Caffeine for Endurance Athletes: Does It Really Improve Performance?
- Rebecca
- Aug 4
- 4 min read
When it comes to sports nutrition, the foundation of performance isn't supplements — it's food.
The biggest gains come from getting your macronutrients right. If you're not eating enough carbohydrate to fuel training, enough protein to recover, or enough overall energy to support your workload, there's very little point chasing the marginal gains that supplements can offer.
That's why, when I work with athletes, we spend most of our time getting the basics right. In many cases, we never even talk about supplements because there's so much untapped performance simply from improving their day-to-day nutrition.
There are only a handful of supplements that I think are worth discussing, and caffeine is one of them.
Interestingly, caffeine was once banned by the World Anti-Doping Agency (WADA) but was removed from the prohibited list in 2004. Today it's one of the most widely researched and consistently effective performance supplements available.
It has the potential to benefit everyone from footballers and hockey players to marathon runners, Ironman triathletes and ultramarathon runners.
That said, it's definitely not for everyone. Some people experience stomach issues, anxiety or the jitters. Others are incredibly sensitive to even small amounts, while some seem almost unaffected — even after several coffees.
How does caffeine improve performance?
Caffeine has its biggest impact in endurance sports, where research consistently shows an average performance improvement of around 2–4%. Some athletes see even greater benefits, while others notice very little.
A 2–4% improvement might not sound like much, but over the course of an endurance event it can translate into minutes — or even close to an hour.
Athlete | Finish Time | 2% Improvement | 4% Improvement |
10K runner | 50:00 | ~1 min faster | ~2 mins faster |
Marathon runner | 4:00:00 | ~4 min 48 sec faster | ~9 min 36 sec faster |
100-mile ultrarunner | 24:00:00 | ~29 mins faster | ~58 mins faster |
Half Ironman | 5:30:00 | ~6 min 36 sec faster | ~13 min 12 sec faster |
Ironman | 12:00:00 | ~14 min 24 sec faster | ~28 min 48 sec faster |
It's important to remember that these are averages from research studies. No supplement guarantees this level of improvement, but caffeine is one of the few that consistently demonstrates a meaningful benefit.
Why does caffeine work?
Caffeine doesn't give you more energy. One of its biggest benefits is that it reduces your Rating of Perceived Exertion (RPE). In simple terms, the same pace or power output feels easier.
That could mean:
maintaining your marathon pace for longer
being able to hold target power on the bike during an Ironman
pushing harder in the closing kilometres of a race
being willing to keep working when fatigue starts to bite
It also helps keep your brain switched on.
For ultrarunners, the benefit isn't always running faster. Often it's slowing down less because you're making better decisions. You remember to eat. You pace yourself more consistently. You stay focused on technical trails and avoid silly mistakes when fatigue sets in.
The same applies to long-distance triathletes. After eight or ten hours of racing, mental sharpness becomes just as important as physical fitness. Making the wrong decision in transition, on the bike or missing a nutrition feed can cost valuable time or end your race.
Even in team sports, caffeine has been shown to help maintain sprint performance, reaction time and skill execution late in games when fatigue would normally affect performance.
What's the best way to take caffeine?
Coffee is the obvious choice, but it's surprisingly difficult to know how much caffeine you're actually getting.
I love this Which? investigation. It found enormous variation in caffeine content between high street coffee chains. A medium coffee from one café may contain several times more caffeine than a similar-sized drink from another. And it can be the difference between getting the 3-6mg/kg of bodyweight you need — or not, depending on which coffee you choose.
That unpredictability is why many endurance athletes prefer caffeine gels, chewing gum, tablets or sports drinks, where the caffeine content is clearly labelled.
When should you take caffeine?
For most events lasting a few hours, caffeine is typically taken around 45–60 minutes before the start.
For longer races such as Ironman or 100-mile ultramarathons, it's rarely a one-off strategy.
Instead, smaller doses are usually spread throughout the race to maintain the effect without consuming excessive amounts at once. This becomes especially valuable during overnight events when you're battling your circadian rhythm and sleepiness as much as muscular fatigue.
Caffeine has an average half-life of around 3–7 hours, although this varies considerably between individuals. That means it can remain in your system long after you've finished racing, so more isn't always better.
Whatever strategy you choose, practise it in training first. Race day is never the time to discover that caffeine doesn't agree with you.
My own caffeine strategy
I got a much-needed boost from a flat Coke at the last aid station at the Threshold Trail Series Race to the Stones Weekender in July — it's the caffeine not the sugar that helps it seems. So as I build towards the Robin Hood 100 Mile race in September, this is something I'll be testing more rigorously myself.
Top tip: Always practise your caffeine strategy during long training sessions. Never introduce caffeine products for the first time on race day.
Running through the night presents a unique challenge. I don't necessarily expect caffeine to make me dramatically faster, but if it helps me stay alert, avoid tripping over tree roots, remember to keep eating and maintain good decisions after 18 or 20 hours on my feet, it'll have done its job.
Like every aspect of sports nutrition, caffeine works best when it's part of a well-practised race plan — not a last-minute addition. After all, supplements are there to support good nutrition, not replace it.
If you're building towards an event and want to work on your nutrition in the same structured way — whether that's a one-off consultation, or a full training block package — I'd love to help.
Ready to build a nutrition plan that works?Join the next intake of Marathon Ready: Online Nutrition Course, or book a free 15-minute call to discuss your goals. | |
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