Fat Oxidation Rate as a Function of Plasma Lipid and Hormone Response in Endurance Athletes.

Plasma lipid changes during incremental exercise are not well known. The aim of this study was to investigate the relationship among fat oxidation rate, plasma lipids, and hormone concentrations in well-trained athletes. Twenty-six trained triathletes completed a graded cycle ergometer test to exhaustion increasing by 0.5 W.kg(-1) every 10 minutes. Fat oxidation rates were determined using indirect calorimetry. For each individual, maximal fat oxidation (MFO), the intensity at which MFO occurred (Fat(max)), and the intensity at which fat oxidation became negligible (Fat(min)) were determined. Blood samples for lipids and hormones analysis were collected at the end of each stage of the graded exercise test. All variables studied except insulin showed an increase at the end of incremental protocol with respect to basal levels. Free fatty acid reached significant increase at 60%(V) over dot o(2)max and maximal levels at 70%(V) over dotO(2)max. Low-density lipoprotein (LDL) and triglycerides (TG) decreased and showed lowest levels at 60%(V) over dotO(2)max and reaching significant increases after 80%(V) over dot o(2)max. High-density lipoprotein reached significant increase at 60%(V) over dot o(2)max. Adrenaline and noradrenaline increased until the end of the incremental exercise, and significant differences were from 50%(V) over dotO(2)max. These results suggest that exercise intensities are related to plasma lipids levels. In the zone when lipids oxidation is maximal, plasma LDL and TG variation differs from other lipids. These results may have application for the more adequate exercise intensity prescription to maximize the beneficial effects of exercise.