Will Women Ultrarunners Surpass the Best Men?

Last October, Courtney Dauwalter won the Big’s Backyard Ultra in Bell Buckle, Tenn., tying the course record. Over almost three days, she covered 283.33 miles to beat all the men. It seemed a giant leap for womankind in the long debate over male vs. female endurance.

Except that male runner Karel Sabbe was still going strong in a sister event in Antwerp, and he eventually logged 312.5 miles. Comparing the two performances, Sabbe beats Dauwalter by almost exactly 10 percent. That’s an important number. Remember it.

Flash back a few decades: In the mid-1970s, when women started running marathons more regularly, it soon became apparent that some were very good at the 26.2-mile distance — and even ultra distances. A few experts began speculating that women would eventually outpace men.

In 1992, Nature magazine, a leading scientific journal, even carried a letter from two esteemed physiologists predicting that women would catch and surpass men in the marathon by 1999. Time proved them seriously wrong. In 2021, the world records stand almost exactly 10 percent apart (2:01:39 vs 2:14:04), right where they were in 1990, and right where they are in the Backyard Ultra. Ten percent has proved a sticky number.

Still, the debate continues because it’s fascinating and may have some physiological explanations behind it. Also, on occasion, a woman does beat all the men and win an ultra race as Courtney Dauwalter did last fall in the Backyard Ultra.

In a new research review in Sports Medicine, Nicholas Tiller, a physiology researcher and ultra runner at UCLA, takes the deepest dive yet into the subject with a paper that’s 21 pages long and includes 217 references. Tiller’s not primarily interested in the stats; he strives for a balanced view of the potential physiological mechanisms. Below is a summary of Tiller’s findings, along with additional comments from him, and U.S. ultra running stars Camille Herron and Michael Wardian.

First, a few important stats

In one review of 92,000 marathon performances, the average female ran 4:54 vs. 4:28 for the average male — a difference of 10 percent. An equally large number of ultra performances reveal a gap slightly less than 10 percent. In the Ironman Triathlon, males generally surpass females by 10 percent except in the last event — the marathon — where the difference is just 7 percent. In bicycling races of 400 to 500 miles, women equal men, and in ultra-distance swimming races, they surpass men by 14 percent. In other words, different sports yield different results because they’re based on different physiological and mechanical (bicycles frames, cross-country skis, etc.) contributions.

Looking at muscle characteristics

On average, women have an advantage in Type 1 muscle fiber percentage, 44 percent vs. 36 percent. Since Type 1 fibers promote long-term aerobic performance, Tiller finds this fact “speculative but compelling.” The increased diameter of male muscle fibers sometimes restricts blood flow in the arteries; this could limit endurance efforts by men. Women also exhibit less fatigue in the respiratory muscles.

Central command, i.e., the brain

This one is tough to partition, as physiological and social/psychological questions crowd together. Some studies have shown that men are more competitive and risk-taking. But is this a good thing? Certainly not in the marathon where women are known to pace themselves better than men. Only one ultra-marathon study has looked into this phenomenon, reaching the same conclusion.

Better fat burning

From the 1970s, women’s ability to store and burn more fat was the first explanation offered in arguments about superior ultra abilities. This physiology hasn’t changed of course. But it’s also true that fat is mostly dead weight on a running body, though less so on a bike or in the water (where it provides a floatation advantage).

Tiller finds the fat-burning advantage minimal, and also offset in ultra-events by the fact that athletes can stop to refuel en route. They don’t have to carry all their calories in their cells. Alternatively, he proposes that women ultra-runners might benefit from their lower calorie requirements (the result mostly of lower body weight) vs. men. This means they don’t have to eat as much during an ultra-race — a potential benefit because consuming foods, especially sugars, can lead to GI distress.

Speaking of GI distress

This gets complicated and tilts in more than one direction. Women might need to consume less food and fluid (they have a lower sweat rate than men) in an ultra race, but they also have a smaller stomach and slower rates of gut emptying. In studies, they have reported a higher incidence of GI issues than men.

Oxygen power

There’s no doubt that males’ higher testosterone gives them bigger muscles, more red blood cells, a higher VO2 max, and faster times in the 100 meters, mile, marathon, and beyond. After all, sustained exercise involves getting more oxygen where it’s needed. In fact, at virtually all running distances, women trail men by that-now-familiar 10 percent.

However, as races move into a sort of super-ultra category, this becomes less crucial, and the difficult-to-define “muscle fatiguability” becomes more important. Somewhere out there, in mostly unknown territory, we will find more answers. But we haven’t gotten there yet.

Will the fastest woman soon catch the fastest man in ultra marathon races?

Nicholas Tiller, lead study author and author of the 2020 book The Skeptics Guide To Sports Science: “There isn’t a simple answer to this question. It’s crucial to distinguish between elite and non-elite athletes, and also to consider different sports. In ultra distance open water swimming, for example, females regularly beat males by a long way. In ultra running, I suspect that the average finish time of the 10 fastest males will always be quicker than the 10 fastest females. That said, we need to encourage more female entrants to run ultras to achieve a comparable pool of athletes.”

Michael Wardian, record holder for fastest time in the World Marathon Challenge — 7 marathons in 7 days on 7 continents: “I have seen women excel at ultra distances and totally expect that women could be the favorites for certain ultra races, especially those where mindset, planning and execution are critical.

“Women are just as strong and fast as men. I actually love seeing ladies take down us boys at various events. That said, I am going to try just as hard to bring it against a female as I would a man.”

Camille Herron, winner of the 2017 Comrades Marathon, and international races at 50K, 100K, and 24 hours: “My performances objectively confirm that I get closer to the men’s best times the longer I run. I definitely believe I will continue to close the gap, and perhaps exceed a men’s world-best time. I believe it will happen beyond 48 hours — likely at 1000K or 6 days.

“What works in my favor? I seem to resist fatigue in my muscles better than most people; I’m good at taking in a lot of calories during races; I can power nap to recharge my brain; and, I consider myself mentally tough/intelligent/positive. I’m physically strong/resilient, and can handle consistently high training mileage. I’ve averaged over 100 [miles] per [week] for 14+ years now and should hit 100,000 lifetime miles in the next year or so (I’m age 39).”