Metabolic adaptation to prolonged exercise in severely obese subjects.

In investigating the metabolic adaptation to prolonged exercise in markedly obese subjects, we compared blood glucose, plasma lactate, free fatty acids, insulin and glucagon concentrations during 3 h of treadmill exercise in nine severely obese male patients (OB) (weight excess 84 +/- 7 per cent of their ideal body weight) and in nine healthy controls (C). Speed and slope of treadmill were selected to give a similar oxygen consumption in both groups (OB: 1.61 +/- 0.08 1/min; C: 1.72 +/- 0.07 1/min). Under these conditions, heart rate was similar in both groups, whereas ventilation was significantly lower in overweight subjects. In obese patients, plasma free fatty acid (FFA) levels were higher in the basal state (OB: 740 +/- 43 mumol/l; C: 602 +/- 40 mumol/l, 2 P less than 0.05) but showed a lower increase during the exercise period (OB: + 576 +/- 135 mumol/l; C: + 1071 +/- 100 mumol/l, 2 P less than 0.02). This impaired FFA mobilization was related to significantly higher insulin (IRI) levels throughout the exercise period as shown by the regression line of exercise-induced FFA increase (y, mumol/l) vs mean plasma IRI during exercise (x, microU/ml): y = 1238 - 60 x, r = -0.709, 2 P less than 0.001. Lack of glucagon increase could also contribute to the lower rise of FFA in obese subjects. A correspondingly increased contribution of carbohydrates to the energy supply is suggested by a significant decline in blood glucose and higher lactate plasma concentrations during the second half of the exercise period in overweight patients. These abnormalities could represent a metabolic limitation for performing prolonged exercise in markedly obese patients.