Are the reductions in triacylglycerol and insulin levels after exercise related?

Moderate exercise improves insulin sensitivity and reduces triacylglycerol (triglyceride; TG) concentrations. We hypothesized that changes in insulin sensitivity are an important determinant of exercise-induced changes in postprandial TG concentrations. Altogether, 38 men and 43 women, all of whom were normotriglyceridaemic and normoglycaemic, each underwent two oral fat tolerance tests with different pre-conditions: control (no exercise) and prior exercise (90min of exercise at 60% of maximal O₂ uptake the day before). Venous blood samples were obtained in the fasting state and for 6h after a high-fat mixed meal. In the control trial there were significant correlations between log fasting TG concentration and log fasting insulin concentration (r = 0.42, P < 0.0005) and between log postprandial TG response (area under the curve) and log postprandial insulin response (r = 0.48, P < 0.0005). Prior exercise reduced the fasting TG concentration by 18.2±2.2% (mean±S.E.M.) (P < 0.0005), the postprandial TG response by 21.5±1.9% (P < 0.0005), the fasting insulin concentration by 3.8±3.1% (P < 0.01) and the postprandial insulin response by 11.9±2.5% (P < 0.0005). However, there was no relationship between the exercise-induced changes in log fasting TG and log fasting insulin (r = 0.08, P = 0.50), nor between the exercise-induced changes in log postprandial TG response and log postprandial insulin response (r = 0.04, P = 0.70). These data suggest that the reductions in fasting and postprandial TG levels elicited by a session of moderate-intensity exercise are not mediated by an increase in insulin sensitivity.