Effects of a 24-h CHO-Poor Diet on Metabolic and Hormonal Responses During Prolonged CHO-Loaded Leg Exercise

Abstract

This study examined the effects of a pre-experimental period of arm exercise followed by a 24-h carbohydrate (CHO)-poor intake, intended to reduce initial hepatic glycogen levels, on substrate and endocrine responses during prolonged CHO-loaded leg exercise. Seven subjects pedaled a cycle ergometer for 60 min at 62% V̇O₂ max in the two following conditions: 1) after leg CHO loading followed by a 60-min arm exercise and a 24-h CHO-poor diet (CHO_L+P), and 2) after leg CHO loading only (CHO_L). Greater blood concentrations of free fatty acids (1.2 vs 0.9 mEq·L^-1), glycerol (0.41 vs 0.20 mmol·L^-1), norepinephrine (2.09 vs 1.14 ng·ml^-1), and epinephrine (0.38 vs 0.19 ng·ml^-1) were observed in the CHO_L+P as compared to the CHO_L condition at min 60 of exercise. Insulin concentration was significantly (P < 0.05) lower in the CHO_L+P condition at rest and during exercise. There were no significant differences during exercise between the two conditions in blood glucose, lactate, glucagon, and cortisol concentrations. It is concluded that changes in blood glucose concentration do not solely account for metabolic and hormonal adaptations during prolonged leg exercise and that a pre-experimental period of arm exercise and CHO-poor diet, in spite of an increase in leg muscle glycogen, may provide a stimulus for such adaptations. It is suggested that the liver glycogen content may be involved in the regulatory mechanism.

Key words

glycogen store - norepinephrine - insulin - free fatty acids - glycemia - prolonged exercise in humans