What is Endurance performance?
Endurance performance is determined by the capacity of the athlete's heart to pump unusually large volumes of blood and oxygen to the muscles. This allows the muscles to achieve higher work rates before they outstrip the available oxygen supply, developing skeletal muscle anaerobiosis (a reduced oxygen content of the cells). Training increases 'cardiovascular fitness', especially by increasing the body's maximum capacity to consume oxygen (VO2 max). This effect results from an increased maximum capacity of the heart to pump blood (the cardiac output) and an enhanced capacity of the muscles to consume oxygen. These adaptations delay the onset of skeletal muscle anaerobiosis during vigorous exercise, thereby reducing blood lactate concentrations in muscle and blood at all exercise intensities above the so-called 'anaerobic threshold' and so allowing the exercising muscles to continue contracting for longer, at higher intensities, before the onset of fatigue. In addition, these changes increase the capacity of the muscles to use fat as a fuel during exercise, thereby enhancing endurance performance.