Caffeine may be just the exercise booster you need—as long as you don’t over do it, say experts

“It’s a great performance enhancer,” Susan Kitchen, a Sports Certified Registered Dietitian (CSSD) and USA Triathlon and Ironman Certified Coach tells Fortune.

But she notes that caffeine—whether ingested through coffee, soda, or energy chews or drinks—can be a tricky supplement to incorporate into your exercise routine—and that it might not be right for some people at all. Here’s how to approach working out under the influence of caffeine.

What is caffeine and how does it work?

Caffeine is a stimulant found naturally in a range of plants, including coffee beans, cacao beans, kola nuts, tea leaves, and yerba mate, according to the Library of Medicine; while it’s most often extracted from coffee beans, the kind of caffeine found in soda is largely produced synthetically in China, while sports nutrition products and other supplements may contain caffeine from either natural or synthetic sources. 

The way that caffeine aids with energy is by blocking the action of the chemical adenosine, which promotes calmness, relaxation, and sleepiness. Recent studies have also shown it to be associated with a lower chance of diabetes and improved metabolism.

How caffeine can affect a range of workouts

Nanci Guest, a sports dietitian at the University of Toronto, says that anyone aiming to be active can benefit from caffeine—whether they’re racing a marathon, playing a game of pickleball, or simply going for a walk.

Guest, also a strength and conditioning coach, pointed to a study of sedentary men, which found that after caffeine ingestion, they were able to do more exercise than those who didn’t have caffeine—without feeling like they were working harder, either.

“For the average person, if you want to lose weight or just get more fit, when you have a cup of coffee before you do your morning walk and you end up walking 45 minutes versus 30 minutes, that’s absolutely getting a bonus,” Guest tells Fortune.

People who are more serious about their workouts—like runners training for marathons or avid gym-goers—can benefit from caffeine too, according to Guest.

“If you’re doing sprint intervals because you’re going to the Olympics, you’re going to get that benefit,” Guest says. “If you’re just doing a weight training workout at the gym…you’re going to get a boost.”

In addition to blocking feelings of sleepiness, caffeine lowers your rate of perceived exertion, or RPE, during a workout, meaning it doesn’t feel as difficult. “You get a burst of energy and you don’t feel like you’re working as hard as you would feel if you didn’t have the caffeine,” Guest says. 

Guest explains that for cyclists, for example, having caffeine could make a hard ride feel easier—so that instead of dreading the painful burn of an uphill pedal, they might feel ready and energized. 

“When you encounter that hill, [it isn’t] going to be quite as bad if you’re under the influence of caffeine,” Guest says.

How to add caffeine into your workout routine

Your morning cup of coffee could be used to your advantage—in fact, Guest encourages coffee consumption, citing its many longevity benefits in addition to the caffeinated boost it provides to workouts.

But to maximize the benefits of caffeine, it’s important to pay attention to timing and dosage, says Kitchen, who notes that its effects typically peak an hour after consumption.. 

She recommends ingesting it 45 minutes before your workout, or, if you want it to peak towards the end of your session, 20 minutes before.

However, different forms of caffeine are metabolized at different rates, Kitchen says. Natural forms of caffeine found in coffee and tea, for example, take longer to peak in the bloodstream than those found in sports nutrition products like gels, energy chews, and gum.

The most precise approach for pre-workout intake, says Kitchen, is to use the guide of 2-3 milligrams per kilogram of bodyweight; to figure out your weight in kilograms, simply divide your weight in pounds by 2.2. So someone weighing 125 pounds, for example, weighs about 57 kilograms, and, if using 2 milligrams per kilogram of that bodyweight, would wind up with a 114 milligram pre-workout dose.

Caffeine quantities can vary from coffee to coffee, though, Guest says. For those looking to be more precise—or who don’t drink coffee—there are other options, like caffeine pills, which will have exact milligram quantities per pill, or sports nutrition products.

An 8-oz cup of coffee typically has 90 milligrams of caffeine, while sports nutrition supplements or caffeine pills can range from 35 to 300 milligrams—more like three cups of coffee in the higher dose—so choose carefully.

“It’s what somebody enjoys,” Guest says.

Kitchen advises a trial-and-error approach to find your best dose, and to start small with more like 1-2 milligrams per kg of bodyweight, and see how you feel.

Those doing longer workouts, such as people racing marathons or triathlons, could also utilize caffeine as a helpful tool to stave off fatigue, Guest and Kitchen both point out.

“Caffeine has the greatest effect as you get more tired,” Guest says. So a marathon runner may want to time out smaller doses of caffeine (25-35 milligrams) in the form of energy gels or chews, for example, during their race or long run so that the caffeine boosts them when fatigue is highest.

Be aware of caffeine risks

For most adults, 400 milligrams of caffeine—about two to three 12-ounce cups of coffee—a day should be safe, according to the U.S. Food and Drug Administration. Too much caffeine, though, can lead to increased heart rate, heart palpitations, high blood pressure, insomnia, anxiety, nausea, headache, or the jitters. But individuals vary widely as far as how sensitive they are to it and how quickly they can eliminate it from their body.

Most people will know if their body is sensitive to caffeine, just from consumption in daily life, Kitchen says, noting that anxiety or increased heart rate means you probably should be cautious about caffeine supplementation. Those who have heart conditions, take medication that elevates their heart rate, and tend to experience anxiety should likely steer clear entirely, she says.

“If you struggle with anxiety, having caffeine is not the thing to do,” Kitchen tells Fortune, as it will only amplify the feeling.

As far as caffeine impacting sleep, Kitchen argues that getting enough is more important to your performance than the supplement itself. She recommends people cut off caffeine by 10:00 a.m., as it takes roughly 12 hours for it to leave your system entirely. That is especially important for anyone who struggles with sleep anyway.

You might have heard that caffeine dehydrates you, but studies have shown it’s not the case. Water is still the best way to stay hydrated but while caffeine might make you urinate more, as it’s a natural diuretic, it’s not actually dehydrating you.

Finally, be mindful of your caffeine source, urges forensic toxicologist Justin Brower, who advises using caution with supplements and to avoid pure caffeine powders that are easy to over-consume without precise measurements.

“Don’t take supplements if you just don’t know what they are,” Brower tells Fortune.

At the end of the day, you simply need to listen to your body, experts advise, with the experts emphasizing that it’s all about trial and error—and that nothing should get in the way of your sleep or wellbeing, even if it could potentially enhance your performance.

“You need to see your own individual response,” Guest says. “Most people can tell how they feel.”

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