Influence of diet and training on the metabolic responses to maximal exercise in man
thesisposted on 01.02.2013, 09:21 by Stephen A. Wootton
The aim of the studies reported in this thesis was to use an all-out cycle ergometer test (the Anaerobic Work Test - AWTl as a laboratory testl of fatigue during truly maximal dynamic exercise in the attempt to determine il how the body copes with the challenge of maximal exercise and iil what factors govern the ability of an individual to perform maximal exercise. Whilst differences in musculature accounted for a major portion of the variance in the ability to perform maximal cycle ergometer exercise, much of the remaining variance may be attributable to differences in training status. The differences in the ability to generate power over the AWT observed between male and female subjects could be principally attributed to differences in body size and musculature. Although there was little'relationship between functional capacity and the aerobic capacity of the individual, an enhanced ability to generate power could also be associated with a high aerobic capacity. Maximal cycle ergometer training was found to result in marked improvements in the ability to perform maximal exercise, whilst endurance training neither impaired nor enhanced performance. The ability to perform a second bout of maximal exercise was found to be dependent apon the duration of recovery between bouts, although not influenced by alterations in either carbohydrate-status or blood acid-base status. Attempts to perform repeated 65 bouts of maximal exercise with either 30 or 60s recovery resulted in pronounced fatigue-induced decrements in performance and marked increases in blood lactate. Peak plasma adrenaline, plasma noradrenaline, blood lactate and blood glucose concentrations following 6s of maximal exercise averaged 1.7 nmolll, 3.30 nmolll, 2.68 mmolll and 4.63 mmolll respectively whilst the corresponding values after 30s averaged 4.31 nmolll, 12.91 nmolll, 11.93 mmolll and 5.35 nmol/l./on the basis of the changes in muscle metabolites over the AWT, the greatest power outputs generated 6ver the initial seconds of maximal exercise were associated with the greatest rates of ATP turnover from non-oxidative metabolism (7.7-12.4 mmollkg dm/sl and was the p=d,uct of maximal rates of phosphagenolysis and glycolysis. The rate of ATP \, turnover appeared to decrease in association with a reduction in power output as exercise preceded, primarily as a result of a reduction in the rate of CP utilisation. ATP turnover over 30s of maximal exercise ranged from 5.15-7.59 mmol/kg dm/s. The metabolic condition following 30s of maximal elercise wa~ comparable to that observed following a wide variety of exhaustive high-intensity exercise tasks: muscle ATP, CP and lactate concentrations averaged 13.7, 28.8 and 89.3 mmol/kg dm respectively. Whilst interval training resulted in an enhanced ability to perform single and repeated bouts of maximal exercise, the imporvements in performance could not be attributed to a greater provision of energy from non-oxidative metabolism. The storage and utilisation of CP and ATP, and the accumulation of lactate, were unaltered; however, glycogen storage and mobilisation of glucosyl units increased by 341 and 631 respectively resulting in a greater accumulation of hexose monophosphates. A metabolic basis of muscular fatigue during maximal cycle ergometer exercise, and the influence of training on these processes, was then discussed. 'The accumulation of hydrogen ions within the working muscle was proposed as a common factor that would influence both the rate at which ATP was resynthesised and utilised.
- Sport, Exercise and Health Sciences