Influence of short-term submaximal exercise on parameters of glucose assimilation analyzed with the minimal model

Abstract 

After exercise, glucose uptake in tissues increases by insulin-dependent and -independent mechanisms. We evaluated whether these two effects of exercise on glucose disposal can be detected with the minimal model technique. Seven healthy volunteers were submitted at random order to two frequently sampled intravenous glucose tolerance tests (FSIVGTTs), one at rest and the other 25 minutes after a 15-minute exercise test. This exercise included 5 minutes of increasing workload on a cycloergometer followed by 10 minutes at 85% of the maximal theoretic heart rate. Bergman's minimal model of insulin action was used to analyze the two FSIVGTTs and produced the following parameters: coefficient of glucose tolerance (K_g), ie, the slope of the exponential decrease in glycemia between 4 and 19 minutes after intravenous glucose; insulin sensitivity (S_l); and glucose effectiveness at basal insulin (S_g). S_g was divided into its two components: basal insulin effectiveness ([BIE] S_l × basal insulin) and glucose effectiveness at zero insulin ([GEZI] S_g − BIE). After the exercise bout, subjects had an increased K_g (3.44 ± 0.44 v 2.06 ± 0.28 × 10⁻² · min⁻¹, P < .02), S_l (11.43 ± 1.27 v 6.23 ± 0.97 × 10⁻⁴ μU/mL · min⁻¹, P < .01), and S_g (4.40 ± 0.55 v 2.81 ± 0.36 × 10⁻² · min⁻¹, P < .02). The increase in S_g was mainly explained by a 60% increase in GEZI (3.6 ± 0.57 v 2.25 ± 0.36 × 10⁻² · min⁻¹, P < .02), but also by an increase in BIE (0.80 ± 0.12 v 0.47 ± 0.08 × 10 ⁻² · min⁻¹, P < .05). Thus, a FSIVGTT sensitively detects an acute increase in glucose assimilation after exercise, as demonstrated by an increase in K_g and its two components S_l and GEZI. GEZI seems to provide a measurement of the non—insulin-mediated recruitment of glucose transporters in exercised muscles. In addition, FSIVGTT protocols have to be carefully standardized for previous exercise, since minimal model measurements are sensitive to these acute effects of muscular activity.

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