Caffeine

What it is

Caffeine is a stimulant that blocks adenosine — the signal that makes you feel tired — reducing perceived effort and increasing alertness. It is found in coffee, tea and, in measured doses, pre-workouts and tablets.

What the evidence shows

Endurance and perceived effort. Well-supported· human data Caffeine is one of the genuinely proven ergogenic aids. The ISSN position stand concludes it improves endurance performance and reduces how hard a given effort feels, across many well-controlled trials.

Strength and power. Well-supported· human data Benefits here are real but generally smaller and more variable than for endurance — useful for training quality and strength-endurance more than a reliable one-rep-max boost.

Fat burning as a headline claim. Marketing claim Caffeine slightly raises metabolic rate and is in most fat-burner products, but this is a minor effect and not a meaningful weight-loss strategy on its own.

Who it suits

Most people training for endurance or wanting sharper focus and lower perceived effort. Habitual coffee drinkers still benefit, though the acute kick is blunted.

Practical notes

Effects build over 30–60 minutes and the half-life is around 5 hours, so afternoon and evening doses can wreck sleep — the thing that actually drives recovery. Effective performance doses are individual and often lower than people assume. See how long a dose lingers with the caffeine calculator.

Sources

Guest NS, et al. ISSN position stand: caffeine and exercise performance. J Int Soc Sports Nutr 2021;18:1

Frequently asked questions

Does caffeine improve performance?

Yes. It is one of the few supplements with strong, consistent evidence, especially for endurance, and with useful effects on strength-endurance, alertness and perceived effort. The ISSN position stand rates it clearly ergogenic.

When should I take it before training?

Effects typically build over 30–60 minutes and it has a long half-life (around 5 hours), so late-day doses can disrupt sleep. Our caffeine calculator estimates how much is left in your system over time.

Does tolerance build up?

Regular users adapt somewhat, and habitual intake blunts the acute kick. Some people cycle it or keep training doses separate from daily coffee, though the performance benefit persists for most.

How much is too much?

Performance doses are individual and lower than many assume. High intakes cause jitters, raised heart rate, anxiety and poor sleep. People who are pregnant, or who have heart rhythm or blood-pressure conditions, should be especially cautious and seek medical advice.