In any long-distance run, from the half marathon to ultras, the winner isn’t the runner who looks the best right off the starting line, but the one who stays the strongest as the miles stack up.

…muscle damage and associated fatigue is the main impediment to performance in ultramarathons…

Fatigue resistance – the ability to avoid the effects of running that force you to slow down – is an important objective for all endurance athletes to stay strong, regardless of the sport. But while VO2 max and lactate threshold training might get the spotlight for staving off fatigue in milers and half marathoners, respectively, those going longer need to focus on another training strategy.

“We start having other variables that begin to compete [with VO2 max and lactate threshold] for priority,” Cliff Pittman, coaching development director at Carmichael Training Systems and Molly Seidel’s ultramarathon coach, tells Runner’s World. “That’s where durability enters the chat.”

Basically, building durability means maintaining your energy, mind-body connection, and form, even after hours of running.

Another way to think about it: Durability is a more endurance-focused version of the umbrella “fatigue resistance” term, explains Pittman.

Pittman’s team measures dips in durability by looking at reductions in pace, increased cardiovascular drift (when your heart rate climbs throughout a workout, despite no increase in intensity), loss of force production, worsening running economy, and other biomechanical changes, all over several hours at a fixed effort level.

Research also backs up the importance of durability, particularly in ultramarathons. A 2025 study says “muscle damage and associated fatigue is the main impediment to performance in ultramarathons; more performance-limiting than aerobic capacity, running economy, or gastrointestinal distress.”

Below are the four training strategies Pittman employs to build durability, the same techniques he uses with Seidel, who recently qualified for the Western States 100-miler by running the Black Canyon 100K in 8:25:13, placing fourth overall.

1. High-Volume Zone 2 Running
Periodisation is a popular training strategy that means structuring training so you arrive at a race in peak physical shape. In 5K training, for example, runners start with zone 2 work to make their aerobic engine bigger. Then, as training progresses and the race approaches, the intensity of the training gets higher and includes more 5K race-specific speedwork.

“In ultrarunning, that concept is inverse,” Pittman explains. “We’ll start with VO2 max work, progress to lactate threshold, and then end with high-volume endurance-specific focus where the majority of work is zone 2.”

It’s practical physiology, explains Pittman. Raising your VO2 max elevates your aerobic capacity, improving lactate threshold allows you to access more of that aerobic potential, and zone 2 work unlocks the ability to sustain many hours of that submaximal effort.

For example, Pittman has seen ultramarathon athletes take a blood test that reveals they’re operating at 95 percent of their VO2 max, which at first seems great. Upon closer inspection, though, they were operating at 95 percent of a low overall aerobic capacity. That’s most likely because they didn’t prioritise VO2 max work early on in their training. “We have to raise that aerobic ceiling first so that we have more space to build up,” says Pittman.

The definition of “high volume” depends on the runner. For Seidel, high volume was actually less than some of her peak marathon training weeks, which at times reached well above 100 miles. “We kept her roughly around 13- to 14-hour weeks, which translates to about 90 to 100 miles or so,” Pittman says.

While training for the Black Canyon 100K, her long runs eclipsed 50 kilometres only twice. But instead of mixing in high-intensity VO2 max or threshold days late in the build, as she would during marathon training, they focused on consecutive days of high-volume zone 2 running.

2. Add Controlled Intensity to Long Runs to Amplify Fatigue
Durability isn’t just about running long; it’s about running strong. On most ultramarathon courses, like Western States, climbs demand more effort, descents challenge mechanics, and moves by other runners can influence intensity fluctuations. Purposefully pushing the pace during zone 2 long runs helps rehearse these race-day occurrences and allows athletes to train through calculated doses of fatigue.

This strategy includes placing structured zone 3 blocks into lengthy zone 2 efforts. “Zone 3 plays a critical component in ultrarunning,” Pittman says. “Being able to respond to moves or surges by competitors, or specific parts of the course, is important in a race.”

For example, early in Seidel’s training for Black Canyon, Pittman prescribed a three-hour zone 2 run that included a 30-minute steady-state (zone 3) push close to an hour into the run. Later in the cycle, that zone 2 run became four hours, and the 30-minute zone 3 surge moved close to the three-hour mark of the run, simulating a late-race boost.

For non-elite ultrarunners, Pittman cautions against replicating workouts that are catered to world-class runners like Seidel. “This is an elite level workout,” he says. “I wouldn’t give a three- to four-hour run with 60 minutes of zone 3 on the back end to just anybody.”

Instead, try adding two 15-minute zone 3 bursts (separated by five minutes back at zone 2) at around the one-hour mark of a three-hour long run. Attempting intensity you’re not prepared for is a quick way to get sidelined, and this strategy is a good way to test out your capabilities without straining too much. “Success always comes back to consistency and repeatable training,” Pittman says.

3. Use Mini-Blocks to Stack Stress
Spreading out the stress of an ultramarathon into manageable chunks is the best way to build durability and avoid injury. “We can’t go out and run 100 miles in one shot to prepare for a 100-mile race,” Pittman says. “This is one way to get as close as we can.”

Mini-blocks are two- or three-day stretches that safely simulate race fatigue. They often start with an intense workout on day one and decrease the training load each of the subsequent two days. This adds volume instead of intensity so the body experiences recovery overnight, but is still working through the fatigue of the harder day one effort.

A three-day mini-block for Seidel might look like this:

• Day 1: 3-hour long run with 40 minutes of steady-state (see above)
• Day 2: 4- to 5-hour zone 2 long run
• Day 3: 2-hour zone 2 run
• Day 4: Rest

These blocks allow you to test fueling strategies, assess form under targeted fatigue, and boost psychological resilience.

Recovering from dense training blocks like these is crucial to developing durability. Using TrainingPeaks software, chronic training load (CTL; a rolling six-week training load average), acute training load (ATL; a seven-day short-term fatigue measure), and training stress balance (TSB; a rough approximation of freshness) all help Pittman and his team monitor Seidel’s fitness and fatigue trends throughout training. The precise numbers don’t really matter too much to Pittman, but he looks at the overall fluctuation in these figures from Seidel’s baseline to evaluate if his training plan supports a healthy balance of volume and recovery.

Without special software or a full-time coach helping you maximise every aspect of your training, mini-blocks present an especially tough challenge. Overtraining is an easy trap to fall into without strict guidelines, especially when dealing with high volume.

In this case, Pittman recommends athletes begin with two-day mini-blocks. For example, try a long run with controlled intensity (mentioned above) on day one, followed by a two- to three-hour zone 2 run on day two, followed by a rest day.

This structure allows you to get back-to-back endurance efforts without the pressure of a third consecutive high-volume day. “When we can break up a race effort into manageable chunks and then repeat it over time, we start stacking up good stress,” Pittman says. “Repeated submaximal stress is always better than single heroic workouts.”

It’s also crucial to protect your easy running days because if they aren’t truly easy, you won’t be able to optimise your volume or recover enough for your body to adapt to your training. Pittman includes short zone 1 easy days in his plans for Seidel, often capped at just one hour. “Taking that step back on easy days allows us to take two to three steps forward on the hard days,” he explains. “Keeping easy days easy allows us to absorb the hard work better.”

4. Emphasise Running Well While Carrying Fatigue
What does “running well” actually mean? According to Pittman, it’s “ultimately just performance in general – a lack of degradation.”

During Seidel’s 100K, she only experienced a drop in efficiency (measured by TrainingPeaks by dividing normalised power or graded pace by average heart rate) of about 5 percent over the course of the entire race. Think about that: Finishing 62-plus miles while still operating at 95 percent of your starting efficiency—that level of durability is built on more than just a strong zone 2 foundation.

What that looks like in training is maintaining form and perfecting a fueling strategy.

In a 5K, good form means keeping up a high-powered stride to sustain fast paces. In long-distance races like ultras, it’s all about avoiding three main points:

1. A breakdown in joint stiffness, which you need to be springy and propel forward.
2. Increased ground contact time, which steals your energy and raises injury risk.
3. Progressive neuromuscular fatigue, which you need to maintain for muscle activation and force production.

All of these things will inevitably occur when repeating the same motion over time, but the goal is to push them off as long as possible. “We’re not trying to maintain textbook-perfect biomechanics,” Pittman explains. “We’re trying to prevent major mechanical collapse.”

How do you train that? It’s not with form drills like a 5K runner would use. It all comes back to controlled repetition. Pittman says that running enough on race-relevant terrain, practising downhill running under fatigue (toward the end of a long run), stacking aerobic stress across days (mini-blocks), and adding intensity late into long runs are the best ways to preserve form in the final third of a long-distance race. The more you practice running on fatigued legs, the better you get at it.

“[Another] big component [of running well] is fueling tolerance,” Pittman says. “You get palate fatigue where the last thing you want to do is take in more gels. But you have to realise that those resources are so precious that you have to continue to be able to fuel yourself despite that.”

Finding a few different flavours of the same brand of gel may help make your in-race fuelling digestible, or switching to an entirely different fuel source for the second half of the run. Whatever your strategy may be, practising it during training is the only way to know how you’ll tolerate it during a race.

Failing to nail down a strategy could result in anything from a lack of necessary energy to major GI issues. You can be the fittest person in the race, but if your fuelling is lacking, that’s a disaster waiting to happen, Pittman says.

At the end of the day, Pittman’s approach to durability training is deliberately simple and even boring at times. “There’s no magic, no gimmicks,” he says. “It’s all evidence-based. I really don’t think there are any secrets in the sport.”

READ MORE ON: endurance long run