Insulin sensitivity measured by the minimal model: No associations with fasting respiratory exchange ratio in trained athletes

The aim of this study was to examine the role of fasting insulin concentrat ions and tissue insulin sensitivity on whole-body substrate oxidation in 61 well-trained subjects. Subjects underwent a frequently sampled intravenous glucose tolerance test (FSIVGT) after a 10- to 12-hour overnight fast. Min imal model analysis was used to determine insulin sensitivity (S-i). A week later, fasting (10- to 12-hour) respiratory exchange ratio (RER) was measu red at rest and during exercise at 25%, 50%, and 70% of peak power output ( W-peak). Prior to these measurements, training volume, dietary intake, and muscle fiber composition, substrate concentrations, and enzyme activities w ere determined. The average fasting plasma insulin concentration was 7.3 +/ - 2.4 muU/mL (4.0 to 10.5 muU/mL), and the mean S-i was 14.0 +/- 6.1 x (10( -4) min(-1) . muU(-1) . mL(-1)) (2.6 to 26.3 x 10(-4) min(-1) . muU(-1) . m L(-1)), There was no significant correlation between fasting plasma insulin concentration and S-1 (r = -.14, P = .336) or between these measurements a nd fasting RER, measured at rest and during exercise at 25%, 50%, and 70% W -peak. Only VO2max and the proportion of type 1 muscle fibers were signific antly correlated with S-i (r = .30, P = .045 and r = .34, P = .026, respect ively), and waist-to-hip ratio (WHR) was significantly correlated with fast ing plasma insulin concentration (r = .35, P = .006). In conclusion, S-i an d fasting plasma insulin concentration were not associated with fasting RER at rest and during exercise of increasing intensity in trained athletes wh o have high S-i. Copyright (C) 2001 by W.B. Saunders Company.