Unlocking Stronger, Longer Runs: The Missing Link That Fuels Fatigue Resistance
Fatigue kills pace. It’s the unseen barrier stopping athletes—from casual 5K runners to elite ultrarunners—from pushing past their limits.
That’s where muscular endurance comes in. Coach Scott Johnston, the guiding force behind UTMB champions Tom Evans and Ruth Croft, says this targeted approach isn’t just another training fad—it’s the game-changer that can transform how long and how well you run.
Why Muscular Endurance Trumps Traditional Training
While VO₂ max, lactate threshold, and HIIT are staples of endurance regimes, Johnston focuses on fatigue resistance at the muscle level. Here's why:
Frontier muscle fibers (Type IIa) — versatile and adaptable — lie between slow-twitch (Type I) and fast-twitch (Type IIx). They can champion both endurance and power if trained correctly.
Standard high-intensity training overtaxes the entire cardiovascular system, limiting muscular benefits as fatigue sets in. Johnston noticed that athletes’ heart rates—and paces—plummeted mid-session, signaling whole-body exhaustion. Runner's World
His solution? Train those frontier fibers directly—with controlled muscular stress that avoids overwhelming cardio systems. It’s smarter, not harder.
What Worked for Champions: UTMB Triumphs
Johnston put his theories into action with weighted uphill workouts as part of his ultra-focused plan for Evans and Croft. They carried backpacks filled with water (over 25 lbs), completing steep climbs totaling more than 1,000 meters of elevation. After the uphill load, they dumped the weight and ran back down at threshold pace. This brutal combo mimics ultra terrain, building deep muscular endurance and race-ready fatigue resistance. Runner's World
No Gear? No Problem. Scaled Workouts for Every Runner
Not everyone races UTMB—and thankfully, you don’t need to train like it. Johnston recommends a more accessible session:
Weighted Uphill Starter Workout:
10-minute warm-up jog
6 × 5-minute intervals up a steep hill or StairMaster (3–4 RPE) with 10–15% bodyweight carried
60 seconds rest between intervals
10-minute cooldown
Progress gradually: longer intervals or fewer reps until you hit 30 continuous minutes.
Prefer the Gym? Here’s a Muscular-Endurance Circuit You Can Do Anywhere
Train smarter—even indoors—with a session that targets those frontier fibers in running motion:
10-minute warm-up jog
6 × 10 split jumps (lunge-jump alternating legs, ~1 jump/sec, rest 60–90s)
6 × 10 squat jumps (low, explosive squats, ~1 jump/sec, rest 60–90s)
6 × 10 step-ups per leg (use a box ~75% knee height, control on the way down)
6 × 10 forward lunges, alternating legs, 1 rep/sec
10-minute cooldown jog
How and When to Weave in These Sessions
Once a week is ideal—serving as a buffer between other quality workouts or recovery days.
Start early in your training cycle. This builds a muscular base that makes high-intensity intervals pay off later.
Don’t skip the easy miles! Aerobic foundation matters. Your slow-twitch fibers need that base to help clear lactate when your frontier fibers kick in.
Recovery: The Secret Ingredient You Can't Skip
Johnston warns: it may feel manageable in the moment, but the next day? “You can hardly go down the stairs.” That soreness signals local muscular fatigue—not cardiovascular burn—so rest is critical.
Bottom Line: Run Stronger, Smarter
Muscular endurance isn’t optional—it’s foundational. By isolating and training the frontier muscle fibers with purpose (and just enough weight), you build a deeper kind of fatigue resistance. Then, when you hit VO₂ max or threshold intervals, your body responds—not collapses. Start now, and your later miles (and races) will feel a lot stronger.