What Is a Pacer in an Ultramarathon? Everything You Need to Know

The Person Running Next to the Runner

If you have ever watched the final miles of a 100-mile race and noticed that some runners have a companion jogging alongside them while others are alone, those companions are pacers. They entered the course legally, they are following the rules, and their entire job is to keep one specific person moving forward.

A pacer does not compete. They do not receive a finish time. They carry nothing the runner cannot also carry. Their only function is presence — and in the context of a race that has been going for 20 to 30 hours through darkness, heat, altitude, and exhaustion, presence turns out to be the thing that determines whether someone finishes or quits.

When Pacers Are Allowed

Most ultramarathons that allow pacers set a specific mileage point where they may join. For a 100-mile race, this is typically somewhere between mile 50 and mile 75. The exact pickup point varies by race and is published in the official race guide. Some races permit pacers only for the final third of the course. A few elite-only races, including the Barkley Marathons, prohibit pacers entirely as a point of principle.

For races shorter than 100 miles — most 50Ks and 50-milers — pacers are usually not permitted at all. The logic is that the shorter the race, the less the mental and navigational challenge that pacers are designed to address.

The runner must check the race guide for their specific event. Rules vary significantly. Western States 100 allows pacers from the Foresthill aid station at mile 62. Hardrock 100 allows them from mile 40 in either direction. Some races have no pacer allowance at all.

What a Pacer Is Allowed to Do

The list of permitted pacer activities typically includes:

Navigation and course knowledge. Knowing the route, keeping the runner on trail, and watching for course markings is one of the most valuable things a pacer provides. At hour 25 of a 100-miler, a runner’s ability to read course ribbons and stay on trail degrades significantly. A fresh pacer who has previewed the route can prevent a costly wrong turn.

Conversation and distraction. Talking through the miles, keeping the runner’s mind occupied, and preventing the spiral of negative thought that causes DNFs in otherwise physically capable runners. A good pacer knows when to talk and when to shut up.

Monitoring the runner’s condition. Watching for signs of hypothermia, hyponatremia, disorientation, or medical distress and flagging anything serious to aid station personnel.

Encouraging the runner to eat and drink. Runners in the late miles frequently lose their appetite and need reminders, or sometimes firm encouragement, to keep calories going in.

Carrying their own supplies. A pacer carries their own food, water, headlamp, and any mandatory gear for the course conditions. They should not rely on the runner’s crew or aid station resources.

What a Pacer Cannot Do

Pacers are strictly prohibited from carrying any items that belong to the runner or providing physical assistance. Specifically:

• No carrying the runner’s pack, poles, or gear
• No physically supporting or pulling the runner
• No pacing more than one runner at a time
• No switching off pacer duties mid-segment without race director approval in some events
• No receiving aid from crew on behalf of the runner at non-crew-accessible points

The fundamental rule is that the runner must do the race themselves. A pacer accompanies. The moment a pacer starts carrying the runner’s burdens — literal or figurative in the physical sense — it crosses into prohibited territory.

Who Makes a Good Pacer?

The best pacers are experienced trail runners who have been on the course before, can navigate confidently in the dark, and have the temperament to subordinate their own preferences to the runner’s needs for several hours. They need to match whatever pace the runner can manage — which in the final miles of a 100-miler may be a 20-minute hiking pace — without showing impatience.

Equally important is the relationship. Many runners choose a close friend or training partner who knows their personality, their breaking points, and how to talk to them when things are bad. Some runners want aggressive encouragement. Others want quiet company. The pacer who delivers the wrong version of support at the wrong moment can do more harm than running alone.

The Mental Case for Having One

The research on why pacers help is fairly straightforward: ultramarathon DNFs in the final third of races are predominantly mental, not physical. A runner who quits at mile 80 almost always had the physical capacity to finish. What they ran out of was the will to keep going through discomfort while alone in the dark.

A pacer changes the math on that decision. The obligation to a person who drove four hours and trained for months to run with you is a powerful force. Most runners describe the arrival of their pacer as the most important moment of a long race — not because anything physically changed, but because they were no longer alone with the worst version of their own thoughts.

Related: Aid Stations at Ultramarathons — What to Expect | Medical Support at Ultras | Should I Run an Ultramarathon?