A Data-Driven Primer on the IAU 24-Hour World Championships

A data-driven look at trends in 24-hour running in advance of the 2023 IAU 24-Hour World Championships.

By on November 30, 2023 | Comments

The 2023 IAU 24-Hour World Championships are happening in Taipei on December 1 and 2. You might say it’s the Olympics of 24-hour running: It attracts many of the best runners in this discipline who race for their national team, and it’s been four years since the last such championships (1).

The format and strategy are simple in 24-hour races. You go as far as you can in 24 hours while running on a looped course. But, to borrow from a literary classic from my childhood, “it’s too bad ‘simple’ and ‘easy’ don’t mean the same thing (2).”

In this article, we’re looking at 24-hour races. Think of this article as a primer on the race format, current records as of November 2023, and pacing strategies so we’re all ready to cheer on these top runners and our favorite national teams.

Camille Herron - 2019 IAU 24-hour world champion - feature

Camille Herron on her way to setting a world record at the 2019 IAU 24-Hour World Championships. Photo: U.S. National 24 Hour Running Team

[Editor’s Note: We kindly remind readers that the Running the Numbers column is a just-for-fun analysis. While we always endeavor to analyze accurately, we limit the scope of each article in order to make the work doable for author Mallory Richard, and the results digestible for readers like you.]

The Basics on the 2023 IAU 24-Hour World Championships

The 2023 event will start at 10 a.m. local time on December 1. The course has something of a lollipop shape, which each lap measuring 2 kilometers (1.24 miles.)

According to the list of entrants the International Association of Ultrarunners (IAU) published on November 8, 2023, the world championships will include 262 runners from 41 countries. Countries with at least three runners competing in a single gender category are eligible for the team event. The scores of each country’s three best performers will be used to determine the team’s ranking. A concurrent individual competition will recognize the best individual racers.

The races are bound to be exciting. At the 2019 event in Albi, France, Camille Herron set a new world record and Aleksandr Sorokin’s winning result was also a Lithuanian national best. In many respects, conditions in Taipei will be conducive to strong performances. Each lap in Taipei covers 2k compared to the 1.5k loop at the previous world championships, so runners may face less congestion.

Taipei offers a generally warm and humid climate, which is less conducive to fast running. That said, a passing weather system looks to be offering below-average temperatures, an overcast sky, and some rain this weekend, what could make for pretty excellent running.

Earlier this week, we published an article about the history and evolution of the 24-hour world record, if you’re looking for even more information on this race format.

Strategies for 24-Hour Running

Like so many competitive ultramarathons, attrition represents a major wildcard at the IAU 24-Hour World Championships. Camille Herron described hours 14 to 18 as the period when runners are most likely to encounter issues. At that point, they have logged many miles on the same flat, unforgiving terrain in which they continuously use the same muscle groups and – if things are going well – minimal fluctuations to their pace.

The hairpin turn at the end of the lollipop-shaped course will further exacerbate the strain to their ankles, knees, and hips. Overuse injuries are a very real threat. Non-stop running takes a toll on their gastrointestinal systems. Around hour 14, the sun goes down, and so does the temperature. Athletes will feel the impact of sleep deprivation.

Combined, these factors mean that 24-hour races are incredibly fascinating to follow, despite their on-paper simplicity. Like in other competitive ultramarathons, every runner at this event will need to constantly evaluate their race plan and execution and make adjustments in real time, based on their performance goals, personal fitness, and their assessment of the competition. Some runners will start out too aggressively, some runners will intentionally start at a slightly faster pace than they expect to finish, and some runners will mete out their energy to remain strong in the final 10 hours — and to possibly even muster the strength for surges.

Aleksandr Sorokin - 2022 IAU 24 Hour European Championships winner

Aleksandr Sorokin, after winning the 2022 IAU 24-Hour European Championships, in a new world record. Image: Marius Antanaitis screen capture from race video

Data on 24-Hour Pacing and Attrition

Camille Herron provided iRunFar with a copy of the splits from the 2019 IAU 24-Hour World Championships. The IAU shared its splits from the 2022 24-Hour European Championships. We used these datasets to create the balance of this article.

Both datasets support Herron’s observation that an unvarying (or barely varying) stride on flat terrain in a competitive environment leads to some blowups. A quarter of the athletes from the European championships dataset — 25% of the women and 25% of the men — had stopped running before the 23-hour mark.

Running the Numbers - Attrition Rate 24-Hour Runners

Table showing attrition rates in the 2022 24-Hour European Championships

We see the toll in runners’ splits as well. Runners generally start out at consistent paces, with modest changes from one lap to the next in the earliest hours of the race. As the race progresses, even top performers can encounter issues that require them to slow down and troubleshoot. In the 2019 IAU 24-Hour World Championships, the first “lap” was a partial lap of approximately 0.1 kilometers, so I combined the first and second laps. As a result, the following charts for the 2019 world championships may look as though many athletes started slow before settling into a faster pace on subsequent laps, but they certainly did not.

Lap Paces for Groups of Runners

For the charts below, I calculated the average pace for each lap for each of the following groups for each gender:

  • The 10 participants who ran the farthest.
  • The 10 participants who covered the least distance among those who ran the full 24 hours.
  • The 10 participants whose final distance results were in the very middle between the two groups above (called mid-pack in the chart below.)

I only showed each group’s average pace up to the farthest lap when the group still had 10 runners in that cohort.

2019 IAU 24-Hour World Championships Paces by Group

2019 IAU 24-Hour World Championships Paces by Group

Chart illustrating the pacing of different groups of runners throughout the 2019 IAU 24-Hour World Championships.

2022 24-Hour European Championships Paces by Group

2022 24-Hour European Championships Paces by Group

Chart illustrating the pacing of different groups of runners throughout the 2022 24-Hour European Championships.

You can see that in each race and for each group, the average pace per lap tended to increase as the race progressed, but the top men and women slowed the least. This is worth noting for American fans, because Nick Coury ran a negative split when he set a new American record in 2021, doing it so masterfully that you’d be forgiven for thinking that’s common in these races.

The chart above suggests that, when considered as groups, the top-10 men and the top-10 women had the most even and consistent pacing of the six groups shown. This speaks volumes about their fitness and race execution. It does not, however, mean the top runners had perfect races. As the charts below indicate, the top runners engaged in plenty of troubleshooting.

Nick Coury - 2013 World 24 Hour Team

Nick Coury (front left) with the rest of the U.S. 24-hour team at the 2013 IAU 24-Hour World Championships. Photo courtesy of Nick Coury.

The charts below show the pace per lap for each of the top-five runners in the women’s and men’s individual races. I only included the top-five runners in these charts (as opposed to 10) to keep the charts legible.

Every time you see a dramatic spike in one of the lines, that represents a lap that was significantly slower than the laps before and after. This means the runner in question either walked a lap, or stopped running to care for themselves in some way.

As someone with limited personal experience and zero success with fixed-time races, I was surprised to realize the best runners were not immune to mid-race issues. The charts below gave me a deeper appreciation of what they’re accomplishing — they might be stopping to change layers, get medical treatment, puke, or regroup on the toilet just like the rest of us. But when they start running again, they find a way to get back to the fast running they were managing before. It’s not perfect execution; it’s masterful problem-solving.

The degree to which this occurs is revealed in a powerful example from Camille Herron — according to her, she spent more than 56 minutes of the 24-hour race window at the 2019 world championships in the aid station or toilets. Her race included medical/physiotherapy care, puking, and taking the time to consume the right fuels to settle her stomach. While any one of those issues would have justified quitting for plenty of runners, Herron was still on course in the final minute of the event, like many of the other top finishers. The effort got her a world record.

Lap Paces for the Top Five Women at the 2019 IAU 24-Hour World Championships

Running the Numbers - 2019 24-Hour World Championships Top 5 Women - pacing

Chart illustrating the pacing for each lap of the top-five women at the 2019 IAU 24-Hour World Championships.

Lap Paces for the Top Five Men at the 2019 IAU 24-Hour World Championships

2019 24-Hour World Championships Top 5 Men - pacing

Chart illustrating the pacing for each lap of the top-five men at the 2019 IAU 24-Hour World Championships.

Appreciating the Results

Now that we’ve discussed just how challenging this race format is and how many things can go wrong, let’s talk about what these athletes accomplish amidst those challenges. It’s not always easy to appreciate the significance of the results at the IAU 24-Hour World Championships, because an exceptional runner’s average pace will be one that many ultrarunners can hold for at least a few miles. Similar to a backyard ultra, the best runners are working with paces and effort levels our minds can grasp, but proceed to rack up stunning mileage totals.

The histograms below show the distribution of results within the men’s and women’s individual races. As you can see, the 2019 world championships was one of very few 24-hour races where the overwhelming majority of runners covered at least 100 miles (160k) in the time available. With the sport of ultrarunning gaining additional popularity over the past four years, it will be exciting to see how the results at the 2023 race compare.

Distribution of Men’s Results at the 2019 IAU 24-Hour World Championships

2019 24-Hour World Championships Men's Results Distribution Chart

The chart above shows that the majority of participants in the men’s race totaled over 100 miles in 24 hours. The source for this data is the results from the “UltraRunning” magazine website, supplemented by the IAU’s results list (because the UltraRunning results omitted the two finishers who totaled fewer than 26 miles.)

Distribution of Women’s Results at the 2019 IAU 24-Hour World Championships

2019 24-Hour World Championships Women's Results Distribution Chart

The chart above shows that the majority of participants in the women’s race totaled over 100 miles in 24 hours. The source for this data is the results from the “UltraRunning” magazine website, supplemented by the IAU’s results list (because the UltraRunning results omitted the finisher who totaled fewer than 26 miles.)

The Desert Solstice Track Invitational is an annual 24-hour track race held in Arizona. As an invitation-only event, entry is reserved for elite athletes who meet the race’s qualifying standards. Because ultramarathons are unpredictable, many of the athletes who gain entry do not meet or exceed the race performance that allowed them to qualify for the event. It’s a reminder that, as for the world championships, a bad day is a very distinct possibility for any elite athlete starting a 24-hour race.

However, Desert Solstice is also a useful benchmark for the world championships because its qualifying standards help us appreciate the number of elite performances we see in a single race (the 2019 IAU 24-Hour World Championships) and give us a sense of what to anticipate for 2023.

% of men and women in the 2019 24-H WC who achieved Desert Solstice qualification standard

Table showing the percentage of men and women in the 2019 IAU 24-Hour World Championships who achieved the Desert Solstice Track Invitational qualification standard.

Of note, the qualification standards for the world championships vary greatly from country to country. In Canada, for example, an athlete must have covered a minimum of 180k in a 24-hour race to qualify for the women’s team, but athletes from other countries have gained entry with personal bests of less than 100 miles.

The concept of running for 24 hours straight is familiar to many of us mid-pack runners because we have taken 24 or more hours to finish a 100 miler. To fathom the enormity of the challenge for competitors in the IAU 24-Hour World Championships, it can be helpful to consider their 100-mile splits, and then think about how they keep running for hours after that.

For example, Aleksandr Sorokin completed his 105th lap at the 2019 world championships with 11:46:57 elapsed. That meant he had covered 160.3k, or just over 100 miles. He then nearly repeated that feat, finishing his 209th lap with 23:56:29 elapsed and winning the men’s individual race.

Similarly, Camille Herron calculated her 100-mile split as 13:17:25, which was even faster than Marisa Lizak’s winning time at Desert Solstice that same year, which “UltraRunning” magazine recognized as the fastest 100-mile run of any woman on North American soil in 2019.

Closing Thoughts

As always, this is something of an armchair analysis, because it draws on incomplete splits from a couple races. And yet, there’s a lot to dig into here, especially for ultrarunning fans who are less familiar with fixed-time races.

We’ve attempted to quantify the competitiveness of the upcoming race and the challenges of obtaining a competitive result in this discipline. If you find yourself in a position to follow the event in real-time on race day, you’ll be able to appreciate the reasons why, as Camille Herron pointed out, the event gets really interesting around hour 14.

Call for Comments

  • How do you think the level of competition in the 2023 IAU 24-Hour World Championships individual race will compare to 2019?
  • Which athletes will you be following this year?
  • Whether from your own personal experience or analysis, do you have any insights on effective pacing strategies in fixed-time ultras?


  1. I feel compelled to point out there’s some nuance in this statement. When I say the race will attract the best athletes in the discipline, I don’t want this to be misread as all of the best athletes in the discipline. As has been covered elsewhere, participation in the IAU 24-Hour World Championships is generally self-funded by the athletes. They may receive financial support from their national governing body, but the amount of that funding varies by country. Furthermore, like the Trail World Championships, some top athletes are unable to attend because of other races in their schedule. For example, Amanda Nelson currently holds the Canadian women’s record for 24 hours, but is recovering from running 57 yards at the 2023 Big Dog’s Backyard Ultra in late October. In short, fans of the sport will have a large number of elite athletes to cheer for at the IAU 24-Hour World Championships in Taipei, and their performances there will inspire their peers as well as us regular folk.
  2. The literary classic is Steve Perry’s 1996 novel, “Shadows of the Empire.” The novel expanded the storytelling of the Star Wars galaxy by recounting the adventures of Luke Skywalker, Leia Organa, Lando Calrissian, Chewbacca, R2D2, and C3PO between the conclusion of “The Empire Strikes Back” and the opening scene of “Return of the Jedi.” The novel was part of a multimedia release that also included a video game and action figures. “Shadows of the Empire” has been designated part of the “Star Wars Legends,” since the Star Wars films numbered Episodes I-VI are the only products released prior to April 25, 2014, that are considered part of the official Star Wars canon. Regardless, I believe “Shadows of the Empire” has the power to resonate with trail runners and ultrarunners in many subtle and profound ways, not least of which is Perry’s ability to combine humor and poetry. Who hasn’t had a race where it felt like “the nerf waste hit the ventilator shaft,” or struggled on a technical ridgeline and thought to themselves, “It might be a long afternoon. Or a short one…”
Mallory Richard

Mallory Richard is a data analyst and trail runner in Winnipeg, Canada.