ABSTRACT
Most exercise scientists would agree that the physiological determinants of peak endurance performance include the capacity to transport oxygen to the working muscle, diffusion from the muscle to the mitochondria, energy production and force generation, all infl uenced by signals from the central nervous system. In general, the capacity of the pulmonary system far exceeds the demands required for ventilation and gas exchange during exercise. Endurance training induces large and signifi cant adaptations within the cardiovascular, musculoskeletal and haematological systems. However, the structural and functional properties of the lung and airways do not change in response to repetitive physical activity and, in elite athletes, the pulmonary system may become a limiting factor to exercise at sea level and altitude. As a consequence to this respiratory paradox, highly trained athletes may develop intrathoracic and extrathoracic obstruction, expiratory fl ow limitation, respiratory muscle fatigue and exercise-induced hypoxaemia. All of these maladaptations may infl uence performance.
INTRODUCTION
There is general consensus that the capacity of the respiratory system is overbuilt for the demands placed on ventilation and gas exchange by highintensity exercise.1 For all but the highly trained, the limiting factor to exercise performance at sea level is the capacity for maximal oxygen transport to the working muscle. With training, structural and functional adaptations occur in the cardiovascular and musculoskeletal systems. The stresses placed on the chest wall, airways and gas exchange mechanisms by heavy exercise challenge the limits to provide adequate minute ventilation and gas exchange in an environment where the demand exceeds supply. In these instances, the respiratory system is the limiting factor – arterial hypoxaemia ensues and VO2max and performance are affected.
