Caffeine ingestion reverses the circadian rhythm effects on neuromuscular performance in highly resistance-trained men

Abstract

Purpose: 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. © 2012 Mora-Rodríguez et al.