Effects of Muscle CHO-Loading Manipulations on Hormonal Responses During Prolonged Exercise

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Abstract
This study examined the effects of a pre-experimental period of muscle carbohydrate (CHO)-loading manipulations followed by a 24-h CHO-poor diet, intended to increase muscle glycogen content and reduce hepatic glycogen levels, on substrate and endocrine reponses during a period of prolonged exercise. Seven subjects pedaled a cycle ergometer for 70 min at 64% leg .ovrhdot.VO2 max [maximum O2 consumption] after normal CHO intake (CHON) and after leg muscle CHO loading (CHOL), both of these procedures being followed by period of arm exercise (70 min; 70% arm .ovrhdot.VO2 max) and 24 h CHO-poor intake. CHON, as compared to CHOL condition, resulted in greater blood concentrations of free fatty acids (1.8 vs. 1.3 mmol .cntdot. l-1), glycerol (0.41 vs 0.28 mmol .cntdot. l-1), norepinephrine (2.2 vs. 1.5 ng .cntdot. ml-1), epinephrine (0.90 vs. 0.27 ng .cntdot. ml-1) and cortisol (47 vs. 23 g .cntdot. dl-1) at min 70 of exercise. Insulin concentrations during exercise showed a strong tendency to be lower in CHON than in CHOL condition, although the differences were not significant. There were no significant differences between the 2 conditions in blood glucose, lactate and glucagon concentrations. Muscle CHO-loading manipulations intended to specifically increase the muscle glycogen content are associated with the difference in metabolic adaptation and hormonal changes during exercise.