How Do You Pace the Ultramarathon?

Track fans had their eyes fixed on Sacramento in July for the USATF outdoor track championships, but that wasn’t the only championship event in the running world. That weekend also played host to the Western States Endurance Run, a 100-mile ultramarathon that’s arguably one of the most storied ultra-endurance events in the world.

The big story at this year’s Western States was a strong push through the first 60 miles of the race by Max King, a latecomer to ultramarathoning who boasts very impressive track and marathon credentials, including a national-caliber 3km steeplechase PR.

Alas, Max King faded in the final third of the race, passed by eventual winner Rob Krar, who finished the hundred-mile trek in just under fifteen hours.

For the better-known running distances like the 5k or the marathon, it’s pretty well-accepted that even pacing is the best strategy (here’s some research). But how about the ultramarathon?

Does the ideal pacing strategy change when you push out your race distance far beyond the length of a marathon?

Identifying the ideal pacing strategy

A study published in 2004 by Mike Lambert and a team of other researchers at the University of Cape Town in South Africa looked to find some answers to these questions.

In the study, Lambert et al. analyzed the 10km splits of 67 high-level ultramarathoners at the 1995 and 1997 IAU World Challenge, a 100 km ultramarathon.

By sorting the runners into groups based on their finish time and applying statistical analysis to their intermediate splits, Lambert et al. were able to identify what type of pacing strategy led to a good race outcome.

Fast runners vs slow runners

Unlike many ultramarathons (including Western States), the course at the IAU World Challenge is a flat loop course, which makes comparing split times much easier.

Unlike the pacing of elite runners in shorter events, everybody at the IAU World Challenge 100k slowed down over the course of the race—even the podium finishers.

But critically, the most successful runners were the ones who slowed down the least.

The fastest group of runners only ran their last 10k loop 15 percent slower than their first, and they were able to maintain their initial pace up to about 50 km into the race before slowing at all.

The pacing of the slower runners dropped off by 40%, and they started to slow significantly earlier. Even the middle-of-the-pack ultramarathoners slowed by 25-30%.

Further, the fastest runners also had less variability in their splits, meaning they didn’t have any big surges or drastic drop-offs in pace.

Now, some of this might be incidental: a runner with stomach problems or one who tripped and fell would obviously have more split-to-split variability than one who didn’t.

Low split variation and gradual slowdown

And one of the study’s other findings—that the faster runners started out at a higher speed than the slower runners—is almost surely correlative, not causative.

But the combination of low split variation and a more gradual slowdown in the best ultramarathoners makes a strong case for efficient pacing in the ultramarathon.

Why do runners slow down?

This still doesn’t provide a direct answer as to why even very successful ultramarathoners tend to slow down in the latter portions of the race.

Lambert et al. propose a number of different possible reasons.

• First among these is fueling: even with very high carbohydrate intake, there comes a point where your body’s ability to absorb carbohydrates limits how fast you can run, because faster paces necessitate higher carbohydrate utilization and you can only absorb carbs so fast.
• Interestingly, Lambert et al. point out that this threshold occurs around 40-50km in most people when running at a moderate pace, right around where the best runners in their study started to slow.
• Alternatively, muscle fatigue or simply pacing mistakes by the slower runners could account for much of the slowdown.

Whatever the cause, it’s not unique to ultramarathon running.

A 2008 review study by Chris Abbiss and Paul Laursen at Edith Cowan University in Australia cites research on Ironman triathlons and long-distance cycling races that shows a similar progressive slowing of pace in the later stages of the competition.

Unlike in a 5k or even a marathon, a progressive (though gradual) slowing of pace after about 50km (31 miles) appears to be part of the ideal pacing strategy—at least according to the research published to date.

Conclusion

Scientific evidence isn’t always in-step with the latest training and racing strategies, but it does help explain the reasons behind the phenomena we observe on race day.

If you are shooting for success in your next ultra race, you should maintain your goal pace as evenly as possible for as long as possible.

Although some slowing is probably inevitable after running for a few hours, you should do your best to keep the slowdown as gradual as possible.