A pacer is a runner who joins an ultramarathon competitor partway through the race to help them finish. The pacer is not racing. Their job is to keep their runner moving, safe, eating, hydrating, and mentally in the game during the back half of an event that, by mile 60, can feel like a full psychological unraveling. For a 100-mile race, pacers typically join at the 50-mile mark. For a 50-miler, somewhere around 30 to 35 miles. Each race has its own rules, so confirming the specifics with your runner before race day is non-negotiable.

In this article

• What does a pacer actually do on course?
• What do you need to do before race day?
• How fit do you need to be to pace an ultra?
• What gear does a pacer need?
• What is the difference between a pacer and a crew member?
• What are the rules around pacing?
• Frequently asked questions

What does a pacer actually do on course?

The short answer: everything the runner needs that is physically and legally possible given the race rules. The longer answer breaks into five distinct roles you will be playing simultaneously, often while running uphill in the dark at 2 a.m.

1. Manage nutrition and hydration

By mile 60 of a 100-miler, a runner may stop wanting to eat or drink entirely. This is one of the fastest ways a race falls apart. Your job is to track calorie intake, remind your runner to eat every 30 to 40 minutes, and get creative when everything tastes wrong. Carry backup snacks. Know which foods work for your runner and which do not. At some point you will be having a firm but patient conversation about why they need to take in 200 calories right now, even if the idea makes them want to lie down on the trail.

2. Set and hold pace

Your runner has a goal, or at least a minimum standard to make cutoffs. Your job is to hold that pace with them, not ahead of them. One of the most common pacer mistakes is going out too fast because you feel fresh. Your runner has already run 50 miles. Calibrate to their effort level, not yours.

3. Navigate and keep them on course

Cognitive function drops sharply in the late miles of an ultra. Runners miss trail markers. They take wrong turns. They have been known to walk in circles. Study your section of the course before race day, know the key turns and landmarks, and keep one eye on the trail at all times.

4. Manage their mental state

This is the part nobody fully prepares for. Ultramarathons put people through dramatic emotional swings. Your runner may cry, rage, go silent, declare they are dropping, or say things they will be embarrassed about later. Do not take it personally. Your job is to stay steady, read what they actually need (distraction, quiet, a firm push, a permission slip to walk), and keep moving. One experienced pacer described it as being a therapist, a coach, and a friend in one body, running.

5. Be the safety net

Sleep deprivation, dehydration, and caloric deficit at mile 70 can produce confusion, poor balance, and impaired judgment. You are the person watching for signs that something is medically wrong. If your runner is stumbling badly, talking incoherently, or showing signs of serious distress beyond the normal suffering of the sport, you escalate to race medical staff.

What do you need to do before race day?

The biggest pacing mistakes happen because the pacer showed up underprepared. Here is what to lock in before the race starts.

• Read the race rules. Every race handles pacing differently. Some prohibit pacers entirely on 50-milers. Most allow them from the halfway point on longer events. Some have designated pacer-entry points. If you break a rule, the runner gets disqualified, not you.
• Know the course section you are running. Study the elevation, key trail junctions, aid station locations, and the conditions you are likely to hit (night running, technical terrain, altitude).
• Have a detailed conversation with your runner. Do they want you to talk or stay quiet during hard sections? Do they want to be pushed or just held steady? What are their goal times and minimum cutoff times? What foods work at mile 70? What do they look like when they are about to quit, and how do they want you to respond?
• Train for your leg. If you are pacing 20 to 30 miles of technical mountain trail through the night, you need to be fit enough that the effort is well within your capacity. You cannot help your runner if you are suffering yourself.
• Coordinate logistics with the crew. Know when and where you hand off, who has the drop bags, and how you get back to the finish area after your leg ends.

How fit do you need to be to pace an ultra?

More fit than the distance alone suggests. You are not just running 20 or 30 miles. You are running them at the end of a long day, likely at night, possibly on technical terrain, while mentally managing another person. The standard guidance is that your pacing leg should feel well within your comfortable long run range, not a new distance challenge for you. If you are pacing miles 60 to 80 of a 100-miler, you should be able to run 25 miles on a tired day without it being an event.

Do not underestimate the overnight factor. Running at 3 a.m. after a full day of waiting, sleeping in a car, and bouncing between aid stations hits harder than you expect. A good pre-race meal, consistent hydration through the day, and a short nap before your leg are not optional, they are part of the job.

What gear does a pacer need?

You are not just keeping yourself alive out there. You may end up carrying things for your runner, providing backup nutrition, and donating gear if they need it. Here is what a prepared pacer brings.

Item	Why it matters
Headlamp + backup batteries	Non-negotiable for any leg with night miles
Moisture-wicking tee and layers	You will overheat on climbs and freeze on ridgelines within the same hour
Trail running hat	Shields from sun, holds heat at night, keeps sweat out of your eyes on climbs
Nutrition for your leg plus 20% extra	You may feed your runner from your supply when theirs runs out or stops working
Hydration vest or handheld	Aid stations can be 8 to 20 miles apart
Rain layer and emergency blanket	Weather changes fast. Mountain races especially
Your runner's race bib number and emergency contact	In case of medical escalation you need to provide this instantly
Fully charged phone	Navigation backup, crew communication, emergency

What is the difference between a pacer and a crew member?

Crew members support the runner at designated aid stations. They are the pit crew: food, dry socks, new shoes, a hot meal, and emotional reset between legs. They do not run with the athlete.

A pacer runs the course alongside the athlete. They are mobile support, covering specific race miles rather than specific checkpoints. Some people do both across a race weekend. A common setup for a 100-miler is one or two crew members managing aid stations while two or three pacers divide the back half of the course into legs of 20 to 30 miles each.

If you are being asked to do both, get explicit about logistics early. Trying to crew at mile 50, then pace miles 55 to 80, then crew again at mile 85 requires your own transportation plan, your own nutrition strategy, and more sleep management than most people anticipate.

What are the rules around pacing?

Rules vary by race, but here are the common standards you will encounter across most major events in North America.

• Pacers are typically not allowed until a specified point in the race, often the 50-mile mark for 100-milers.
• "Muling," which means carrying your runner's mandatory gear or race supplies for them, is prohibited at most events. The Leadville Trail 100 is a notable exception. Carry your own stuff plus anything extra your runner wants in your pack voluntarily.
• At some races the pacer must also be registered, either formally or informally, at a pacer check-in. Confirm this well before race day.
• Pacers cannot receive aid on behalf of the runner at aid stations in most races. The runner has to check in and interact with the station themselves.
• If you break a rule, the penalty falls on the runner. This is not a gray area. Know the rules.

Frequently asked questions

Can anyone pace an ultramarathon, or do you need to be an ultrarunner yourself?

You do not need to have run an ultra yourself, but you do need to be fit enough to comfortably cover your pacing leg on technical terrain, potentially overnight and in variable weather. The more important qualities are reliability, mental steadiness, and a genuine commitment to your runner's race over your own experience.

How far in advance should a pacer start preparing?

At minimum 6 to 8 weeks out. You need time to train for your specific leg, study the course, and have multiple conversations with your runner about their plan, their nutrition, and how they handle the inevitable low points. Show up less prepared than this and you become a liability rather than an asset.

What happens if a pacer has to drop out mid-leg?

In most races, a pacer can step off the course at any aid station without affecting the runner's race, as long as the runner continues independently. This is why knowing the course and the aid station locations matters. If you have a genuine emergency, communicate immediately with race officials and the crew.

Is pacing allowed at every ultramarathon?

No. Most 50-mile races do not allow pacers. Many 100-milers allow them from the halfway mark. Some shorter ultras or international events have no pacer provision at all. Always verify with the specific race's current rules, as policies change year to year.

Do pacers need to carry their own mandatory gear?

In most cases, yes. Pacers are on the same trails as the runners and are subject to similar safety requirements. Some races require pacers to check in with specific mandatory items (headlamp, emergency layer, etc.). Confirm the current pacer gear requirements with the race director before race day.

What should a pacer do if their runner wants to drop?

First, stay calm. Wanting to quit at mile 70 is not unusual. Hold pace, offer food, let them walk for a bit, and remind them of their goal without pressuring them. If after 20 to 30 minutes the desire to drop has not lifted, respect it. Your job is to support the decision they make, not to override it. Safety always comes before a finish time.