but 4 ATP are created so the body gains 2 ATP to use for muscular contraction.
Training this system is aimed at increasing tolerance to lactate, the removal of lactate and improving the rate at which glycolysis produces ATP.
Deepening on what you want to achieve, the work to rest ratio will vary for example , If you want the system to completely recover and clear the accumulated lactic
acid you would use a ratio of 1:6 , 6 seconds of rest for every second of work. But a ratio of 1:3 can be used to produce a greater bodily response to lactate and carry
some of the fatigue into the next set of repeats. If you want to build your bodies capacity for lactate then the 1:6 ratio should be repeated often. But if your aim is to
be able to tolerate lactate build up a ratio of 1:1 or 2:1 would be best.
(Image 3)

5. Oxidative System.
The oxidative system is made up of four processes to produce ATP: (Image 4)
• Slow glycolysis (aerobic glycolysis)
• Krebs cycle (citric acid cycle or tricarboxylic acid cycle)
• Electron transport chain
• Beta oxidation
Slow glycolysis is exactly the same set of reactions as fast glycolysis. This forms two ATPs. The difference between the slow and the fast glycolysis is that the end
product pyruvic acid is converted into a substance called acetyl coenzyme A , rather than lactic acid. After this process more ATP can be produced by funnelling acetyl
coenzyme A through the Krebs Cycle.
The Krebs cycle is a series chemical reactions that continues the oxidization of glucose that was started during glycolysis. The production of the slow glycolysis , Acetyl
coenzyme A enters the Krebs cycle and is broken down in to carbon dioxide and hydrogen allowing two more ATPs to be produced. The hydrogen produced in the
Krebs cycle, plus the hydrogen produced during glycolysis combines with two enzymes called NAD and FAD and is transported to the Electron Transport Chain.
Hydrogen is then carried to the electron transport chain, and combined with oxygen to form water to prevent acidification of the hydrogen formed in the Krebs cycle.
This chain requires oxygen and also produces 34 ATPs.
Unlike glycolysis, the Krebs cycle and electron transport chain Beta Oxidisation can metabolise fat as well as carbohydrate to produce ATP. Lipolysis is the term used to
describe the breakdown of triglycerides into the more basic units of glycerol and free fatty acids. Before these free fatty acids can enter the Krebs cycle they must go
through the process of beta oxidation. These reactions reduce free fatty acids to acetyl coenzyme A and hydrogen. Acetyl coenzyme A can now enter the Krebs cycle.
The oxidative system is used primarily during rest and low-intensity exercise. At the start of exercise it takes about 90 seconds for the oxidative system to produce its
maximal power output, Training this system can help to improve the systems response time to exercise. Beyond this point the Krebs cycle supplies the majority of
energy requirements but slow glycolysis still makes a some energy. The slow glycolysis is important during events lasting several hours or more.