Impaired glucose tolerance after endurance exercise is associated with reduced insulin secretion rather than altered insulin sensitivity

Abstract

Paired frequently sampled intravenous glucose tolerance tests (FSIGT) were performed on five highly trained athletes within 2 hours of completing a 6-day ultramarathon run (E) and after 2 weeks of complete rest (R). Severe exercise increased free fatty acid (FFA) levels (E 1.2 ± 0.16 v 0.42 ± 0.07 mmol/L, P < .01) and norepinephrine levels (E 573 ± 141 v 224 ± 33 pg/mL, P < .01), with only moderate reductions in glucose tolerance (glucose disappearance [Kg] E 1.06 ± 0.2 v R 1.7 ± 0.3 min-1 × 102, P < .05). The minimal model analysis of FSIGT data using the method of Bergman et al (Endocr Rev 6:45-86, 1985) showed a reduced second-phase insulin secretion ([Φ2] E 5.2 ± 1.3 v 13 ± 2.2 μU/mL · m..