Easy/Moderate Fartlek Workouts For Improving Endurance

One of our favorite semi-structured workouts involves short, controlled intervals within an easy/moderate aerobic run. The easy/moderate fartlek can work for any athlete looking for a fun way to level up their aerobic efficiency. Here’s how it works.

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I don’t think that running coaches need to be high-performance runners themselves. I don’t even think they need to run at all, at least not for their whole lives. However, if a coach is not currently training, I do think they need to have pushed themselves in running at some point in their past, plus have a persistent and vivid memory. That’s because the brain has an ability to forget some basic principles:

5 miles is really freaking far, and a number on a training plan can miss that.

In the moment, hard workouts can be disconcerting and uncomfortable in ways that fade with time.

Some mornings, every fiber in your being wants to do anything but run.

Running–like anything that pushes our capabilities in any part of life–can be hard. Like really, really hard. And I think coaches need to strive to understand that in a visceral, undeniable way. You don’t need to taste the bile from a hard workout alongside athletes you coach, but you do need to remember the bitterness if you write 20 x 400 meters on a training plan.

I constantly try to ground my coaching in what it actually entails for the athlete. That always brings me back to the first principle above–5 miles is FAR. Heck, a mile is far. It’s easy to gloss over what numbers in a training log actually mean, but we are asking big things of our bodies and brains. I am currently looking out the window to a spot that is 5 miles away, and right now, couch-bound in my stained sweatpants, it looks as practical to run there as it does to jump to the moon.

So in addition to tracking physical responses to training, my co-coach Megan and I try to also track emotional responses to new sessions. And across our sample of athletes, easy/moderate fartleks have the most consistently joyous and excited training log updates. They have also preceded breakthroughs in all events from 5Ks to road marathons to 100 milers. Here’s how they work.

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What Is A Fartlek? 

Easy/moderate fartleks involve a certain distance or time with periodic controlled intervals throughout the run. The first element is the foundation of the workout–an easy/moderate run. All easy/moderate runs involve starting very easy. As the run progresses, athletes have permission to find ease of motion without urgency, while covering ground with smooth flow on flats/downhills and efficient purpose on uphills. Normal easy/moderate runs are faster if an athlete feels good, slower if they don’t. In other words, an athlete defaults to easy running unless the body (not just the brain) is yearning for more.

The second element is the fartlek. On a normal easy/moderate run, effort is dictated by the body and terrain, with more effort when things feel good and when the terrain dictates it, like on uphills. On an easy/moderate fartlek run, effort varies based on the interval placement and duration, with the body and terrain dictating the effort on the in-between sections. The focus of the run is the aerobic system, so the intervals are usually 10K to 1-hour effort or easier. 

My go-to coaching example using 10 miles as a baseline distance:

  • 10 miles easy/moderate (at 15 minutes and every 5 minutes after, do 1 minute moderately around 1-hour effort or a bit easier)

After a very easy 15 minutes to warm-up, the athlete picks up the pace for a smooth and strong minute. The next 4 minutes are easy running, then another quick minute (20 minutes into the run). That pattern continues to the end of the run (at 25 minutes, 30 minutes, etc.), with the time between intervals picking up in effort if an athlete feels good. By the end of the run, the overall mile splits may even approach marathon effort, depending on where the faster intervals fall. Other examples:

  • 10 miles easy/moderate (at 20 minutes and every 8 minutes after, do 2 minutes around half marathon to marathon effort)
  • 10 miles easy/moderate (at 15 minutes and every 6 minutes after, do 90 seconds around half marathon effort, with the last 30 seconds of each interval closer to 10k effort)

You can imagine infinite variations, particularly if you have recently taken mushrooms: 

  • 10 miles easy/cantaloupe (at 15 minutes and every pumpkin pie after, do a oneness at galactic effort).

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Why Fartleks Work

The aerobic system is wild. We try to summarize it with tests for VO2 max, lactate threshold, ventilatory thresholds, and others. But even when we think we can approximate the aerobic system in a specific athlete at a given time, there are way more input variables that inform the test results than we could ever hope to measure. Often, that leaves training theory with a conundrum: yes, we know a general approach works, and across a large population of athletes, we have theories why. However, we might never know exactly why specific sessions work for a specific athlete, or why different athletes respond differently.

Given that complexity, it’s best to work from general principles that adapt based on how an athlete responds. Most training should be easy, some runs steady and up to tempo, some runs harder above tempo. A very tricky part of being a coach and/or athlete is how to encourage easy running without totally forgetting that steady running serves a purpose too.

That’s where easy/moderate runs come in. Easy/moderate or steady runs can improve lipid metabolism, encouraging glycogen recovery at faster paces, which is particularly key for efficiency in events like marathons and 50Ks. They may improve the power and recruitment of Type I slow-twitch muscle fibers, which are essential for all endurance events. Possibly they spur production/efficiency of mitochondria and capillaries. And the increased output above easy running improves muscular strength and resilience.

I think steady running sometimes gets a bad reputation because athletes do it way too often as they first start out. If it’s used in moderation, it can add immensely valuable area under the aerobic curve.

The fartleks add some extra spice. Here’s a dated and unnecessary reference that I can’t get out of my head: the chef Emeril Lagasse putting spice into a dish and screaming “Bam!” That’s what the fartlek portions can do for the aerobic system. Do you feel like your running economy and aerobic development are stagnating? Here are some fartleks on top of a steady run! BAM! 

The fartleks push athletes into zone 2 in a 3-zone model, between steady and tempo, which studies find can be a sweet spot for longer-term aerobic development. They also improve speed and possibly even fatigue resistance as a run goes on, due to the demands on glycogen recovery and the neuromuscular system. 

And unlike a normal hard workout, there is plenty of time for recovery, so the session is not too difficult. The recoveries sometimes act as extended “floats”–improving how the body processes byproducts of fatigue. Think of it as an easy run with the heat turned up, rather than a hard run with the heat turned down.

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Psychological Rationale

This might be the biggest reason to try these easy/moderate fartleks–some athletes absolutely love them. I started the article talking about how far 5 miles is, how brutal track workouts can be, how motivation comes and goes. Easy/moderate fartleks can serve as major training sessions without the emotional lift, because they are slow burns that get gradually more difficult, and athletes are instructed not to push much unless they feel good. 

They break up the effort into manageable chunks, and psychology research generally shows that makes large tasks more manageable. That also makes them the perfect treadmill workouts (you can put each fartlek portion on an uphill to break up easy days). 

Plus, they are purposeful. Setting out for 5 or 10 miles can be completely, mind-numbingly overwhelming or boring. In winter, the doldrums are magnified ten-fold. That makes it especially important to insert play and purpose into some runs. Set out on a droll 10-miler, and you’re sometimes punching the clock. But then you start randomly accelerating like you’re playing a game of tag with a ghost? Add a good playlist, and it’s hard not to find a reminder of why you started running in the first place.

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Training Theory

Easy/moderate fartleks are a workout, so space them out with other intense sessions in the context of a week. Don’t do them early in a training build, since they could elevate injury risk, and they require base fitness to be efficient.

Make sure the fartlek portions do not exceed 10k effort–any harder than that risks a reduced aerobic contribution. That’s fine in moderation for fast workouts, but given that this session won’t be quite as fast as a traditional interval workout, it’s key not to overdo it. Threshold or easier is the ideal effort–around what you could sustain for 1 hour or longer. If it burns or you have to slow down a bunch after each fartlek is done, that’s too hard.

They are perfect for flat or rolling long runs (here’s an example from my long run last week) and relaxed mid-week workouts in a lower intensity week. Megan and I also incorporate them as a secondary mid-week session for advanced athletes in some instances (i.e. Tuesday fast workout, Thursday easy/moderate run or fartlek, weekend long run). 

You can adjust the terms of engagement depending on your goals, playing with the interval length and intensity. For example, you can do 3 minutes at marathon effort every 8-10 minutes for a workout that’s lower intensity, but still accumulates a lot of steady running for aerobic efficiency prior to marathons or ultras. You can do them on technical trails to practice the biomechanics of faster trail running. Or you can focus more on 10k effort for shorter races or during a speed build.

Easy/moderate fartleks are sneaky workouts that control effort. Feeling down about aerobic development, speed, or motivation? 

BAM! Fartlek time.


David Roche partners with runners of all abilities through his coaching service, Some Work, All Play. With Megan Roche, M.D., he hosts the Some Work, All Play podcast on running (and other things), and they wrote a book called The Happy Runner.

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