It means exactly what you think it means. Blacking out while running is like any other "blackout" experience. It involves a sudden reduction of blood flow to the brain that results in a temporary loss of consciousness. So there's no surprise that this can happen to runners—but let's figure out what causes them. Read on to learn the reasons why a runner may black out and how to prevent it from happening again.

What Happens To The Body When You Black Out

Ultimately, it's when there's not enough blood getting to your brain. Blood carries oxygen throughout the body. So when a faint is triggered, it's because your blood pressure has dropped too far for the blood to flow to your brain and it doesn't have access to enough oxygen.

So What's the Cause?

The overall best response to why runners black out is dehydration. The most obvious way this can happen is simply by not drinking enough fluids. When you lose or use more fluid than you drink, your body doesn't have enough fluid to function normally. So maybe before you headed out for your run, you felt fine, then a few miles go by and you see stars or begin to feel faint. This is because as you run you're sweating out more fluids and your output is higher than your input.

Another cause is exposure to the sun's UV rays. This causes your body's blood temperature to rise and accelerates this dehydration process. However, when you're dehydrated your blood sugar levels decrease, which is important to note if it's caused by the heat versus fluid input.

Not eating enough pre-run is another cause. This is a result of your blood sugar being too low which affects the blood flow to your brain.

If you black out while running despite being properly nourished and hydrated, you may have an underlying medical issue. One possibility is a heart-related issue; we advise seeing a doctor to discuss this with.

How To Know If You're Going to Black Out

While fainting alone may typically not be dangerous, blacking out while running can be. Blacking out while moving at high speeds can cause you to lose your balance and fall to the ground. This moment of being "blacked out" can cause you be injured on the way down. To make sure this doesn't happen, make sure you are aware of these signs before a blackout occurs. Warning signs can include dizziness, nausea, sweaty palms and/or tunnel vision. The phrase "seeing stars" tends to explain the feelings of being dizzy or faint.

Don't Let It Happen (Again)

If you've ever experienced blacking out while running then you know you never want it to happen again. Make sure you nourish your body properly before and after your run. If you're feeling a bit hazy before you run, rest a little longer and try to drink three cups of water. Keep in mind, the more you sweat, the more dehydrated you become. Eat a smaller meal with carbohydrates, lean protein, and healthy fats about two to three hours before running.

Never run unless you feel like yourself. Run when you feel good and stop when you don't. Blacking out while running can be dangerous and if it happens more than once, talk with your doctor.