Exercise is a major physiological challenge to the body, affecting all the main body systems. An accompanying increase in muscle metabolic rate results in an increase in O2 demand and a requirement for an increased rate of removal of CO2 and other metabolites, including lactic acid and ketone bodies. Exercise thus requires substantial increases in muscle blood flow with maintenance of mean arterial pressure (MAP). In addition, despite the increased rate of energy metabolism, normoglycaemia must be preserved. Finally, exercising muscle generates a large amount of heat, yet core temperature must be controlled.