Caffeine is one of the few supplements with a solidly proven effect on endurance performance. But between the dose, the timing and the form (coffee, capsule, gel, drink, chewing gum), many runners and cyclists get it wrong: too early, too much, or tried for the first time on race day. Here’s the complete protocol, before and during exercise, with a concrete marathon plan.
In short: a dose of 3 mg of caffeine per kilo of body weight (about 200 mg for 70 kg) is enough for most athletes. Take it about 60 minutes before the start for a race lasting less than 2 hours. For longer events such as the marathon, save some of the caffeine for the second half of the race. Don’t go above 6 mg/kg, and always test your protocol in training.
Why caffeine works in endurance sport
Caffeine acts mainly on the brain: it blocks adenosine, a molecule that builds up with fatigue. As a result, effort feels easier at the same pace, concentration holds up better and the end of the race is easier to manage. A systematic review by Ganio et al. (2009) reports an average improvement of around 3% in endurance performance, with big differences between athletes. Over a 3:30 marathon, that can mean several minutes.
The dose: less than you’d think
- The reference dose: 3 to 6 mg per kilo of body weight, according to the International Society of Sports Nutrition position stand (Guest et al., 2021).
- Small doses work too: effects have been seen from 1 to 3 mg/kg (Spriet, 2014), with fewer side effects.
- Above 6 mg/kg: no extra benefit, but more risk of jitters, racing heart, stomach problems and poor sleep.
- The daily limit: 400 mg a day for a healthy adult, from all sources (coffee, tea, soft drinks, gels).
| Weight | 3 mg/kg | 6 mg/kg (useful maximum) |
|---|---|---|
| 55 kg | 165 mg | 330 mg |
| 70 kg | 210 mg | 400 mg (daily limit) |
| 85 kg | 255 mg | 400 mg (daily limit) |
For reference: an espresso contains about 60 to 100 mg of caffeine, and a caffeinated gel 25 to 100 mg depending on the brand. Always read the label.
Timing: as important as the dose
Caffeine starts to work 30 to 45 minutes after you take it, and its level in the blood peaks at around 45 to 60 minutes. The effect then lasts for several hours.
- Races under 2 hours (10K, half-marathon, short sportive): take your whole dose about 60 minutes before the start. Example: start at 9 am, caffeine at around 8 am.
- Races over 2 hours (marathon, long sportive, trail): take part of the dose before the start, or none at all, and save the rest for the second half, when fatigue sets in.
A caffeine plan for the marathon
In a marathon, the hardest stretch is often between km 28 and km 35. The idea is for the caffeine to kick in at that point, so you take it about 45 to 60 minutes before:
| Your target | First caffeinated gel | Second gel (optional) |
|---|---|---|
| Under 3 hours | around km 18-20 (65 to 75 min into the race) | rarely needed |
| 3 to 4 hours | around km 18-22 (85 to 90 min) | around km 28-30 (120 to 130 min) |
| Over 4 hours | around km 20 (90 to 100 min) | around km 30 (135 to 150 min) |
In total, aim for 200 to 300 mg over the whole race, including any pre-race dose, without going above 6 mg/kg. These caffeinated gels replace some of your regular gels: they count towards your carbohydrate per hour.
Which form of caffeine?
- Coffee: handy before the start, but its caffeine content varies a lot from cup to cup.
- Capsule or tablet: the most precise dose, ideal before the start.
- Caffeinated gel: carbohydrate and caffeine in one go, the simplest option during the race.
- Caffeinated drink: a more gradual intake, useful on the bike or if gels don’t agree with you.
- Caffeinated chewing gum: some of the caffeine is absorbed through the mouth and works faster, in about 10 to 15 minutes. Handy for a late-race boost.
Should you stop drinking coffee before the race?
There’s no need. Recent studies show that regular coffee drinkers also benefit from caffeine in races (Guest et al., 2021). Cutting it out for several days can even cause headaches and tiredness just before your goal race. Keep your usual habits, and take your race dose on top, staying within the limits.
Side effects to watch for
- Stomach problems: caffeine speeds up your gut. If you’re sensitive, choose small doses and avoid coffee just before the start.
- Jitters and a racing heart: a sign the dose is too high for you.
- Disturbed sleep: caffeine stays in your body for several hours. For an afternoon or evening race, reduce the dose.
Caffeine should be avoided or limited during pregnancy and in people with heart problems, high blood pressure or anxiety: ask your doctor.
Always test in training
Test your protocol on 2 or 3 long runs or rides at race pace: same product, same dose, same timing. Note how you feel 30 to 60 minutes after taking it, your gut comfort and your sleep the following night. On race day, change nothing.
Ograal calculates your fueling, you slot in your caffeine
In Ograal, when you add your race to the calendar with its duration and your start time, the app calculates your carbohydrate per hour, your drink and your gels. All you have to do is swap one or two gels for their caffeinated version at the times given in this guide. For details of the calculations, see How our plans are calculated.
Create your free Ograal account
Key takeaways
- Dose: 3 mg/kg is enough for most athletes; never more than 6 mg/kg or 400 mg a day.
- Short race: the whole dose 60 minutes before the start.
- Long race: save caffeine for the second half; in a marathon, first caffeinated gel around km 18-22.
- No need to stop drinking coffee before the race.
- Test everything in training.
Sources
- Guest, N. S., et al. (2021). International Society of Sports Nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition, 18(1), 1. DOI: 10.1186/s12970-020-00383-4
- Ganio, M. S., et al. (2009). Effect of caffeine on sport-specific endurance performance: a systematic review. Journal of Strength and Conditioning Research, 23(1), 315-324. DOI: 10.1519/JSC.0b013e31818b979a
- Spriet, L. L. (2014). Exercise and sport performance with low doses of caffeine. Sports Medicine, 44(Suppl 2), S175-S184. DOI: 10.1007/s40279-014-0257-8
- Desbrow, B., et al. (2012). The effects of different doses of caffeine on endurance cycling time trial performance. Journal of Sports Sciences, 30(2), 115-120. DOI: 10.1080/02640414.2011.632431
- Kerksick, C. M., et al. (2018). ISSN exercise & sports nutrition review update: research & recommendations. Journal of the International Society of Sports Nutrition, 15(1), 38. DOI: 10.1186/s12970-018-0242-y
