What happens to your body during an ultramarathon

Ultramarathons are races ranging from 50 to 4,345 km in distance. Your body can go through a lot of stress during these grueling tests of human endurance.
During races, nausea and vomiting are the most common problems for runners. Some runners may get blurry vision.
Sleepiness and hallucinations are problems in longer races lasting more than 24 hours.

Ultramarathons are a growing sport in the US and globally. In these grueling tests of human endurance, your body can go through a lot of stress.

Following is a transcript of the video.

In 2018, more than 108-thousand people finished ultramarathons in the US alone. An ultramarathon is any race longer than 42 kilometers. Races can range anywhere from 50 to over 4,000 kilometers. But one of the more common lengths covers about 100 kilometers and takes, on average, 17 hours to finish.

In some of the longer races, half of the runners never see the finish line. Because these races not only push you to your mental limit they take a toll on your body both inside and out.

Ultra runners endure pretty extreme conditions. The Badwater Ultramarathon, for example, covers over 4,000 meters of elevation through Death Valley, in July, one of the hottest months of the year. Temperatures reach up to 47 degrees Celsius, causing headaches and dizziness in many runners.

But even if you’re running in more comfortable weather, you could be feeling sick to your stomach. One of the most common issues in any ultramarathon is nausea and/or vomiting. It affects about 37% of people who complete a race, but it’s also the number one reason runners won’t finish in the first place.

That’s because running disrupts your digestion. It diverts blood away from your stomach to your muscles. And since ultramarathons last so long, many races provide sandwiches, pasta, and other carb-loaded meals. As a result, that food will sit around undigested, causing problems. But if your stomach isn’t slowing you down, your eyes could be causing you grief.

Windy conditions can dry out or damage the cells that pump a protective liquid layer over your cornea, which can cause your cornea to swell up and blur your vision. During the Hellgate 100K for example, runners report losing most of their vision by the end. They call it "Hellgate Eyes."

But no amount of protection or preparation can prevent one symptom: Sleepiness. For a 17-hour race, it might not be so bad. But longer races can stretch to more than 24 hours, which can make sleepy runners more prone to trips and falls or worse, hallucinations.

The Barkley Marathons, for example, is a race where runners are given 60 hours to finish 161 km. In 2005, one runner reported that he thought he saw houses at the top of the mountain and believed he was their garbageman sent to pick up the trash.

Despite all these health hazards, ultrarunning is a growing sport. One study found that compared to marathoners, ultrarunners are more likely to do it for nature and a sense of purpose than for the competitive aspect. So if you’re up for the challenge, plenty of races are on trails through natural areas, so at least you’ll get a great view!