TL;DR: Caffeine can be a relevant tool for endurance athletes if dosage, timing, and tolerance are tested in training.
- Studies typically point to a small performance improvement of around 2–4% in some endurance athletes.
- A commonly used dose is 3–6 mg of caffeine per kg of body weight, typically 30–60 minutes before the start.
- Caffeine should be part of an overall fueling plan with carbohydrates, fluids, and electrolytes.
- Coffee, capsules, gels, and chews can all be used, but they have different pros and cons.
- Test caffeine in training first, as response, stomach comfort, sleep, and side effects vary from person to person.
For many endurance athletes, coffee and caffeine are a regular part of everyday life. But how much is habit, and how much is evidence-based? Research suggests that caffeine can, for some, contribute to a small but measurable boost in performance—especially when dose and timing are individualized.
Here you’ll get a complete overview of what studies typically show and how you can translate it into a realistic strategy in training and competition. The goal is for you to use caffeine as part of your energy planning in a responsible way—with a focus on tolerance, stomach comfort, and common sense.
Caffeine and endurance: how big is the effect?
Meta-analyses and international expert reviews indicate that caffeine can contribute to a small improvement in performance for a portion of endurance athletes, often cited at around 2–4%. This is seen especially in disciplines such as running, cycling, triathlon, and cross-country skiing, where you work at moderate to high intensity for extended periods at a time.
In practice, it can typically show up as:
- A shorter time to complete a given race, for example a marathon
- A longer time to exhaustion at a set intensity
- The same pace or watts at a lower perceived exertion
For a marathon runner, a 3% improvement could theoretically amount to several minutes, but the actual effect varies and depends, among other things, on dose, timing, habitual intake, and individual response.
The response is individual. Some notice a clear boost, others experience only a small difference, and a few primarily experience side effects. That’s why caffeine is a tool you should try in training before making it a fixed part of your race plan.
How does caffeine affect endurance?
Caffeine primarily affects the central nervous system. Put simply, caffeine can, among other things:
- Affect adenosine receptors in the brain, which in some may contribute to increased alertness and reduced feelings of fatigue
- Increase the release of adrenaline, which can contribute to sharper focus and the sense that hard work feels a bit easier
- In some, contribute to a small reduction in perceived discomfort, which can make it easier to maintain intensity late in a race
Some studies suggest that caffeine may, in certain situations, affect how the body uses fat and carbohydrate as fuel, but the picture is not clear-cut. In practice, it’s especially perceived exertion and alertness that many endurance athletes highlight themselves.
Dose and timing without compromises
Most studies that find a performance-related effect typically use 3–6 mg of caffeine per kg of body weight in healthy adults. For a 70 kg athlete, that corresponds to roughly 210–420 mg of caffeine.
In practice, it can make sense to:
- Start at the low end, for example around 3 mg of caffeine per kg of body weight
- Avoid going far above 6 mg per kg, as higher doses do not necessarily provide a greater effect but can increase the risk of jitters, palpitations, and stomach issues
- Keep an eye on total daily intake so you stay within general recommendations, typically around 400 mg of caffeine per day for adults and lower for pregnant people
Caffeine is absorbed relatively quickly and typically reaches peak concentration in the blood after 30–60 minutes. Many studies use:
- Intake about 30–60 minutes before the start as the main dose
- For long competitions such as marathons, long-distance triathlons, or ultraruns, a starting dose combined with smaller amounts along the way
At the same time, there are indications that very frequent and high caffeine consumption in daily life can reduce the perceived acute effect for some. Some athletes therefore choose to adjust caffeine intake in the days leading up to the season’s most important competitions. It’s important to test what works for you—both physically and mentally.
Caffeine in your fueling plan in practice
On race day, caffeine is typically part of an overall plan for carbohydrates, fluids, and electrolytes, so you can support energy delivery throughout the effort.
A practical way to work with caffeine is to use sports nutrition where carbohydrates and caffeine are combined, for example:
This can make it easier to:
- Get carbohydrates and caffeine at the same time when intensity is high
- Dose caffeine in smaller portions instead of one very large dose
- Time smaller caffeine intakes for demanding parts of the race—for example long climbs, intervals, crosswinds, or the final part, when mental fatigue may be felt more strongly
A typical strategy for a long-duration race could, for example, be:
- About 45–60 minutes before the start as the main caffeine dose via capsules, coffee, or gel
- One to three smaller caffeinated gels or chews in the second half of the race, depending on duration, tolerance, and total daily intake
At the same time, your carbohydrate strategy should be in place via gel, drink, or bar, and fluids and electrolytes should be adjusted to duration, intensity, and temperature. Here, carbohydrate and electrolyte drinks such as Carbo Race Electrolyte or dedicated electrolytes for optimal fluid balance can be relevant parts of the plan.
Choosing a caffeine source for your sport
Research does not indicate that caffeine in capsules is inherently more effective than caffeine from coffee or other caffeinated drinks when the total amount of caffeine is the same.
That said, the different sources each have their own strengths and weaknesses:
- Coffee can be a tasty and easily accessible solution, but the caffeine content varies per cup, and coffee can cause stomach issues for some close to hard activity
- Capsules provide easy and precise dosing in milligrams without extra fluid or flavor, but they do not deliver carbohydrates, so energy must come from other sources—for example with caffeine products like a caffeinated energy gel
- Sports nutrition such as gels, chews, and effervescent tablets is easy to consume on the move and can combine carbohydrates, caffeine, and possibly electrolytes, but often requires getting your stomach and gut used to it
If you want a complete overview, you can take a closer look at a sample mix of energy gels (with and without caffeine) and choose the solutions that match your discipline, your intensity, and your tolerance.
Side effects, sleep, and special groups
Most adults tolerate caffeine in moderate amounts, but high or unfamiliar doses can cause issues that may be unhelpful on race day.
Typical side effects may include:
- Restlessness, nervousness, and jitters
- Palpitations or an uncomfortable awareness of heart rate
- Stomach problems such as nausea, stomach pain, or diarrhea
- Sleep difficulties, especially with intake later in the day
Some groups should be extra cautious with caffeine, including:
- Pregnant and breastfeeding people, who should follow health authority or physician recommendations
- People with heart arrhythmias, high blood pressure, pronounced anxiety, or sleep problems
- Children and adolescents, especially in combination with strong energy drinks
High caffeine consumption that is stopped abruptly can also cause temporary symptoms in some, such as headaches and fatigue.
Although caffeine can have a mild diuretic effect, research suggests that regular coffee drinkers typically do not become dehydrated with moderate intake. During hard training, especially in hot conditions, a solid strategy for fluids and electrolytes remains important.
How to test caffeine in your training
If you want to use caffeine as part of your performance strategy, the key is to test it just as systematically as you test shoes, pacing, and your energy plan.
For example, you could do it like this:
- Choose a relevant workout—for example a tempo session, a long run with progression, or a race-specific interval session
- Start low with about 2–3 mg of caffeine per kg of body weight 45–60 minutes before starting via coffee, capsules, or a caffeinated gel
- Evaluate systematically by noting how your stomach felt before, during, and after; what perceived exertion was like at a known pace or watts; and how sleep was if the session was late
- Adjust one factor at a time—for example dose, timing, or source—so you can better assess what makes the difference
- Build it into an overall race plan once you’ve found something that works for you, and combine caffeine with carbohydrates, fluids, and electrolytes—possibly with both gels and electrolytes for optimal fluid balance
For many, caffeine can be a relevant tool in endurance sports, but it should be seen as a supplement to training, sleep, and basic nutrition. Use research as a guideline, test strategies well in advance, and adapt them to your body, your sport, and your goals.