title: The effect of caffeine on endurance performance after nonselective beta-adrenergic blockade.
abstract: OBJECTIVE
  This study was designed to test the hypothesis that combined administration of propranolol and caffeine (Pr+C) would increase endurance performance compared with the administration of propranolol alone (Pr) if caffeine would be able to increase plasma free fatty acid (FFA) availability and/or lower plasma potassium concentration compared with propranolol administration alone.
  
  
  METHODS
  Fifteen volunteers participated in the double-blind placebo-controlled randomized cross-over study. An endurance exercise test until exhaustion was performed after ingestion of placebo (Pl), 80-mg propranolol (Pr), and 80-mg propranolol plus 5 mg x kg(-1) caffeine (Pr+C).
  
  
  RESULTS
  Endurance time (+/-SD) was 79.3 +/- 20.4 min in the Pl trial, 22.6 +/- 10.8 min in the Pr trial and 31.2 +/- 17.2 min in the Pr+C trial (P < 0.001). The difference between the Pr and Pr+C trials just failed to reach statistical significance (P = 0.056). Plasma FFA concentration and plasma potassium concentrations were similar in the Pr and Pr+C trials, but differed significantly from the Pl trial (P < 0.05).
  
  
  CONCLUSIONS
  Although there was a clear tendency for an improved performance in the Pr+C trial compared to the Pr trial, this improvement was not associated with increased plasma FFA concentration and/or reduced plasma potassium concentration in the Pr+C compared to the Pr trial. These results do not support the hypothesis that caffeine improves endurance performance by stimulating lipolysis or lowering plasma potassium concentration.
authors.affiliation: NUTRIM, Department of Human Biology, Maastricht University, The Netherlands. m.vanbaak@hb.unimaas.nl
authors.forename: M A
authors.initials: MA
authors.lastname: Van Baak
authors.forename: W H
authors.initials: WH
authors.lastname: Saris
mesh_terms: D000293:Adolescent; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D004311:Double-Blind Method; D004347:Drug Interactions; D005227:Fatty Acids / Q000097:blood; D006801:Humans; D008297:Male; D010807:Physical Endurance / Q000187:drug effects* / Q000502:physiology; D011188:Potassium / Q000097:blood; D011433:Propranolol / Q000494:pharmacology*
chemical_list: D000319:Adrenergic beta-Antagonists; D000697:Central Nervous System Stimulants; D005227:Fatty Acids; D002110:Caffeine; D011433:Propranolol; D011188:Potassium