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How to Run 100 Miles - The Knitty-Gritty from An Expert Ultra Running Coach

Many times during a hundred miles, you may convince yourself that it is impossible. I'm here to tell you, armed with the right knowledge and training and a whole lot willpower you can run 100 miles.

Coach and Ultrarunner Julie after a 100 mile race

Is it possible to run a 100-mile race?


20 hours in, running feels impossible, or at least impossibly stupid. When the night gets long and things get uncomfortable, the demons come out. When people say that ultrarunning is “more mental than physical,” this is the moment they are trying to explain. The hundred miler is the arena where impossible becomes tangible if you are willing to stay the course and do the heavy lifting.


When I ran my first hundred, I ran 40 miles, hiked the next 40, and shuffled painfully for the final 20. I was bright-eyed and brand new to the world of ultramarathoning. I ran with a ten dollar watch and I wrote the time cutoffs in Sharpie on my arm, just in case. I had never run through the night before, and both my doubts and legs grew heavy as the hours dragged on. At two in the morning, my confidence faltered. I sat down, tears stinging, desperate to quit. Would it be the finish line, the clock, or the limit of my determination that would end my race?


Over a decade later, I can humbly tell you that I’ve mastered running 100 miles. I never underestimate the distance, but now when the gun goes off and the crowd pushes forward, I trust my feet to run until the end (unless something wild happens). There is a significant amount of walking in a hundred miler, even a fast one, but a disciplined endurance athlete can hold the reigns and continue running 15 hours in. A 13-minute pace feels a lot different on mile 80 legs than mile 8 legs. Experienced ultramarathoners know when it is appropriate to walk and when it’s time to giddy up. Volunteer at an ultra; you will be amazed how many people run to the finish.


How long does it take to run 100 miles? Can you do it in a day?


Cutoffs for 100-mile races vary depending on the terrain. The current world record is currently 10 hours, 51 minutes, and 39 seconds, which means holding a 6:31 min/mile pace around a track. Not many ultrarunners can maintain such a blistering speed, and speed is not always the goal. Ouray 100 takes place in the young, steep San Juan Mountain range in Colorado. With over 42,000’ of climbing up several summits and passes over 13,000’ up, the final cutoff is 52 hours, and most finishers will run through two nights. Fast is a relative term in ultrarunning. The winner of a race could finish in 18 hours, but the back of the pack might take 34 hours to complete the same race.


Generally, most 100-milers take 20-30 hours. It is technically possible to do it “in a day” if that day includes running all night long without sleep. 24 hours is widely considered the gold standard for an average race with a typical elevation profile. Some races have special buckles for finishing faster if the course is especially mountainous or challenging (the sub-24 buckle is the most common, and it is a badge of honor in the ultrarunning community).


In general, the flatter the course, the faster the course. Individual race cutoffs are determined by the director, however, so a flat course does not necessarily mean you have to run more, it just means that participants find gravel loops more runnable than traversing canyons and volcanoes.


Do you sleep during a 100-mile race?


Coach Julie running through the night in a 100 mile race

No. Very few people plan sleep breaks, although short trail naps - curled up in an emergency blanket like a Chipotle burrito - are not uncommon, depending on your race goals.


I was chasing down first place female at Bryce Canyon and got sicker than I’ve ever been in a race. I vomited every time my heart rate spiked, which it tends to do when you are running. I walked, dry heaving for 40 miles, determined not to quit but growing exponentially dehydrated and calorie deficient. I froze at night because I was dressed to run, not layered to hike. My body hurt everywhere. I had two options: quit with a valid reason, or finish with a horrible time.


The real grit and tenacity of the ultra is not achieved by comparison, even though competition can be fun and motivating. Someone will always run faster than you, have a better day than you, or beat you the next time. The real spirit of the ultra: I faced my demons and I won. I walked away from the fight with my head high. I finished the thing I said I would do. I did the work.


I curled up in a sleeping bag at an aid station and let my goals float off into the cold atmosphere and stopped caring about everyone zipping by. The race changed into a measurement of my integrity when no one was watching me and the competition was gone. Sleep helped me stay on target and think clearly, not emotionally. My clients know: you are not allowed to quit a race before you sleep. I got up at sunrise, ate a pancake, stopped throwing up, and left to get my buckle.


If you are going to sleep during 100, keep it short and recognize that it is going to be a cold and rough experience to get going again. You will do it, though, because you are tougher than discomfort. Sleep can be a powerful tool as long as you recognize that you pay for it on the clock.


What does running 100 miles do to your body?


Running for 24 hours will sap every molecule of glycogen from your legs within the first thirty miles. It will slow your digestion because blood is demanded elsewhere to constantly deliver oxygen to your muscles and cool your system. It will decimate your electrolytes, especially your sodium levels, if you are not careful. Rarely, runners get rhabdomyolysis from damaging their muscle cells faster than their liver could filter them out of their blood. There are stories of runners who go temporarily blind due to ultramarathon-associated visual impairment (UAVI), or essentially corneal swelling. Hallucinations are common because a tired mind fills in blanks, even if the blanks do not make much sense. I once saw a stranger taking out the trash in the middle of El Paso desert. Training for the race, especially with uninformed or inconsistent training, commonly leads to overuse injuries and all the -itis’s (tendonitis, bursitis, fasciitis etc.).


More commonly: the hundred exhausts you, starves you, compels you to brush your teeth after eating so much sugar, and creates a thirst unlike any other. Drinking lukewarm water and Tailwind for thirty hours is disgusting. Your muscles will get tight and leathery. Salt will crust your skin and dirt will fill your pores. Tendons and ligaments get inflamed and angry.


Your mind will fatigue, and your eyes will bug out from watching your headlamp dance all over the trail hour after hour. The skin on your toes may bubble up and blister. A few days later you’ll still be sore, and a few weeks later a toenail or two might fall if you’re doing it right. You will chafe in terribly unpleasant places, which you will discover in that first salty shower, but you will not mind because you earned it. After the race, your feet might swell up for a day or two as they heal. The next day you will eat everything in your fridge and then order Door Dash.


The week after your race, you feel proud and happy with a grin inexplicably plastered across your face because you know something the rest of the world can barely understand. But then you may find yourself sinking into the post-race blues. A tremendous amount of time, thought, and energy is spent building, working, and sweating over one day. When the buckle is on the shelf and life returns to normal, ultrarunners often find themselves depressed and listless. Hop on UltraSignup and find your next goal. It is very hard to do one ultra and then quit. The blues will slowly fade.


Ask an ultrarunner why they run 100 miles. They will each have a unique answer, but none of them will tell you it's for exercise. Running 100 miles is not a workout. It’s not increasing your strength - it is breaking you down cell by cell. The hundred miler is a test of physical determination as well as mental determination. It’s one of the most grueling measurements of endurance and a total attack on your reality.


Precious metals are refined through heat to remove contaminants and achieve the highest level of purity. Think of the hundred-mile footrace as the pressure and heat that separates our internal impurities and leaves us with truth, reality, and answers. Are you resilient enough? Can you do this? Are you going to quit because it hurts? Is this too hard for you? If it sounds spiritual, philosophical, or emotional - that’s because it is.


How many people run 100-milers?


In 2022, there were 10,186 finishers of the 100-mile distance. The average fluctuates quite a bit year over year, and some people finish multiple 100s in a year, which is not accounted for in the data. Overall, the trend is that more and more people every year take on this enormous challenge. Ultrarunning as a sport is on fire.


Number of ultra-distance races in 2022: 2,642

Trend: This is an 18% increase over the 2021 number of races (2,242). If we were to ignore 2020 and focus on the 2019 pre-covid number, then this represents an 8% increase above the number of races in 2019 (2,442).

Number of first-timers finishing an ultra-distance in 2022: 29,323

Trend: This is a 12% increase over the 2021 number of first timers (26,260). If we were to ignore 2020 and focus on the 2019 pre-covid number, then this represents a 9% decrease below the number of first timers in 2019 (32,106). In our sport’s history, it is still the second highest number of first timers in a year and not by much over 3rd (2018: 26,280).


How do I prepare for 100 miles?


Ultrarunner Julie all smiles during a 100 mile race

Ask yourself three questions:

  1. What is my goal? To get a buckle? To finish in the top? To hit a time?

  2. How much endurance experience do I have? Have I run 100ks? A marathon? Trail races?

  3. How much time am I willing to commit?

The secret of ultrarunning is simple: if you want to run long, you must be willing to run long. The biggest mistake I see new ultra runners make is confusing ‘working hard’ with ‘working long.’ For example, some of the best ultra training could be backpacking. When training for a hundred, it is productive to work a 12-hour shift on your feet and then hit a 15-mile run in the dark. To run an ultra well means being willing to commit to time on your feet. Not every run, but at least once or twice a week you must be willing to spend the hours building your endurance, especially if you are new to the sport. You do not have to run 75 miles a week to finish 100-mile races, but you do need to have consistently long runs that challenge both your legs and your patience.


Experience is the best teacher. Start researching. Look at many methods, articles, blogs, and YouTube videos. Look at maps, run parts of the course, talk about it with friends and jump onto forums. Read race reports and mentally submerge yourself in the concept. Do not underestimate mental preparation even though it’s not on your training schedule. Hire a coach if you’re open to trusting other’s experience and training resources – a coach can highlight what you do not know and hold you accountable to a rock-solid strategy so that you are able to bring your best to race day. Be willing to experiment. Be humble enough to submit yourself to the work. Consider the sacrifice before you set the goal.


How much training do I need for a 100-mile run?


It depends where you are starting from. If you’re interested in hundreds, you probably have some experience in distance running and a solid endurance base. A 50-mile runner could jump to a 100-miler in six months, and that number is estimated from personal experience building athletes to execute race day injury-free. Jumping up in distance risks the repetitive use injuries: ITB syndrome, shin splints, plantar fasciitis, and all the running problems non-runners love to accuse us of. It is important to take enough time building a strong foundation to prevent those injuries. A newer runner may need a year to rack up the mileage and endurance, especially if they choose a more challenging course.


Be smart when you build your endurance. Consistency is the key. Build, back off, build again. Push your limits, let them rebound as you recover, and then push them again. Run slowly. If you push your endurance limits randomly or radically, you can expect to pay for it on the back end with inefficient, painful recoveries and injuries or punishing race days. Many motivated people can go out and finish a 50-miler, but how well they finish it (and how they feel afterward) will correlate to the time they put in ahead of time. The goal should always be to bring your best effort, regardless of what the clock says. The best ultrarunner is the one having the most fun, and it is very difficult to have fun if you are running in pain.


Running 100 miles is not just for the buckle. If you really love distance running, make sure your heart is also in it for the training. So much is gained intrinsically by the discipline, dedication, and submission to the long run. On my very first ultra, I had one drop bag – filled with all the wrong things – but on the outside I wrote a quote from Emerson: The reward of a thing well done is having done it.


Why a 100-mile belt buckle?


Traditionally in the United States, you win a belt buckle for finishing 100-mile race. This stems from the very origin of the sport: horse racing. The Western States 100-mile horse race became the first 100-mile footrace when Gordy Ainsleigh participated on foot in 1974. The prize for the horse raise was, unsurprisingly for a bunch of California cowboys, a big shiny buckle. Gordy finished the race within 24 hours (the time cutoff for the horses), and the hundred miler was born.


Only four years later, 62 runners started the race and ultrarunning has been exploding since.


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