ABSTRACT

Purpose:

‍The main goal of this study was to assess the acute effects of 3 and 6 mg of caffeine intake per kg of
body mass (b.m.) on maximal strength and strength-endurance in women habituated to caffeine.

Methods:

‍Twenty-one healthy resistance-trained female students (23.0 ± 0.9 years, body mass: 59.0 ± 6.6 kg), with a daily
caffeine intake of 5.8 ± 2.6 mg/kg/b.m. participated in a randomized, crossover, double-blind design. Each participant
performed three experimental sessions after ingesting either a placebo (PLAC) or 3 mg/kg/b.m. (CAF-3) and 6 mg/kg/b.m.
(CAF-6) of caffeine. In each experimental session, the participants underwent a 1RM test and a strength-endurance test at
50 %1RM in the bench press exercise. Maximal load was measured in the 1RM test and the time under tension, number
of preformed repetitions, power output and bar velocity were registered in the strength-endurance test.

Results:

‍The one-way ANOVA showed a main effect of caffeine on 1RM bench press performance (F = 14.74; p < 0.01). In
comparison to the PLAC (40.48 ± 9.21 kg), CAF-3 (41.68 ± 8.98 kg; p = 0.01) and CAF-6 (42.98 ± 8.79 kg; p < 0.01) increased
1RM bench press test results. There was also a significant increase in 1RM for CAF-6 when compared to CAF-3 (p < 0.01).
There was a main effect of caffeine on time under tension during the strength-endurance test (F = 13.09; p < 0.01). In
comparison to the PLAC (53.52 ± 11.44 s), CAF-6 (61.76 ± 15.39 s; p < 0.01) significantly increased the time under tension
during the maximal strength-endurance test.

Conclusion:

‍An acute dose of 3-to-6 mg/kg/b.m. of caffeine improves maximum strength. However, these doses of
caffeine had minimal ergogenic effect on strength-endurance performance in women habituated to caffeine.