You can have your coffee and drink it too Original paper

A robust body of evidence demonstrates that consuming 3–6 milligrams of caffeine per kilogram of body mass (mg/kg) before exercise improves performance over a wide range of durations and intensities.^[1] However, it remains unclear whether regular caffeine intake reduces the magnitude of — or even offsets — this effect.

This meta-analysis of 60 randomized controlled trials investigated the influence of habitual caffeine consumption on the ergogenic effect (i.e., improvement in physical performance) of supplementing with caffeine before exercise. Of the 1,137 participants, 958 were men and 179 were women.

Analyses were performed to determine whether habitual caffeine intake’s influence on this ergogenic effect differed between exercise types (endurance, power, and strength), men and women, and trained and untrained participants. Subgroup analyses were performed according to the relative caffeine dose before exercise, whether this dose was lower or higher than the participants’ average daily habitual caffeine consumption, and the caffeine withdrawal period prior to the intervention.

Compared with placebo, caffeine improved overall exercise performance to a small degree, and the effect did not differ between exercise types. Caffeine improved exercise performance to a similar extent in men and women, as well as in trained and untrained participants. Additionally, habitual caffeine consumption did not influence the effect, overall or in any of the subgroups.

Caffeine doses of <3 mg/kg and 3–6 mg/kg (but not >6 mg/kg) improved exercise performance, regardless of whether the dose before exercise was higher or lower than the participants’ usual daily consumption. The period of withdrawal (i.e., <24 hours, 24–48 hours, or >48 hours) had no effect.

Only 5 studies included doses of caffeine of >6 mg/kg, so it remains to be determined whether there is any benefit at greater doses. It’s been suggested that to maximize caffeine’s ergogenic effect, the preexercise dose should exceed the habitually consumed dose.^[2] A potential explanation for the lack of an ergogenic effect at caffeine doses of >6 mg/kg is an increased occurrence of side effects (e.g., anxiety and nausea).