FREE FATTY-ACID METABOLISM IN AEROBICALLY FIT INDIVIDUALS

The impact of aerobic fitness level on the production and disposal of serum free fatty acids was investigated in 26 normal young volunteers. The fitness level was ascertained by history and confirmed by determi nation of maximal aerobic capacity. Energy expenditure and substrate o xidation at rest were measured with indirect calorimetry. Free fatty a cid turnover was measured with an infusion of [C-14]palmitic acid. Ail tests were done greater than or equal to 48 h after the last bout of exercise. The sedentary (SED) volunteers had higher rates of systemic delivery of fatty acids than aerobically fit (FIT) individuals (532 +/ - 53.4 vs. 353 +/- 62.3 mu mol/min; P = 0.05). This difference was acc entuated when the values were normalized to fat-free mass (9.2 +/- 0.8 and 5.9 +/- 0.98 mu mol.kg(-1).min(-1) for SED and FIT, respectively) . Fatty acid oxidation was similar between FIT and SED volunteers in a bsolute numbers (209 +/- 25 vs. 202 +/- 21 mu mol/min, respectively; N S) as well as when normalized to fat-free mass (3.8 +/- 0.9 vs. 3.6 +/ - 1.4 mu mol.kg(-1).min(-1), respectively; NS). In contrast, the nonox idative disposal of serum fatty acids was higher in SED (330 +/- 46.1 mu mol/min) than in FIT individuals (144 +/- 52 mu mol/min; P = 0.026) . Thus, the ratio of nonoxidative to oxidative disposal rates of fatty acids was higher in SED than in FIT individuals (1.65 +/- 0.29 vs. 0. 75 +/- 0.17; P = 0.021). The data support the hypothesis that high aer obic fitness level is associated with a low rate of systemic delivery of fatty acids at rest. Nevertheless, subjects with high aerobic fitne ss levels have fat oxidation at the same rate as unfit individuals.