title: Effects of caffeine on neuromuscular fatigue and performance during high-intensity cycling exercise in moderate hypoxia.
abstract: OBJECTIVE
  To investigate the effects of caffeine on performance, neuromuscular fatigue and perception of effort during high-intensity cycling exercise in moderate hypoxia.
  
  
  METHODS
  Seven adult male participants firstly underwent an incremental exercise test on a cycle ergometer in conditions of acute normobaric hypoxia (fraction inspired oxygen = 0.15) to establish peak power output (PPO). In the following two visits, they performed a time to exhaustion test (78 ± 3% PPO) in the same hypoxic conditions after caffeine ingestion (4 mg kg-1) and one after placebo ingestion in a double-blind, randomized, counterbalanced cross-over design.
  
  
  RESULTS
  Caffeine significantly improved time to exhaustion by 12%. A significant decrease in subjective fatigue was found after caffeine consumption. Perception of effort and surface electromyographic signal amplitude of the vastus lateralis were lower and heart rate was higher in the caffeine condition when compared to placebo. However, caffeine did not reduce the peripheral and central fatigue induced by high-intensity cycling exercise in moderate hypoxia.
  
  
  CONCLUSIONS
  The caffeine-induced improvement in time to exhaustion during high-intensity cycling exercise in moderate hypoxia seems to be mediated by a reduction in perception of effort, which occurs despite no reduction in neuromuscular fatigue.
authors.affiliation: Department of Physical Education, São Paulo State University (UNESP), Rio Claro, SP, Brazil.
authors.forename: Bruno P C
authors.initials: BP
authors.lastname: Smirmaul
authors.affiliation: Faculty of Physical Education, University of Campinas (UNICAMP), São Paulo, SP, Brazil.
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: de Moraes
authors.affiliation: Endurance Research Group, School of Sport and Exercise Sciences, University of Kent at Medway, Chatham Maritime, Kent, ME4 4AG, UK.
authors.forename: Luca
authors.initials: L
authors.lastname: Angius
authors.affiliation: Endurance Research Group, School of Sport and Exercise Sciences, University of Kent at Medway, Chatham Maritime, Kent, ME4 4AG, UK. s.m.marcora@kent.ac.uk.
authors.forename: Samuele M
authors.initials: SM
authors.lastname: Marcora
mesh_terms: D000328:Adult; D054874:Athletic Performance; D002110:Caffeine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D015444:Exercise; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D008297:Male; D018763:Muscle Fatigue / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine
keywords: Altitude; Central fatigue; Exercise performance; Perception of effort; Peripheral fatigue