This Is The Most Useful Pace

If you want to be a long distance runner, then you need to run and you need to run quite a lot, which means that most of your running should be at a comfortable or moderate effort because you can't sustain running the necessary mileage at high outputs and fast running does not compensate for low mileage. In a recent episode, number 136, I explained why overall mileage is the most important factor in physical development of a long distance runner. So, if we want to be strong, distance runners then the next topic is the right intensity for the majority of your running.

What does it mean to run easy? It’s simple to dismiss this question by saying that "easy is easy, if you would call your effort easy, then it’s right”. I used to be okay with that answer but not any more. In fact, I'm not even a fan of the word 'easy' anymore when it comes to most of the running you should do. Some runs should be easy - like when you really need net recovery from a very hard day or a race. But I now use the words comfortable and moderate to describe the intensity that most endurance runners should be doing most of the time.

Runners come from different backgrounds. Many factors shape each person’s ideas of what ‘easy’ feels like because the word fits onto one end of a scale that includes hard, discomfort, pain, and other subjective terms. Subjective terms are defined differently among people and even by the same person over time or in varied circumstances. 

When it comes to training to be a runner, each session should have a purpose. Perhaps it’s more skillful to begin by illuminating the purpose of so called easy running. Again, I'm now using the term easy to describe a running session with the purpose of maintaining base fitness while creating little strain, so the impact on the body and mind allow for net recovery on the day. I think better terms for what most of your training running should feel like is better described as comfortable or moderate.

Renato Canova calls the slowest runs in his system, regeneration runs, which are intended only for recovery. For elite athletes these are to be run slower than 80% of marathon pace. Well-trained but amateur athletes, might run these sessions slower than 70% of marathon pace, owing to the slower relative pace required for the same physiologic demand when comparing elites to trained amateurs. A very rough conversion, with extrapolation estimates for less fit runners, puts this at 65-75% of maximum heart rate. It’s also worth quoting Canova’s comments for runners training for the marathon where he writes, “As for runs at a speed that is lower than 80% of marathon speed, they will certainly not influence performance determining factors in athletes who have already achieved a good condition. They may however be used as warm-up exercises before a training session, for recovery at the end of a training session, to increase the number of kilometers covered during a week, and to favor recovery (“regeneration”) after particularly heavy training sessions.” (from International Athletic Foundation book, Marathon Training: A Scientific Approach, by Enrico Arcelli and Renato Canova, 1999).

Jack Daniels' Easy pace is 59-74% of V̇O2max (from Daniel’s Running Formula, 3rd ed). Elite marathon runners can run the marathon at ~86% of V̇O2max, which makes Jack Daniel’s Easy paces 68-86% of marathon pace for elite runners. The range includes faster paces than Canova but you'll notice it's the same, otherwise. Daniels also writes that this range is about 65-78% of maximum heart rate. Of course, your heart rate will vary even at the same pace if, for example, you’re running your Easy run after some time off versus the day after a very hard or long session.

The goal of the analysis I’m making is to shed light on what are considered the slowest useful paces by some of the best endurance running coaches so that we can find commonalities to use as a tool for calibration of your own training programs.

While Canova emphasizes that the utility of these runs are for recovery, and more specifically to clear lactate from the muscles and body, we know this is not physiologically true. Lactate is back to resting levels passively and within an hour, even for the hardest workouts. And, indeed recovery runs - or runs that stimulate recovery - are and oxymoronic fallacy. Daniels, who was actually an academic physiologist in addition to being a coach, provides the valid justification for Easy runs as broadly benefiting the cardiovascular system and skeletal muscle cells in ways that enhance the capacity for endurance. I’ve previously explained how these runs provide the largest endurance gain for the least strain, in episode 68.

We can follow a similar practice looking into the details of the most famous and successful distance running coaches like Arthur Lydiard, Bill Bowerman, Colm O'Connel, and many others. Lydiard’s system was a bit complicated but the paces corresponding to the easiest training runs were still quite fast and probably a faster - certainly not slower - than the Regeneration and Easy paces of Canova and Daniels. The most extreme, and the most notable exception, was Ernst Van Aaken who originated 'long slow distance' and advocated nearly all running (~90%) at <70% of maximum heart rate. Regardless of the specific name or label used for the intensity we're considering, the vast majority of coaches find the slowest useful training effort to still require some attention. Perhaps a practical rubric is to ask if you're running with good form (rather than shuffling) and could imagine running at that pace for a 50K. But, the consensus seems to be that running your regular training runs at easier efforts - paces similar to ultra-marathons longer than 50K - may not be very useful as a physical development stimulus. I state it this way, as a physical development stimulus, because there are reasons to go out for longer and slower training sessions; when you're developing something specific like an aspect of your gear, nutrition, hydration, or mind.

So, this is what the greatest coaches of all time say. What does the science show?

A 2010 study concluded “Training at <2 mM blood lactate appears to play an important role in improving the power output to blood lactate relationship. Excessive training near threshold intensity (3-6 mM blood lactate) may negatively impact lactate threshold development“. In fact, lactate is my second most preferred measurement for identifying this threshold. My first preferred measurement is gas exchange but that's even less practical. If you have your own lactate meter, then you can do a lot of self-evaluation to learn how it feels to be at the right intensities, and maybe how your heart rate correlates with lactate levels under different conditions such as prior food consumption, temperature, exercise duration, and terrain incline. Most running should be at an intensity where blood lactate levels do not rise more than about 0.5 mmol...maybe 1.0 mmol above resting values (which are typically about 1.0-1.5 mmol to begin with). For many athletes it will work pretty well to simply keep blood lactate levels below 2.0 mmol. There have been several analyses of the training intensity distribution of well-trained runners. I covered these in episode 112 on intensity zones. 72-95% of the miles run by high-performing distance runners is at an intensity where blood lactate levels would not rise appreciably above resting level.

In a 2020 study in Nature Communications titled Human running performance from real-world big data, the authors wrote "Our findings can be interpreted as faster runners train typically at lower relative intensities which is consistent with high-intensity performance improvement due to low-intensity training.” Statements like this are, however, easy to misapply because the words ‘lower relative intensities’ can be interpreted to mean very different things to different people - by itself it holds no useful information. The meaningful values behind the vague statement are 64 to 84% of vm  - a mathematical term that is slightly above critical power, and gives us a translation of the big-data study to have found, among many things, that faster runners spend most of their running volume below 80% of maximum heart rate. And, while this is a very rough conversion, and requires some averaging assumptions, it's accurate enough for comparison. You’ll see that it's in line with the relative intensities for Regeneration and Easy paces described by Canova and Daniels, respectively.

Though I'm not always a fan of using heart rate in training, it can be useful. So, I encourage you to try running over flat and smooth terrain at 70-80% of your maximum heart rate for up to 2 hours. Pay close attention to how that feels at 20- or 30-minute increments; stop and take notes about it. Do that once in a while and really dial in how that feels. I think that most people from track background will call that pretty easy or at least very comfortable while many ultra-marathon runners who came to the sport without a formal running background may think of it as harder than easy...maybe comfortable or even moderate.

My observations are that many mountain trail runners are running too slow on flatter terrain and too fast on inclines during training runs intended to develop endurance and stamina. For many trail runners, it can be difficult to transition to flatter terrain in the winter. The right paces are quite a bit faster than we’re used to running, and it’s possible to be very fit for mountain training and then find that a week of so-called easy efforts - if done at the right paces - is quite fatiguing over flatter terrain and smoother surfaces. What often happens is that mountain runners transition to flat terrain, find that easy runs are quite a bit faster than they were in the mountains and pat themselves on the back. But, in fact, they should be running those easy runs even faster on the flats - the pace-effort relation needs to be recalibrated. Without this recalibration, mountain runners who find themselves training on roads and treadmills in the winter can take a step backward in their development. The have to spend half the season getting their vertical legs back after having lost stamina due to overly polarized training - running a lot of very easy miles and some very fast intervals while neglecting the moderate paces that should be the bulk of training. Race performances only come back toward the end of the season and the cycle starts all over again without much, if any, gain from year to year.

The message you're hearing may be to avoid making your easy running too easy when it's a training day. Indeed, I find that many ultra-marathon runners run their easy days too easy when they are on flatter terrain but it's equally true that many other runners run them too hard. So, let's just put it very simply. Most of your running should be at a comfortable or moderate effort. When in doubt err toward easy rather than hard. Heart rate no more than 80% of maximum can be the upper limit for most people, most of the time. When in doubt err toward 70%. If you find that your heart rate increases considerably after you’re fully warmed up and while maintaining the same pace over a longer run - say, more than 6 bpm over an hour - even when you're staying cool and hydrated, then your running too fast for your current metabolic capacities. Either run a bit slower the next time or shorten your workouts at that pace. On flat terrain, you can think about paces that are a bit slower than a marathon race, perhaps approximating a 50K race; that'll be about right for many people. Take note that when you're on trails or hilly terrain, it may require walking to keep the right intensity.

How much of your running should be at this level? For ultra-marathon runners, you could do nearly all of it at this level. And, without exception, the clear majority of your running should be at this level. As a rough guide, let's say that >70% of your mileage should be at this easy-comfortable-moderate effort.