The Effect of Substrate Utilization, Manipulated by Nicotinic Acid, on Excess Postexercise Oxygen Consumption

Increased fat oxidation during the recovery period from exercise is thought to be a contributing factor for excess postexercise oxygen consumption (EPOC). In an attempt to study the effect of serum free fatty acid (FFA) availability during exercise and recovery on the EPOC, nicotinic acid, a potent inhibitor of FFA mobilization from adipose tissue, was administered to five trained male cyclists prior to, during, and after a bout of cycling at 65 % VO₂max. In the nicotinic acid trial, a 500 mg dose of nicotinic acid was ingested prior to exercise, and 100 mg doses were ingested at 15, 30, and 45 min exercise, and 30 min recovery. The cyclists also completed a trial under control conditions. Serum FFA, serum glycerol, RER and VO₂ were monitored during rest, exercise, and recovery, each of which was 1-h in duration. Nicotinic acid ingestion prevented the increase in serum FFA that occurred during exercise in the control trial. FFA levels during the nicotinic acid trial were significantly lower than control values during both exercise and recovery. Serum glycerol levels were also significantly lower during exercise in the nicotinic acid trial, indicative of a reduction in lipolysis. RER was mot significantly different at rest or during exercise; however, RER values were significantly lower during recovery in the control trial, indicative of greater fat oxidation. For both treatments, postexercise VO₂ remained elevated above resting levels at the completion of the 1 -h recovery period. However, the magnitude of EPOC was significantly reduced after FFA blockade with nicotinic acid (3.4 ± 0.6 l vs 5.5 ± 0.7 l). These results support the hypothesis that increased FFA metabolism during exercise and recovery is an important contributing factor to the magnitude of EPOC.

Key words

Metabolism - free fatty acids - lipolysis - respiratory exchange ratio - niacin