Why Do Marathon Runners & Triathletes Collapse? (Risks & Prevention Tips)

You’ve all seen it. Marathon runners and triathletes cross the finishing line only to collapse in a heap. Many people assume this shouldn’t happen to professional athletes, but it does. Many things contribute to this, from hot weather to poor preparation.

So why do marathon runners & triathletes collapse? It could happen for a variety of reasons. Heatstroke, dehydration, hyponatremia, jelly legs, hitting the wall, postural hypotension, or undiagnosed cardiac conditions. Some of these can be treated, and most can be avoided. 

I’ll cover all of these and finish with pointers on how to prepare for the event. That way, you can reduce the likelihood of any of these happening to you.

What Causes Runners & Triathletes to Collapse?

Runners and triathletes collapse during and after a race for different reasons. Most of them, like heatstroke and hyponatremia, come from hot weather and poor fluid intake. Heart attacks are more genetically associated; more on that shortly. (Source)

Dehydration and Heatstroke

By the time you feel thirsty, you’re at the point where you’re dehydrated. Ensure you’ve consumed sufficient fluids before and throughout the race. Even if you don’t feel like it, my tip is to drink wherever it’s provided, or at least every second time. This activity will help reduce getting dehydrated.

Suppose the weather is hotter than you’re used to; the chance of heatstroke rises. Wearing sunblock protects you from the sun’s rays, and drinking cool water before and during the race will help prevent this.


Be careful, though, about drinking water only. Too much plain water can dilute the sodium in your blood. This effect is called hyponatremia. Symptoms include vomiting, becoming confused, and eventually collapsing. Mixing your fluid intake with energy or fruit drinks can help prevent this. 

Why Do Runners’ Legs Give Out?

There are three main reasons runners’ legs give out, mainly at the end of the event. The first two are nicknamed ”hitting the wall” and “jelly legs.” They’re exactly what they sound like; the runner’s legs and body are physically unable to go any further. Then again, the most likely cause is postural hypotension, and it’s a result of the race. 

Hitting the Wall

When your body has given everything it has and can’t take another step, it’s called hitting the wall. Even though the mind wants to go further physically, you can’t. 

The primary contributor to hitting the wall is that the body has run out of carbohydrates to burn and is accessing purely fat. The process of turning fat into fuel is slower, causing the body to stop as it doesn’t have enough energy. (Source)

Jelly Legs

The final stage of your body telling you that enough is enough is when your legs give out. They’re called jelly legs, as that’s what they feel like. They feel all soft and buckle right under you. It’s your body’s last attempt at stopping you from doing any permanent damage.

Postural Hypotension

You’ve heard the phrase what goes up must come down, right? The same applies to a running event. You’ve gone all out, your heart rate and blood pressure are higher than usual, and you’re generating loads of adrenalin. Then the race ends! 

Your heart rate drops, your blood slows down its circulation in your legs, and your body doesn’t know how to react. What happens? You collapse. It’s a similar sensation to standing up too quickly and feeling dizzy. While nowhere near as concerning as the previous two, it still requires immediate medical attention.

Are Athletes More Prone To Heart Attacks?

People believe athletes are less likely to have heart attacks as they’re perceived to be healthier than sedentary people. In many cases, this is true, but only sometimes. It’s rare for a professional runner to have a heart attack mid-race, and if they did, it’s probably related to sudden cardiac arrest.

Sudden Cardiac Death 

A seemingly healthy person that dies unexpectedly from a heart attack falls under the condition known as sudden cardiac death (SCD). It’s not as simple as stating that the person was, in fact, healthy.

The leading cause of SCD is faulty electrical signaling in the heart. There are four contributors to this. Three are genetic, and the fourth is a result of physical action: 

  • Thickened Heart Muscle: Passed on via genetics, it’s where the heart muscle grows too thick. The heart struggles to pump blood, causing a rapid heart rate.
  • Long QT Syndrome: Fast, chaotic heartbeats, brought on by a heart rhythm condition, usually diagnosed at birth.
  • Heart Birth Defects: Some people are born with blood vessels and heart defects that can cause blood flow restrictions.
  • Blunt Chest Injury: A brutal hit to the chest, often from playing contact sports or being hit with equipment. This trauma can change the heart’s electrical signaling.

How Often Do Athletes Collapse?

There isn’t a lot of data available to give accurate figures. What we do know is that collapsing from heart-related conditions is more common in student athletes. 

It’s estimated that SCD occurs in young athletes between 1 in 50,000 and 1 in 80,000. It’s also more common in males than females. (Source)

How to Avoid Collapsing While Racing

Being well prepared for an event, both mentally and physically, goes a long way toward preventing these issues from occurring. It doesn’t end there. Preparation begins before, at the start of, and needs maintenance throughout the event.

Before the Event

Give yourself an extra day of rest, preferably the day before the event. Check out our article When Should You Taper for A Triathlon? How To Properly Do It! for more details on this.

I’ve talked a lot about hydration, and it’s vital that you drink the equivalent of two eight-ounce glasses of water two hours before the event. Then an hour before the race, try to eat at least 300 calories of nutritious food; this is necessary to top up on those carbohydrates you’ll need.

And finally, don’t overdress. A contributor to heat stroke can also be too many layers. If it’s too cold for you pre-race, wear an old shirt, or a trash bag, you can discard that once the race starts. (Source)

At the Start Line

Ask yourself how you’re feeling. Have you had enough rest? Is your body pain-free? Have you consumed the right amount of food and fluids? Do you believe you can run 26 miles today (or whatever the event distance is)?

If the answer to any of those questions is no, then as tough as a decision it is, you may be better off pulling out now. Any of these could contribute to you hitting the wall, or worse.

During the Event

Be aware of feeling thirsty, remember I said earlier that this is a sign of dehydration. You must drink fluids, but not purely water, as often as possible. Marathon and triathlon events provide aid stations at equal spacing along the course so you can hydrate. Events with more sponsors also tend to offer energy drinks, fruit, and protein bars. 

Top up your energy levels as often as possible to give your body the fuel to keep going.

How to Use Marathon Aid Stations | Race Day Tips

Listen to your body; if you’re feeling weak or tired, or jelly legs are approaching, it’s time to call it quits. It’s better to DNF (did not finish) than to hurt yourself and possibly land in the hospital. 

Marathons and triathlons can be grueling events on your body, so prepare before and be aware during, and you’ll have the best possible experience.

We also recommend that you check out our post “Why and When You Should Quit Triathlon? When To Avoid It!


An extreme triathlete who have competed in dozens of triathlons including IronMans and Extreme triathlons.

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