If you could design the wearable tech of your dreams for endurance training and performance, what primary data would you choose to display on the face of the device? Would it be heart rate? Heart rate variability? Cadence and stride length? Real-time pace? Mechanical power? Blood lactate level? VO2?
The possible choices are pretty much endless, and each of those options has pros and cons that provide fodder for spirited debate. But there鈥檚 another, less heralded pick that doesn鈥檛 get much attention鈥攁nd according to , it may trump them all. Well-known cycling expert Louis Passfield of the University of Kent鈥檚 Endurance Research Group, along with Italian researchers Andrea Nicol貌 and Carlo Massaroni, make the case for 鈥渞espiratory frequency,鈥 or breathing rate, which is simply how fast you鈥檙e panting.
The gist of the argument is that breathing rate offers a surprisingly accurate听estimate of how hard you鈥檙e working鈥攕omething more typically quantified by asking an athlete to subjectively rate their effort on a scale of 1 to 10 (or 6 to 20, an effort scale that is more often used for historical reasons). Unlike VO2 (the amount of oxygen you鈥檙e using, which requires fairly cumbersome lab equipment to measure), breathing rate is easy to measure with a chest strap, although most current wearables don鈥檛 bother to record or display it. And unlike heart rate, your breathing rate responds rapidly to sudden changes in effort like you鈥檇 see during an interval workout.
Normally, respiratory physiologists focus on the total amount of air you鈥檙e breathing in and out, which depends on both your breathing rate and the depth of each breath. But those two factors have during exercise. The size of each breath increases primarily in response to the metabolic disturbances in your muscles and blood, like the rising levels of lactate produced by hard exercise. Your breathing rate, on the other hand, seems to depend more on the outgoing signals from your brain to your muscles. And that鈥檚 important, because perception of effort鈥攁ccording to but scientists鈥攊s also determined by the magnitude of these outgoing signals from the brain.
The scientific debate about the neuroscience of 鈥渆ffort鈥 is interesting, but from a practical perspective, what鈥檚 more relevant is that, empirically, effort and breathing rate . This remains true, the authors of the new paper argue, even when you change the conditions in various ways, such as raising body temperature, prefatiguing your muscles, and so on.
And breathing rate responds so rapidly that it鈥檚 a good marker even during sprint interval training. Here鈥檚 some data showing the relationship between breathing rate and perceived effort during 30 minutes of cycling continuously or during sprint intervals of 40, 30, or 20 seconds. The breathing frequency is presented as a percentage of maximal, all-out breathing frequency:
In addition to real-time monitoring of breathing rate, there鈥檚 a lot of sophisticated post-workout analysis you can do with it, as the paper (which is free to read online) goes on to demonstrate. You can analyze how much of a workout was spent in different breathing zones. You can get an overall picture of how hard a workout was by calculating your average breathing rate for the entire session. Since breathing rate responds so much more quickly than heart rate, this average will give you a more accurate view of your session鈥檚 difficulty, especially if you had lots of pace changes.
There are, however, some challenges to using breathing rate as a training indicator. While the research is conflicting, sports like running and rowing tend to have somewhat different breathing responses, because some athletes unconsciously match their breathing rate to their stride rate鈥攁 phenomenon known as entrainment. In swimming, you have to sync your breathing to your strokes to avoid drowning. Obviously that鈥檚 not the case in running, but the jarring impacts of each step do shake your breathing muscles and make it more likely that you鈥檒l synchronize your breathing to some multiple of your step rate, though there鈥檚 a lot of variability from person to person. That means breathing rate may be pulled up or down by your stride rate, rather than being perfectly proportional to your sense of effort. For those reasons, analysis of breathing rate may be best suited for cycling.
There鈥檚 also what I think of as the 鈥溾 problem, in reference to a 1963 Peanuts cartoon in which Linus suddenly becomes uncomfortably aware of the presence of a strange object in his mouth. Breathing rate is something you can choose to control, if you want. Unless you鈥檙e really maxed out, you can choose to slow your breathing down (and your body will automatically compensate by breathing more deeply) or speed it up (resulting in shallower breaths). My general opinion is that you鈥檙e better off letting your body dictate when and how you breathe, but once you start tracking your breathing rate and perhaps even choosing to accelerate or decelerate based on its value, I suspect it will be hard to avoid becoming uncomfortably aware of your ability to alter it.
So, to return to the question I posed at the top, if I were designing my dream wearable tech, it probably wouldn鈥檛 have breathing rate as the primary display screen. Still, Passfield and his colleagues make a strong case that the metric should be in the conversation. If it鈥檚 easy to build the measurement into future wearables, it seems like an interesting extra source of data to slice and dice after a workout.
The authors note one other point in passing: 鈥淎necdotally, athletes report monitoring the breathing sounds of their opponents as a gauge of their physical effort during endurance competitions.鈥 If, as the research seems to suggest, breathing rate really is a subtle gauge of effort, this means you can also monitor the breathing of your competitors, listen for changes, and be confident that you鈥檙e getting some real insight into how much longer they can hold on. Unless, of course, they鈥檝e read this article, too.
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