Caffeine and Training: How the World's Favourite Stimulant Boosts Performance
Caffeine is one of the very few supplements that reliably works. Here's the evidence on strength, endurance and focus — and how to dose it right.
Most supplements are hype wrapped around a tiny effect. Caffeine is the rare exception: it is one of the most researched ergogenic aids in the world, and the evidence for a real, repeatable performance boost is strong. That is exactly why it is in almost every pre-workout on the shelf.
How Caffeine Works
Caffeine blocks adenosine, the molecule that builds up through the day and makes you feel tired. With adenosine blocked, perceived effort drops, alertness rises and the nervous system fires more readily. The main effects are central — they happen in the brain and nervous system — which is why a hard set simply feels easier under caffeine.
What It Actually Improves
- Endurance: the most robust effect — longer time to exhaustion and better performance in prolonged efforts.
- Strength and power: a smaller but real boost, especially when you are tired or under-slept.
- Focus and reaction time: sharper attention and quicker responses.
- Perceived effort: hard work feels less hard, so you can push a little further.
How to Dose It
- Effective range is about 3–6 mg per kg of bodyweight — roughly 200–400 mg for most people.
- Take it 30–60 minutes before training so blood levels peak during your session.
- Start at the low end and see how you respond; sensitivity varies a lot between people.
- More is not better — high doses add jitters, a racing heart and anxiety without adding performance.
Timing, Tolerance and Sleep
Caffeine has a half-life of about 5–6 hours, so a mid-afternoon or evening dose is still in your system at bedtime, wrecking the very sleep your recovery depends on. Train late? Use a smaller dose or skip it. Tolerance also builds with daily use, so keeping doses modest — or cycling down periodically — keeps caffeine working when you need it. If you are pregnant, sensitive to stimulants, or have a heart condition, keep intake low and check with a doctor.