Conclusion
Caffeine taken before exercise has fairly consistent support for a modest boost in endurance performance. Coffee can produce a similar effect when the caffeine dose is matched to what a pill would deliver. The effect size is moderate and varies by exercise type and individual.
A common approach is 3 to 6 mg of caffeine per kg of body mass, taken 30 to 60 minutes before exercise.
How much does it help?
In endurance exercise, performance improvements of roughly 2 to 7 percent have been reported. One time-trial study found both coffee and caffeine were about 5 percent faster than placebo. Strength and muscular endurance also tend to improve, though the difference is less clear for lower-body exercises.
A lower sense of effort (perceived exertion) is thought to be part of why caffeine helps.
What the research shows
The evidence base includes several meta-analyses, an umbrella analysis that pools them, and trials comparing coffee with pure caffeine. The overall direction is positive, but effect sizes vary. Genetic differences in caffeine metabolism and habitual intake may change how much an individual responds.
Cautions
- Intake later in the day can interfere with sleep
- Reduce or stop if you notice a racing heart, anxiety, or stomach discomfort
- People with heart conditions, arrhythmia, or who are pregnant should consult a physician about caffeine limits
- Regular heavy caffeine users may notice less of an effect
A simple analogy
The same hill is a little easier to climb with a tailwind. Caffeine works somewhat like that tailwind: you can climb without it, but with it the same effort carries you a bit further.