Cellular respiration is the process by which your cells process energy. Anything your body does, including involuntary processes such as digestion and breathing, requires energy, but these demands increase during exercise. Cellular respiration can be done aerobically or anaerobically, which means with or without oxygen. Since sprinters exert themselves to their limit in a race, they'll be using anaerobic respiration, which fatigues the body faster.
The key ingredient in cellular respiration is adenosine triphosphate. This nucleotide is created and consumed in the body many millions of times per day. ATP consists of three phosphates in a carbon framework and is produced by the mitochondria using fats, proteins, amino acids and carbohydrates absorbed from your food. Breaking down ATP releases energy, up to 7.3 kilocalories of energy per mole. This energy can be used by muscle cells to contract, or by any other cells as they undergo their specific functions.
Oxygen is an oxidative electron acceptor; this means it aids the process of ATP consumption. After a phosphate is broken off in the presence of oxygen, the ATP molecule becomes adenosine diphosphate, or ADP, which can be reused by the mitochondria very easily. There is a limit to how much oxygen your body can transport through the bloodstream for cellular respiration, known as your VO2 max. Above the VO2 max, any ATP will be produced anaerobically using a different cellular process.
Sprinting Above the VO2 Max
Sprinters pushing themselves to their absolute limit will quickly extend above their VO2 max. Their heart rate will plateau, and they won't be able to breathe any faster. Above the VO2 max, anaerobic respiration takes over the production of additional ATP to meet the demands of the sprinter's muscles. This process is significantly more complex than aerobic respiration. Your body gets ATP through phosphocreatine and glycolysis instead, without leaving ADP for the mitochondria to reprocess.This makes anaerobic respiration far less efficient; the body will only be able to produce ATP anaerobically for a short time before it fatigues.
Extending Your Thresholds
Your VO2 max is not set in stone; you can strengthen your circulatory and respiratory systems through training and exercise to increase your aerobic threshold, which will decrease the amount of time your body spends above the VO2 max and help you avoid fatigue while sprinting. Interval exercises, or short bursts of high-intensity anaerobic exercise followed by periods of more relaxed aerobic exercise, quickly strengthen the cardiovascular system, giving you a higher VO2 max. With regular interval training, you'll see a noticeable decrease in your fatigue in a few weeks.