Caffeine on Race Day: Dose, Timing and the Long Race

Most triathletes already use caffeine on race morning, often without thinking of it as a supplement. A coffee with breakfast, a caffeinated gel on the bike, some cola at a run aid station: by the finish, the total can be surprisingly large.

Caffeine also happens to be one of the best-evidenced performance aids in sport. The question for most age-groupers isn't whether it works but how to use it well: how much, when, whether your daily coffee changes anything, how it fits into a race that might last five to seventeen hours, and how to avoid paying for it with a sleepless night, a racing heart or an upset stomach.

This article covers what the evidence says, where it comes from, and where it runs out.

How caffeine works

Caffeine's main action is to block adenosine receptors in the brain and elsewhere. Adenosine builds up during waking hours and with effort, and it contributes to feelings of tiredness. By blocking it, caffeine reduces perceived effort and fatigue, improves alertness, and may also have effects on muscle and the nervous system.

In practice, the most noticeable effect for endurance athletes is that the same pace or power feels easier. That's useful in a long race, where how hard you perceive the effort to be strongly shapes how fast you choose to go. TriForward's "Racing by Feel vs. Racing by Numbers" explains why perceived effort matters so much in pacing.

The ISSN position stand

The best summary of the research is the International Society of Sports Nutrition (ISSN) position stand on caffeine and exercise performance, published by Guest and colleagues in 2021. Its main conclusions were:

• Caffeine acutely improves many, but not all, aspects of exercise performance.
• Aerobic endurance shows the most consistent moderate-to-large benefit, although the size of the effect varies between individuals.
• Performance improvements are consistently seen at 3–6 mg/kg of body mass.
• The minimum effective dose isn't clear, but may be as low as 2 mg/kg.
• Very high doses, such as 9 mg/kg, carry a high incidence of side effects and don't appear to be needed.
• The most common timing is 60 minutes before exercise, but the best timing depends on the source. Caffeinated chewing gum, for example, may need less lead time than capsules.
• Caffeine helps both trained and untrained people.
• Individual differences in performance effects and side effects, such as poor sleep or anxiety, may come from genetic differences in caffeine metabolism, from physical and psychological responses, and possibly from habitual intake.
• Alternative forms such as gum, mouth rinses, energy gels and chews have mainly been shown to help aerobic exercise.
• Caffeine can help in hot conditions and at altitude.

Inference: for a 70 kg athlete, 3–6 mg/kg works out at roughly 210–420 mg. Caffeinated gels vary widely in how much they contain, so reaching that range from gels alone may take several, and the only way to know is to read the labels.

The triathlon field study

Most caffeine research is in cyclists or runners in a lab. One of the few triathlon-specific trials was published by Potgieter, Wright and Smith in 2018 in the International Journal of Sport Nutrition and Exercise Metabolism.

Twenty-six triathletes took part: 14 men and 12 women, with an average age of about 38 and around 13 hours of training a week. That's closer to a real age-group population than most sports-science samples. In a double-blind, randomised crossover design, they took 6 mg/kg of microencapsulated caffeine or a placebo 60 minutes before completing an Olympic-distance triathlon in the field.

• Total time was 1.3% faster with caffeine: 149.6 minutes versus 151.5 minutes on average.
• The swim was 3.7% faster: 33.5 versus 34.8 minutes.
• Rating of perceived exertion didn't change, which the authors interpreted as athletes doing more work at the same perceived effort.
• Post-race cortisol and peak blood lactate were higher with caffeine.

The participants' habitual caffeine intake averaged 413 mg a day, but with a very wide spread (standard deviation 505 mg). The authors concluded that triathletes with relatively low habitual intake might use 6 mg/kg 45–60 minutes before an Olympic-distance race. Differences between men and women and individual responses were described in the full paper but not quantified in the abstract.

Inference: a 1.3% gain on a two-and-a-half-hour race is about two minutes. That's meaningful, but it's an average. Some athletes will gain more, some nothing, and the study didn't test long-course distances.

Does your daily coffee blunt the effect?

A common belief is that regular coffee drinkers need to cut caffeine for days before a race to "resensitise". The best test of this is a 2017 study by Gonçalves and colleagues in the Journal of Applied Physiology.

Forty endurance-trained male cyclists were split into three groups by habitual caffeine intake: low (about 58 mg a day), moderate (about 143 mg a day) and high (about 351 mg a day). Each completed a simulated cycling time trial of around 30 minutes after taking 6 mg/kg of caffeine, a placebo, or nothing, in a double-blind crossover design.

• Caffeine improved the time trial compared with both placebo and control: about 29.9 minutes versus 30.8 and 31.1 minutes.
• Habitual intake didn't influence the effect. There was no relationship between how much caffeine athletes normally consumed and how much they benefited.
• The number of individual "responders" was similar across groups: 8, 7 and 5 athletes in the low, moderate and high groups improved by more than the test's normal variation.

This was a male-only sample, and the effort was short. But it suggests that a caffeine "taper" isn't necessary for most athletes. Inference: cutting out coffee abruptly in race week can cause headaches, low mood and poor sleep in some people, which may do more harm than any small sensitivity gain.

Caffeine during long races

In long-course racing, the timing question is harder. A single dose an hour before the start may have faded by the run, especially in an Ironman.

Cox and colleagues addressed part of this in a 2002 study in the Journal of Applied Physiology. Competitive athletes cycled for two hours at a steady 70% of peak oxygen uptake, taking in carbohydrate, and then completed a time trial. In the first study, 12 athletes tried four approaches:

• 6 mg/kg one hour before exercise: time trial 3.4% better than placebo.
• 1 mg/kg every 20 minutes during the steady ride (6 mg/kg in total): 3.1% better.
• Coca-Cola in the last 20 minutes of the steady ride and during the time trial: 3.1% better.

A second study with eight athletes found that cola late in exercise improved performance, and that about 2.2% of the gain was due to the caffeine itself rather than the extra carbohydrate. The authors concluded that the benefit of 6 mg/kg didn't depend on timing, and that switching to cola late in exercise was just as effective despite a much lower caffeine dose, about 1.5 mg/kg. The abstract doesn't report the athletes' sex.

That study was 2 hours plus a time trial, not 10 hours. But it supports the familiar long-course strategy of keeping some caffeine for later in the race, and the idea that smaller doses late on can still help.

Gels, gum and chews

Many triathletes take caffeine as part of their race fuel rather than as tablets. The ISSN position stand notes that gum, mouth rinses, gels and chews have mainly been shown to help aerobic exercise, and that gum may act faster than capsules.

Practical points, which are inference rather than tested protocols:

• Read the label. Caffeine content varies widely between brands and flavours.
• Know which of your gels contain caffeine, and plan where in the race you'll take them.
• Account for aid-station cola, which can add up over a long marathon.
• Practise in training. Caffeine can increase gut motility in some athletes, which adds to the gut stress of high carbohydrate intakes. TriForward's "Gut Training" covers how to train tolerance to race fuel.

Sleep before an early start

Race mornings often start at 4 am. The night before, nerves, travel and an unfamiliar bed already make sleep worse. Caffeine adds to the problem.

A 2023 systematic review and meta-analysis by Gardiner and colleagues in Sleep Medicine Reviews pooled 24 studies of caffeine and subsequent sleep. Caffeine:

• Reduced total sleep time by about 45 minutes.
• Reduced sleep efficiency by 7%.
• Lengthened the time taken to fall asleep by about 9 minutes.
• Increased time awake after falling asleep by about 12 minutes.
• Reduced deep sleep by about 11 minutes.

The authors estimated that, to avoid losing sleep, coffee containing about 107 mg should be taken at least 8.8 hours before bed, and a standard pre-workout drink (217.5 mg) at least 13.2 hours before.

Inference for triathletes: if you aim to be asleep by 9 pm before an early race, an afternoon coffee on race eve may be enough to cost you sleep. The day-before rule is simple: keep caffeine in the morning. TriForward's "Does More Sleep Make You Faster?" covers the wider evidence on sleep and performance.

Sleep after the race

The same evidence applies after the finish. In a long race, caffeine taken in the final hours will still be active when you try to sleep that night.

Inference: an Ironman finisher who takes caffeinated gels and cola through the marathon and finishes in the evening may struggle to sleep, on top of the soreness and high heart rate that already follow a long race. That's an acceptable trade-off for many athletes on race day, but it's worth knowing about, especially if you have to travel the next day. TriForward's "After the Finish Line" covers what Ironman recovery involves.

Safety and upper limits

Caffeine is widely used, but it isn't harmless at high doses, and race-day protocols often exceed everyday intakes.

The European Food Safety Authority's 2015 scientific opinion on caffeine safety concluded that, for healthy adults:

• Single doses up to 200 mg, about 3 mg/kg for a 70 kg adult, raise no safety concern, including when taken less than two hours before intense exercise in normal conditions.
• Habitual intake up to 400 mg a day raises no safety concern for non-pregnant adults.
• Up to 200 mg a day raises no concern during pregnancy or breastfeeding.

Inference: 6 mg/kg for a 70 kg athlete is 420 mg in one go, more than double the single-dose level EFSA assessed as raising no concern. That doesn't make it dangerous for everyone, and the ISSN supports it for performance, but it means the higher end of the range is outside the safety assessment for single doses. Starting at the lower end is the cautious approach.

Side effects at higher doses can include jitteriness, anxiety, a fast heart rate, gut upset and poor sleep. People vary greatly in how quickly they clear caffeine.

Building a caffeine plan in training

The evidence gives a range, not a prescription. A sensible way to turn it into a personal plan, which is inference from the studies above rather than a tested protocol, looks like this:

1. Write down your normal daily intake, including tea, coffee, cola and energy drinks. It's your baseline and helps you judge what's extra on race day.
2. Start low. Try about 2–3 mg/kg before a key session and see how you feel, including your heart rate, gut and sleep that night.
3. Change one thing at a time. Don't trial a new caffeine dose on the same day as a new gel, a new breakfast or a new bike position.
4. Rehearse the race pattern. For a long-course race, use a long brick or long ride to practise the timing you'd use on race day, including caffeine later in the session.
5. Set a total budget for the day, add up every source, and keep it within what you've tolerated in training.
6. Plan for the start time. If your race starts early, practise an early session with the same pre-race caffeine timing, so you know how it affects your gut and toilet routine.

Keep notes. Responses vary between people, and the best-supported dose for one athlete may leave another jittery.

A typical race-day scenario

The following is illustrative, not drawn from a case study. An age-grouper racing their first Ironman has two strong coffees at 4 am, takes a caffeine tablet before the swim "to be sure", uses caffeinated gels every 45 minutes on the bike because they taste better, and drinks cola at every run aid station.

Inference: depending on brands, that could exceed 9 mg/kg over the day, the level the ISSN associates with frequent side effects. By the run, the athlete feels shaky, has a fast heart rate on easy sections, and their stomach is unsettled. Afterwards, they can't sleep.

A more deliberate plan would set a total caffeine budget, spread it across the day, use non-caffeinated fuel for most of the bike, and save caffeinated products for the second half of the bike and the run. All of it would be tested in long training sessions first.

Common mistakes

• Not counting all sources, especially gels, energy drinks and cola.
• Assuming more is better. The evidence supports moderate doses.
• Trying a new caffeine product on race day.
• Abruptly cutting out coffee in race week to "resensitise".
• Drinking coffee late on race eve and then struggling to sleep.
• Using caffeine to cover under-fuelling. It can make effort feel easier, but it doesn't replace carbohydrate. See TriForward's "90–120g of Carbs an Hour".

What we don't know

• The best caffeine strategy for an Ironman. There are no randomised trials over full long-course distances.
• How caffeine interacts with heat, dehydration and high carbohydrate intake over many hours.
• How much sex, age and genetics change the response. Most studies are in young men; the triathlon field study included women but didn't quantify sex differences in its abstract.
• Whether race-day caffeine harms post-race recovery through lost sleep in a meaningful way.

References

• Guest NS, VanDusseldorp TA, Nelson MT, Grgic J, Schoenfeld BJ, Jenkins NDM, et al. International Society of Sports Nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition, 2021;18(1). doi:10.1186/s12970-020-00383-4
• Potgieter S, Wright HH, Smith C. Caffeine improves triathlon performance: a field study in males and females. International Journal of Sport Nutrition and Exercise Metabolism, 2018;28(3):228–237. doi:10.1123/ijsnem.2017-0165
• Gonçalves LS, Painelli VS, Yamaguchi G, de Oliveira LF, Saunders B, da Silva RP, et al. Dispelling the myth that habitual caffeine consumption influences the performance response to acute caffeine supplementation. Journal of Applied Physiology, 2017;123(1):213–220. doi:10.1152/japplphysiol.00260.2017
• Cox GR, Desbrow B, Montgomery PG, Anderson ME, Bruce CR, Macrides TA, et al. Effect of different protocols of caffeine intake on metabolism and endurance performance. Journal of Applied Physiology, 2002;93(3):990–999. doi:10.1152/japplphysiol.00249.2002
• Gardiner C, Weakley J, Burke LM, Roach GD, Sargent C, Maniar N, et al. The effect of caffeine on subsequent sleep: a systematic review and meta-analysis. Sleep Medicine Reviews, 2023;69:101764. doi:10.1016/j.smrv.2023.101764
• EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific opinion on the safety of caffeine. EFSA Journal, 2015;13(5):4102. doi:10.2903/j.efsa.2015.4102