POSTMARATHON PARADOX - INSULIN-RESISTANCE IN THE FACE OF GLYCOGEN DEPLETION

Acute physical exercise enhances insulin sensitivity in healthy subjec ts. We examined the effect of a 42-km marathon run on insulin sensitiv ity and lipid oxidation in 19 male runners. In the morning after the m arathon run, basal serum free fatty acid concentration was 2.2-fold hi gher, muscle glycogen content 37% lower (P < 0.01), glycogen synthase fractional activity 56% greater (P < 0.01), and glucose oxidation redu ced by 43% (P < 0.01), whereas lipid oxidation was increased by 55% (P < 0.02) compared with the control study. During euglycemic-hyperinsul inemic clamp, whole body glucose disposal was decreased by 12% (P < 0. 01) because of a 36% lower glucose oxidation rate (P < 0.05), whereas the rate of lipid oxidation was 10-fold greater (P < 0.02) than in the control study. After the marathon, muscle glycogen content correlated positively with lipid oxidation (r = 0.60, P < 0.05) and maximal aero bic power (V-o2peak; r = 0.61, P < 0.05). V-o2peak correlated positive ly with basal lipid oxidation (r = 0.57, P < 0.05). In conclusion, 1) after the marathon nm, probably because of increased lipid oxidation, the insulin-stimulated glucose disposal is decreased despite muscle gl ycogen depletion and the activation of glycogen synthase; 2) the contr ibution of lipid oxidation in energy expenditure is increased in propo rtion to physical fitness; 3) these adaptations of fuel homeostasis ma y contribute to the maintenance of physical performance after prolonge d exercise.