This is the second installment of Good Fit, a column about exercise.
At some point last fall, as I prepared to run a marathon, the algorithm sent me to Kim Clark. She has cute outfits, and a ponytail that reaches her waist. Her hair bounces behind her as she runs. She posts many videos of herself running on her Instagram, where she goes by the handle @trackclubbabe.
Clark is also fast, which she brags about: Her Boston Marathon qualifying time is right there in her bio, where she also advertises a series of training plans titled Fast Fall, Fast Marathon, and so on. And like many fitness and running influencers, Clark posts splits from her own training runs.
You might think these split times would be fast—the pacing goals you have to practice every day to run your Fast Marathon in your Fast Fall. You would be wrong. These times are decidedly not fast, 12 or 13 minutes per mile. (Clark does her runs pushing a stroller these days, which slows her down, but she’s clear that this is not far off from a typical run pace for her.) Here’s how Runner’s World described a 12-minute mile in 2018: “roughly the same rate at which Terry Fox ran across Canada on one good leg and one prosthetic leg in 1980.” That’s kind of mean! But to put it plainly: Clark, a lot of the time, runs very slowly.
She is also not alone. The more I looked, the more I started seeing other coaches advising that athletes slow down their paces—to cover up their watch face with tape if they have to, and especially, to quit looking at other people’s splits on social media. This directive isn’t about fostering a more inclusive running community; that’s just a side benefit. Many coaches like Clark argue that purposefully slowing down the bulk of your training is itself a route to achieving faster times on a race course, and ultimately beating the competition.
“For most of my life, I just went out the door and did whatever felt good, and finished huffing and puffing,” says Erin Williams, a runner based in Kansas City who posts under the Instagram handle @runstrongmama. She has since adjusted her running habits so that she finishes many workouts still feeling good, like she could keep going if she wanted to. “Fact,” she recently wrote in one caption: “Pace is the least important thing about your run!”
Williams worked with a coach for the first time in 2017, and then completed a certification so she could coach others herself. In addition to slow days, this meant adding focused speed workouts to her training regimen. “What I started learning is that when you’re doing really hard work 1–2 days a week, you can’t go out and do a pretty fast ‘easy’ run,” she explains.
This is the idea behind covering lots of miles at a slow pace: It allows you to truly push the pace on “hard” days, as well as build up more weekly mileage than you could if you were trying to run fast every time you lace up, which is crucial for distances like the marathon or even the 10k. This makes intuitive sense—rest more, have the will and enthusiasm to work very hard a small portion of the time. Proponents of slow running argue further that it has a suite of specific physiological benefits, like increasing the number of mitochondria, or cellular “powerhouses,” in your body. The study of how mitochondria are affected by various kinds of training is ongoing, as the authors of a 2021 paper on how trout responded to HIIT exercises explain. (This kind of work requires biopsying the muscle, which makes it tricky to do in humans—hence the fish). In any case, a mix of both fast and slow workouts increasingly seems to be the best way to make you the best runner you can be, particularly since many of us lace up, as Williams used to, with the misguided idea that running will typically involve some “huffing and puffing.”
As for what that mix should be, many running influencers who started popping up on my feed specifically reference a paradigm called “polarized training,” in which 80 percent of one’s workouts are done at a slow pace (one at which you can hold a conversation comfortably), and 20 percent at a rather hard pace.
This is, after all, what many of the greats do. The concept comes from Stephen Seiler, an exercise scientist at the University of Agder in Norway. In a 2010 review paper, Seiler looked at descriptive studies of the training habits of competitive endurance athletes ranging from runners to rowers to cross-country skiers. In technical terms, what he found was that “the predominance of low-intensity, long-duration training, in combination with fewer, highly intensive bouts may be complementary in terms of optimizing adaptive signaling and technical mastery at an acceptable level of stress,” explaining that what he observed specifically by poring over studies of elite athletes was that 80/20 split.
I contacted Seiler to talk to him more about this: Did this apply to non-competitive athletes? Recreational runners? Were the people on Instagram right? Why had my coaches in high school never taught me to slow down? It turned out his coaches hadn’t either.
“I was trained in that atmosphere of ‘no pain no gain,’ ” Seiler explains, looking Room Rater–ready in front of a wall of books and speaking to me over Zoom through what sounded like a professional microphone. He recalls puking on the bus after track practice. He lived in Arkansas and Texas before moving to Norway in 1995, where he observed local elite athletes and realized “a lot of their workouts were not painful,” spurring him to eventually publish an analysis of the training habits of internationally competitive Norwegian rowers in 2006, and then his broader survey across sports.
Seiler followed up his work on elite endurance athletes with a look at how more ordinary people may benefit from the 80/20 split. The results are mixed. For a 2014 paper (which I first saw referenced in the caption of a Reel, where else?) he, along with researchers at the European University of Madrid, randomly assigned 30 recreational runners to one of two training plans: one that included a bunch of time at a mid-level intensity, and one that was polarized. After 10 weeks, the participants ran a 10k.
Both groups saw improvements in their 10k paces, and the average time for runners in the polarized plan improved by an additional half minute. However, this result was not statistically significant (the study was pretty small). Seiler and his co-authors chalked this up to the fact that some runners did not adhere perfectly to the prescribed running schedules, arguing that if you look at the runners who truly did polarized training, they clearly performed better. (The problem is: Who sticks to their training schedule?)
Another study, published in 2020 by researchers in Italy, assigned 38 runners to two training groups, one that followed a polarized plan, and one that followed a “focused endurance training” plan, where the majority of the work was done at medium or high intensity. The researchers had them complete a 2-kilometer run at the end of the program (which is, granted, relatively short), along with some other tests. They found that the main difference between the two groups was how much time they spent training: The group that spent more time running fast saved a bunch of time. Again, this was pretty small study. “Research exploring a polarized approach in recreational athletes has been limited because it’s actually proven hard to get recreational athletes to do easy runs or rides,” explains an article on Fast Talk Labs, a hub of science-backed training information for coaches that Seiler collaborates with.
What becomes clear as I’m talking to Seiler, who consults for athletic teams alongside doing research, is that his pitch to the general public is not about adopting a highly specific breakdown-of-exercise regime, but rather that we should consider more leisurely workouts to be just as good and necessary as the hard ones. He is a scientist, but he’s become a little bit of an exercise guru, and the spirit of his advice holds true whether you are trying to beat your race time or you’re starting a new jogging routine simply for fun and stress relief. “We’ve gotta be friends with ourselves and find balance,” he explains. “I get so many emails that say ‘I’m actually enjoying the process again.’ ”
And what’s notable is that in all of the training plans in the above studies—even the one with a lot of high-intensity work—a significant amount of training, at least 40 percent, is done at an easy effort level, as measured by heart rate. Scientists can quibble about the exact amount of low-intensity versus higher-intensity training. The message for the rest of us should be simpler: Around half—and maybe way more—of our workouts should be relaxed, particularly if you are training for an event or activity that will require you to be on your feet (or in your boat or strapped to skis) for a while. (And then some much smaller slice is fast—maybe even a little painful.) When it comes to paces for super long runs of up to 20 miles in marathon training, “as far as I’m concerned, there is no such thing as ‘too slow,’ ” writes Hal Higdon, author of, among many things, Marathon: The Ultimate Training Guide.
This might sound a little obvious: You can’t just do sprinting workouts to prepare for a distance race; moving at a relaxed pace allows you to practice covering a lot of ground without burning out your body and your brain. But the idea of going slow isn’t just combating some kind of innate or American instinct to burst out the door quickly. It’s combating technology and social networks that have made it harder and harder for runners of all skill levels to not fixate on pace.
In 2003, as Seiler was observing the habits of Norwegian athletes, Garmin came out with the first wearable “watch” for athletes, the Forerunner 101, a rectangular device displaying distance, time, and the calculation that results from dividing one into the other: pace. One reviewer recalls that it resembled “a small mobile phone strapped to your wrist.” Runner’s World ran a review beneath the line “Too much information? Impossible,” explaining that it uses the same GPS technology that “is becoming more common in motorized navigation.” In 2009, shortly before Seiler published the wide-ranging review paper, a service called Strava launched that allowed athletes to upload their Garmin workouts to a social network where all could see how far and how fast they’d traveled. Strava co-founder Michael Horvath once explained that he had wanted to recreate the camaraderie he’d felt on his rowing team in college. “What motivates you are your teammates and the people around you which drives you to push your limits,” he said in a Q&A on the website CyclingTips.
This is a cute idea of community, but Strava can also become a source of pain: “I’ve interacted with a lot of athletes who are embarrassed to have a slow run uploaded to Strava where everyone can see it,” says Matthew Fitzgerald, the author of 80/20 Running: Run Stronger and Race Faster By Training Slower, which is based on the principles in Seiler’s research. To soothe the competitive feelings that can come up during a slow run, Fitzgerald has a slogan: “slow run Wednesday, fast run race day.” This is hard to do: I have found myself actively haunted by splits I’ve seen friends and family upload to Meta’s various social media properties; on my own jogs I wonder why, if I spend so much time running, I’m not as “skilled” as they are at the sport. Some of this is garden-variety jealousy, some of this is summed up by the maxim “social media is a highlight reel situation,” but a bunch of it is the fact that GPS technology has made it so that we always have a little numerical assessment of our runs at the ready.
Sure, the advent of GPS and social media are not the only factors that make slow running so hard—additional culprits include impressing your IRL running group, passing a guy in front of you at the park, a long-held misconception that exercise is supposed to always hurt—but they don’t help. My own Garmin has, for weeks, been sitting battery-dead atop a bunch of books. I’ve been instead measuring distance traveled with my iPhone’s health app—only a loosely accurate way to measure distance, which is the point—and focusing instead on returning from runs with energy remaining for more runs.
On her Instagram, Kim Clark often urges runners to stop caring what other people think of their paces, and to use a running watch primarily to measure heart rate to ensure they stay in the lowest zone when they’re supposed to be having an easy day. (Clark occasionally advertises a watch brand called Coros on her account). This strategy is worth pursuing even if you’re not after a fast race time, or any race time at all. Listening to your body, going easy, avoiding comparing yourself too much to others—this is what makes running a sustainable practice.
Slow running can be difficult. If you’re used to running at a certain pace, it can take patience to make the switch to running that feels relaxed, says Tammy Whyte, a coach based in Chicago who also advertises her expertise on Instagram. (She highlighted the importance of slow running recently by dancing to a remix of “Oops! … I Did It Again.”) Whyte explains that if you’re doing slow running right, some slow days will be even slower than others, if, for example, you’ve done a hard workout recently or been up all night with a sick child. She uses data from her athletes’ running watches to observe if they’re actually paying attention to their effort level rather than trying to hit a specific time, even if it’s a slow one. “I should see a variety of paces for your easy runs depending on how your body is feeling,” she explains.
Talented runners, says Seiler, “know what they’re good for—they’re not influenced by somebody running past them on their easy day.” When it comes to paces during training, “they put their ego at the door.”