We determined the effect of suppressing lipolysis via administration of nicotinic acid (NA) on fuel substrate selection and half-marathon running capacity. In a single-blinded Latin square design, 12 competitive runners completed four trials involving treadmill running until volitional fatigue at a pace based on 95% of personal best half-marathon time. Trials were completed in a fed or overnight fasted state: 1) Carbohydrate (CHO) ingestion before (2 g CHO·kg·BM-1), and during (44 g·h-1) [CFED]; 2) CFED plus NA ingestion [CFED-NA]; 3) fasted with placebo ingestion during [FAST] 4) FAST plus NA ingestion [FAST-NA]. There was no difference in running distance (CFED 21.53 ± 1.07, CFED-NA 21.29 ± 1.69, FAST 20.60 ± 2.09, FAST-NA 20.11 ± 1.71 km) or time to fatigue between the four trials. Plasma free fatty acids (FFA) and glycerol concentrations were suppressed following NA ingestion irrespective of pre-exercise nutritional intake but were higher throughout exercise in FAST compared to all other trials (P<0.05). Rates of whole body CHO oxidation were unaffected by NA ingestion for CFED and FAST, but were lower in FAST compared to CFED-NA (P<0.05). CHO was the primary substrate for exercise in all conditions, contributing 83-91% to total energy expenditure with only a small contribution from fat-based fuels. Blunting the exercise-induced increase in FFA via NA ingestion did not impair intense running capacity lasting ~85 min nor alter patterns of substrate oxidation in competitive athletes. While there was a small, but obligatory use of fat-, the oxidation of CHO-based fuels predominates during half-marathon running.
- high-intensity running
- nicotinic acid
- substrate utilization
- Copyright © 2015, Journal of Applied Physiology