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Energy System Training – Part 2 – Energy Production and Expenditure

Posted 25th October 2015 by Josh Schouten

In Energy System Training – Part 1  we had a quick introduction to energy systems training (EST) and the two primary pathways – aerobic and anaerobic.  So where does this energy come from, and where does it go?

Energy Production

Contracting muscles get their energy (ATP) from the breakdown of glycogen stored in the muscles/liver, and glucose from the blood stream. There should be no surprise that your macronutrients play an important role here, as glucose come primarily from carbohydrates (CHO). Yes, in the new EST phase you have a license to eat more CHO’s. The energy from food (mainly CHO) is broken down and stored in the muscles and liver.  A muscle contraction demands the release of energy from these cells to fuel movement.  Now you know why exercise can help you burn calories, get ripped, loose fat, and build/maintain lean muscle mass.

Energy comes from the food we eat, it is stored in the cells and then called upong when muscle contract takes place.

Energy Expenditure

In an anaerobic environment (without oxygen) the preferred fuel source for ATP production is CHO, followed by fats.  In an aerobic environment (with oxygen) our bodies will look to burn protein (amino acids), CHO, and fats.  Have you ever wondered why endurance athletes are often labeled as “skinny fat” – they have very little lean muscle mass due to their aerobic training , leaving their body fat percentages higher than many people think. 

The body is continually monitoring its current state of ATP.  The required rate of energy production, the duration of energy production and the work to rest ratio dictates the environment that the body will be placed into energy domands that need to be maintained.

There are many different expression of energy output that depends on the amount of force being produced and the length of the activity being performed. Weightlifting, track and field, jumping, throwing and sprinting are all explosive sports that require a fast rate of energy production in a short period of time,  or a high anaerobic demand (world record 100m = 9.58sec, average velocity = 37.58kmph). Anaerobic EST training requires a high rest to work ratio because the body used high volumes of ATP in a short duration of time.  The body then needs a long rest duration to replenish the high levels of ATP used during explosive activity.

At the other end of the continuum triathlon, cycling, marathon, and endurance sports have a low demand for sustained energy, an aerobic demand (world record marathon = 2:03:59, average speed =20.28kmph). The rest to work ratio required during aerobic training is lower than anaerobic EST because the demands for ATP are lower and therefore last for longer duration in an oxidative environment.

The following force-fatigability relationships apply:



Digging Deeper Into EST

Conventionally, there are three energy systems that share the task of ATP production:

Anaerobic Alactic (ATP-CP) – high power, short duration, immediate energy, 10-12-seconds

Anaerobic Lactic (Glycolytic) – moderate power, short duration, intermediate energy 10-seconds – 2-minutes

Aerobic (Oxidative) – low power, long duration, long-term sustainable energy 2minutes and upwards


Each energy system has a power and a capacity component. 

The power component is defined by the rate at which that energy system can start producing ATPs.

The capacity component is the duration at which an energy system can maintain ATP production.

There is always a trade off between the amount of power you can exert and the total capacity of effort you can produce over a period of time.  Performing a maximal (95%+ of 1RM) one-time explosive movement will not fatigue the athlete in the same way as performing multiple repetitions at a submaximal load.  Remember that the two anaerobic systems (ATP-PCr and glycolysis) are used for short duration high power outputs, whereas the aerobic energy system (Oxidative) is capable of production sustainable low power outputs.

Many athletes make the assumption that explosive movements or high strength movements only use the anaerobic systems, but this is far from true.  The above diagram and the below graph shows that the aerobic system contributes to energy production for efforts lasting less than 30-40-seconds (sub 500m).  Anything over 500m in the blow example of running, is dominated by the aerobic energy system no matter how hard you are going.



Anaerobic and aerobic energy system testing and training can be used to improve athletic perofmance for athletes of all sports.  There is always a tradeoff between speed, power, strength and endurance.  It makes sense that different athletes are able to produce different amount of power anaerobically versus aerobically.  Which type of athlete are you?  What is your sport and how can you trian to increase your sports performance?  Stay tuned for the next EST post.