Endurance training has little effect on active muscle free fatty acid, lipoprotein cholesterol, or triglyceride net balances

Abstract

We evaluated the hypothesis that net leg total FFA, LDL-C, and TG uptake and HDL-C release during moderate-intensity cycling exercise would be increased following endurance training. Eight sedentary men (26 ± 1 yr, 77.4 ± 3.7 kg) were studied in the postprandial state during 90 min of rest and 60 min of exercise twice before (45% and 65% V̇o2 peak) and twice after 9 wk of endurance training (55% and 65% posttraining V̇o2 peak). Measurements across an exercising leg were taken to be a surrogate for active skeletal muscle. To determine limb lipid exchange, femoral arterial and venous blood samples drawn simultaneously at rest and during exercise were analyzed for total and individual FFA (e.g., palmitate, oleate), LDL-C, HDL-C, and TG concentrations, and limb blood flow was determined by thermodilution. The transition from rest to exercise resulted in a shift from net leg total FFA release (−44 ± 16 μmol/min) to uptake (193 ± 49 μmol/min) that was unaffected by either exercise intensity or endurance training. The relative net leg release and uptake of individual FFA closely resembled their relative abundances in the plasma with ∼21 and 41% of net leg total FFA uptake during exercise accounted for by palmitate and oleate, respectively. Endurance training resulted in significant changes in arterial concentrations of HDL-C (49 ± 5 vs. 52 ± 5 mg/dl, pre vs. post) and LDL-C (82 ± 9 vs. 76 ± 9 mg/dl, pre vs. post), but there was no net TG or LDL-C uptake or HDL-C release across the resting or active leg before or after endurance training. In conclusion, endurance training favorably affects blood lipoprotein profiles, even in young, healthy normolipidemic men, but muscle contractions per se have little effect on net leg LDL-C, or TG uptake or HDL-C release during moderate-intensity cycling exercise. Therefore, the favorable effects of physical activity on the lipid profiles of young, healthy normolipidemic men in the postprandial state are not attributable to changes in HDL-C or LDL-C exchange across active skeletal muscle.