Bodybuilding is a demanding, high intensity sport.

Health and safety concerns abound, especially for those serious enough to be competing at a professional level. It wasn’t long ago that Dallas McCarver suffered a massive health scare after collapsing onstage at the Arnold Classic 2016. And later died much too soon (though most likely not directly related to his fainting on stage).

So what is it that makes bodybuilders collapse onstage? It’s actually kind of a complicated answer. The good news is, unless you have an underlying condition, these accidents are not likely to leave you with any permanent damage. Here are the 5 most common reasons that bodybuilders collapse or pass out while posing onstage:

1) Dehydration

This one is a bit obvious, but arguably also the most important. Hydration is the key to human life. We are about 60-70% water, after all. When bodybuilders cut down on carbs and fats leading up to a show, they also sometimes wind up extremely dehydrated. When you become dehydrated, the volume of your blood decreases, but since that same amount of blood still has to travel all around your body, the heart is working a lot harder to move it around. This can cause a variety of symptoms — headaches, general fatigue, and confusion are three of the big ones. Add all of that to the flexing and physical exertion of a show and you have a recipe for disaster. More specifically, a recipe for dizzy spells and fainting onstage.

2) Cramping

Cramping onstage is another common problem that can lead a bodybuilder to collapse. A number of things can cause this one, including dehydration. Another very common cause of onstage cramping is low sodium. Sodium is an essential electrolyte that bodybuilders often lack going into a show because, again, they’ve usually been cutting down their water weight and body fat very intensely before a show. Excessive sweating can also significantly deplete a body’s store of sodium. The resulting muscle twitches and cramps can sometimes make it painful or even impossible for a bodybuilder to stand upright onstage.

3) Holding Their Breath

It’s true — holding your breath while you flex can cause you to faint! Many bodybuilders hold their breath onstage to maximize the appearance of every single muscle as they strain. For some people, this alone is enough to make them pass out. But your chances of fainting or collapsing are higher if there are other factors present as well. Dehydration plays a role, which is yet another reason it’s the #1 most important factor on our list. It’s also true that whenever you’re standing for a long period of time blood tends to be pulled into your lower body, and therefore away from your brain, by gravity. Over time, the combination of all these factors is another reason that holding your breath while flexing can cause you to collapse onstage.

4) Low Blood Sugar

This is another diet one related to cutting down. When bodybuilders cut down on carbs, their intake of sugar, or glucose, is also greatly reduced. Glucose is another vital enzyme that your cells break down for energy. When you have low blood sugar your blood pressure drops and less blood flows to the brain. Your brain then causes you to faint in response because it no longer has enough blood to sustain vital functions. This is another common reason that bodybuilders pass out onstage.

5) Underlying Conditions

Unfortunately, many people have underlying health problems that are completely undetectable until it’s too late. Problems with your heart, your blood pressure, or your nervous system can combine with any of the above components in a potentially fatal way when competing. Roughly 40,000 people in America are born every year with heart defects, but only a fraction of them ever know. It may never impact them – but if they become an athlete, or overexert themselves, it has the potential to fatally stop their heart. While some underlying conditions are complete unknowns, others are well within your control to manage responsibly. Bodybuilders who are smokers, or who drink heavily, are at a higher risk of collapsing due to their generally poor immune conditioning. These underlying conditions can play a huge role in who does and doesn’t collapse onstage.

Heart conditions and other congenital defects are beyond human control – but everything else on this list isn’t!! Make sure that when you exercise you stay hydrated, manage your diet responsibly, and do your best to practice the sport in a safe and healthy way.