Many runners think of endurance as an aerobic engine problem, which training your heart, lungs, and other aspects of your body’s oxygen delivery systems can solve. But as you run longer and longer distances, those systems don’t usually limit performance. It’s the muscles—beaten up over hours of repetitive motion—that can no longer keep up with the demand.
This is the problem coach Scott Johnston aims to fix with muscular fatigue-resistance training.
In his buildup to ultramarathons, including the 2026 Hardrock 100, 2025 Ultra-Trail du Mont-Blanc (which he won), and 2023 Western States Endurance Run (which he also won), runner Tom Evans zeroes in on fatigue resistance with the help of his coach, Johnston. This has allowed Evans to climb stronger, descend faster, and keep producing force deep into the races.
The workouts Evans does are extreme—because he is one of the best endurance athletes on the planet who has trained for years—but the principles behind them can help anyone looking to run longer.
Here are the workouts that make up an average week of muscular fatigue-resistance training, how they support and boost your muscles’ ability to fight performance declines and run longer, and how to train for maximum gains.
What Muscular Fatigue Resistance Training Actually Looks Like
Johnston defines muscular fatigue resistance or endurance as the ability of the working muscles to keep producing force after hours of repeated motion.
Easy running mostly relies on slow-twitch muscle fibers that are already highly fatigue-resistant. High-intensity efforts like sprints call on strong and powerful fast-twitch muscle fibers, but they have very little endurance capability. Intermediate fast-twitch fibers (or type IIa) land in the middle of this spectrum—they are able to produce more force than slow-twitch fibers, but also take on endurance characteristics with proper training. Johnston calls these “frontier fibers” because they land at the “frontier” of your endurance capabilities.
Traditional high-intensity interval workouts, such as hill repeats or mile repeats, can train those intermediate fibers, too. However, they also carry a high full-body fatigue cost, which limits the quality an athlete can maintain before fatigue overcomes them, Johnston explains.
Muscular endurance training is designed to repeatedly load those fibers without the full-body fatigue cost.
The Workouts That Help You Fight Muscular Fatigue
Muscular fatigue-resistance workouts live in the middle ground between pure strength and pure endurance. These sessions ask the muscles to produce relatively high force over and over again—building the fatigue resistance needed for long climbs, descents, and hours of mountain running—without the full-body fatigue cost of high-intensity running.
Regardless of which workout you decide to add, Johnston recommends just one muscular endurance effort per week. Once you start, your stride should begin feeling noticeably stronger within a handful of weeks.
Weighted Uphill Session
Weighted uphill workouts (think fast hiking) are Johnston’s go-to workout for muscular endurance training in ultrarunners because they’re incredibly specific to the sport.
“It’s a really focused type of training to try to get to just those fibers that are limiting our endurance and target them exclusively,” Johnston says. In other words, the workout builds race-specific fatigue resistance in the legs by building up those intermediate muscle fibers.
They’re also not very time-consuming, often taking up less than an hour.
For an elite runner like Evans, this type of session might involve roughly 1,000 meters of uphill running (and hiking) with added weight (often 25-plus pounds), Johnston says.
Mountainous ultramarathons aren’t just climbing contests; they also require runners to handle repeated eccentric loading as the quads absorb impact on long descents, which weighted downhill running helps train.
A weighted uphill and downhill workout is probably extreme for those starting out with incline sessions, so Johnston recommends the below session to build fatigue resistance in the legs, without risking injury.
How to do it:
- 10-minute warmup jog
- 6 x 5-minute StairMaster (or steep hill) intervals at 3-4 RPE pace carrying 10-15% bodyweight; rest for 60 seconds in between
- 10-minute cooldown jog
Remember, weighted uphills are basically fast hiking, so brisk walking at a significant incline with weight on your back could be your 3-4 RPE pace for this workout.
Resistance-Training Workout
Runners ready to add muscular fatigue-resistance workouts to their own training for the very first time should start with the following gym circuit Johnston originally developed for athletes to do in their hotel rooms on the road.
Johnston says that beginning with a weighted uphill session with zero prior muscular endurance training can add unnecessary injury risk. When in doubt, it’s better to complete the workout below first, then move to weighted uphills.
How to do it:
The Workouts That Support Muscular Fatigue-Resistance Training
The rest of the week’s workouts support muscular endurance work by raising aerobic capacity, improving sustainable speed, increasing strength, and promoting recovery and adaptation.
Long Run With Tempo Work
The long run supports muscular endurance training by delivering the most important training ingredient: aerobic volume.
“The biggest stimulus to aerobic development is volume of work,” Johnston says. For ultrarunners, that volume builds the foundation for everything else—weighted climbs, tempo work, and the ability to keep running for hours.
For advanced athletes, Johnston likes progression-style long runs. A three-hour run for Evans might start with an hour in zone 1, build to zone 2 in the second hour, and finish with zone 3. By the time the faster running begins, the legs are already tired and muscle glycogen stores are lower, forcing the runner to produce quality movement when the body has less readily available fuel.
Johnston says operating in a low-glycogen state sends a strong signal to the muscles to become more aerobically adapted—essentially, better at using fat for fuel—which helps sustain pace late in a long effort. This also allows the legs to run easier as you enter late miles in a race.
Not every runner needs to finish long runs hard, though. For many runners, the aerobic stimulus of the long run itself is often the best method to support muscular endurance training without overloading fatigue, Johnston says.
Tempo Sessions
Threshold training supports muscular endurance building by improving the body’s ability to run faster for longer. These sessions teach your body to clear lactate and train your legs to work harder for more miles, upping their speed endurance.
“The way you increase the speed at threshold is by training below it,” Johnston says. “Target an intensity that is between the first and second [lactate] thresholds, and spend as much time there as we can.”
Johnston describes the intensity as somewhere between marathon and half-marathon pace, or what he calls “fun fast” or about a 7 out of 10 on an RPE scale where 1 is barely moving and 10 is an all-out sprint.
For Evans, Johnston made threshold work more race-specific by adding a steep incline to mimic long climbs Evans would face. In his build for Hardrock, Evans did these sessions on a custom Woodway treadmill at a 25 percent grade, which is far steeper than a standard gym treadmill can reach.
A typical session for Evans consists of three minutes at his “fun fast” effort followed by one minute slightly easier, repeating the pattern for about 40 minutes. Johnston also closely measured Evans’s blood-lactate level between intervals to keep it at the right level during the entire effort.
In Evans’s previous builds, Johnston had him do a flat tempo run later in the same day after an incline threshold effort. For Hardrock, Johnston upped the ante and used a 40-minute flat tempo run as a direct lead-in to an incline threshold session.
The good news is that most runners don’t need a 25 percent grade, immediate blood-lactate testing, or the ability to do double-workout days to benefit from quality threshold training.
Traditional flat-ground efforts like the tried-and-true 30-minute tempo run or threshold hill workouts on standard treadmills at your “fun fast” effort can help most runners increase their speed over a longer distance, including on race day.
Strength Sessions
“The stronger you are, the more benefit you’re going to get from muscular endurance training,” Johnston says. If a runner can barely do a single step-up or Bulgarian split squat with bodyweight, then basic strength is limiting endurance, he continues.
By raising an athlete’s max strength for a few weeks with heavy, low-rep strength work, a muscular endurance training program becomes more effective.
“We’re not interested in adding muscle mass here,” Johnston says. “We’re just interested in increasing strength.” Go for heavy loads (85 to 95 percent of an athlete’s one-rep maximum), low-rep counts (like three to six), and two- to five-minute recovery breaks between exercises. This allows the main stimulus to be neurological instead of metabolic, Johnston explains.
Johnston suggests one or two max strength sessions per week, often emphasizing single-leg movements that mimic the motions of running.
Easy Runs
The weighted uphill sessions, tempo runs, and strength training only work with a strong aerobic base. This is why a muscular fatigue-resistance training program “still relies very heavily on basic aerobic training,” Johnston says. “That volume needs to stay high.” Easy or zone 2 runs help you build volume.
“If you can’t do in a week what you intend to do in a day, then you’re going to struggle,” Johnston says. For someone training for their first marathon, that means building toward sustaining roughly 26 miles of weekly volume before adding in more high-effort runs.
Matt Rudisill is an Associate Service Editor who has been with Runner's World since 2025. A Nittany Lion through-and-through, Matt graduated from Penn State in 2022 with a degree in journalism and worked in communications for the university's athletic department for three years as the main contact and photographer for its nationally-ranked cross country and track & field teams. Matt was also heavily involved in communications efforts for Penn State football, men's basketball, and women's gymnastics. In his role with Runner's World, Matt has interviewed Olympians, world champions, and countless experts in the field to create service content that helps runners of all ages and experience levels train smarter and race faster. When he’s not out jogging, Matt can be found tweeting bad takes about the Phillies or watching movies.