The regulation of exercise performance by a complex anticipatory system

Abstract

The present thesis examined the hypothesis that self-paced exercise performance and pacing strategies are regulated by a complex intelligent system in advance of a failure to maintain homeostasis in one or more physiological systems. In the first study, ten trained cyclists performed 20 km cycling time-trials in hot (35°C) and cool (15°C) conditions. The power output was reduced in the heat despite core temperatures that were sub-maximal and not different from those measured in the cool condition. Significantly, the reduction in power output was associated with a lower IEMG activity in the active muscle, suggesting that the brain recruited less muscle even at sub-maximal body temperatures. Thus, self-paced exercise in the heat was regulated in advance of thermoregulatory failure. This model was then applied to conditions where the oxygen content of the air was elevated (yperoxia). Eleven subjects performed 20km time-trails, and it was found that a higher power output was maintained throughput hyperoxic (F₁O₂0.21), and that the IEMG activity was elevated in hyperoxia. The subjective rating of perceived exertion (RPE), measured using the Borg scale, was similar in both this and the first study, despite differences in power output. It was suggested that the RPE may play a mediatory role.