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 and full squat exercises against four incremental loads (25%, 50%, 75% and 90% 1RM), at maximal velocity. Trials took place 60 min after ingesting either 6 mg kg −1 of caffeine or placebo. Two trials took place in the morning (AM PLAC and AM CAFF ) and two in the afternoon (PM PLAC and PM CAFF ), all separated by 36–48 h. Tympanic temperature, plasma caffeine concentration and side-effects were measured.

Results

Plasma caffeine increased similarly during AM CAFF and PM CAFF . Tympanic temperature was lower in the mornings without caffeine effects (36.7 ± 0.4 vs. 37.0 ± 0.5 °C for AM vs. PM; p < 0.05). AM CAFF increased propulsive velocity above AM PLAC 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 BP 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.