Abstract
The purpose of this study was to delineate the respective roles of aging and endurance training on glucose disposal. Thirty-two subjects (16 middle-aged men: 8 cyclists [MAcy], and 8 sedentary men [MAsed] and 16 young men: 8 cyclists [Ycy] and 8 sedentary men [Ysed]) were compared in this study. After overnight fasting, glucose was administered intravenously (0.5 g · kg −1, 30% solution) and insulin-glucose interactions were assessed by measuring indices of insulin sensitivity (SI) and glucose effectiveness (Sg) using Bergman's minimal model. Sg includes basal insulin effectiveness (BIE) and glucose effectiveness at zero insulin (GEZI). Endurance training improved SI and Sg in all subjects, regardless of age ( P < .05), but an increase in GEZI was found only in young men ( P < .05). An effect of aging was found in sedentary subjects, who exhibited a lower SI ( P < .05) when older. However, this effect disappeared with training, in which SI was nearly identical in young and middle-aged subjects. There was a correlation between SI and ο 2max in middle-aged men ( r = .76, P < .01). These data suggest that the higher glucose uptake in endurance-trained male cyclists was mostly attributable to an increase in non—insulin-dependent glucose uptake in the young men and to an increase in its insulin-dependent component in the middle-aged men.
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