title: Dose effect of caffeine on testosterone and cortisol responses to resistance exercise.
abstract: BACKGROUND
  Interest in the use of caffeine as an ergogenic aid has increased since the International Olympic Committee lifted the partial ban on its use. Caffeine has beneficial effects on various aspects of athletic performance, but its effects on training have been neglected.
  
  
  OBJECTIVE
  To investigate the acute effect of caffeine on the exercise-associated increases in testosterone and cortisol in a double-blind crossover study.
  
  
  METHODS
  Twenty-four professional rugby-league players ingested caffeine doses of 0, 200, 400, and 800 mg in random order 1 hr before a resistance-exercise session. Saliva was sampled at the time of caffeine ingestion, at 15-min intervals throughout each session, and 15 and 30 min after the session. Data were log-transformed to estimate percent effects with mixed modeling, and effects were standardized to assess magnitudes.
  
  
  RESULTS
  Testosterone concentration showed a small increase of 15% (90% confidence limits, +/- 19%) during exercise. Caffeine raised this concentration in a dose-dependent manner by a further small 21% (+/- 24%) at the highest dose. The 800-mg dose also produced a moderate 52% (+/- 44%) increase in cortisol. The effect of caffeine on the testosterone:cortisol ratio was a small decline (14%; +/- 21%).
  
  
  CONCLUSIONS
  Caffeine has some potential to benefit training outcomes via the anabolic effects of the increase in testosterone concentration, but this benefit might be counteracted by the opposing catabolic effects of the increase in cortisol and resultant decline in the testosterone:cortisol ratio.
authors.affiliation: Horticulture and Food Research Institute of New Zealand, Hamilton, New Zealand.
authors.forename: C Martin
authors.initials: CM
authors.lastname: Beaven
authors.forename: Will G
authors.initials: WG
authors.lastname: Hopkins
authors.forename: Kier T
authors.initials: KT
authors.lastname: Hansen
authors.forename: Mathew R
authors.initials: MR
authors.lastname: Wood
authors.forename: John B
authors.initials: JB
authors.lastname: Cronin
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Lowe
mesh_terms: D000328:Adult; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis* / Q000378:metabolism; D008297:Male; D012463:Saliva / Q000737:chemistry*; D013647:Task Performance and Analysis; D013739:Testosterone / Q000032:analysis* / Q000378:metabolism; D014891:Weight Lifting / Q000502:physiology*
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine; D013739:Testosterone; D006854:Hydrocortisone