Effect of two doses of caffeine on muscular function during isokinetic exercise

Studies provide equivocal results regarding the ergogenic properties of caffeine during high-intensity exercise.

The primary aim of this study was to examine the effects of two doses of caffeine on peak/average torque, power output, and total work of the knee extensors and flexors during two bouts of high-intensity exercise.

Fifteen active men (mean age = 26.4 ± 3.9 yr and body mass = 82.7 ± 2.9 kg) initially completed a familiarization bout on the isokinetic dynamometer, followed by three subsequent trials separated by at least 48 h. Exercise consisted of two bouts of 40 repetitions of maximal knee extension and flexion of the dominant leg at a contraction velocity equal to 180°·s. Before each trial, subjects abstained from caffeine intake and intense exercise for 48 h. Treatment order (5 and 2 mg·kg of anhydrous caffeine or placebo) was randomly assigned to subjects using a single-blind, randomized, counterbalanced, crossover design. A 3 (treatment) × 2 (sets) ANOVA with repeated measures was used to detect differences in performance across treatment and time.

Compared with placebo, caffeine significantly (P < 0.05) enhanced peak knee flexion torque, knee extension/flexion total work, and knee extension/flexion power in bout 1 with no effect in bout 2. Only the 5-mg·kg dose of caffeine improved performance, with the magnitude of performance improvement ranging from 5% to 8%.

Data suggest that a relatively high (5-mg·kg body weight) but not low (2-mg·kg body weight) caffeine dose is ergogenic for maximal knee extension/flexion exercise.