The DNF: 10 Reasons it Happens to Runners and How to Avoid It

In running, and especially with trail running and ultramarathons, there is one thing that is certain; there will be uncertainty. On race day, you’ll run in to all sorts of scenarios and factors that can help make or break your day. DNF – or Did Not Finish – are three dreaded letters that no runner wants to carry. Throughout this article, we will explore the common causes for a DNF, why they happen, and how you can avoid them becoming an obstacle to the finish.

Two runners top out on Handie’s peak @ 14,000+ft at the hardrock 100 mile.

Two runners top out on Handie’s peak @ 14,000+ft at the hardrock 100 mile.

Conflicting Interests

This all comes down to your WHY. Why are you doing this race? Is it for personal reasons? Can the reason be taken away from you? If nobody knows about the result of your race, will it make a difference? Your why is what will keep you going when the racing gets tough. If your main goal is to take first place and break a record, the thought of quitting is going to overtake your mind as soon as the initial endorphins of the starting line start to wear away.

If your why is a personal reason, this will make a huge difference. If you are raising money for a charity, or because running makes you happy and you believe it makes you a better person, or because bonding with the community makes you feel whole, or because the outdoors give you a sense of calm and accomplishment, nobody can take this away from you and it will be there to power you through the race. Everybody will have a different reason; the key has to be that the reason cannot depend on something that could be lost to circumstances that are external to you.

Mismanaging Fuel

Most runners are able to process around 120-240 calories per hour. While racing, calories burned can easily equate to a range of 400-900+ in an hour. Glycogen can be stored at around 15g per kg of body mass, so, a 175 pound carboloaded runner might be able to max out at 1,200g of glycogen stores. This is good for 4,800 calories. Some quick math will show that eventually, and perhaps very quickly, we will run out of glycogen stores, not be able to process calories fast enough, and our bodies will have to rely on fat. 

Put in to simpler words, you will not be able to process all the calories you need in a timely fashion. Your body will have to dig in to reserves, and may burn some fat reserves along the way. Gorging yourself at aid stations may not do much more than make your stomach sloshy, indigestive, and uncomfortable. Be consistent with your fueling, but don’t over-do it.

Failing to Recognize the Significance of Time

It can be easy to let the element of time get in your head. There’s the common saying that time is money. Playing off from that, let time be an investment in your race day.

Fishing a rock out of your shoe = 3 seconds. Getting a blister in 5 miles from failing to fish out the rock is a missed investment on your time.

Filling up your bottle at an aid station = 6 seconds. Bonking from dehydration in 4 miles from failing to hydrate is a missed investment on your time.

Taking off your vest to get a calorie bar out of the back = 10 seconds. Having no energy for 8 miles until the next aid station (and potentially farther) is a missed investment on your time.

Similarly, taking too much time in places can really add up. Seeing the clock tick can lead to anxiety in your race, especially if it leads to your planned schedule, PR, or cut-off times being at risk.

Grab your food at the aid station and eat it on the go vs while standing there.

Resist chatty interactions with friends at aid stations.

If you’ve got to go #1 and you are going for a podium or a time that means a lot to you, you might consider not stopping. You know what that means. Like dirt, it washes out. If you choose this route, spray some water down there to wash away/dilute the salts and acid. 

The Chair

If you are doing an ultra, there is almost guaranteed to be a time when you get the opportunity to wander into an aid station and find a big, empty, cupholder lined, shade-covered, servant volunteer surrounded chair with your name on it. Add a campfire and vat of hot chocolate and cream of potato soup if you are on a nighttime segment.

Do. Not. Sit. Down. 

As a survival technique, your mind will make an attempt to protect you from the miles and perceived danger ahead through an influx of feel-goods. This, combined with a buildup of lactic acid will make getting your a…  butt out of the chair exponentially more difficult. 

Instead, we recommend grabbing your food (ask for a little bag – aid stations commonly have them… or save a sea turtle and just double fist those googey PB&Js) and eat on the go.


Truth. Source: @ultrarunningmemes

Truth. Source: @ultrarunningmemes


Been There, Done That Mentality

Same dice, different roll. Same race, different situation. Just because you have done the race once doesn’t mean it is going to be the same race every time. There will be a different field of runners, different weather and trail conditions, and you will be a different person from 365 days ago. As Ben Franklin said, “By failing to prepare, you are preparing to fail.”

Mental Training is Equally Important as Physical Training

Taking plenty of time to visualize, study, and read about your upcoming race will prepare you to know (more about) what to expect. Having a long term race preparation plan will help you to better handle adversity in the race. If you can picture yourself at each stage of the race and go in with a plan, you’ll be that much more efficient when things start getting tough. (We’ve got tons of info on this one in those two links)

Breaking Status-Quo

Switching up routine on the day of a race is a good way to find yourself having a bad time. If you’ve been training with granola bars for the past 3 months, don’t start taking gels on race day. The same can be said with race day apparel; especially shoes. If you haven’t been training with it, you don’t know how you are going to react. Those brand new shorts might leave you chafed, and those new shoes might leave you blisters. Minimize your uncertainty by sticking to what is tried and true.

Radiate Positivity

When you smile, your body releases dopamine, endorphins and serotonin. Endorphins are a natural pain reliever. Serotonin functions as an anti-depressant. If you are feeling down during a race, smiling to yourself is your shortcut to feeling good!

When passing somebody or going in to an aid station, smile and mention something positive. This connection with other people (who will reciprocate the positivity) is contagious and can be a big, long lasting boost to your day. 

The Caffeine Conundrum

Caffeine. It is addictive. We live in a culture where coffee and caffeination is celebrated. I am guilty of imbibing in sometimes too much of it. However, there is a time and a balance for using it on race day. Caffeine is a gastrointestinal stimulant. It can cause irritation and inflammation of the stomach lining. Your stomach probably has extra blood in its lining from running by the middle of your race – a natural reaction. Caffeine can aggravate the soreness further. The effects can lead to diarrhea, vomiting, and cramping.

Coffee and cola are two common caffeine sources on race day. Both are highly acidic, which can further exacerbate stomach irritation.

As a diuretic, caffeine can cause us to rid of our hydration and some electrolytes before our bodies can benefit from them. It is important to also take down water and electrolyte-rich non-caffeinated fluids during a race to prevent dehydration.

Respect the Taper

You’ve spent the last few months training, and probably the past few weeks training especially hard. Take the time to taper properly. This means going slow when a slow day is scheduled. Reduce your volume to allow for time for your entire body to start to repair itself. 

Along these lines is planning for potential jet lag. If you are doing some traveling, giving yourself a couple/few days of buffer time to adjust to the time zone will help relieve some of the stress on your body. Take naps and sleep full nights.

In conclusion, physical endurance is just a piece of the racing puzzle. Knowing your mind, your gear, your nutrition, and the course are all valuable pieces as well. You’ll need all of them to see the complete picture. By using the above, you’ll find yourself avoiding the low spots other racers have and you’ll be on your way to the finish.

What difficulties have you encountered in a race that lead you to DNF or want to DNF? How did you overcome this? Leave a comment below!

Four Pass Loop

Just outside the mountain town of Aspen, Colorado lies one of the pinnacle trail running experiences in Colorado: The Four Pass Loop. Enveloped by flowered tundra, alpine lakes, jagged peaks, lush grasses, streams, and every color in the spectrum, this giant loop takes you for a ride, as its name claims, over four separate mountain passes.

Leadville 100 Mile

Rich with mining history, the Race Across the Sky is one of America’s original 100 milers and one of the most competitive. Bring your high-altitude lungs!

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4 years ago

Something that was almost the final nail in the coffin for me was not having any (or enough) warm clothes in my drop bags at miles 80ish in the middle of the night. I started to shiver uncontrollably and damn near cost me my race; although It killed an hour of my first ultra

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