The espresso before training, the pre-workout powder, the energy drink on the way to the gym: caffeine is the most frequently used performance-enhancing substance in sport — and one of the few for which the evidence is convincing. In the Sporternährungscoach programme, caffeine counts as an A supplement, meaning a substance with good evidence. Even so, more is not better, timing plays its part, and anyone hoping to use it as a substitute for missing sleep is only postponing the problem. Here you will find the mechanism of action, dose, timing, habituation and side effects — with the figures from the course material.
How caffeine works: the thing with adenosine
Caffeine is a natural active substance found in coffee, mate, guarana berries and tea plants. Its most important effect is based on a competitive inhibition of the adenosine receptors and the resulting stimulation of the central nervous system.
Adenosine accumulates in the brain over the course of a waking day and docks onto its receptors — that produces the feeling of tiredness. Caffeine has a similar molecular shape and occupies these receptors without activating them. The adenosine is still there, it just no longer gets through. So caffeine does not make you awake, it masks the tiredness signal — and as soon as it has been broken down, the adenosine that has meanwhile accumulated further makes itself heard.
After intake, caffeine reaches the blood quickly. The highest blood concentration is reached within 30 to 90 minutes and falls on average after 3 to 5 hours to half of the peak value. In total it has a performance-enhancing effect for about 3 to 6 hours. How strongly caffeine works in an individual probably also depends on genetic factors — that has not been conclusively clarified.
What caffeine actually delivers in training
The training names three proven directions of effect — partly in the head, partly directly in the body:
- It reduces the perception of fatigue, effort and pain. The same effort feels easier, which makes the difference in long or hard sessions.
- It stimulates the central nervous system and increases muscle contraction, for example.
- It can increase the release of fatty acids and the uptake of carbohydrates in the gut — relevant above all in long endurance efforts during which carbohydrates are taken in continuously.
Together with water and carbohydrates, caffeine is therefore one of only three nutrients that appreciably influence performance when taken during an effort. That puts much of what otherwise goes into pre-workout tins into perspective.
The A classification: why caffeine is judged differently from the rest
In the training, supplements are divided into groups according to the quality of the evidence. Group A supplements are supported by good evidence, and their use can make sense in specific situations in sport. Caffeine is one of them — as is creatine, for which scientific studies in healthy, trained people show that an adequate dose has a directly or indirectly positive effect on performance.
In group B are substances with a plausible mechanism but no proof of performance benefit yet. Take L-carnitine: its role as a transporter of fatty acids into the mitochondrion is undisputed — whether supplementation improves performance is so far unclear.
And even within group A there is a reservation that the course material expressly records: no supplement is suitable for all situations, people or sports, and inadequate use or dosing can even impair performance or health. So "A" does not mean "for everyone" but "well documented, where it fits". How this looks with other substances is shown in the articles on creatine, on taking creatine monohydrate and on carnitine.
Dose: 3 to 6 mg per kilogram of body weight
The figure that matters: 3 to 6 mg of caffeine per kilogram of body weight are needed to achieve the desired performance-enhancing effect. Earlier studies often used 5 to 6 mg/kg; more recent research shows that as little as 3 mg/kg is equally effective. At 70 kg that is around 210 to 420 mg — for comparison: an espresso delivers roughly 60 to 80 mg depending on the bean and preparation, a cup of filter coffee somewhat more.
The lower limit is the more interesting one: anyone who achieves the same effect with 3 mg/kg as with 6 has fewer side effects and more room to go up when it really counts.
When to take it?
Caffeine is usually taken one hour before the effort, so that the maximum blood concentration is reached at the start of the effort. In longer endurance efforts it can also be taken only during the competition and spread over several doses. The training names three application schemes:
- 3 to 6 mg/kg of body weight one hour before the effort
- or 3 to 6 mg/kg, divided into doses of 0.3 to 1.0 mg, spread across the whole competition
- or 1 to 2 mg/kg no later than 30 minutes before the end of the competition
The strategy should be tested individually in order to minimise unwanted side effects — in training, never for the first time on competition day. There the rule applies anyway: only eat and drink what has been tried out beforehand.
Habituation and tolerance
Here lies the practically most important point: the effects appear to be somewhat greater and to last longer in people not accustomed to caffeine. Anyone drinking four cups a day accordingly notices less from the espresso before training — the body adapts, among other things, the adenosine receptors.
A moderate dose of 3 mg per kilogram of body weight per day also appears to be unproblematic over longer periods. If you want the effect back for a competition, reduce consumption in the days beforehand — that too belongs tested in advance, because withdrawal brings headaches and irritability for some people. In competition week that is not a good combination.
Side effects — and who they affect
Possible side effects occur above all in people not accustomed to caffeine. They include:
- Racing heart and irregular pulse
- Trembling
- Sleep disturbances
- Headaches
At higher doses, gastrointestinal complaints and inner restlessness are often added — a real performance killer in endurance sport. Anyone with cardiovascular complaints, who is pregnant, who takes medication or who repeatedly notices heart palpitations should have their caffeine consumption assessed by a doctor.
One myth belongs cleared up here: the long-prevailing opinion that caffeine has a dehydrating effect because it is diuretic is based on old studies and does not apply, at least in people accustomed to caffeine. Coffee counts towards your fluid balance — how much you need is set out in the article Drinking in everyday life.
Caffeine is no substitute for sleep
Because the blood concentration only falls to half after 3 to 5 hours, an espresso at 5 p.m. is still half in your system at 10 p.m. In caffeine-sensitive people that is enough to worsen the time it takes to fall asleep and the proportion of deep sleep. If you train in the evening, it is therefore better to check whether the performance gain is worth the price.
The flaw in the reasoning behind it is more fundamental: caffeine blocks the tiredness signal, it does not remove the tiredness. Adaptation, recovery and hormone balance depend on sleep, not on the feeling of alertness — as covered in the article Sleep: your key to health and performance. The vicious circle sets in quickly: little sleep, more caffeine, even worse sleep. That stress and lack of sleep also have hormonal consequences is shown in the article on cortisol; how reliable the numbers from your watch are is set out in the one on sleep trackers.
Course tip from update Akademie: How supplements are classified by evidence, which doses are documented and how to advise athletes seriously instead of chasing trends is what you learn in the Sporternährungscoach programme at update Akademie — with dedicated modules on competition nutrition, supplements and evidence-based working. Alongside your job and close to practice.
Frequently asked questions about caffeine before training
How much coffee corresponds to the recommended dose?
At 70 kg body weight, the range of 3 to 6 mg/kg lies between around 210 and 420 mg. Depending on the bean, roast and preparation, that is roughly three to six espressos. Since the caffeine content varies widely, coffee is only partly suitable for precise dosing.
Does caffeine work for strength training too?
Yes. The reduced perception of fatigue, effort and pain as well as the stimulation of the central nervous system work independently of the sport. The effect is most noticeable where perceived effort is the limiting factor.
Do I have to give up caffeine for the effect?
Not necessarily. The effect is greater and longer-lasting in those not accustomed to it, but it does not disappear in habitual users. If you want to maximise the effect for a competition, reduce consumption in the days beforehand — and test that out in training in advance.
Is caffeine allowed in competition?
Yes. Caffeine has not been listed on WADA's doping list since 2004. Before that it was banned above a certain threshold.
Why does caffeine barely work for some people?
How and whether caffeine works in an individual probably also depends on genetic components — that has not been conclusively clarified. Added to that are habituation, sleep status and the timing of intake.
Conclusion
Caffeine is one of the few supplements where the evidence catches up with expectations: category A, 3 to 6 mg per kilogram of body weight, around one hour before the effort, an effect lasting about 3 to 6 hours. Those not accustomed to it feel the most — and at the same time are most likely to risk a racing heart, trembling or a restless night. That is why every caffeine strategy is tried out in training, not in competition. As an enhancer, caffeine is well documented. As a substitute for recovery, it does not work.
