INTRAVENOUS GLUCOSE-TOLERANCE TEST-DERIVED GLUCOSE EFFECTIVENESS IN PHYSICALLY TRAINED HUMANS

Glucose effectiveness (S(G)) and insulin sensitivity of sedentary and physically trained males were estimated by the minimal model approach. Trained subjects, who ran 86 +/- 10 km/wk and had 37% higher maximal oxygen consumption than that of sedentary subjects (56.2 +/- 1.2 vs. 40.9 +/- 1.4 ml.kg-1.min-1, P < 0.01), were studied 16 h and 1 wk after their last training session. After overnight fasting, glucose was administered intravenously (300 mg/kg body wt) within 2 min, and insulin was infused (approximately 13-20 mU/kg given over 5 min) from 20 to 25 min after administration of glucose. Glucose disappearance constant values as an estimate of glucose tolerance were significantly higher in trained subjects after 16 h and 1 wk of their training session (3.29 +/- 0.48 and 3.60 +/- 0.64%/min) than in sedentary subjects (1.92 +/- 0.30%/min, P < 0.05). Insulin sensitivity in trained subjects measured after 16 h and 1 wk of their last training session (26.2 +/- 4.4 and 24.3 +/- 6.0 x 10(-5) min-1.pM-1) was also higher than that of sedentary subjects (10.3 +/- 1.2 x 10(-5) min-1.pM-1, P < 0.05). S(G), the ability of glucose itself to increase peripheral glucose uptake and suppress hepatic glucose output, was significantly higher in trained subjects after 16 h and 1 wk of their last training session (0.028 +/- 0.003 and 0.030 +/- 0.004/min) than in sedentary subjects (0.017 +/- 0.002/min, P < 0.05). Non-insulin-dependent component of S(G) (GEZI) was higher in trained subjects after 16 h and 1 wk of their last training session (0.021 +/- 0.003, 0.023 +/- 0.003/min) than sedentary subjects (0.013 +/- 0.002/min, P < 0.05). However, the basal insulin component Of SG was similar among the three groups (0.007 +/- 0.003 and 0.007 +/- 0.002/min for trained subjects 16 h and 1 wk after their last training session and 0.004 +/- 0.001/min for sedentary subjects, P > 0.05). Thus S(G), Particularly GEZI, is higher in trained subjects than in sedentary subjects.