How do pacers work?

In long-distance running events such as marathons, pacer runners are often used to help other runners know how fast they are going, and limit the amount of extra work they need to do to stay at their intended running speed.

Pacers are often volunteers who are experienced distance runners, that will run at a specific speed and wear either clothing or a flag that shows what speed they are pacing at.

During the 2026 London Marathon, organised pacers ran at a wide range of speeds varying from two hours and 45 minutes all the way to seven hours and 30 minutes.

"You're motivating people and trying to encourage them at your pace," two-time London Marathon pacer Nina Farine-King told BBC Sport.

"It's different at different paces."

To keep on track, pacers are regularly monitoring their speed via smart watches and timers that are dotted around the course.

Nina said that at the London Marathon, pacers are required to be within a minute of their projected time halfway around the course and at the end, must be no slower than 30 seconds off their intended time, and no faster than a minute before their projected time.

"I started off pacing because a friend in my run crew paced me at 50 minutes for a 10-kilometre race. I achieved my goal and it evolved from there.

"Now, it is really rewarding to help people achieve their goals and give back to a community that has given so much to me."

Pacers are also used in smaller and community based running events, including regularly featuring at Parkrun races.

Runners will often go into events with a planned target time in mind. This can range from a specific time to achieving a personal best, and their pre-race training is often based around that time.

Unlike in training, where runners would have to monitor their own speed, pacers take some of the work out of their hands so that they can focus on running.

"There's a lot of maths involved," said Nina, who paced at a time of five hours and 15 minutes during Sunday's London marathon.

"I wore two watches and was consulting the clocks around the course. A lot of planning and training goes into it."

Some runners may not have smart watches or are used to pacing themselves, so having a visual pacer on the course throughout a race can make a big difference in whether or not someone achieves their goals.

"We're just like the runners doing the race, but we're also volunteers," Nina explained.

"We get medals too, just the same as everybody else."

The role of a pacer will vary and depend on the speed of the pacer, their experience, and those running around them.

For elite or faster runners, their focus is specifically on performance, and issues such as nutrition and hydration are the bigger priorities.

Right at the back of the field there can be first-time runners, those that are happy to just get around the course, and those whose priorities are more about enjoying the experience than worrying solely about their performance.

"For elite athletes, it's less chat and more time-focused and conversations are more about hitting speeds, taking on fluids and carbohydrates," Nina explains.

"[London] had our first 2:45 pacer this year. It went all the way back to 7:30, where there is a more party atmosphere and all the runners are stopping to high-five the crowd and dance, so it's a very different atmosphere."

Another factor is remaining disciplined and sticking to the time they are pacing at.

For many runners, there is a temptation to use any energy left in the final few hundred meters for a sprint finish.

Nina has found the best way of being a pacer and not giving in to that urge, but also helping others achieve their goal.

"That is the one thing I struggle with as it's just habit," she explained.

"When I pace, I do look around me towards the end and if anyone is looking strong enough, I will encourage them to give it their all at the end.

"Anyone who is faster than me has achieved their goal pace if they've been sticking to me."

When it comes to elite runners, the world of pacing can be very different.

The 2026 London Marathon was historic in the fact that two runners officially crossed the line in under two hours.

In 2019, Eliud Kipchoge completed the Ineos 1:59 Challenge, although this was deemed not an official time.

One of the reasons for this was because Kipchoge used a large number of pacers during the race, who formed a shielding formation around him and regularly rotated fresh runners in to replace runners who had paced for nearly 5km.

With this being deemed not in fair race conditions, it goes against World Athletics rules for road racing which state that pacers must be 'bona-fide competitors' and 'must start the competition together with all other international elite athletes, must be recorded in the race start list, timed like other international elite athletes and if they complete the race, they must be officially ranked'.

At that level, there are elite level pacers who can take the role on a more serious and permanent role.

On other occasions, top athletes have acted as pacers in certain events. Alex Yee, who won gold in the men's triathlon at the 2024 summer Olympics in Paris, paced British elite athletes during the London marathon for the first 28km.

Elite pacers can technically win races if their contract permits them to.

During last month's Berlin half marathon, Kenya's Dennis Kipkemoi almost won the race as a pacer, having been toe to toe with compatriot Andrea Kiptoo for the majority of the race, only to step aside in the final moments and later admitting the protocol of being a pacer had not been clear to him.

This article is the latest from BBC Sport's Ask Me Anything team.