title: Caffeine ingestion reverses the circadian rhythm effects on neuromuscular performance in highly resistance-trained men.
abstract: OBJECTIVE
  To investigate whether caffeine ingestion counteracts the morning reduction in neuromuscular performance associated with the circadian rhythm pattern.
  
  
  METHODS
  Twelve highly resistance-trained men underwent a battery of neuromuscular tests under three different conditions; i) morning (10:00 a.m.) with caffeine ingestion (i.e., 3 mg kg(-1); AM(CAFF) trial); ii) morning (10:00 a.m.) with placebo ingestion (AM(PLAC) trial); and iii) afternoon (18:00 p.m.) with placebo ingestion (PM(PLAC) trial). A randomized, double-blind, crossover, placebo controlled experimental design was used, with all subjects serving as their own controls. The neuromuscular test battery consisted in the measurement of bar displacement velocity during free-weight full-squat (SQ) and bench press (BP) exercises against loads that elicit maximum strength (75% 1RM load) and muscle power adaptations (1 m s(-1) load). Isometric maximum voluntary contraction (MVC(LEG)) and isometric electrically evoked strength of the right knee (EVOK(LEG)) were measured to identify caffeine's action mechanisms. Steroid hormone levels (serum testosterone, cortisol and growth hormone) were evaluated at the beginning of each trial (PRE). In addition, plasma norepinephrine (NE) and epinephrine were measured PRE and at the end of each trial following a standardized intense (85% 1RM) 6 repetitions bout of SQ (POST).
  
  
  RESULTS
  In the PM(PLAC) trial, dynamic muscle strength and power output were significantly enhanced compared with AM(PLAC) treatment (3.0%-7.5%; p≤0.05). During AM(CAFF) trial, muscle strength and power output increased above AM(PLAC) levels (4.6%-5.7%; p≤0.05) except for BP velocity with 1 m s(-1) load (p = 0.06). During AM(CAFF), EVOK(LEG) and NE (a surrogate of maximal muscle sympathetic nerve activation) were increased above AM(PLAC) trial (14.6% and 96.8% respectively; p≤0.05).
  
  
  CONCLUSIONS
  These results indicate that caffeine ingestion reverses the morning neuromuscular declines in highly resistance-trained men, raising performance to the levels of the afternoon trial. Our electrical stimulation data, along with the NE values, suggest that caffeine increases neuromuscular performance having a direct effect in the muscle.
authors.affiliation: Exercise Physiology Laboratory, University of Castilla-La Mancha, Toledo, Spain. Ricardo.mora@uclm.es
authors.forename: Ricardo
authors.initials: R
authors.lastname: Mora-Rodríguez
authors.forename: Jesús
authors.initials: J
authors.lastname: García Pallarés
authors.forename: Álvaro
authors.initials: Á
authors.lastname: López-Samanes
authors.forename: Juan Fernando
authors.initials: JF
authors.lastname: Ortega
authors.forename: Valentín E
authors.initials: VE
authors.lastname: Fernández-Elías
mesh_terms: D000328:Adult; D002110:Caffeine / Q000008:administration & dosage*; D016022:Case-Control Studies; D000697:Central Nervous System Stimulants / Q000008:administration & dosage*; D002940:Circadian Rhythm; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004435:Eating; D015444:Exercise; D006801:Humans; D008297:Male; D053580:Muscle Strength / Q000187:drug effects* / Q000502:physiology; D010807:Physical Endurance / Q000187:drug effects; D055070:Resistance Training; D013739:Testosterone / Q000097:blood; D055815:Young Adult
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine; D013739:Testosterone