Weighted Vests, Circuits, and the Truth About Muscular Endurance

Shortcuts disguised as ways to build muscular endurance, like weighted vest hikes and fatigue circuits, often add stress without meaningful adaptation. In this video, CTS Coach Cliff Pittman breaks down what muscular endurance actually is in ultrarunning and why imitation is not the same as specificity. We cover what the research supports and what does not transfer.

The takeaway is simple: focus on the work that actually drives adaptation, because these so-called shortcuts do not just fall short, they add fatigue, increase injury risk, and take time away from what matters most.

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HOST

Cliff Pittman is the Coaching Development Director at CTS, leading the Ultrarunning and Cycling Coaching staff with a specialty in guiding athletes from first-time ultrarunners to elite competitors at races like Western States 100, Leadville 100, and the Triple Crown of 200s. A competitive trail and ultra athlete himself, Cliff brings firsthand experience and a rare ability to turn complex training science into simple, actionable coaching.

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Find more free resources here: https://trainright.com/blog/

Resources:

• https://pubmed.ncbi.nlm.nih.gov/39330706/
• https://pubmed.ncbi.nlm.nih.gov/38165636/
• https://pubmed.ncbi.nlm.nih.gov/21615190/

Transcript

The Shortcut Trap In Ultrarunning

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Ultra runners love a clever workaround and a shortcut that looks like hard work. Weighted vest hikes, post-run fatigue circuits, high rep lunges, stacks on top of long runs. The idea is that if you can engineer the right kind of fatigue, you can build muscular endurance faster than just simply running more. Now, it's an intuitive idea, and it mostly doesn't work. I'm Cliff Pittman, Pro Ultrarunning Coach and Director of Coaching at CTS. Coach athletes from first-time ultrarunners to professional and world-class athletes. And today we're talking about what muscular endurance actually is, why the training interventions most athletes reach for create unnecessary stress without meaningful adaptation.

What Muscular Endurance Really Means

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And what the evidence actually supports so let's start with the definition because this is where the confusion begins. Now, in a general sense, muscular endurance is the ability of a muscle or muscle group to sustain repeated contractions over time without excessive fatigue. But that definition doesn't do enough work for ultra running. Now in our sport, muscular endurance

Weighted Vest Hiking Under The Microscope

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isn't about holding a plank for five minutes or grinding through a brutal gem circuit. It's about the capacity of your legs to withstand tens of thousands of impact cycles up and down steep and technical terrain for 8, 12, 24 or more hours without crumbling. Not peak force production, but sustained force production over time, under fatigue, on terrain. We've also started calling this durability, and if you want the full breakdown of durability as a performance variable, I have a dedicated video on exactly that. Link is on the screen. Now let's talk about the methods athletes commonly reach for and why they don't deliver what people think they deliver. First is weighted vest hiking. There's a camp in endurance coaching that advocates heavily for this approach. The idea that loading the body with external weight during uphill hiking builds leg strength and tissue resilience needed for mountain ultrarunning. Now the logic sounds reasonable on the surface. Add load, you hike uphill, you build durability. In mountaineering or military context, and I say this from my own military background, there's a legitimate case for it. But ultralunning isn't alpine climbing, and the demands are not the same. A 2024 peer-reviewed study tested trained trail runners at vest loads of 0%, 5%, and 10% of body mass. Now, as load increased, time to exhaustion decreased significantly. The authors found that increasing vest load produces an exponential loss of performance, driven primarily by neuromuscular disruption, but not meaningful metabolic adaptation. So it made the effort feel harder, it did not make the athletes more durable. And the injury risk is very real. Weighted backpacks alter your mechanics and load your spine in ways that don't always show up until something goes wrong. So here's really the honest question to ask yourself. Is a weighted vest hike meaningfully better than just putting on your race kit, loading it up with the required gear, and going out for a run? In almost all cases, no. The run has the specificity advantage every single time. Weighted vest hiking isn't inherently bad. In self-supported or multi-day context, there may be a legitimate role for it. But as a primary muscular endurance strategy for trail and ultrarunning, it is a solution in search of a problem.

Why High Rep Circuits Miss The Mark

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Second is high rep strength circuits. This one goes by a lot of different names. You've probably seen them marketed as functional strength for runners, or mountain legs, or fatigue resistance training. The format is usually the same. Post-run lunges, air squats for time, kettlebell circuits designed to leave you absolutely wrecked. The idea is that you're simulating race fatigue, conditioning your muscles to keep producing when they want to stop. But here's the problem. These circuits drive heart rate into aerobic training zones. They feel like productive work, but they lack the mechanical loading and tendon behavior and movement specificity that actually transfer to the trail. You're not building durability, you're just adding fatigue. And if an athlete told me that they did 30 minutes of air squats and lunges after the long run, I'd just say I'd rather you go out for another 30 minutes on your run. The specificity is better, the adaptation is better, and the return on investment is better. Now the research supports this. A 2023 systematic review and meta-analysis in sports medicine found that heavy and pliometric strength training improved running economy and distance runners. Low load, high rep training, like mountain leg circuits and the format most fatigue protocols use, showed little to zero benefit. A running economy wasn't the only thing being measured, but the pattern is consistent. The strength work that actually transfers to performance looks nothing like the work most athletes are doing in the name of muscular endurance. Those circuits feel productive, but the adaptation isn't there.

Imitation Versus True Specificity

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Third, and this is the root of both mistakes, confusing imitation with specificity. Some coaching philosophies argue that because ultra-running demands prolonged muscular endurance, training should deliberately replicate that fatigue through accumulated loading in the gym or under a vest. But the specificity principle does say that training adaptations are specific to the stresses you apply. And that part is correct. But here's where the application goes wrong. Imitation is not specificity. Specificity means the stress you apply drives adaptations that transfer to your event. It does not mean your training has to look like your event in order to work. You already produce tens of thousands of muscle contractions on the trail, and adding more of the same in the gym compounds stress. It doesn't build new capacity. The goal of the weight room isn't to replicate what running already does, it's to build qualities running can't build on its own. So heavy loads, explosive output, tissue resilience, complementary stressors that support performance, not imitations of it. A specificity in this context doesn't mean copying your sport, it means supporting it. So what actually works?

What Actually Builds Durability

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Well, the answer isn't complicated and it's not going to sell any programs or books. Run more. Run on terrain that looks like your race. And do that consistently over time. That's it. Research from Malay and colleagues found that neuromuscular fatigue and ultramarathon events is driven by cumulative mechanical and metabolic stress, the kind that only develops through sustained sports-specific training, not mimicking and gym, not contrived through added load, but built on the trail over time. So what about athletes who can't add more volume or don't have access to specific terrain? Well, the answer still isn't fatigue circuits. It's optimizing what's already there, smarter intensity distribution, strategic terrain exposure when possible, and strength work that complements running rather than imitating it. When I prescribe strength for ultra runners, I'm looking at bilateral and unilateral lifts, plyometrics, and progressing toward high load, low volume work as the training cycle advances. Just two to three sessions per week early in the build and scaled back to once per week or every eight to nine days in peak volume phases. The weight room has a real role in ultra-marathon performance. It's just not the role that most people assign

Strength Training That Transfers To Trails

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to it. And one more thing worth naming carefully: ultra-running fatigue isn't just peripheral, it's not just tired quads. The fatigue mechanisms in this sport are multifactorial, local muscle damage, glycogen depletion, and central fatigue, where the brain reduces voluntary motor drive as a protective response to accumulated stress. Muscular endurance isn't just about legs, it's about systems. And systems adapt best through consistent, specific exposure, not workarounds and shortcuts.

Systems Fatigue And Final Takeaways

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Here's where it lands. Muscular endurance, real durability, is not a puzzle to solve in the weight room or with a weighted vest. It's not a formula you crack with the right fatigue protocol. It's a very well-understood adaptation that develops reliably through strategic terrain-specific running and appropriately loaded strength work. Volume, specificity, consistency. That's the framework. Major in the basics, minor in the marginal gains. Weighted vest hikes and mountain leg circuits are not marginal gains, even. They're no gains at all. They add fatigue, increase injury risk, and pull training time away from the work that actually drives adaptation. The basics, running enough, running specifically, recovering well, and getting strong in the right ways are where the adaptation lives. Simple doesn't mean easy. It means you've done the work to understand what actually matters. And you had the discipline to stop chasing everything else.

What To Watch Next And Coaching

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If this reframed how you think about building muscular endurance, the durability video goes deeper on why this quality determines who holds up late in a race and who does not. So watch that next. And if you want coaching that applies these principles to your specific goals and event, visit trainride.com to connect with the CTS coach and subscribe for more coach driven ultra running education.