FATTY-ACID KINETIC RESPONSES TO RUNNING ABOVE OR BELOW LACTATE THRESHOLD

During running exercise above the lactate threshold (LT), it is unknow n whether free fatty acid (FFA) mobilization can meet the energy deman ds for fatty acid oxidation. This study was performed to determine whe ther FFA availability is reduced during running exercise above compare d with below the LT and to assess whether the level of endurance train ing influences FFA mobilization. Twelve marathon runners and 12 modera tely trained runners ran at a workload that was either above or below their individual LT. Fatty acid oxidation (indirect calorimetry) and F FA release ([1-C-14]palmitate) were measured at baseline, throughout e xercise, and at recovery. The plasma FFA rate of appearance increased during exercise in both groups, running above or below the LT, but the total FFA availability for 30 min of exercise was greater (P < 0.01) in the below LT group (marathon, 23 +/- 2 mmol; moderate, 21 +/- 2 mmo l) than in the above LT group (18 +/- 3 and 13 +/- 3 mmol, respectivel y). Total fatty acid oxidation (indirect calorimetry) greatly exceeded circulating FFA availability, regardless of training or exercise grou p (P < 0.01). No statistically significant exercise intensity or train ing differences in fatty acid oxidation were found (above LT: marathon , 71 +/- 12, moderate, 64 +/- 17 mmol/30 min; below LT: marathon 91 +/ - 12, moderate, 60 +/- 5 mmol/30 min). 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 ex ercise compared with moderate endurance training.