Postmarathon paradox: insulin resistance in the face of glycogen depletion

Am J Physiol. 1996 Feb;270(2 Pt 1):E336-43. doi: 10.1152/ajpendo.1996.270.2.E336.

Abstract

Acute physical exercise enhances insulin sensitivity in healthy subjects. We examined the effect of a 42-km marathon run on insulin sensitivity and lipid oxidation in 19 male runners. In the morning after the marathon run, basal serum free fatty acid concentration was 2.2-fold higher, muscle glycogen content 37% lower (P < 0.01), glycogen synthase fractional activity 56% greater (P < 0.01), and glucose oxidation reduced by 43% (P < 0.01), whereas lipid oxidation was increased by 55% (P < 0.02) compared with the control study. During euglycemic-hyperinsulinemic 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 aerobic power (Vo2peak; r = 0.61, P < 0.05). Vo2peak correlated positively with basal lipid oxidation (r = 0.57, P < 0.05). In conclusion, 1) after the marathon run, probably because of increased lipid oxidation, the insulin-stimulated glucose disposal is decreased despite muscle glycogen depletion and the activation of glycogen synthase; 2) the contribution of lipid oxidation in energy expenditure is increased in proportion to physical fitness; 3) these adaptations of fuel homeostasis may contribute to the maintenance of physical performance after prolonged exercise.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Blood / metabolism
  • Energy Metabolism
  • Glucose / metabolism
  • Glucose Transporter Type 4
  • Glycogen / deficiency*
  • Glycogen / metabolism
  • Glycogen Synthase / genetics
  • Glycogen Synthase / metabolism
  • Humans
  • Insulin Resistance*
  • Lipid Metabolism
  • Magnetic Resonance Imaging
  • Male
  • Monosaccharide Transport Proteins / genetics
  • Monosaccharide Transport Proteins / metabolism
  • Muscle Proteins*
  • Muscles / anatomy & histology
  • Muscles / metabolism
  • Oxidation-Reduction
  • Physical Endurance*
  • RNA, Messenger / metabolism
  • Running*

Substances

  • Glucose Transporter Type 4
  • Monosaccharide Transport Proteins
  • Muscle Proteins
  • RNA, Messenger
  • SLC2A4 protein, human
  • Glycogen
  • Glycogen Synthase
  • Glucose