Energy systems tradeoff - power vs yield


Energy systems is the topic most VCE PE students have difficulty wrapping their head around. Here is a small table and description that should help you understand and compare the differences between the energy systems.

It is important that we understand that each energy system has advantages and disadvantages and hence why they are all being used during the energy system interplay. (Definition alert: Energy system interplay simply refers to the energy systems working together, but at different rates, to supply the ATP required for an activity).

When you look at the table above you will notice that there is a trade-off between Power and Yield for each of the energy systems. As power increases (ie the rate of ATP resynthesis: or going from ADP back to ATP increases) the Yield (number of ATP being produced) decreases.

The factor that affects the power or rate of replenishment is affected by the amount of reactions that need to take place to produce the ATP. As Creatine Phosphate (the fuel used in the ATP CP system) only essentially has one bond to break the reaction is very fast, and hence ATP can be resynthesised very quickly. This is why ATP CP is the predominant energy system used in short duration, maximal intensity activities. The trade off however is that the supply of Creatine Phosphate is quite limited and the number of ATP produced is quite low (1).

When trying to determine which energy systems are being utilised you also need to take into consideration the following factors:

Time/Duration of the activity: As it takes a period of time for Oxygen consumption, extraction, transport to working muscles and then producing energy Aerobically we need to rely upon Anaerobic energy systems to help supply more ATP to meet the demand. The longer the duration typically the lower the intensity and greater use of the aerobic energy system.
Intensity of the activity: As the intensity of exercise increases the demand for ATP increases too (and therefore it needs to be resynthesised at a faster rate in order to maintain exercise).
Aerobic Fitness of the Individual: An athlete with a higher VO2 max will be able to produce more energy aerobically, than an untrained individual working at the same intensity, therefore the athlete will have less reliance upon the Anaerobic energy systems for supplying ATP.
Recovery time (and type) for the athlete: Passive recovery permits faster ATP CP restoration and an Active Recovery helps remove Lactic Acid (and the fatiguing by-product of H ions) at a faster rate.
The availability & restoration of chemical/food fuels: CP is a chemical fuel, food fuels are Carbohydrates and Fats, Fuels are Muscle Glycogen and Muscle Triglycerides. Limited fuel or no fuel obviously restricts rate of production.
The body is always trying to produce the ATP needed aerobically but this depends on whether the:


Anytime there is a shortfall of energy (that can’t be made up by the aerobic energy system) our body must rely on the Anaerobic energy system(s) to make up the shortfall (ATP CP used only if the fuel Creatine Phosphate is still available)

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