In this article, I will make mention of Usain Bolt, widely regarded as one of the greatest anaerobic athletes in history, and his performances in the 100m and 200m sprints.
Nevertheless, an athlete participating in events characterised by very brief durations and exceptionally high power outputs will be utilising the same energy systems.
ATP-PC System
The initial step involves the utilization of the high-energy fuel creatine phosphate (also known as PC or phosphocreatine). Creatine phosphate transfers its phosphate to ADP in order to regenerate ATP. The breakdown of creatine phosphate does not depend on the presence of oxygen, making the ATP-PC system an anaerobic system.
This energy system is designed for immediate use during short-duration activities (lasting 0-10 seconds) that require high intensity and explosiveness, such as the 100m sprint, hence the recruitment of fast-twitch muscle fibers.
The main benefit of this system is its immediate energy production rate, while its drawback lies in being limited by the amount of creatine phosphate stored in the muscles. Once creatine phosphate levels start to decrease in the muscles, ATP must be regenerated from another source. This energy system has a high production rate but a low capacity!
Anaerobic Glycolysis
Anaerobic glycolysis is the process of partially breaking down glycogen in the absence of oxygen. Formerly referred to as the lactic acid system, it generates ATP during high-intensity activities (>85% of maximum heart rate) lasting from 5 to 10 seconds up to 1 minute.
Anaerobic Glycolysis consists of several intricate reactions, which make it slower to initiate compared to the ATP-PC System. However, it generates double the amount of energy for ATP resynthesis as the ATP-PC System. Due to the absence of oxygen, glycogen is not completely broken down, leading to the production of a fatiguing by-product known as lactic acid (lactate + hydrogen ions).
100m Sprint Energy System Interplay
When sprinting, the muscles need to contract repeatedly, requiring ATP to be replenished from alternative fuel sources. Initially, these sources are found within the muscles, such as ATP-PC (the phosphagen system) and the anaerobic glycolysis system, which do not need oxygen to produce ATP. Another way to produce ATP is through the aerobic system, which does require oxygen.
The creatine phosphate and ATP stored in the muscles are adequate for maximum effort lasting 5-10 seconds. After this, energy is derived from anaerobic glycolysis, which produces lactic acid as a by-product, leading to increased muscle cell and blood acidity.
All three systems work simultaneously, albeit to different extents. In sprinting, it is estimated that around 95% of energy production comes from the anaerobic system (85% from phosphate and 10% from anaerobic glycolysis), with only 5% coming from aerobic oxygen. Therefore, the 100m sprint is predominantly an anaerobic activity relying heavily on the ATP-PC system for energy supply!
200m Sprint Energy System Interplay
Prior to the race commencing, the primary energy system at play is the aerobic glycolytic system, given the minimal energy demand in the muscles due to the low intensity of Usain's activity while walking and standing still. At this point, he is maintaining a steady state as the supply of oxygen is meeting the demand for oxygen. However, as he moves onto the starting blocks, immediate physiological responses begin in anticipation, leading to an increase in heart rate. When the race starts, the explosive movements required at the start and the maximal intensity from the beginning lead to the dominance of the ATP-PC energy system. This system is favored because it can rapidly supply energy from the chemical stores already present in the muscles. During the initial 100 meters (first 10 seconds), this system is the most prevalent, with peak power occurring around 5 seconds into the race. As the phosphocreatine (PC) stores in the muscles start to deplete quickly, anaerobic glycolysis becomes the predominant energy system after 10 seconds. This system has the ability to regenerate 2 ATP from each glycogen molecule, and due to its rapid resynthesis and ongoing physiological responses (such as an increase in ventilation and cardiac output), it remains the primary energy system until the race concludes at 19 seconds.
While the aerobic energy system does provide some energy required, it is not a significant amount due to the high power and resynthesis rate needed. A steady state is also not achieved because the oxygen supply cannot meet the oxygen demand, given the short duration (19 seconds) and continuous sprint at maximum intensity.
After the race, the workload decreases significantly, but Usain Bolt continues to take deep breaths as he experiences oxygen debt/EPOC. He needs to replenish the energy used during anaerobic work, from both the ATP-PC energy system and the anaerobic glycolytic energy system.