Summary
Five men were studied during exercise to exhaustion on an electrically braked cycle ergometer at 70% of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVq0xe9tqqrpepC0xbbL8F4rqqrFfpeea0xe9sq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0Firpepe0de9vr0-vr% 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaKaaGkqadAfaga% GaaOWaaSbaaSqaaiaab+eadaWgaaqccawaaiaabkdacaqGGaGaaeyB% aiaabggacaqG4baameqaaaWcbeaaaaa!3C9E!\[\dot V_{{\text{O}}_{{\text{2 max}}} } \]. The four experimental treatments were as follows: fasted for 36 h (A); fasted (36 h) and refed with glucose (B) or glycerol (C); postabsorptive (overnight fast, D). In B and C the subjects were given a drink containing glucose or glycerol (lg per kg body weight) 45 min before starting exercise. A placebo drink was given 45 min before exercise on treatments A and D. Despite an increased availability of circulating free fatty acids, β-hydroxybutyrate and glycerol exercise time to exhaustion was significantly lower after fasting (treatment A 77.7±6.8 min) compared with treatment D (119.5±5.8 min). Refeeding with glucose or glycerol did not significantly improve performance (92.4±11.8 min and 80.8±3.6 min respectively) compared with treatment A and lowered circulating levels of FFA and β — HB during exercise compared with A. Despite the probability of low liver glycogen levels after fasting, none of the subjects became hypoglycaemic (blood glucose <4 mmol · l−1) during exercise and their blood lactate concentrations were not high at exhaustion. Plasma levels of branched chain amino acids (BCAA) decreased progressively during exercise on treatments A, B and C and were considerably lower at exhaustion compared with treatment D. Falling plasma concentrations of BCAA during prolonged exercise may be implicated in the generation of central fatigue.
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Maughan, R.J., Gleeson, M. Influence of a 36 h fast followed by refeeding with glucose, glycerol or placebo on metabolism and performance during prolonged exercise in man. Europ. J. Appl. Physiol. 57, 570–576 (1988). https://doi.org/10.1007/BF00418464
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DOI: https://doi.org/10.1007/BF00418464