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The physiology of events like the Ultra-Trail du Mont-Blanc is radically different from “short” events like the marathon

Immediately after stumbling across the finish line of the 2019 Ultra-Trail du Mont-Blanc, the legendarily punishing mountain-ultra-trail event, 56 runners hobbled over to the National Ski and Mountaineering School in the French resort town of Chamonix. Waiting there was a team of scientists with a roomful of lab equipment to measure the precise physiological toll of their exertions. The problem: one of the tests required them to run on a treadmill for four minutes while their breathing was measured. Many of the super-fit ultrarunners couldn’t stay on the treadmill for that long, so the scientists altered the protocol on the fly and shortened the treadmill run to three minutes.

Running ultras is hard; so is studying them. Can you really get volunteers to run on a laboratory treadmill for 24 hours? Well, yes, you can—and Guillaume Millet, a researcher at the Université Jean Monnet Saint-Etienne in France (and himself an accomplished ultrarunner) has been there, done that, and published the paper. But you get more plentiful and realistic data by studying ultrarunners in the wild. So Millet and his colleagues recently published the sixth in a series of studies from that 2019 UTMB. Here are some of the insights from those studies about what it takes to run through the mountains for hours on end, and how your body responds to the challenge.

Long and Short

This year, about 10,000 runners will participate in seven different UTMB races over the course of a week in late August. The runners studied in 2019 ran one of two “short” distances (25 and 34 miles) or three “long” ones (62, 90, and 105 miles). The distance is just part of the story: the longest race, for example, also includes almost 33,000 feet of climbing and descending. The men’s winning time in 2019 was over 20 hours.

The range of distances provided a perfect opportunity to test how leg muscle fatigue responds to different durations of running. It’s pretty obvious that your quadriceps and calves will be weaker right after you run 100 miles. But it’s less clear where that fatigue originates. Is it your muscles? Your brain? The signaling pathway along your spinal cord that sends messages from the brain to the spinal cord? Millet and his colleagues put the runners through a series of neuromuscular strength tests before and after the races. There was a test of voluntary strength, but they also used magnetic stimulation of the brain and electric stimulation of the nerves to elicit involuntary muscle contractions, in order to tease out exactly where strength was lost.

After the long races, voluntary quad strength decreased by 38 percent, compared to just 27 percent in the short races. Part of the fatigue arose in the brain: even though the subjects were trying to push as hard as possible, the outgoing signal from their brains was smaller. The muscles themselves were also weaker: for a given level of electric stimulation, they produced less force. (The spinal cord played only a minor role.) In the quads, the difference between short and long races was explained by more muscle fatigue, rather than more brain fatigue.

Surprisingly, though, calf strength declined by 28 percent after both the short and long races: in this case, the extra distance didn’t seem to make a difference. When you compare these results to previous ultrarunning studies, a somewhat confusing picture emerges. Beyond a certain point—about 15 hours of racing, the data suggests—longer races don’t seem to make your muscles more tired. That may be because you can go faster in shorter races, and intensity is a key cause of fatigue—particularly if you’re hammering down quad-busting mountainsides. The scientific picture remains murky, but if you happen to run one of these races, you might want to adopt “After 15 hours, it won’t get any worse!” as an encouraging mantra.

Men and Women

Ultrarunning is one of the rare sports where top women sometimes beat top men—a feat that always prompts discussion about the physiological differences between sexes, and whether women have ultra-friendly characteristics that help them overcome the edge in muscle strength and red blood cell count that men get from testosterone. That’s a long and involved debate, but one of the hypotheses is that women’s muscles fatigue more slowly than men’s. It does appear that women have, on average, a higher proportion of endurance-linked slow-twitch muscle fibers, and better blood flow to feed those fibers.

In the UTMB data, women did indeed seem to show less muscle fatigue after the race. Here, for example, is the individual (dashed lines) and average (solid lines) data for quadriceps strength in men (blue) and women (red), before (PRE) and after (POST) the races:

The men were stronger before the race and stronger after the race—which makes sense because they had to propel bigger and heavier bodies through the mountains—but they had a bigger strength decline. This fits with previous research showing better muscular endurance in women.

There’s a twist, though. The researchers also asked each runner to rate their “competitive intentions” on a scale of 0 to 10, with 0 corresponding to “I tried to do the best time possible” and 10 corresponding to “Fun mode: my only goal was to finish the race.” Here’s what those scores looked like in the short and long races:

In this case, the men seemed to be more focused on their time, particularly in the short races—which, it turns out, is where the differences in muscle fatigue were most pronounced. This opens a different can of worms regarding potential sex differences in competitiveness. On one hand, this idea seems irrelevant to the question of why top women can compete with top men in ultra races, because the women who win races are clearly not in “fun mode.” On the other hand, women have repeatedly been shown to pace themselves better in endurance events, an observation that may be linked to overly competitive (or, to use the technical term, “stupid”) early pacing by men.

Millet’s new data can’t answer these questions, but it adds to the evidence that patterns of fatigue tend to be different in men and women. The elephant in the room, though, is participation rates. Only 257 of the 2,543 starters in 2019 were women. Until the numbers are more even, it’s risky to draw any general conclusions about sex differences.

Flat and Hilly

There have been numerous attempts to figure out which physiological traits predict how you’ll do in an ultra trail race. For ordinary road marathons, the three key parameters are VO2 max (the size of your aerobic engine), lactate threshold (which roughly tells you how much of your engine capacity you can use over a long period of time), and running economy (the efficiency of the engine). But those three factors are less useful in trail ultras: a study I wrote about a few years ago found that standard lab tests had decent predictive ability over 50K, less value over 80K, and no use at all over 160K.

Two of the things that make trail ultras so different are (as the name suggests) the terrain and the distance. It’s one thing to measure running economy on a treadmill in the lab. But how much does your running economy change when you’re climbing a steep hill? Or when your legs are rubberized by 20 hours of running? Millet and his colleagues explored both those questions: they tested running economy on a level treadmill, and also at an uphill gradient of 15 percent, before and immediately after the races.

Here again there was a counterintuitive result: running economy got worse (meaning the runners had to spend more energy to cover a given distance) after the short races, but not the long races. Previous research has shown that both intensity and duration of exercise can hurt running economy, but there seems to be a threshold where if you’re going slow enough, your running economy won’t suffer no matter how long you’re out there. In fact, an earlier study found that running economy actually improved after the 200-mile Tor des Géants race, perhaps because an ordeal that brutal trims any wasted motion from your stride.

As for the effect of slope, previous research has found that the most efficient runners on level ground aren’t necessarily the most efficient going uphill: running up mountains is a unique and specific skill. But the new data found that post-race changes in efficiency on level ground were strongly correlated with changes in uphill efficiency, which suggests that the underlying cause—mostly likely stride-altering fatigue in the muscles, rather than changes in your metabolism—affects your stride whatever the terrain.

For better or worse, none of this makes UTMB any easier. Millet even co-wrote a whole book called How to Succeed at UTMB (the English translation is unfortunately out of print), collecting the accumulated scientific research and practical wisdom from runners and coaches who specialize in mountain trail ultras. It’s a hefty read, and drives home the point that, from a physiological point of view, these races are not simply extra-long marathons. “It’s more complicated,” Millet told me at a conference a few years ago. “That’s probably why I like it so much: it’s more interesting.”

Most Olympic marathoners spend their youth focused on running. They join track clubs, compete in national championships, and pursue the sport from an early age.

Julia Mayer’s journey was very different.

Today, Mayer is Austria’s marathon record holder, a multiple national record holder on the roads, and an Olympian. Yet for much of her athletic life, running was not her primary sport.

For 16 years, she played soccer.

Then she discovered something that would change her life.

“I noticed that I was really fast in the fun runs and that it was really, really fun,” Mayer said when reflecting on her transition from soccer to distance running.

What began as curiosity quickly became a passion. She eventually made the bold decision to leave soccer behind and focus entirely on running. It was a move that surprised many people around her, but Mayer believed she had found her true athletic calling.

The decision proved to be the right one.

Within a few years, Mayer developed into one of Europe’s top marathon runners. Her steady improvement carried her from local races to the international stage, where she began rewriting Austria’s record books.

She now holds Austrian records in the marathon, half marathon, and road 10K. Her marathon best of 2:26:08 established her as the fastest female marathoner in Austrian history. Her performances in the half marathon and 10K have further cemented her place among the country’s all-time great distance runners.

Her rise culminated with qualification for the 2024 Olympic Games in Paris.

Competing in the Olympic marathon represented the realization of a dream. On one of the most challenging marathon courses ever used for the Olympics, Mayer ran courageously against the strongest field in the world and finished 55th in her Olympic debut.

Behind the scenes, success has come through extraordinary dedication. During marathon preparation, Mayer trains twice a day and covers approximately 200 kilometers, or 124 miles, each week. The workload demands discipline, patience, and a deep commitment to continuous improvement. 

What makes her story especially inspiring is not simply the records or the Olympic appearance.

It is the fact that she found her greatest talent later than many elite runners.

In a sport where athletes are often identified at a young age, Mayer’s journey serves as a reminder that potential does not always reveal itself early. Sometimes it takes years of experience, a willingness to try something new, and the courage to follow a different path. 

The former soccer player who once chased a ball across a field is now chasing history on the roads of Europe.

And according to those closest to her, her best performances may still be ahead.

For runners of every age and ability, Julia Mayer’s story delivers a powerful lesson: it is never too late to discover what you are capable of.

From soccer player to Olympian, her journey proves that remarkable achievements can begin when least expected.

Megan Keith produced the performance of her career in Oslo on Thursday night, shattering one of Scotland’s longest-standing distance running records and cementing her place among Britain’s greatest female 3000m runners.

The 24-year-old clocked a sensational 8:28.35 over 3000m, breaking the Scottish outdoor record that had stood for nearly four decades. In doing so, Keith eclipsed the previous mark of 8:29.02, set by Scottish legend Yvonne Murray back in 1988, ending a record reign that had lasted 38 years.

Keith’s breakthrough run was more than just a national record. The performance also propelled her to third on the UK outdoor all-time list, placing her behind only two of Britain’s most celebrated distance runners — Paula Radcliffe, who leads the rankings with 8:22.20, and Laura Weightman, whose 8:26.07 remains the second-fastest outdoor mark by a British woman.

The significance of Keith’s achievement is amplified by the calibre of athletes she now joins in the record books. For decades, Murray’s mark stood as one of Scottish athletics’ most untouchable records, surviving generations of elite competitors. Keith has now succeeded where many outstanding runners have fallen short, announcing herself as one of the leading distance talents in British athletics.

Her time also compares favourably with the best performances produced indoors. Olympic medallist Laura Muir ran 8:26.41 indoors in Karlsruhe in 2017, underlining just how exceptional Keith’s outdoor effort in Oslo truly was.

The run continues a remarkable rise for the Scottish star, whose progression over recent seasons has transformed her from a promising prospect into a genuine force on the international stage. Running with confidence and composure against elite competition, Keith demonstrated both the speed and endurance required to challenge the very best in Europe and beyond.

With the World Championship season gathering momentum, Keith’s record-breaking display sends a powerful message. Not only has she etched her name into Scottish athletics history, but she has also established herself as a serious contender in one of the sport’s most competitive events.

In Oslo, Megan Keith did far more than break a record. She ended a 38-year wait, climbed into the upper echelon of British distance running, and delivered a performance that may prove to be a defining moment in her career.

British middle-distance talent Phoebe Gill took another significant step forward in her return to top form, producing a determined victory over 800 metres at the Meeting de Marseille in France on Wednesday.

Competing in challenging, wind-affected conditions, the 19-year-old demonstrated both resilience and composure as she held off a late charge from Switzerland's Veronica Vancardo to secure the win in 2:00.81. Vancardo finished just three hundredths of a second behind in 2:00.84, underlining the fiercely contested nature of the race.

While the margin of victory was narrow, the result represented another encouraging milestone for Gill as she continues to rebuild momentum following her injury setback. The young Briton showed impressive race awareness and strength in the closing stages, maintaining her advantage despite the difficult conditions that made fast running a challenge throughout the evening.

The Marseille triumph adds to a growing body of evidence that Gill is steadily progressing toward her best form. Earlier in her comeback campaign, she clocked 2:01.50 for 800m in Bydgoszcz before demonstrating her versatility with a strong 4:05.53 performance over 1500 metres at the BMC Grand Prix meeting in Trafford.

Those performances have highlighted not only her improving fitness but also her ability to compete across multiple distances as she carefully builds her season. The Marseille victory now provides further confirmation that the European junior star is moving in the right direction.

Gill emerged as one of Britain's most exciting middle-distance prospects through a series of breakthrough performances as a teenager, earning widespread recognition for her fearless racing style and remarkable maturity. Injury temporarily interrupted that upward trajectory, but her recent results suggest she is steadily rediscovering the form that made her one of the sport's brightest young talents.

With each race, the signs of progress become increasingly evident. Winning in difficult conditions and under pressure from a quality field is often a stronger indicator than a fast time alone, and Gill's latest success demonstrated exactly those qualities.

As the summer season gathers pace, the Marseille victory offers another confidence boost for the British teenager, whose return continues to gain momentum. If her recent progression is any indication, Gill could soon find herself back among the leading names on the European middle-distance circuit. 

The NCAA Track and Field Championships delivered a moment few could have predicted as Ja’Kobe Tharp produced one of the most astonishing performances in the history of sprint hurdling, rewriting the record books in spectacular fashion.

Competing in the opening round of the men’s 110-meter hurdles, the Auburn star stunned the athletics world by clocking an incredible 12.75 seconds, becoming the first athlete ever to break the 12.80-second barrier. In doing so, he eclipsed the long-standing world record of 12.80 set by Aries Merritt in 2012, a mark that had stood as one of the sport’s most revered achievements for more than a decade.

What makes Tharp’s breakthrough even more remarkable is the scale of his improvement. Entering the championships, the defending NCAA and U.S. champion had recorded a season-best of 13.05 seconds. Yet under the brightest spotlight, he unleashed a performance that exceeded every expectation, slicing an extraordinary 0.26 seconds from his personal best in a race that instantly became one of the greatest ever run.

The achievement sent shockwaves throughout the track and field community. While Tharp arrived in Eugene as one of the leading contenders for the NCAA title, few envisioned a performance capable of redefining the limits of the event. Instead, the American hurdler delivered a race for the ages, combining flawless technique, explosive speed, and impeccable rhythm from the first hurdle to the finish line.

The historic run not only secured his place in athletics history but also transformed the outlook of the championship. With the world record now in his possession, Tharp advances to the final as the overwhelming favorite, carrying momentum that could make an already unforgettable weekend even more extraordinary.

For years, the 12.80 barrier appeared untouchable. On a stunning day at the NCAA Championships, Ja’Kobe Tharp proved otherwise, producing the kind of performance that reminds fans why sport remains so unpredictable. In a matter of seconds, he turned a routine qualifying round into a landmark moment that will be remembered for generations.

The world record no one saw coming is now a reality—and Ja’Kobe Tharp is the man who changed history.

A new chapter in middle-distance running may have begun in Oslo after American teenager Cooper Lutkenhaus produced one of the most remarkable performances of the season, narrowly defeating reigning Olympic champion Emmanuel Wanyonyi in a thrilling men's 800m contest at the Diamond League meeting.

The 17-year-old sensation shocked a world-class field by crossing the finish line first in a race that came down to the smallest of margins. After an intense battle over the final metres, Lutkenhaus held off Wanyonyi by just one hundredth of a second, producing a dramatic finish that left the packed stadium in disbelief.

From the opening lap, the pace was relentless as the leading contenders positioned themselves for a fierce showdown. As the athletes entered the home straight, Wanyonyi appeared poised to unleash his trademark finishing kick. However, Lutkenhaus refused to be intimidated, matching the Olympic champion stride for stride before producing a perfectly timed lean at the line to secure a historic victory.

The result marks a breakthrough moment for the young American, who continues to establish himself as one of the brightest talents in global athletics. Defeating an Olympic champion at a Diamond League event is a feat many athletes spend entire careers pursuing, yet Lutkenhaus achieved it before reaching adulthood.

For Wanyonyi, the narrow defeat does little to diminish his status as one of the world's premier 800m runners. The Kenyan once again demonstrated his exceptional class and competitiveness, pushing the race to a world-class standard and forcing his young rival to deliver the performance of a lifetime.

Beyond the result itself, the race offered a glimpse into what could become one of the sport's most exciting rivalries in the years ahead. With established stars and emerging talents now pushing each other to new heights, the men's 800m continues to evolve into one of athletics' most captivating events.

On a memorable night in Oslo, the spotlight belonged to Cooper Lutkenhaus. At just 17 years old, he stood toe-to-toe with an Olympic champion and emerged victorious, announcing himself to the athletics world in spectacular fashion.