The Myth of Synchronized Breathing
In the game of Mindball, two players compete to push a ball whose motions are dictated by their brain waves, as measured by electrodes on their scalps. The harder you try, the weaker the force you exert on the ball. This (as the author and philosopher Edward Slingerland noted in his 2014 book Trying Not to Try) is a modern incarnation of the ancient Chinese paradox of wu wei, or effortless action. And it’s strangely reminiscent of the challenges we encounter in pursuit of running well.
That’s what popped to mind when I read a new paper in the European Journal of Applied Physiology, from Appalachian State University researcher Abigail Stickford and her colleagues, about synchronization between breathing and stride rate while running. People have been speculating about that link for more than a century: a 1912 paper showed that fish “breathe” in sync with the movement of their pectoral fins; and Roger Bannister himself published a paper on the physiology of breathing during exercise in 1954, a few months after his first four-minute mile, which noted as an aside that all the study’s subjects had unconsciously synced their breathing to a submultiple of their stride rate.
More recently, evidence has suggested that experienced runners are more likely to lock into a synchronized pattern—what scientists called entrainment or (equivalently) locomotor-respiratory coupling—than novices. The details of the pattern change depending on how fast you’re going; at a comfortable pace, for example, many runners settle into one complete inhale-exhale cycle for every four steps. Combine that with similar observations from across the animal kingdom, and you start to suspect that there might be something useful about it. Perhaps you should even seek to consciously match your breathing to some particular multiple of your stride rate, as many training manuals have suggested over the years. But here’s where the wu wei comes in: as soon as you start making conscious changes to automated functions like breathing, things get complicated.
There are plenty of examples of entrainment among animals. It’s clear from the research that birds, for example, breathe in time with the flapping of their wings. But that’s partly because they don’t have a diaphragm to control breathing independently, so they use their chest and abdominal muscles for both breathing and flapping. Similarly, horses and other four-legged animals breathe in sync because the body positions and impact forces of galloping or running make it more physically difficult to breathe out of sync, especially at faster speeds.
Of course, we’ve got diaphragms and run on two legs, so it’s not clear why humans should still have entrainment for running and cycling. (Swimming, in contrast, is obvious, and the body positions in rowing impose constraints similar to those faced by a galloping horse.) One possibility is that the habit is just an evolutionary leftover, serving no useful purpose. There’s some pretty cool research on “central pattern generators,” which are neural networks in the brain and spinal cord that automate rhythmic motions like walking and breathing outside of conscious control. Thanks to these pattern generators, cats with key parts of their brains removed can still be electrically stimulated to walk on a treadmill, and their breathing still locks in with stride rate. Even though we’re no longer quadrupeds, our pattern generators may still default to coordinating breathing and running rhythms.
But there may also be a more practical reason for synchronization, if it makes running more efficient or makes it feel easier. Lots of studies have indeed found evidence that running at a given pace takes less energy when breathing is synchronized. Unfortunately, lots of other studies have found the opposite, so it’s hard to draw firm conclusions. And even if it turns out to be true, it’s not clear how or why entrainment should save energy.
The question Stickford’s new study explores is whether entrainment is related to what’s going on in your mind. Compared to novices, experienced runners have more pronounced entrainment patterns; they’re also more likely to have an “associative” focus, meaning they pay more attention to internal cues like the movement of their bodies and how they’re feeling. Perhaps these two phenomena are linked: with practice, we learn to tune into the subtlest signals from our bodies that tell us when we’re running more efficiently, for example by synchronizing breathing with stride rate.
To find out, Stickford and her colleagues collected data from 25 highly trained male runners, measuring their stride rate, breathing rate, and running economy (how much energy they burn to sustain a given pace) at 6:42 and 6:00 mile pace. Immediately afterwards, they answered a questionnaire designed to assess their relative focus on internal (associative) and external (dissociative) thoughts during the run. Their degree of breathing-stride entrainment was quantified by calculating what percent of breaths (either inhales or exhales) started at the same point in the stride cycle during a 30-second period.
There are good reasons for hypothesizing that how you focus your thoughts might influence your breathing patterns. Back in 2018, I wrote about some research by Linda Schücker of the University of Münster in which volunteers were asked to think about their running form, their breathing, or the scenery around them while their running economy was measured. Thinking about their form made them 2.6 percent less efficient; thinking about their breathing made them 4.2 percent less efficient, presumably because they slowed from 34.0 breaths per minute to 28.7. Running form and breathing are important, but consciously trying to improve them seemingly backfired.
The experienced runners in this study didn’t need to be told to focus internally. As expected, they scored very highly on the assessment of internal focus, with 23 of the 25 subjects being classified as primarily associative. And the runners with the strongest bias toward associative thoughts tended to be the most efficient, though the pattern wasn’t particularly pronounced. But the answer to the study’s central question was a bit anticlimactic: the runners were no more or less likely to synchronize their breathing with their strides based on their choice of attentional focus, and there was no evidence that those with greater synchronization were more efficient.
Their entrainment scores at both speeds averaged around 60 percent, which is the fraction of breaths that started at roughly the same point in the stride cycle. That’s a relatively high degree of entrainment, as expected for experienced runners. But it’s worth emphasizing again that there was no single pattern that predominated. In an earlier publication based on the same study data, the researchers reported that the most commonly observed ratio was two complete stride cycles (i.e. four steps) for every complete breathing cycle (inhale/exhale), a ratio of 2:1. That was only observed 29 percent of the time, though. The next most popular ratios were 5:3 and 5:2, each observed 19 percent of the time. Try to imagine deliberately planning to take five breaths for every three strides. Assuming you’re not a professional conga player, superimposing those two rhythms would be extremely challenging. If nothing else, this should convince you that synchronization is not something expert runners consciously choose to do. It’s happening under the hood.
This may seem like a somewhat unsatisfactory conclusion. We still don’t know why runners synchronize their breathing, and we still don’t know whether it’s useful. And we’re stuck with observational studies like this one, instead of interventional studies where, for example, we would actually alter each runner’s attentional focus to see what changes. That’s a hard problem to solve, because of the wu wei issue. Whether we’re talking about breathing patterns, running cadence, or the content of your thoughts, the characteristics of good runners all seem to contain an element of effortless action. As in Mindball, the harder you try, the more elusive the goal becomes. That doesn’t mean you can’t improve, or that we have nothing to learn from emulating great runners. But it suggests to me that, rather than mimicking the end result, we’re better off emulating the things they did to become great runners—starting, most obviously, with running a lot.
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