How much does caffeine actually help performance?
Caffeine is one of the most reliable legal ergogenic aids there is: at 3-6 mg/kg about an hour before exercise it delivers small but real gains across endurance, strength, and power. The effect is biggest for endurance, and it varies from person to person.
Caffeine is the rare supplement where the evidence is both large and boring in its agreement. An umbrella review pooling 21 separate meta-analyses found it ergogenic across the board: aerobic endurance, muscle strength, muscle endurance, power, jumping, and sprint speed. The 2021 ISSN position stand says the same thing. When the reviews of reviews line up this cleanly, you can stop wondering whether it works.
The catch is how big the effect is. This isn’t a switch that turns you into a different athlete. Strength gains land around 2-7%; endurance is where caffeine looks best, roughly 2-4% off a time trial. A meta-analysis of meta-analyses pegged the strength effect at a standardized mean difference of about 0.18, which is small, and muscle endurance a bit higher at 0.30. Modest numbers, but consistent and essentially free, which is why nearly every governing body treats caffeine as a real performance aid rather than a gimmick.
The dose is unfussy
Aim for 3-6 mg/kg about 60 minutes before you start. For a 75 kg person that’s roughly 225-450 mg, from a couple of strong coffees up to a pre-workout scoop. Going above 6 mg/kg mostly buys you jitters, a racing heart, and a wrecked night’s sleep with no extra performance. Doses as low as 2-3 mg/kg still do something, and gum, gels, and mouth rinses work too and kick in faster, which helps if coffee sits badly mid-race.
Genetics and tolerance: less settled than the marketing
Here’s where it gets murky. A well-cited 2018 RCT found caffeine only helped fast CYP1A2 metabolizers cycle faster, and may have slowed the slow ones. That result launched a thousand DNA-test upsells, but a 2020 crossover trial found the same gene shifted the cognitive response while leaving exercise performance untouched across genotypes. Habitual coffee drinkers don’t reliably lose the benefit either.
The practical read: at 3-6 mg/kg an hour out, caffeine is one of the safest bets in the supplement aisle. Skip the genetic test, watch the clock so it doesn’t cost you sleep, and expect a sharper edge, not a transformation.