Energy Systems of the Anaerobic Athlete

Updated: Dec 29, 2021


For the purpose of this article I will reference arguably the greatest anaerobic athlete of all time, Usain Bolt, and his events (100m and 200m sprints). However, an athlete who's event duration is very short with extremely explosive high power outputs, they will be engaging the same energy systems.

ATP-PC System

The first process involves the high energy fuel phosphate creatine (PC also known as creatine phosphate). Creatine phosphate donates its phosphate to ADP to resynthesise ATP. The breakdown of PC does not require the presence of oxygen, therefore the ATP-PC system is known as an anaerobic system.

This energy system is for immediate activity for activities of short duration (lasting 0-10 seconds), high intensity & explosive activities, such as the 100m sprint, therefore fast twitch muscle fibres are recruited.

The advantage of this system is that it is immediate/fast rate The disadvantage is that the system is limited by the amount of PC stored in the muscles. Once PC begins to deplete at the muscle, ATP must be resynthesised from another substance. This energy system has a high rate but low capacity!


Anaerobic Glycolysis

Anaerobic Glycolysis refers to the incomplete breakdown of glycogen without oxygen. This system used to be known as the lactic acid system & resynthesises ATP during high intensity activities (>85% max HR) that last up from 5-10 sec up to 1min.





Anaerobic Glycolysis involves a number of complex reactions. Therefore its not as quick off the mark as the ATP-PC System, but produces twice as much energy for ATP resynthesise as the ATP-PC System. Because oxygen is not present, the glycogen is not totally broken down & a fatiguing by-product called lactic acid (lactate + hydrogen ions) is formed.

100m Sprint Energy System Interplay

Sprinting requires repeated muscle contractions with ATP needing to be replenished from other fuel sources. Initially these sources are found within the muscle, they include ATP-PC (the phosphagen system) and the anaerobic glycolysis system. These systems require no oxygen in order to produce ATP, a third pathway used to produce ATP is the aerobic system, and this pathway requires oxygen.


The creatine phosphate and ATP stored within the muscles are sufficient to enable maximal effort for 5-10 seconds. Beyond this time, energy is provided by anaerobic glycolysis. One of the by-products of anaerobic glycolysis is lactic acid, which results in higher muscle cell and blood acidity.


It is important to note that all three systems are used simultaneously although at varying degrees. Its estimated that during sprint events approximately 95% of energy production comes via the anaerobic system (85% phosphate, 10% anaerobic glycolysis), and only 5% from aerobic oxygen. Thus, the 100m sprint is an anaerobic event relying heavily on energy supply from the ATP-PC system!

200m Sprint Energy System Interplay

Before the beginning of the race, the most predominant energy system is the aerobic glycolytic system, as the demand for energy in the muscle is low, due to the low intensity as Usain is walking and standing still. He is currently in a steady state as oxygen supply is meeting oxygen demand, although as he steps up onto the blocks, acute responses begin to take place in anticipation, therefore heart begins to rise. As the race begins the explosive movement required out of the blocks and maximal intensity from the beginning of the race causes the ATP-PC energy system to be most dominant. This is because energy can be supplied the quickest from the chemical stores already in the muscle. For the first 100m (10 seconds), this system is the most dominant and peak power occurs after 5 seconds into the race. Although as the PC stores in the muscle rapidly begin to deplete, anaerobic glycolysis becomes the most dominant after 10 seconds. This system is capable of resynthesising 2 ATP from each glycogen molecule and as resynthesis occurs quickly and acute responses are still taking place (increase in ventilation and cardiac output) this remains the most dominant energy system until the end of the race – 19 seconds total.


The aerobic energy system still contributes some energy to the demand required but not a significant amount as the power and rate of resynthesis needed is high. Also a steady state is not reached as the oxygen supply can never meet the oxygen demand, due to the event being small duration (19 seconds) and a continuous sprint at maximal intensity.


At the finish of the race, the workload decreases dramatically, although Usain Bolt still takes deep breaths as he is in oxygen debt/EPOC. He must repay the energy used when working anaerobically – both from the ATP-PC energy system & the anaerobic glycolytic energy system.


#coachingworks #coachingwithsparks #indoorcycling #periodisation #sparksintolife #inscydppd #coaching #cyclecoaching #cycling #fatloss #weightloss #endurancetraining #wprime #inscyd #runningppd #metabolicprofiling #criticalpower