Influence of Fatigue on the Determinants of Endurance Exercise Performance

Abstract

Both psychological and physiological factors contribute to exercise performance at different exercise intensities. Measuring the characteristic physiological responses of an athlete at different exercise intensities makes it possible to predict the tolerance for exercise at a given work rate using the so-called power-duration relationship. While estimating athletic performance in this way is widely practiced, it is possible that the physiological responses typically measured at a given work rate are altered by factors relating to fatigue during long duration events. The purpose of this thesis was to investigate the plasticity of the power-duration relationship in the face of psychological stress and prolonged fatiguing exercise. Firstly, the thesis showed that severe-intensity time trial performance was not different after a prolonged cognitive function task compared to control, in either untrained men or in competitive athletes. Secondly, the thesis investigated the effects of prolonged, fatiguing endurance exercise on the power-duration relationship. Initially, the power asymptote of the hyperbolic power-time relationship critical power (CP) or end test power and the curvature constant of this relationship Wʹ or work done above end test power were not different and highly correlated when estimated from two different 3-min all-out exercise tests (3MT) preceded by 2 h of heavy-intensity exercise. After 2 h of heavy-intensity exercise both EP and WEP were lower compared to no prior exercise (control). Importantly, critical power and W′ established from three separate severe-intensity predication trials conducted immediately following 2 h of heavy-intensity exercise did not differ from F-EP and F-WEP established from a 3MT. F-EP and F-CP as well as F-W′ and F-WEP was ~11% and ~20% lower than C-EP and C-WEP, respectively. Furthermore, C-EP estimated from a 3MT was not different when established after 40 min, 80 min and 2 h of prior heavy-intensity exercise consuming carbohydrates. However, EP estimated after 2 h of heavy-intensity exercise without carbohydrate consumption was lower than all. C-WEP was higher compared to WEP estimated after 80 min of prior heavy-intensity exercise, 2 h of heavy-intensity exercise with and without carbohydrate consumption but was not different compared to estimates established after 40 min of prior heavy-intensity exercise. Firstly, this thesis has demonstrated that time trial performance is not affected by the psychological stress induced by prolonged cognitive tasks in trained athletes. Secondly, it has been demonstrated that prolonged heavy-intensity exercise alters both CP and W′. Thirdly, the results showed that the 3MT is a reliable and valid test to estimate CP and W′ in a fatigued state and that the decrease in CP, but not W′, after prolonged fatiguing exercise can be mitigated by the consumption of carbohydrates.