Caffeine and Exercise: What Does Science Say?

My passion for sports and fitness is at least as great as my passion for coffee and reviewing coffee gear. And as it happens, there is a close connection between caffeine and exercise. Caffeine is not simply considered a stimulant among athletes, but rather a turbocharger for improving exercise performance.

Still, what does improving metabolism actually mean? What does science have to say about the effect, dose and side effects?

Important note: I am not a doctor. I just test and review coffee machines and coffee beans or rant about stupid trends like “proffee.” So, if you have individual questions about caffeine and exercise, be sure to ask a doctor.

Caffeine and Exercise: The Basics at a Glance

When we talk about consuming caffeine to improve exercise performance, there are two main topics: established facts and scientific question marks. Facts include:

But even these facts have not been conclusively clarified. The fact is that the effect of caffeine on people depends on many individual conditions. 

In the sporting environment, genetics as well as regular coffee consumption play a significant role. As do the sport and its challenges as well as the consumption of other substances such as glucose (sugar).

Studies on the Effects of Caffeine in Sports

Scientists are keenly interested in the effects of caffeine on improving performance in athletes. 

There are so many studies and reports that there are now titles like “Not Another Caffeine Effect on Sports Performance Study.”

This paper provides an excellent overview of the current state of facts and first narrows down why athletes are so keen on caffeine in the first place. Although there is no conclusive evidence on individual effectiveness, there is enough evidence that caffeine ingestion has an impact on:

The possible side effects have also been well studied. Side effects such as heart palpitations, sleep disorders, headaches, tremors, etc. were confirmed several times by test subjects in sports studies.

Why Use Caffeine to Improve Performance?

The alkaloid caffeine is officially classified as an ergogenic – a performance-enhancing drug. It belongs to the group of natural purines and is a so-called adenosine receptor antagonist. 

Adenosine has various calming properties. However, if adenosine receptors in the central nervous system are occupied by (similarly structured) caffeine, the opposite of feeling calm happens.

During any form of (sustained) physical activity, the body uses energy, puts strain on muscle groups, the circulation, etc. And in order to protect itself, at a certain point it reacts with fatigue. 

Due to its complex properties, caffeine can not only delay fatigue, it can also support muscle contraction, optimize blood circulation, focus the nervous system and accelerate recovery after a workout.

Strength or Endurance: When Is Caffeine Useful?

Even though a morning dose of caffeine is part of many people’s everyday lives, science has a clear opinion when it comes to caffeine and exercise performance: 

The intake only makes the most sense in sports that primarily require endurance, which is driven by strength (Southward et al. 2018). So we’re talking about endurance athletes like professional soccer players and professional cyclists. 

If you “just” go to the gym to do strength training and stay fit, you don’t need the caffeine intake. At least not during training. The same applies to recreational soccer players or after-work cyclists.

The possible side effects have also been well studied. As I mentioned above, study subjects have confirmed headaches, sleep disorders and a whole host of other symptoms.

When and How Much: The Optimal Caffeine Dosage

To ensure comparability, caffeine-related effects are primarily examined in three doses: 3 milligrams, 6 milligrams and 9 milligrams of caffeine per kilogram of body weight. However, lower concentrations starting at 1 milligram (so-called microdoses) are becoming increasingly interesting to researchers.

It is generally agreed that the best results for athletic performance are achieved at a concentration of between 3 and 6 milligrams of caffeine per kilogram of body weight (for example Pickering & Kiely 2019).

So, if we assume a 3-milligram dose for a person weighing 80 kilograms, they would need 240 milligrams of caffeine to benefit during exercise or sport.

For comparison: How much caffeine does coffee have? That depends on the beans and their natural caffeine content, the roast profile and, last but not least, the preparation method. In our large caffeine study, we had 15 drinks scientifically examined.

Accordingly, a typical shot of espresso has a caffeine content of 68 milligrams, while a cup of coffee from a French press starts at 223 milligrams.

Caffeine Before Exercise?

The highest concentration of caffeine in the blood is measured approximately one hour after ingestion (e.g. White et al. 2016). It therefore seems logical to take the preparation at least an hour before training or participating in competitive sports. This is what most sports scientists currently recommend.

Caffeine While Exercising?

It can take between 1.5 and 9.5 hours for the body to break down half of the caffeine. (National Library of Medicine 2001). This range is determined, among other things, by whether you drink coffee regularly or only use caffeine for exercise (Bell & McLellan 2002). 

That’s why, from a scientific point of view, it is questionable whether you should add more in between long or intense sporting challenges – and whether there will still be a significant effect.

So far, the only evidence that seems to be proven is that you have to find your own rhythm with repeated doses and definitely pay attention to the amount. The first dose should be well below the 3 milligram limit, and all subsequent doses should be taken accordingly (Pickering & Kiely 2019). 

Even if there are still final questions to be answered here, repeated moderate doses seem to be much more effective if you take caffeine at the same time as carbohydrates. (Skinner et al. 2013).

Caffeine After Exercise?

Ambitious cyclists in particular prefer to end their training session in a café. Then there is not only coffee, but also a big piece of cake. Interestingly, this combination seems to be an excellent idea from a scientific point of view:

Caffeine can support so-called glycogen resynthesis (Loureiro et al. 2021). The sugar or carbohydrates in the cake are there to replenish the energy stores in the muscles, brain and organs. The coffee can speed up this process.

This means you can not only shorten your recovery time, but also potentially avoid negative consequences of training too hard.

It has already been observed that caffeine reduces the occurrence of Delayed Onset Muscle Soreness (DOMS) or Exercise-Induced Muscle Damage (EIMD) (e.g. Caldwell et al. 2017). Here, however, the facts are still thin.

Coffee, Pills, Energy Drinks: What Are the Best Sources of Caffeine?

Let’s look at it practically: What happens if you drink a large glass of soda or a nice cup of coffee before a soccer game? You have to pee before the referee has even blown the whistle to start the match. 

What happens if you eat a large piece of high cocoa content chocolate instead? You feel full rather than buzzed because your stomach and intestines are busy.

Even beyond such practical objections, there is increasing evidence that caffeine in the form of liquid isn’t necessarily the best for exercise. Alternative caffeine preparations are now widely available

Both chewing gum and mouthwash (Wickham & Spriet 2018) are currently considered the most effective sources of caffeine because the alkaloid enters the system most quickly via the mucous membranes. However, capsules are more popular because they are easier to dose.

When it comes to overall effectiveness, the International Society of Sports Nutrition isn’t the only body to conclude (in an article from 2021) that it almost doesn’t matter in what form the caffeine is taken.

Caffeine and Exercise: Side Effects and Potential Dangers

Heart palpitations, sleep disorders, increased blood pressure, dilated blood vessels, nervousness … The possible side effects of caffeine in a sporting context are no different than in everyday life. Here, however, they are almost better studied and documented (e.g. de Souza et al. 2021).

What is much more interesting for science is the question of whether athletes can use the habituation effect to protect themselves from possible side effects and at the same time benefit better from the positive effects.

There is at least some evidence that tolerance and habituation (for example through daily morning coffee) are incredibly important for runners, footballers and the like. Otherwise, the physical strain under the influence of caffeine can become very great.

However, there is a good hack if you have overdone it: you can reduce caffeine levels through exercise. After all, your performance is accelerated on all levels.

In terms of health and performance, it generally remains questionable how substantial the effects actually are. Most studies report moderate improvements after ingestion. If any.

Metabolism and Fat Burning: Can You Lose Weight With Caffeine?

Most people start fitness classes and weight training programs to become fitter, slimmer and sexier. Anything else would be a lie. 

Not only in this context, caffeine is also considered a “slimming agent” (ugh) and a “calorie killer” (sigh). Even though such labels immediately put a bad taste in my mouth, the facts are pretty solid:

For example, a meta-study combining various practical studies came to the conclusion that caffeine can definitely have an influence on weight and body fat percentage (Tabrizi et al. 2018).

According to other studies, several conditions must be met for this to happen. You need a high caffeine concentration in your blood and urine, you should be a regular coffee drinker and you need to exercise regularly to achieve a moderate effect (e.g. Westerterp-Plantenga et al. 2005 & Ramirez-Maldonado et al. 2021).

In other words: Caffeine does not make you slim, but only supports the effect of actual “slimming products” such as regular exercise. Who would have thought.

Is That Doping?

In my opinion, the progress and relativization in caffeine research is best demonstrated by the fact that the World Anti Doping Agency (WADA) removed the substance from its doping list in 2004.

If its effects were really as bad as we might think, caffeine would still be banned in competitive sports – which was actually the case from 1984 to 2004.

However, the World Anti-Doping Agency has given the alkaloid “under observation” status. This means: As soon as any athlete studies find out that the substance can do more, it will immediately end up back on the doping list.

Caffeine and Exercise: (Not) a Conclusion

Is caffeine good for going higher, faster, further? Guaranteed. But the extent to which caffeine consumption ensures better results is far from clear.

Aside from all the studies, I think it’s important that you listen to your body and work on improving your fitness before you trust the effects of caffeine tablets and the like.

In addition, symptoms of fatigue are an essential protective mechanism. It’s not just a loss of attention that’s an urgent indication you should get off the bike or put the dumbbells away. 

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