Sources of Energy for Exercise, Edexcel A2 PE

Dietry manipulation, carbo-loading, hydration, creatine loading. 


Energy Systems

  • ATP, adenosine triphosphate, is a chemical compound that fuels muscular contraction.
  • Carbohydrate, fat and protein (macronutreints) are the energy providers. 

There are 3 ways that ATP, the energy currency, is produced; aerobic energy system, the ATP-PC system (anaerobic), and the lactic acid system (anaerobic).

ATP- PC System

The ATP molecule is used as energy when it is broken by the ATPase enzyme to leave an ADP (Adenosine Diphosphate) molecule and Pi phosphate ion. PC (Phosphate –Creatine) stores in the body are broken down by an enzyme called Creatine Kinase in an exothermic reaction, and then the Phosphate is attached to the ADP molecule in a coupled, endothermic reaction to reproduce ATP. During recovery, PC stores are restored by an endothermic reaction. 

Lactic Acid System

This system starts with a glycogen molecule, the body’s storage of energy (glucose). The glycogen molecule goes through a process named glycolysis where there are glycolytic enzymes present; Glycogen Phosphorylase and Phosphofructokinase. From this process, 2 ATP molecules are produced and pyruvic acid. As there is no oxygen present, lactic acid is produced by enzyme called Lactate Dehydrogenase (LDH), which converts pyruvic acid into lactic acid. Eventually, lactic acid inhibits the process of glycolysis. 

1 of 8

Energy Systems

Aerobic System

The process begins the same as the lactic acid system, where a glycogen molecule experiences glycolysis and glycolytic enzymes produce 2 ATP molecules and pyruvic acid. However, because oxygen is present in this energy process, Acetyl CoA is produced, followed by Citric Acid. After these products have been made, a process called the Krebs Cycle occurs which undergoes a mixture of complicated chemical reactions and ultimately produces 2 more ATP molecules, and an Electron Transport Chain consisting of 34 ATP molecules.  

2 of 8

Dietary Manipulation

A high CHO (carbohydrate) diet improves performance. 2 elements reload depleted muscle glycogen stores and ensure enough CHO is availble to imporove the glycogen stores and hence glycolysis:

  • Immediate post exercise CHO supplements
  • High glycemic index (GI) foods, e.g. bananas and raisins

Carboloading can enhance an endurance athletes performance in events longer than 90 minutess by increasing muscle glycogen stores above  normal levels.

Fat intake for power and edurance athletes should be limited (except for power events such as sumo wrestling) 

3 of 8

Dietary Manipulation

Nutrition plays is a valuable role in an athlete’s performance. Different quantities and proportions of the food groups are altered to suit the needs of the individual, and a poorly suited diet can have a negative impact on a performance. However, an appropriate diet allows the body to function at its optimum each day therefore producing an optimum level performance. Factors to be considered when creating an ideal diet include; the type of exercise (the intensity or duration, anaerobic or aerobic), gender (women do not need as much energy intake as men), body size (height and weight) and age (children do not need as much energy intake as a fully grown adult). 

4 of 8


Aims to increase muscle glycogen stores above normal levels prior to an endurance competition where continuous activity is greater than 90 minutes.

Glycogen Supercompensation

When depletion occurs (reuced levels of liver and muscle glycogen stores), the reacts by vigorously replacing them to above normal resting value. It is a normal reaction to biological stress when the body has been starved of carbohydrates. Supercompensation is the repletion. 

5 of 8

Pre and Post Nutrition


  • Fluids for hydration
  • Light complex CHO such as pasta at least 3 hours before activity
  • Fruit containing complex CHO
  • Small amount of glucose


  • Hypertonic sports drink immediatly after exercise has finished
  • The drink begins to replenish blood glucose and glycogen stores
  • A high CHO meals within 15 minutes of finished exercise to coninue glycogen replenishment
6 of 8


Body Fluid Balance

  • water is lost through sweating at skin surface
  • decrease blood plasma volume
  • reduced blood flow to skin and muscle
  • heart rate increases
  • body temperature rises
  • fatigue sets in

Fluid Intake During Exercise

Water loss of 2-3% can reduce performance. Therefore maintaining hydration during prolonged activity is vital.

7 of 8

Creatine Supplementation

Creatine is stored in skeletal muscle as phosphocreatine (PC). Creatine supplementation increases PC which enhances the ATP-PC system of ATP resynthesis. It is a legal ergogenic aid. 

It is used to increase anaerobic power and lengthen time which they can apply maximal power. Power athletes will use creatine supplementation inorder to help with the training process.

8 of 8


No comments have yet been made

Similar Physical Education resources:

See all Physical Education resources »See all Exercise physiology resources »