Why Easy Running Is the Foundation of Endurance Performance

Easy running is often misunderstood, underappreciated, or done too hard. In this episode, CTS Coach Cliff Pittman breaks down what easy running actually does physiologically and why it forms the foundation of endurance performance.

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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Transcript

Why Easy Days Decide The Week

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If your easy days feel even slightly hard, you're likely compromising your entire training week. Not just that run, the entire week. I'm Cliff Pittman, Pro Ultrarunning Coach and Director of Coaching at CTS. Coach athletes from first-time ultrarunners to professional and world-class competitors. Today, we're talking about easy running, what it actually does, why a lot of athletes get it wrong, and how fixing it might be the highest leverage change you can make in your training.

LT1 And The Aerobic Foundation

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So let's start with something that surprises people. Easy running below your first Wagtay threshold, or what we call LT1, is the foundation of every aerobically dominant event on the planet. Not just ultrarunning, not just trail running, every endurance event. A mile on the track at a maximal effort is approximately 80% aerobic. So by the time you get to 5k, it's closer to 95%. A marathon or ultramarathon is essentially 100%. The aerobic system is the engine regardless of the distance, and easy running is how you build it. I cover LT1 in detail in my training zones video. And if you haven't watched that one, it's worth doing alongside this one. The short version is that LT1 is the point where lactate begins to rise above resting baseline, but your body can still manage it comfortably. Now everything below that line is where your easy running lives. So what is easy running actually doing for

What Easy Running Builds

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you? Well, below LT1, your body drives specific adaptations that you cannot efficiently access at higher intensities. Mitochondrial biogenesis, the energy-producing engines inside your muscle cells multiply with consistent aerobic stimulus. Capillary density, your muscles develop a richer blood supply, improving oxygen delivery over long efforts. Fat oxidation efficiency. Your body gets better at using fat as fuel and sparing glycogen for when you actually need it. And aerobic enzyme activity, the biomechanical machinery that underlies all of your endurance capacity. Enigo San Milan, who has worked extensively with Tour de France cyclists and elite endurance athletes, has shown that athletes with the highest mitochondrial density and fat oxidation capacity are the ones who spend the most time at genuinely easy effort. Steven Seiler's research across elite athletes in multiple sports confirms the same pattern. This isn't a fringe idea. It's how the best endurance athletes in the world train, including the ones we work with at CTS. Now here's the principle that reframes everything else in this video. Every session in a well-designed training plan has a very specific physiological target. Hard sessions target VO2 max or lactate threshold, neuromuscular adaptation, and easy sessions target mitochondrial development, fat oxidation, capillary density, and aerobic enzyme activity. So when

The Zone 3 Trap

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you run easy days too hard, you've drifted into moderate effort or zone three, what we call steady state. Here's the problem with that. If we aren't targeting that effort specifically, the aerobic adaptations you get in zone three are not meaningfully better than what you get in zone two. But the recovery cost is significantly harder. You're paying more to get roughly the same return, and that cost gets subtracted directly from your ability to execute and absorb hard sessions. Now hard work only produces adaptation if the body can recover and absorb it. Easy days done right make your hard days count. Easy days done wrong make your hard days suffer.

Recovery Runs Vs Endurance Runs

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At CTS, we talk about two types of easy runs. And the distinction matters. A recovery run is what we call zone one, which is RPE 1 to 4, and the value here is circulatory. You're moving blood, flushing fatigue, and preparing the body for what comes next. It's not a primary adaptive stimulus. It's recovery. An endurance run is zone two, RPE 5 to 6, and still below LT1, but this is where the mitochondrial and fat oxidation adaptations are primarily driven. This is meaningful aerobic development. Now both sit below LT1 and both count towards your easy training volume, but they serve very different purposes. And knowing the difference helps you design sessions with intention. So why

Why Easy Days Get Too Hard

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do most athletes run too hard on easy days? Well, there's four reasons. The first is a lack of internal awareness, and honestly, this is the most common one and the most understandable. For a lot of athletes, easy has simply never been defined in a meaningful way. If you're newer to structure training or you haven't yet built the volume that teaches your body what different efforts feel like, moderate effort becomes your default. It feels normal because it's all you know. Now this isn't a criticism, it's just a calibration problem, and it's very fixable. The more you train, the more you run, and the more intentional you are about effort across different sessions, the more your internal awareness sharpens. Easy starts to feel distinct from moderate. The reference point develops with experience. But until it does, you need external tools to anchor it. Heart rate, RPE, the talk test, and we'll get to those. The second is junk miles misconception, that easy running has been dismissed as junk miles for decades, particularly in track and roadrunning culture. The belief is that if it is a hard, it isn't working. Now let me be direct about that. There are no junk miles if the effort is appropriate. The only junk is running easy miles too hard. The third is social and external pressure. Strava segments during what should be easy runs and training partners who are faster or more competitive. Pace on a screen shared publicly and compared to others. Your training log is not your audience. Your race performance or the level of joy you get out of training are the only metrics that really matter. And the fourth is self-validation. Slow feels wrong or unproductive, and slow feels like everyone else is working harder than us. But here's the question we're sitting with. Do you want to train fast or do you want to race fast? And you rarely get both.

Recovery Debt And Heart Rate Drift

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Now let's talk about the hidden cost that most athletes never connect to their easy day behavior. Every minute above LT1 on an easy day creates a recovery debt. The debt gets paid somewhere, usually on your next hard session, your next long run, or maybe your sleep quality. Most athletes who wonder why their hard session feels flat or underperforming never look back at what their easy days actually were. There's also a physiological phenomenon called cardiovascular drift that makes this worse than most people realize. Even at the same pace, heart rate rises over time as run extends, as core temperature increases and plasma volume shifts. An athlete who starts an easy run at the top of zone two will drift into zone three within 30 to 45 minutes without even changing the pace at all. That means truly easy effort requires starting slower than most athletes are comfortable with. Same

Polarized Training And More Volume

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sport, same goal. Athlete A trains 10 hours per week with 70% of that time below their LT1. Now that's seven hours per week in the zone where the primary aerobic adaptations live. Now athlete B trains 12 hours per week with 80% of that time below LT1. That's 9.6 hours per week below their LT1. So athlete B gets 37% more time where mitochondrial development and fat oxidation are maximized. And here's the key point. Athlete B runs more because their easy days are actually easy. Lower recovery cost per session means a higher ceiling on weekly volume. Both assets are doing aerobic work. The difference is how much of it sits below LT1, where the most important adaptations live. And notice what the polarized model does with the remaining 20%. Siler's research shows that the hard work, the 20% above LT1, sits at genuine high intensity. Here's the most vivid practical illustration of easy effort done right. If

Easy Effort As A Race Strategy

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you're pacing a 100-mile race, the athlete who goes out at RPE 7 in the first 20 miles is gonna slow down dramatically, most likely stop entirely. Now the athlete who goes out of RPE 5 to 6 doesn't just survive the back half. They pass people in the final 30 miles who went out entirely too hard. Easy, early effort isn't just a survival strategy. It's a competitive strategy. And the same principle applies to every training week. The athlete who protects their easy days doesn't just survive the week. They show up to hard sessions ready to actually do hard work. And the hard work drives the adaptation that makes them faster. So what

How To Gauge Easy Effort

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is easy actually look like? Well, Steven Siler's 80-20 concept, and this is important to understand correctly, is actually session-based, not time-based. So 80% of sessions below LT1. That's zone one recovery runs and zone two endurance runs combined. For most athletes training six to ten hours per week, that means roughly four out of every five runs should be genuinely easy. Not 80% of the time within each run, but the whole session. Here's what easy feels like on the run conversational pace. Full sentences without too much effort. This is essentially story time. RPE four to six on a scale of one to ten. You're working, but you could go significantly harder. All day pace. And honestly, if your easy pace feels embarrassingly slow, you're probably really close. Here's what easy looks like in your data. The heart rate will be below your LT1, and pace to heart rate decoupling under 5% on longer easy runs. If it's climbing above that, effort crept higher than it should have. So here's the bottom line. Easy running is not what's left over after hard training. It's the foundation that makes hard training possible. Every session has a purpose. Protect the purpose of your easy days. Zone 1 recovery, restore and repair. Zone 2 endurance runs, build the aerobic engine. Hard sessions drive the high-end adaptation. And the contrast between all three is what make the system work. Keep easy days easy, hard days hard, and run more over time. Just focus on yourself, not your Strava feed. Not your training partners or not the pace on your watch. Your easy pace is your easy pace right now. Just own it, protect it, and plug into the process and let it work. If we want to understand how intensity distribution maps to the three zone and five zone models, my training zones video covers all of that. Watch that one next. And if you want coaching that applies these principles to your specific goals and event, visit trainwrite.com to connect with the CTS coach and subscribe for more coach driven ultra running education.