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ENERGY SYSTEMS
Three key energy nutrients
 The food we take in is broken down into 3 energy nutrients in the
course of digestion: proteins, fats, and carbohydrates
 It is through bioenergetic conversion of these nutrients that our
bodies are able to function and we are able to carry out physical
activity
 Carbohydrates (CHO) are the main source of energy – yielding 4.1
calories per gram
 Protein yields 4.3 calories per gram
 Fat yields 9.3 calories per gram
The role of carbohydrates:
 Most abundant organic substance in nature
 Foods that originate from plants, such as vegetables, fruits, and
grain-based foods such as bread and pasta
 Glucose is the form in which carbohydrates are digested by humans
 it is stored within the skeletal muscle of humans and within the liver
as glycogen
 glucose that is stored can be broken down under the demands of
stress or of muscular activity – it is carried by the blood and brought
into action as an energy source
 the complex process by which energy is supplied throughout the
body and energy-rich material are digested by the body for the
purposes of energy is referred to as metabolism
ATP – Energy Currency
 nutrients that we get from the food we eat must be turned into a
universal form of energy – “free energy” that allows many body
processes to occur
 this “free energy” is ATP – adenosine triphosphate
 ATP captures the chemical energy resulting from the breakdown of
food and it is then used for cellular processes
 an ATP molecule consists of 3 phosphates attached by high energy
bonds to adenosine
 energy is released when a trailing phosphate (P) is broken from the
ATP molecule
 this results in ADP (adenosine diphosphate) plus energy:

ATP  ADP + P + energy
 ATP supplies are used up quickly therefore the body must recreate
new supplies of ATP so that bodily functions can continue
Two Energy Systems
There are 2 methods in which ATP can be re-synthesized:
a) anaerobic system  without oxygen
 occurs relatively quickly in the muscle fibre
 used for powerful but relatively short-lived physical actions
b) aerobic system  with oxygen
 more complicated system
 takes place in the mitochondria
 complete breakdown of glucose, therefore, fats and proteins
must enter the cycle at this stage
These two systems co-exist, overlap and interact in various combinations.
The anaerobic system is more important in short-run, high intensity activity
whereas the aerobic system is the key to endurance events.
All sporting events and physical activity relies on some combination of
aerobic and anaerobic systems.