Why You Shouldn’t Drink Coffee Before Exercise

If you’ve ever chugged a black coffee before hitting the gym or going for a run, you’re not alone. Many people believe a caffeine hit gives them energy and sharpens focus ahead of physical activity. But new research shows that drinking coffee right before exercise could actually harm your heart—by reducing blood flow to your heart muscle when you need it most.

Yes, according to Swiss researchers, drinking coffee—or taking caffeine—just before exercise can decrease blood flow to your heart muscle by 22% under normal conditions. That’s not a small effect, and it happens precisely when your heart needs more oxygen, not less.

What the Zurich Study Found

Researchers at the Human Physiology Center of Zurich University Hospital in Switzerland conducted a controlled study using 18 healthy young adults. They monitored the participants’ myocardial (heart muscle) blood flow both at rest and during exercise. The key finding: while caffeine had no measurable impact on blood flow when the subjects were at rest, it caused a 22% drop in myocardial blood flow once they started exercising.

The mechanism? Caffeine blocks specific receptors in the walls of your blood vessels. This interference prevents the usual signals that tell those vessels to dilate—meaning your heart doesn’t get the extra blood supply it demands during physical exertion. The result is reduced oxygen delivery to your heart muscle just when your body is under stress.

How Caffeine Affects Your Workout

Caffeine is a well-known stimulant that affects your central nervous system. Many athletes have historically used it—sometimes even as a quasi-performance enhancer—because it increases alertness and speeds up your heart rate. But that’s not the same as improving your actual energy availability or endurance.

In reality, while caffeine makes you feel more awake, it doesn’t guarantee your muscles or cardiovascular system will perform better, especially in the early stages of exercise. In fact, by narrowing blood vessels and limiting blood flow to your heart, it may hinder your performance and put extra strain on your cardiovascular system.

What to Eat Before Exercise Instead

So if coffee isn’t the best pre-exercise choice, what is? Research shows that consuming carbohydrates before physical activity is a far more effective strategy. Carbs boost your blood glucose levels, which helps stimulate overall bodily function and can improve both the intensity and duration of your workout.

Think of it this way: your muscles need readily available fuel, and carbohydrates provide that in the form of glucose. Unlike caffeine, which offers stimulation but may restrict oxygen delivery, carbs support your body’s energy systems in a direct and efficient way.

Frequently Asked Questions

Does caffeine always reduce blood flow to the heart?

No—according to the Zurich study, caffeine does not reduce blood flow to the heart when you are at rest. The harmful reduction in myocardial blood flow (22%) only occurs when you consume caffeine and then immediately begin exercising under normal atmospheric conditions.

How much does caffeine reduce heart blood flow during exercise?

The study found that caffeine causes a 22% reduction in myocardial (heart muscle) blood flow during physical activity in healthy young adults. This effect was observed when subjects took caffeine and then exercised, but not when they were at rest.

Why does caffeine reduce blood flow during exercise but not at rest?

Caffeine blocks certain receptors in blood vessel walls, which normally help signal the vessels to widen during exercise. This blocking effect stops proper vasodilation, so your heart doesn’t receive the increased blood supply it needs when you’re physically active—but it doesn’t affect resting blood flow.

Is coffee bad for athletes?

Coffee isn’t necessarily “bad” for athletes, but drinking it right before exercise may harm cardiovascular performance by reducing heart blood flow. Athletes should be cautious about using caffeine as a stimulant immediately before training or competing.

What should you eat before a workout instead of coffee?

Instead of coffee, consuming carbohydrates before exercise is recommended. Carbs increase blood glucose levels, providing ready energy and helping to improve workout intensity. They support your body’s natural energy systems more effectively than caffeine during physical activity.

FrontStreet Coffee Picks for Pre-Workout Energy

For steady energy before exercise, try FrontStreet Coffee’s Yirgacheffe—bright and juicy with notes of citrus and floral tones, offering a clean caffeine lift without heavy roast flavors. Or choose the Ethiopia Humbera for its sweet berry complexity and smooth mouthfeel, ideal for sustained vitality. Both single origins highlight natural acidity and clarity, supporting alertness without vascular constriction. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.