⏵ Pacer guide · Free

How to Pace a Runner in an Ultramarathon

To pace someone in an ultramarathon, you have one job. Keep your runner moving forward. You navigate the course, you make sure they keep eating and drinking, you hold them on pace, and you stay positive when they have run out of their own. Most 100-milers let a pacer join around mile 50 to 60 or at nightfall, you generally cannot carry the runner’s supplies (that is muling, and it is banned in most races), and you want to show up with fresh legs, your own kit, and the course memorized. The science says your biggest job is mental, not physical.

What an ultra pacer actually does

You are the runner’s brain, navigator, and morale when their own are running on empty. You are not out there to set a personal best. You are there to keep one person moving forward through the worst hours of their race. The research on group running is hard to argue with. Runners with company hold a more stable emotional state, a higher pain threshold (more endogenous opioids), and carry less cognitive load because someone else is helping hold the pace. Drafting can save up to about 5.9 percent of metabolic cost. But the real magic is mental. iRunFar calls pacers "emotional mules," and that is the job.

⏵ The four jobs

What you are actually doing out there

NavigateKnow every aid station, climb, and turn. You are the eyes and the map, especially in the dark.
FuelKeep them eating and drinking on a clock. A quiet, slowing runner is usually a runner who is behind on calories.
PaceHold a steady effort they can hang onto. Run the runnable, hike the climbs, and never let the wheels fall off.
LiftBe the optimism. Keep them looking outward and out of their own head when it gets dark.

Pacing is the back half of a bigger support job. For the whole before-and-after picture (drop bags, aid-station choreography, crew access points), read our companion guide on how to crew an ultramarathon.

When are pacers allowed?

This is entirely up to the race, so the first rule of pacing is to read the actual rules. Most 50Ks and 50-milers are solo events. Many 100-milers open a pacer somewhere around mile 50 to 60, or once it gets dark. Here is the general pattern, with Western States as a real example.

⏵ By distance

When a pacer can join, by race length

Distance	Pacer allowed?	Typical rule
50K / 50 mile	Usually not allowed	Most shorter ultras are run solo. Always check the specific race rules.
100K	Sometimes, often from a late aid station	Varies widely. Some open a pacer in the final third, many allow none.
100 mile	Typically from ~mile 50 to 60, or at nightfall	Western States: Foresthill (mile 62), or Michigan Bluff (mile 56) after 8 p.m.

Most races allow only one pacer on course at a time, even when they hand out several pacer numbers so you can swap at certain aid stations. Pacing a first 100 is its own kind of job, so pair this with our first 100-miler guide and how long a 100 takes so you know roughly when your leg will land.

Muling and the rules you cannot break

The rule most pacers get wrong is muling, which is carrying your runner’s food, water, gear, or clothing for them. In the large majority of 100-milers muling is banned, and a violation can disqualify your runner. The Leadville Trail 100 is the famous exception that does allow it. When in doubt, carry only your own kit and never touch theirs.

⏵ Can / can’t

What a pacer may and may not do

Action	Allowed?	Note
Run alongside your runner	Yes	One pacer at a time on course in most races.
Carry your runner’s food, water, or gear (muling)	Usually NO	Expressly forbidden at most 100s. Leadville is the notable exception that allows it.
Carry your own food, water, and lights	Yes	You are expected to be self-sufficient and not draw on the runner’s supplies.
Accept aid at aid stations	Yes	Pacers may take aid, but must enter and leave each aid station with the runner.
Be under 18 years old	Usually NO	Most races require pacers to be at least 18 (waivers sometimes by request).

These are common patterns, not the law. The pacer rules of your specific race are the only thing that counts. Read them in full before race day.

What a pacer should carry

Pack so you can take care of yourself, because in most races you cannot use your runner’s supplies. You want to be the help, never a second person who needs rescuing.

⏵ Pacer kit

The self-sufficient pacer pack

Your own pack, fluids, and caloriesYou must be self-sufficient. Touching the runner’s food or water can be muling.
Two light sources plus backup batteriesA headlamp and a handheld or waist light. Lights fail, and night sections are long.
The course loaded on your watch or phoneYou are the navigator. Know every aid station, climb, and turn before you start.
A small repair and comfort kitAnti-chafe lube, spare socks, blister tape, salt, a buff, basic first aid.
A warm layer and a rain shellNight and altitude get cold. You move slower than a fresh runner and chill faster.
The runner’s plan on paperGoal splits, fueling cadence, drop-bag contents, crew phone numbers, cutoffs.

For the whole kit philosophy (packs, lights, layers, what actually earns its weight), see our ultra running gear list, and for the durability that lets you cover your leg with reserve, our strength and injury-prevention guide.

How to keep your runner eating and moving

More ultras fall apart from a bad stomach and a stalled mind than from a lack of fitness. Your two biggest jobs are getting calories in and keeping the legs turning over. Both come down to a clock and a script.

Fuel on a clock, not on a whim

A common pacer target is roughly 120 to 160 calories per hour, with fluids and electrolytes to thirst. Trained ultrarunners whose guts can handle it often push carbohydrate higher, toward 60 to 90 grams per hour. Whatever the number, stick to the plan your runner trained on. Do not invent a new one at mile 70.

Set a reminder every 20 to 30 minutes and nudge a few bites and a few sips, do not wait for a big intake that a tired stomach is just going to reject. And watch the early signs of underfueling. A runner who goes quiet, slows down, gets snappy, or feels sick is usually behind on calories. Get ahead of it.

Shrink the race to the next small thing

When the distance feels impossible, make it small. "Just get to the next aid station." "Run to that tree, then hike to the top." Keep your runner looking outward, at the trail, the next landmark, the next bite, and you keep them out of the spiral of their own discomfort.

Guard the aid stations. A planned two-minute stop quietly becomes twenty once a tired runner sits down. Decide the stop length before you get there, grab what you need, and get back on the trail. Forward motion, even a walk, fixes more problems than sitting ever will.

Want the real numbers for your runner instead of a generic range? Our free ultra fueling calculator turns body weight, goal time, and expected heat into an hour-by-hour carbs, sodium, and fluid plan you can pace them to. Go deeper in our guides on carbs per hour, sodium per hour, and avoiding stomach problems.

How to pace at night

Night is when most pacers earn their keep. Runners get sleepy, cold, slow, and low, and a missed turn in the dark costs you way more than one in daylight. Your job is to be a moving lighthouse and a steady voice.

Light up like a Christmas tree, and run out front

Carry more light than feels reasonable. A headlamp on your head, a second light on your waist or chest, a third on the back of your pack pointing down at the ground, plus a handheld for scanning trail markers, and backup batteries for all of it. Run a little out front so your runner can follow your beam and see the trail without aiming their own light.

Call out the hazards before your runner gets to them. Roots, rocks, drop-offs, stream crossings, and especially turns. Know the course cold so you never miss a marker. A calm, steady "step up here, rock on your left" for hours is exactly the load you are there to carry.

Manage the cold, the sleep, and the low

You move slower than a fresh runner, so you get cold faster. Have a warm layer for both of you and watch your runner for shivering, slurred words, and stumbling, which mean a bad patch that needs calories, caffeine, and sometimes a short push to the next aid station and some warmth.

The pre-dawn hours are the bottom of most 100s. Keep talking, keep them eating, and remind them the sun is coming. Almost every dark patch lifts with daylight and a little fuel. Treat it like weather, not a verdict.

How to handle a low or angry runner

Almost every long ultra has a low patch, and how you handle it is the difference between a finish and a DNF. The science says optimism is a performance tool, so how you carry yourself is part of the job. The trick is being really positive without turning into a drill sergeant.

Be the optimism, do not commiserate

Point out real, specific progress. "You are climbing strong." "Only two aid stations to the finish." "You are an hour ahead of cutoff." Do not agree about how much it hurts and do not make the race about you. Optimism is contagious, and so is despair, so watch which one you bring.

Match the person. Some runners want jokes and chatter to stay out of their head, others want quiet company and will hate the noise. Ask before the race how they want to be handled when things get dark, so you are not guessing at mile 80.

An angry runner is often a low-blood-sugar runner

If your runner snaps at you, do not take it personally. Getting snappy is one of the clearest signs of underfueling and depletion. Quietly steer them toward calories, fluid, and caffeine, and let the mood come back on its own. Often the apology shows up twenty minutes later once the sugar lands.

When things are really grim, stop trying to fix the mood with words and shrink the world down to the next task. The next bite, the next landmark, the next aid station. Forward motion is the cure. For the runner’s own toolkit, point them to our guide on mental strategies to push through an ultra.

The other side of the low patch is knowing how to push through it as the runner. Send your athlete to our guide on mental strategies to push through an ultramarathon and on how to recover afterward so you are both reading from the same playbook.

How fit do you need to be, and how to hold the pace

You need to be fit enough that your leg is genuinely easy for you, because a struggling pacer is a liability. And you need to get pacing by effort, because the runner’s pace deep in a 100 is a hike-run mix, not a fresh-legs number.

Fresh legs, with reserve to spare

The practical rule. Be able to cover your assigned distance at the runner’s expected pace with plenty left in the tank to talk, navigate, problem-solve, and stay positive. If you are pacing a 10 or 20 mile leg, train until that distance is easy for you. You do not need to be faster than your runner over a fresh marathon, but you do need rested legs and the durability to stay calm and capable for hours.

Show up rested. Sleep well the night before, eat, and warm up before you join, especially if you have been sitting in a cold crew chair waiting for your runner. Your job starts the second they arrive, often in the middle of the night, so be ready to move right away.

Pace by effort, and beware fresh-legs syndrome

Your legs are fresh and the runner’s are not, so your idea of "easy" is way faster than theirs. The classic pacer mistake is dragging a depleted runner along at a pace that feels gentle to you and blowing them up. Hold effort, not your pace. Run the runnable, power-hike the climbs, and let the grade and their fatigue set the speed.

Think grade-adjusted on the climbs and the descents so you are asking for the same effort uphill and down, not the same pace. Our guides on pacing by effort and grade-adjusted pace, plus the calculators below, give you the framework.

Learn to ask for the right effort instead of the wrong pace in our guide on how to pace an ultramarathon by effort, and brush up on moving efficiently uphill in how to power hike and use trekking poles.

⏵ Free calculators for pacers

Turn the ranges in this guide into real numbers for your runner with our free, no-signup tools.

See all free running tools →

⏵ Pace from a real plan, not a guess

The best pacing comes from a runner who shows up with a course-aware plan. Goal splits by segment, a fueling schedule by the hour, and a finish projection that accounts for the vert. Summit Line reads your athlete’s actual training and builds exactly that, so you both know the pace, the fuel, and the cutoffs before you ever clip in. Bring the plan to the aid station and pace to it.

Build a race plan free →See it on a real plan

Keep reading

Pacing is one piece of getting a runner to the line. Here is the rest of it.

Ultra pacer FAQ

What does an ultra pacer do?

You run alongside an ultrarunner, usually in the back half of a long race or through the night, and you become their brain, their map, and their morale. The number one job is simple. Keep your runner moving forward. In practice that means you know the course and the next aid station, you make sure they keep eating and drinking, you hold them on pace and on the trail, and you stay positive when they have nothing positive left. And the research backs this up, your biggest job is mental, not physical. Studies on group running show a more stable emotional state, a higher pain threshold (more endogenous opioids), and less cognitive load when someone else helps hold the pace. iRunFar calls pacers "emotional mules," and honestly that is the job.

When are pacers allowed in a race?

It depends entirely on the race, so read the rules first. Most 50Ks and 50-milers are run solo, no pacers at all. Many 100-milers open a pacer somewhere around mile 50 to 60, or once it gets dark. Take Western States. Pacers can join at Foresthill (mile 62), and if your runner leaves Michigan Bluff (mile 56) after 8 p.m. they can grab a pacer there. Most races let only one pacer on course at a time, even if you get handed several pacer numbers so you can swap people out at certain aid stations. And pacers almost always have to be at least 18.

What should a pacer carry?

Carry everything you need to take care of yourself, because in most races you cannot touch your runner’s supplies. So bring your own pack with your own fluids and calories, at least two light sources plus backup batteries for the night, the course loaded on your watch or phone, a warm layer and a rain shell, and a small kit with anti-chafe lube, blister tape, spare socks, salt, and basic first aid. Bring the runner’s plan on paper too. Goal splits, fueling cadence, drop-bag contents, crew numbers, cutoff times. The one thing you generally cannot carry is the runner’s gear. That is muling, and it is banned in most races.

How do I keep my runner eating and moving?

Make it your job and say it out loud. A common target is roughly 120 to 160 calories per hour, with fluids and electrolytes to thirst, though trained ultrarunners whose gut can handle it often push carbohydrate higher, 60 to 90 grams per hour. Set a reminder every 20 to 30 minutes and nudge a few bites and a few sips, do not wait for a big intake. And watch for the warning signs of underfueling. A runner who goes quiet, slows down, gets snappy, or feels sick is usually behind on calories. To keep them moving, shrink the race down to the next small thing ("just get to the next aid station," "run to that tree, then hike"), keep them looking outward instead of stuck inside their own head, and never let a long sit-down at an aid station turn into a death spiral. Pick a time limit before you get there and get them back on the trail.

What are muling rules?

"Muling" is when a pacer carries the runner’s supplies (food, water, gear, lights, or clothing) or gives mechanical help. In the large majority of 100-milers muling is flat-out banned. You are there for company and safety, and you carry your own stuff. The exception everyone names is the Leadville Trail 100, which does let pacers mule for their runner. The rule changes race to race and a violation can get your runner disqualified, so never assume. Read your race’s pacer rules in full before race day, and when in doubt, do not touch the runner’s gear.

How do I pace at night?

Light up like a Christmas tree and run out front so your runner can follow your beam and see the trail without aiming their own light. Good setup is a headlamp on your head, a second light on your waist or chest, a third on the back of your pack pointing down at the ground, plus a handheld for scanning trail markers, and backup batteries for all of it. Slow down and call out the hazards (roots, rocks, drop-offs, turns) before your runner gets to them. Night is when runners get sleepy, cold, and low, so keep talking, watch for the stumbles and slurred words that mean a bad patch is coming, and have caffeine and a warm layer ready. Know the course cold. A wrong turn in the dark costs you way more than one in daylight.

How do I handle a low or angry runner?

Expect the low patch, because almost every long ultra has one, and treat it like weather that will pass, not a verdict. Stay positive, really positive, without turning into a drill sergeant. Point out real progress ("you are climbing strong," "two aid stations to go"), do not agree about how much it hurts, and do not make the race about you. If your runner snaps at you, do not take it personally. An angry runner is often a low-blood-sugar runner, so quietly steer them toward calories, fluid, and caffeine and let the mood come back. Match the person. Some want jokes and chatter, some want quiet company, so learn their cues ahead of time. When it gets really bad, shrink the world down to the next small task and keep them moving. Forward motion fixes more than words do.

How fit do I need to be to pace?

Fit enough that your leg of the race is genuinely comfortable for you, because a tired or struggling pacer is a liability, not a help. The practical rule is to be able to cover your assigned distance at the runner’s expected pace (which, deep in a 100-miler, is often a hike-run mix far slower than a fresh runner’s pace) with plenty in reserve to talk, navigate, problem-solve, and stay positive. If you are pacing a 10 or 20 mile leg, train until that distance is easy for you. You do not need to be faster than your runner over a fresh marathon, but you do need fresh legs and the durability to be a calm, capable presence for hours, often at night and on technical terrain.

This guide reflects expert-consensus practice and the published rules of major races as of writing, not the rulebook of your specific event. Pacer eligibility, join points, and muling rules change race to race and year to year, so the official rules for your race are the only thing that counts. Read them in full before race day. Fueling and fitness needs vary a lot from runner to runner, so treat the numbers here as starting ranges and adjust to the person in front of you.