title: Carbohydrate dependence during prolonged simulated cycling time trials.
abstract: OBJECTIVE
  We determined the effect of suppressing lipolysis via administration of Nicotinic acid (NA) and pre-exercise feeding on rates of whole-body substrate utilisation and cycling time trial (TT) performance.
  
  
  METHODS
  In a randomised, single-blind, crossover design, eight trained male cyclists/triathletes completed two series of TTs in which they performed a predetermined amount of work calculated to last ~60, 90 and 120 min. TTs were undertaken after a standardised breakfast (2 g kg(-1) BM of carbohydrate (CHO)) and ingestion of capsules containing either NA or placebo (PL).
  
  
  RESULTS
  Plasma [free fatty acids] were suppressed with NA, but increased in the later stages of TT90 and TT120 with PL (p < 0.05). There was no treatment effect on time to complete TT60 (60.4 ± 4.1 vs. 59.3 ± 3.4 min) or TT90 (90.4 ± 9.1 vs. 89.5 ± 6.6 min) for NA and PL, respectively. However, TT120 was slower with NA (123.1 ± 5.7 vs. 120.1 ± 8.7 min, p < 0.001), which coincided with a decline in plasma [glucose] during the later stages of this ride (p < 0.05). For TTs of the same duration, the rates of whole-body CHO oxidation were unaffected by NA, but decreased with increasing TT time (p < 0.05). CHO was the predominant substrate for all TTs contributing between 83 and 94 % to total energy expenditure, although there was a small use of lipid-based fuels for all rides.
  
  
  CONCLUSIONS
  (1) NA impaired cycling TT performance lasting 120 min, (2) cycling TTs lasting from 60 to 120 min are CHO dependent, and (3) there is an obligatory use of lipid-based fuels in TTs lasting 1-2 h.
authors: Mary MacKillop Institute for Health Research, Centre for Exercise and Nutrition, Australian Catholic University, Melbourne, VIC, 3065, Australia.
authors: Samuel L
authors: SL
authors: Torrens
authors: Department of Physical Performance, Norwegian School of Sport Sciences, Oslo, Norway.
authors: José L
authors: JL
authors: Areta
authors: Mary MacKillop Institute for Health Research, Centre for Exercise and Nutrition, Australian Catholic University, Melbourne, VIC, 3065, Australia.
authors: Evelyn B
authors: EB
authors: Parr
authors: Mary MacKillop Institute for Health Research, Centre for Exercise and Nutrition, Australian Catholic University, Melbourne, VIC, 3065, Australia. john.hawley@acu.edu.au.|Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK. john.hawley@acu.edu.au.
authors: John A
authors: JA
authors: Hawley
mesh_terms: D000293:Adolescent; D000328:Adult; D054874:Athletic Performance; D001642:Bicycling; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D015444:Exercise; D006801:Humans; D008066:Lipolysis / Q000187:drug effects; D008297:Male; D009525:Niacin / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D016037:Single-Blind Method; D014803:Vitamin B Complex / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*
chemical_list: D004040:Dietary Carbohydrates; D014803:Vitamin B Complex; D009525:Niacin
keywords: Fat; High-intensity cycling; Nicotinic acid; Performance; Substrate utilisation