Nothing happens without the expenditure of energy. Humans use the energy in ATP to drive all of the reactions in the body, either directly by using the energy of the phosphate bond between the second and third phosphates of ATP, or by siphoning energy from chemical and electrical gradients produced by ATP hydrolysis. Before ATP can be utilized it has to be produced. ATP is made anaerobically through glycolysis, and aerobically using oxidative phosphorylation in mitochondria. Once made, its concentration can be buffered in many cells through the creatine kinase reaction, with phosphocreatine contributing its phosphate to ADP to maintain the ATP concentration during periods of high energy expenditure. Energy expenditure is not solely dependent on the supply of ATP, however. The removal of the products of energy use, especially inorganic phosphate, are as important to function as the supply of ATP. The different components of ATP production and buffering, and inorganic phosphate removal, directly influence human athletic performance. The different phases that phosphocreatine, glycolysis, and oxidative phosphorylation control are graphically demonstrated in the rate of running in world track records as a function of the log of the distance run.

Energetics of human performance

The most interesting races on the track take place when someone goes out fast, takes an early lead, and then is run down by the field. Will the leader hang on, or will someone catch up with a strong finishing kick? The factors involved in human performance include ability, training and motivation. For most people, psychological limitations play a major role in reducing performance. Training and experience produce the confidence needed to reach the fastest time possible. World class runners are “world class” precisely because they have overcome the psychological limitations on performance, and their racing is only limited by physiological factors. Physiological factors include some elements that can be controlled, like rest and diet, and others that cannot, like leg length. The variable elements ultimately involve energy. How much energy is available to drive the myosin ATPase reactions that move muscle? At what rate are the energy supplies used? Can the energy supplies be increased to prolong top flight performance? The starting point for answers to these questions is to look at the relation of the rate of running of world track records as a function of the race distances in Figure 4.1.