Seriously. Easy running is your secret weapon for ultrarunning resilience and trail speed.

We’ve all been there. You’re grooving on a trail run, the right Smashmouth song hits, the trail tilts upward, and before you know it, you’re huffing and puffing while your heart rate skyrockets and legs start to burn.

The most common mistake new trail runners make? Pushing their easy runs (or, let’s be honest, every run) just a little too hard, convinced that faster equals fitter. It’s a paradox: running slower, well, easier, is what actually makes you faster, stronger, and more durable. Here’s how to slow down and nail the effort.

Why Running Easy Works (and What the Science Says)

If you need proof that slowing down works, the science is clear. Though, as always, context matters. Across endurance sports, decades of research show that the best athletes spend most of their time training easy, not hammering.

Exercise physiologist Stephen Seiler (2010) analyzed elite endurance athletes, runners, rowers, skiers, and found a consistent pattern: about 80 percent of their training time happened below the first ventilatory threshold (what we’d call Zone 1–2, or truly aerobic effort), and the remaining 20 percent was moderate to hard. That 80/20 split proved more effective than other methods researchers tested, threshold-heavy programs that kept athletes grinding at a “kinda hard” pace, or high-intensity plans that pushed too hard, too often.

A 2014 study by Stöggl and Sperlich in Frontiers in Physiology found similar results. Endurance athletes following a polarized approach (mostly easy running with a small dose of very hard work) improved VO₂max by 11.7 percent, time to exhaustion by 17.4 percent, and peak power output by about 5 percent compared to athletes using threshold or high-volume moderate training. In plain English: the group doing more slow miles and fewer grindy ones got faster.

More recent analyses (like this 2024 meta-analysis in Sports Medicine) back this up, showing that total low-intensity training volume is one of the strongest predictors of long-term endurance gains. The caveat: most of these studies involve trained athletes in controlled settings, not weekend warriors training for 100-milers. But the underlying principle still holds, and this takeaway from the pros can be extrapolated to beginner runners. Most of your adaptation happens when you go slow enough to stay fully aerobic.

For ultrarunners, this logic hits even harder. Long, slow efforts teach your body to burn fat efficiently, improve cardiac output, and build durability for those all-day efforts on the trail. The goal isn’t to suffer more; it’s to train your body to go farther with less effort. That’s the real magic of easy running; it’s not glamorous, but it works.

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Too Fast? What Does “Easy” Even Mean?

Easy means easy. Like, comically easy in most cases. Easy enough that you could call your mom and leave her a voicemail without gasping mid-sentence.

The simplest test is the talk test. You should feel fully conversational, able to speak in complete sentences without needing a breath break every few words. That usually translates to about a 4–6 out of 10 on the Rate of Perceived Exertion (RPE) scale, depending on the goal of the run. For example, recovery runs should live around 4–5/10, while easy endurance runs can creep up to 5–6/10. If you’re using a five-zone model, that’s Zone 1 or Zone 2.

There are numerous science-based benefits to running easy in training. Photo: Brian Metzler

Many coaches and physiologists prefer using RPE rather than heart rate, since heart rate can be thrown off by everything from dehydration to altitude to stress. If you do want to use heart rate, take the numbers from your watch with a healthy grain of salt. Most wearable devices estimate zones based on population averages that don’t account for individual differences, especially for women and smaller-bodied athletes, who tend to have naturally higher heart rates than what the devices label as “aerobic.”

If you want to get a more accurate picture, you can do a simple field test (like a 30-minute steady effort to find your lactate threshold) or go full science-nerd with a lab test. Think of heart-rate data like bumper lanes in bowling; it can keep you roughly in the right zone, but the real skill comes from learning to feel your effort intuitively.

What’s Happening When You Run Easy

When you run at an easy, truly aerobic pace, your body kicks off a cascade of endurance-building adaptations. You’re improving mitochondrial density (more “engines” in your cells to convert oxygen into usable energy), building capillary networks (more tiny blood vessels to deliver that oxygen to your working muscles), and enhancing your ability to burn fat as fuel, a key skill for ultrarunners.

These changes only happen when you stay aerobic, that is, when your body has enough oxygen to meet energy demands. Run too fast, and you cross into the anaerobic zone, where oxygen supply can’t keep up. That means you’re no longer training your aerobic system; you’re just making yourself tired and cutting into recovery.

So, yes, the run might feel a little too chill. You might even feel like you’re “not doing enough.” But that’s the point. You’re giving your body the oxygen it needs to build endurance from the inside out, the kind that lasts for hours on the trail, not just minutes on Strava.

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Beware the Gray Zone

Ever feel like your runs all land in that medium-hard zone, too fast to be easy, too slow to be a workout? That’s the gray zone (often Zone 3 or steady state, which does have a place in balanced training, but often as a smaller part of structured workouts and long runs), and while it feels productive (“no pain, no gain,” right?), it’s actually one of the least efficient ways to train.

When you spend too much time in this middle ground, you’re constantly dipping into your limited glycogen stores and racking up fatigue, without giving your aerobic system enough stimulus to keep adapting. You’re working hard enough to tire yourself out, but not hard enough to get faster, or easy enough to recover.

Over time, that mid-intensity grind adds up. Muscles stay fatigued, recovery hormones like cortisol creep upward, and your body never fully replenishes its energy reserves. The result? Workouts feel flat, progress plateaus, and those little niggles start turning into full-blown injuries.

Running just a little too hard on your easy days also blunts your ability to go really hard on your workout days. Give even 5 percent too much on recovery runs, and you’ll have 10–20 percent less to give when it counts.

Think of it like flash-cooking a steak on high heat: you end up with burnt edges and a raw middle. What we’re after is medium-rare training, slow enough to build flavor and tenderness, but with enough sear on the edges when it’s time to turn up the heat.

How to Tell If You’re Actually Running Easy

If you can’t carry on a full conversation, you’re already going too hard. You should be able to chat about dinner plans, your weekend, or your favorite episode of The Trailhead without gasping for air. If your running buddy asks for your take on The Life of a Showgirl and you can only manage a grunt, congrats, you’ve failed the talk test.

Easy running should feel smooth, sustainable, maybe even a little boring. On the RPE scale, that’s a 4–6 out of 10. Think “I could keep this up all day” energy, not “I can probably hold on to this effort by my fingertips”.

If you like data, aim for roughly 60–75 percent of your max heart rate or below your aerobic threshold, but don’t let your watch boss you around. Terrain, altitude, and hydration all play a role, so use heart rate as a guide, not gospel.

And remember: on trails, effort matters way more than pace. Hiking steep climbs counts as easy running. Walking isn’t a weakness; it’s a strategy.

The hardest part of running easy isn’t physical, it’s mental. You’ll probably feel slow. Other runners might pass you. That’s okay. The real pros aren’t the ones hammering every run; they’re the ones disciplined enough to chill when it counts. Easy running is a flex, it takes patience, confidence, and trust in the process. It’s not about looking fast today; it’s about staying strong enough to still feel good 10 miles from now.

You can let your ego set the pace now, or let injury and burnout do it for you later.

RELATED: Slowing Down to Immerse in the Landscape

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Run Easy! You’re Running Your Training Miles Too Fast