PLASMA LIPIDS AND PLASMA TRIGLYCERIDE CLEARANCE IN ENDURANCE TRAINED ATHLETES

Abstract

These studies investigated the plasma lipid profile of endurance athletes and their ability to clear intravascular triglycerides (TG). Study I was a cross-sectional determination of the relationship between cholesterol fractions and weekly running mileage. Study II examined the relationships between the changes in total and HDL-cholesterol (HDL-C) and body composition during a training program. Study III employed an intravenous fat tolerance test (IVFTT) and a post-heparin TG clearance to indirectly assess lipoprotein lipase activity in three different training groups. Finally, Study IV examined the effects of a 12-week training program on TG clearance in trained subjects. In Study I there were significant correlations between HDL-C and percent body fat (r = -0.36, p < .001) and miles run per week (r = 0.50, p < .001), the latter relationship remaining significant when statistically adjusted for age, alcohol consumption, or relative body composition. With the increased weekly running mileage in Study II, HDL-C increased by 5.0 mg/dl (p < .01), and total cholesterol remained unchanged. All components of body composition changed significantly, but only the change in lean weight significantly correlated with the change in HDL-C (r = 0.46, p < .025). In Study III the rate of Intralipid clearance correlated with fat weight (r = -0.66, p < .001), fasting TG (r = -0.39, p < .05), and V̇O₂ max (r = 0.64, p < .001). The heparin-induced fractional clearance of TG's correlated to V̇O₂ max (r = -0.51, p < .01) and fat weight (r = 0.47, p < .01). While the runners and the untrained subjects were similar in body composition and lipid profile, when divided into groups, the elite runners were leaner, had higher HDL-C (p < .05), and were able to clear Intralipid (p < .01) and plasma TG's (p < .05) faster than the other groups. There was a trend towards a more favorable lipidprofile and enhanced TG clearance in Study IV, but only V̇O₂ max (p < .05) and post-heparin fractional clearance of TG's (p < .05)improved significantly. These data suggest that endurance trained subjects have higher HDL-C, lower TG, and an enhanced capacity to clear the intravascular compartment of TG's. These changes cannot be explained solely by the body composition or diets of the athletes and must be due in part to changes evoked by their chronic training.