Fatty acid kinetic responses to running above or below the lactate threshold. Kanaley, Jill A., Carl D. Mottram, Paul D. Scanlon, Michael D. Jensen. Endocrine Research Unit, Division of Endocrinology and Metabolism, Pulmonary Function Laboratory, and Division of Pulmonary and Critical Care Medicine, Mayo Clinic, Rochester, Minnesota 55905
APStracts 2:0120A, 1995.
During running exercise above the lactate threshold (LT), it is unknown whether free fatty acid (FFA) mobilization can meet the energy demands for fatty acid oxidation. This study was performed to determine whether FFA availability is reduced during running exercise above the LT as compared to below the LT and to assess whether the level of endurance training influences FFA mobilization. Twelve marathon runners and 12 moderately trained runners ran at a workload that was either above or below their individual LT. Fatty acid oxidation (indirect calorimetry) and FFA release ([1-14C]-palmitate) were measured at baseline, throughout exercise and recovery. Plasma FFA Ra increased during exercise in both groups running above or below the LT, but total FFA availability for 30 minutes of exercise was greater (P < 0.01) in the below LT group (marathon 23 +/- 2, moderate 21 +/- 2 mmol) than in the above LT group (18 +/- 3 and 13 +/- 3 mmol, respectively). Total fatty acid oxidation (indirect calorimetry) greatly exceeded (P < 0.01) circulating FFA availability, regardless of training or exercise group. No statistically significant exercise intensity or training differences in fatty acid oxidation were found (above LT-marathon 71 +/- 12, moderate 64 +/- 17 mmol_30 min-1; below LT-marathon 91 +/- 12, moderate 60 +/- 5 mmol_30 min-1). In conclusion, during exercise above or below LT, circulating FFA cannot meet the oxidative needs and intramuscular triglyceride stores must be utilized. Further marathon training does not enhance effective adipose tissue lipolysis during exercise compared with moderate endurance training. 

Received 5 July 1994; accepted in final form 17 March 1995.
APS Manuscript Number A665-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 March 1995.