POST-MARATHON PARADOX IN IDDM - UNCHANGED INSULIN SENSITIVITY IN SPITE OF GLYCOGEN DEPLETION

Acute physical exercise usually enhances insulin sensitivity. We exami ned the effect of a competitive 42 km marathon run on glucose uptake a nd lipid oxidation in 7 runners with insulin-dependent diabetes mellit us (IDDM), aged 36 +/- 3 yr, BMI 23.9 +/- 0.5 kg m(-2), VO2max 46 +/- 1 ml kg(-1) min(-1), HbA(1c) 7.7 +/- 0.3 %, duration of diabetes 16 +/ - 5 yr, runtime 3 h 47 +/- 8 min. On the marathon day, they reduced pr e-race insulin doses by 26 +/- 8 %, and ingested 130 +/- 33 g carbohyd rate before, 91 +/- 26 g during, and 115 +/- 20 g after the race. Duri ng the run, blood glucose concentration fell from 14.4 +/- 2.0 to 7.4 +/- 3.0 mmol l(-1) (p < 0.05) and serum insulin from 51 +/- 8 to 33 +/ - 8 pmol l(-1) (p < 0.05). Serum NEFA increased by 4-fold (p < 0.05), but fell to the normal level by next morning. Muscle glycogen content was 56 % lower (p < 0.05) and glycogen synthase fractional activity 40 % greater (p < 0.05) in the morning after the marathon as compared to the resting control day. In spite of glycogen depletion, whole body g lucose disposal (euglycaemic insulin clamp) was unchanged, while gluco se oxidation (indirect calorimetry) was decreased by 49% (p < 0.05) an d lipid oxidation increased by 41 % (p < 0.01). There was an inverse c orrelation between the rates of lipid oxidation and glucose uptake aft er the marathon (r = -0.75; p < 0.05). In conclusion: after successful ly managed marathon running in patients with IDDM, insulin sensitivity was not increased in spite of low glycogen content and enhanced glyco gen synthase activity after marathon, probably because of increased li pid oxidation.