Last week, Tom Evans and Ruth Croft won the 2025 UTMB in commanding fashion and under historically tough conditions. Evans, a British runner who has once podiumed and twice DNFed the race, stormed to victory in 19:18:58. New Zealand’s Croft, who finished second at the event last year, seized control in the race’s final third and finished first in 22:56:23.
Both athletes are coached by Scott Johnston of Evoke Endurance, co-author of the now-iconic book, “Training for the Uphill Athlete.” Johnston’s roots are in alpinism and mountain sports like ski mountaineering, which makes his success at coaching athletes for one of trail running’s premier long-course events especially notable. Central to his coaching is a distinctive emphasis on fatigue resistance, also known as muscular endurance. Johnston believes fatigue resistance is the single biggest determinant of ultra-distance performance, more than VO2max or lactate threshold.
“The heart doesn’t get tired in these races,” said Johnston. “What I have seen is that athletes are limited by that fatigue factor out at the muscle.”
Training muscular endurance instead of VO2max or lactate threshold is a somewhat novel approach that seems to be paying dividends for athletes who embrace it. In this article, we explore what Johnston means by fatigue resistance and muscular endurance, and how he trains his athletes to improve their ability to maintain their strength and therefore their pace late in an ultra when everyone else slows down.
Tom Evans, 2025 UTMB champion. Photo: iRunFar/Bryon Powell
Fatigue Resistance and Muscular Endurance
Muscular endurance (ME) is your muscles’ ability to sustain repeated contractions or effort over time. Think of it as how long your legs can keep climbing, descending, or pushing on the flats before they give out. Fatigue resistance is related but slightly different and is defined as the ability to delay the point of muscular breakdown. It’s not just how long the muscle can keep working, but how well it can resist the gradual decline in performance that comes with hours of stress.
Put simply, muscular endurance is the capacity to keep working; fatigue resistance is the ability to keep that capacity from deteriorating. In ultras, particularly vertiginous mountain races like UTMB, the two go hand in hand; athletes with strong ME who can also resist fatigue are the ones still moving well when competitors start to crumble.
Ruth Croft climbing the Grand Col Ferret at dawn during the 2025 UTMB. Photo: iRunFar/Eszter Horanyi
This is echoed in a recent opinion paper in “Sports Medicine” by researchers Nicholas Tiller and Guillaume Millet. In it, they combined observational data with previous research to pinpoint muscle damage as the main obstacle to ultramarathon performance. One data point in the paper is a survey of 824 ultrarunners, where 66% pointed to muscle breakdown as their primary impediment.
How to Train Muscular Endurance
Johnston’s background in alpinism informs his approach to ultra training. He prefers to prioritize muscular endurance work before addressing VO2max or other energy systems in training.
Johnston noticed that many of his athletes failed to maintain sufficiently high heart rate in their higher-end interval work, indicating that their legs simply couldn’t keep up with their already well-developed aerobic engines. To fix that, Johnston uses event-specific workouts like steep uphill hiking, downhill repeats, weighted vests, and tire-drags to overload athletes’ legs. The goal, according to Johnston, is to stress propelling muscles locally without causing global systemic fatigue associated with high-intensity training.
Johnston trained Evans both for his recent win at UTMB and his breakthrough win at the 2023 Western States 100. While his collaboration with Croft is more recent, Johnston says their focus on ME was essential to their success. Johnston believes that by more intentionally focusing on ME via overloading the legs in training, and not the aerobic system, athletes can still access a higher percentage of their VO2max late in races. According to Johnston, Croft hit her highest heart rate just five kilometers from the UTMB finish line, which Johnston points to as evidence of her ability to sustain a higher output when not limited by her muscular endurance.
Training muscular endurance allowed Croft to set her highest heart rate of the event only five kilometers from the finish. Photo: iRunFar/Eszter Horanyi
“For most people in these long races, what I’ve worked on is making it so they don’t see that decline,” said Johnston. “They can still access a relatively high percentage of the VO2max late in the race, whereas if their legs become fatigued, then it doesn’t matter anymore if you’ve got a high VO2max of 90 because you can’t even get close to it when the muscles are so tired.”
Johnston’s idea is, if your legs can’t generate force late in a race, your heart’s oxygen-delivery capacity is moot. To bridge that gap, Johnston’s training, rooted in alpinism and ski mountaineering, seeks to target the legs specifically.
Training the Legs
In training for big, mountainous races like UTMB, Johnston has athletes hike on steep grades, slopes of 10% to 30%, either with water — which has the benefit of being able to be dumped out at the top of the hill so that athletes aren’t descending with unnecessary weight — or a weighted vest. He has his beginner athletes carry about 5% of their body weight, and elites carry 12% to 15%. For terrain-limited athletes, Johnston has them do tire-drags or stair machine sessions to target the legs, ensuring the burn in their legs is the limiter, not aerobic capacity. He also includes downhill repeats and tempo descents to build eccentric strength.
For elites like Evans and Croft, Johnston introduces this training method early in the season and carries it through the year, though he recommends that most people add it into their training the final 10 to 16 weeks before an ultra. He pairs ME-focused training with base training and strength work, and sees it as a way of training muscular durability while preserving athletes’ capacity for high-quality sessions.
“We never do any VO₂max training,” said Johnston. “I’m trying to get the same muscular effect that you’d get from VO₂max intervals, but without the global fatigue cost. You don’t elevate cortisol, you don’t elevate lactate, and recovery is much faster.”
Tom Evans leading the 2025 UTMB late in the race. Photo: iRunFar/Eszter Horanyi
To gauge the effectiveness of his training and track athletes’ progress, Johnston relies on several metrics, including chronic training load (CTL). Calculated in TrainingPeaks, a virtual training platform that Johnston uses with his coaching clients, CTL provides a six-week exponential moving average of an athlete’s training stress. That metric, amongst others like ramp rate and overall assessment of their training stress, helps Johnston tailor the training to each specific athlete.
“Understanding the work capacity and recovery rate of the athlete is important for finding the limit of what they can safely handle,” said Johnston. “With an elite, in some over-reaching blocks, we can see CTL increases of 10 to 15 per week. Every athlete is different and needs to be treated individually.” For a lower-tech way of assessing progress, Johnston recommends athletes build a cairn, or leave a stack of rocks on the hillside where they do their intervals, encouraging them to repeat workouts on the same hill, and see if they move the cairn uphill over time.
Is Muscular Endurance the New Secret?
While ME-specific training is core to Johnston’s philosophy, some question its centrality and relevance to all athletes. While consensus points to ME being important, how exactly to go about it is up for a larger debate. Some proponents argue that increased volume has the dual benefit of both building aerobic capacity and increasing muscular resilience and endurance, and that focusing too much on ME to the detriment of aerobic development might be sacrificing bigger benefits for a marginal gain.
Cliff Pittman, Coaching Development Director for CTS and a professional ultrarunning coach, says ME is one piece of a larger puzzle.
“ME is absolutely one of the most important determinants of performance in ultrarunning,” said Pittman. “But it’s not an adaptation that needs to be isolated if your training is already race-specific. In my view, ME is addressed implicitly in the training of any athlete logging consistent volume over appropriate terrain, especially while wearing their required race-day gear. We just call it endurance training because it’s all-encompassing.”
That assertion is echoed by Tiller and Millet’s paper, which points to training volume alongside strength training and fueling, rather than specifically targeting and overloading the muscles through weighted training and tire-drags, as being contributors to success. Other studies have also strongly pointed toward training volume as a major predictive factor in ultramarathon performance.
Ruth Croft, 2025 UTMB champion. Photo: iRunFar/Bryon Powell
Methods of overload, like using a weighted vest while running or hiking uphill, are also debated in the literature. The goal is to increase the load being carried by muscles, but evidence suggests that the added resistance meaningfully changes the whole running or hiking movement. Not only can that make training less specific — a 2023 study found that carrying weights that exceeded 10% of trained trail runners’ body weight altered their biomechanics and negatively impacted their performance at submaximal speed — but it can also increase risk for injury in some instances.
All of this said, UTMB is a unique test case in that it involves a lot of hiking, even for an ultramarathon. Looking at Evans’ data, Johnston said that the athlete spent about half the race hiking.
“Running and walking are very different activities,” said Johnston. “It’s like a different sport, and you actually need to train them.”
Pittman agrees that specific events merit specific interventions, like targeting stronger powerhiking for UTMB. But he worries that some nuance could get lost in the weeds. Pittman points out that athletes who are too focused on artificial ME interventions might sacrifice aerobic development, the true cornerstone of ultra training.
Final Thoughts
At the elite level, marginal gains in muscular endurance, like what allows you to hit one’s top heart rate late in the UTMB like Croft did, can make or break a performance. Ultramarathon success is multifactorial, and while two standout results don’t constitute proof, the spotlight on Johnston’s methods highlights an area of training that may deserve more attention. It’s not a silver bullet — no single element of training is — but it offers a useful lens for understanding success.
What is clear is that as the sport grows more competitive, coaches and athletes will need to leave no physiological stone unturned to stay at the top.
Tom Evans was able to outrun and outlast everyone else at the 2025 UTMB. Photo: iRunFar/Eszter Horanyi
Call for Comments
- Have you ever used weighted carries to train for an ultramarathon?
- What is your weak point as the miles add up?
