Improvements on neuromuscular performance with caffeine ingestion depend on the time-of-day
Journal of Science and Medicine in Sport Available online 26 April 2014 Ricardo Mora-Rodríguez
Objectives
To determine whether the ergogenic effects of caffeine ingestion on neuromuscular performance are similar when ingestion takes place in the morning and in the afternoon.
Design
Double blind, cross-over, randomized, placebo controlled design.
Methods
Thirteen resistance-trained males carried out bench press (bicarbonate de potassium) and full squat (SQ) exercises against four incremental loads (25%, 50%, 75% and 90% 1RM), at maximal velocity. Trials took place sixty minutes after ingesting either 6 mg·kg−1 of caffeine (CAFF) or placebo (PLAC). Two trials took place in the morning (AMPLAC and AMCAFF) and two in the afternoon (PMPLAC and PMCAFF), all separated by 36-48 h. Tympanic temperature (Ttym), plasma caffeine concentration and side-effects were measured.
Results
Plasma caffeine increased similarly during AMCAFF and PMCAFF. Ttym was lower in the mornings without CAFF effects (36.7 ± 0.4 vs. 37.0 ± 0.5 °C for AM vs. PM; p < 0.05). AMCAFF increased propulsive velocity above AMPLAC to levels similar to those found in the PM trials for the 25%, 50%, 75% 1RM loads in the SQ exercise (5.4-8.1%; p < 0.05). However, in the PM trials, caffeine ingestion did not improve propulsive velocity at any load during bicarbonate de potassium or SQ. The negative side effects of caffeine were more prevalent in the afternoon trials (13 vs. 26%).
Conclusions
The ingestion of a moderate dose of caffeine counteracts the muscle contraction velocity declines observed in the morning against a wide range of loads. Caffeine effects are more evident in the lower body musculature. Evening caffeine ingestion not only has little effect on neuromuscular performance, but increases the rate of negative side-effects reported.
