The question: After a hard interval workout, does box breathing help you recover faster — or can a “calming” technique actually backfire?
The short answer: A 2025 randomized crossover trial had 40 active university students recover from identical HIIT sessions using box breathing, slow breathing at 6 breaths per minute, or natural breathing. Box breathing kept heart rate elevated longer and left people reporting higher perceived exertion, likely because its built-in breath-holds trap carbon dioxide right when the body is trying to clear it fastest. This is one study in young, healthy, active students, so it doesn’t settle how box breathing performs in other populations or exercise intensities — but it does show a popular technique isn’t automatically the best recovery choice.
What the study did
In a 2025 randomized crossover trial published in PLOS ONE, 40 physically active university students completed the same high-intensity interval training (HIIT) protocol on a bike on three occasions. After each session they recovered with a different method: box breathing (4-second inhale, 4-second hold, 4-second exhale, 4-second hold), slow breathing at six breaths per minute, or natural, unguided breathing. The researchers compared heart rate recovery and perceived exertion across the three conditions.
What it found
Box breathing kept heart rate higher after HIIT than both slow breathing and natural breathing, and participants rated their exertion much higher with it. Slow breathing at six breaths per minute was better tolerated and less stressful than box breathing, and showed a trend toward faster recovery than natural breathing, though not a dramatic advantage. Jesse's explanation is CO2: hard exercise produces a lot of it, and the breath holds in box breathing slow its clearance. The brainstem reads that rising CO2 as a signal to drive a stronger sympathetic response, so the system struggles to settle.
What it doesn’t show
This is one study in young, active students, so it does not settle how box breathing performs in other groups or after other exercise intensities. It tested breathing right after very intense effort, when CO2 is high, not box breathing in calmer settings. Jesse's point is that context matters, not that box breathing or slow breathing fail in general.
Key points
- Right after HIIT, box breathing kept heart rate higher and made the workout feel harder than slow or natural breathing.
- Slow breathing at six breaths per minute was better tolerated, with a trend toward faster recovery than natural breathing.
- The context of a technique matters: breath holds work against the body when it is trying to clear CO2 quickly.
Common questions
Should I stop using box breathing?
The study does not suggest that. It tested box breathing immediately after very intense exercise. Jesse's takeaway is that techniques are not buttons you press: the state your body is in decides what fits.
What does Jesse recommend after a hard workout?
Jesse teaches athletes to start from a faster breathing cadence and work gradually down to a slower one, rather than jumping straight into a strict slow pattern while CO2 is still high. This is his coaching approach, not a protocol tested in the study.
Why would a calming technique raise heart rate?
After intense effort, the body is working to clear CO2. Box breathing's two holds slow that clearance, and the brainstem responds to the rising CO2 by pushing a stronger sympathetic response instead of letting the system settle.
Study cited: Kasap, M. & Aydin, G.R. (2025). Box breathing or six breaths per minute: Which strategy improves athletes’ post-HIIT cardiovascular recovery? PLOS ONE. https://pmc.ncbi.nlm.nih.gov/articles/PMC12622787/
Practice this: 5/5 Coherence Breathing | 10-Min Guided HRV & Heart Resonance
Read the full transcript
Auto-generated from the video captions, so expect small errors.
If you're an athlete or even if you are a weekend warrior, it's likely that you've been implementing breathing techniques into your routines to get the most out of your workout and to enhance your recovery. And this is for good reason. We have all kinds of data. Now, the episode that we're doing today is sort of a surprise that happened in research and occasionally you get these surprises where you're like, "Okay, which one's better?" And then something goes sort of off the rails and that is what is going to happen in today's study. Welcome, by the way. Welcome to the Breathwork channel. My name is Jesse.
This is the Breath Lab. This is where we cover studies and research in the world of breathwork so you can have a more effective practice. And this one especially for those of you who are using breathing techniques to enhance your recovery, you're going to find this to be very valuable because not only did we find one of these techniques that was better than the other, one of the techniques made things worse. Today's study comes to us from plus one. It was published in 2025 and they asked the question, "We have three different breathing mitigations. Let's just test to see which one is going to put
these athletes into a recovery state fastest." So they took 40 trained adult males and they put them through hit workouts, really intense hit workouts and then they said, "Okay, let's try this technique. Let's try that technique. Let's try this technique." Okay, so they did they did three different workouts that were really really intense and they put them into these techniques. The techniques, one was box breathing which is probably the most underrated breathing technique that's out there. It's been studied. It does all sorts of amazing things, but no one does it except for maybe, I don't know, the Navy SEALs, right? They're going out, they're, you
know, kicking ass doing box breathing and here you are never doing it. What's, you know, what's the deal? Um, then of course we have another one which is six breaths per minute. Six breaths per minute is is been studied. I don't know how many studies we've already just even done on this show that shows the benefits of breathing at a pace of six breaths per minute. Now, in this study they just said six breaths per minute. They didn't specifically state was it five seconds in, five seconds out, four seconds in, six seconds out, but six breaths per minute this is our coherence breathing cadence, right?
So two very big heavy hitters that they're putting right after a workout. Now the last one was just brief normal. Just however you feel like breathing, just breathe however you would like. Now, this is where sometimes in research we are surprised and before I get into this the results, what I want you to do is is pause the video. Which one of these do you think actually made things worse? Was it box breathing? Was it six breaths per minute? Or was it just breathe normally? One of them made it worse. That is to say, it put them in a higher stress state. Pause the video.
Let me know below. Okay. Um, I guess I'm waiting. I don't know why I would wait because you're pausing the video. But anyway, okay, I'm going to assume you paused the video. Maybe you liked and subscribed. But let's get through it. So they have these individuals. They said, "Okay, let's do box breathing." Box breathing made it worse. Box breathing actually increased their heart rate, their sympathetic dominance, and their perceived amount of stress and the impact of the of the workout. So it actually made it worse. It reduced their ability to get into a calm relaxed state. I'm going to talk a little bit about why
that is here in just a little bit, but isn't that surprising? Now, they did six breaths per minute and it did help them to calm down. It did start to bring their nervous system down into a recovery state and it was it was nice and fast. However, it was not faster than just breathing normally. Now, what could happen? What is happening here? And you may already have a guess. If you're a fan of the Breathwork channel, if you're a fan of breathwork, you may already have an idea of what the mechanism here that they might have been forgetting about in this study. And I don't
know, should we do another pause the video? Uh, maybe not. Maybe not. If you want to pause the video, go ahead. What do you think is at play here? Why do you think these mitigations either cause it to get worse or were no better than simply breathing at the their own will? Well, what the researchers forgot was the impact of CO2 production post workout. So they did these high impact workouts, high intensity, right? And so you are in this sympathetic state. You are producing more energy and what are the byproducts of being in that that very active state is you also produce more CO2. Higher
CO2 levels in the blood make it more difficult and more stressful to breathe at slower rates. Okay, so when you have something like box breathing which involves two breath holds, you're going to naturally be building up that that CO2 higher. That causes sympathetic levels to rise in your autonomic nervous system. Now, we don't see breath holds in six breaths per minute, but at the same time we don't see breath holds in just breathing naturally. After your workout, what we really see in this study is not is this technique better than that technique. What we should learn from this study is that while techniques are good,
they're not just buttons that you press in on your nervous system and then you make a sudden change. The context in which you do your techniques matters just as much if not more than the technique itself. You have to listen to what is happening in your physiology so that you know how to send a message back into your nervous system. Simply doing a breathing technique doesn't necessarily calm you down. So when it comes to post workout breathing, the thing that we can really take from this is that these breathing techniques are probably not the best thing to do after you work out. Going into a
strict slow breathing method, right? So six breaths per minute. If you think about box breathing, you're even going slower than that. Those are not appropriate wherever you have that high level of CO2. In those cases, we're looking at something that might be a little faster which might not be good in other circumstances, but in the circumstance where you are actively combating high levels of CO2 in your blood and you're recovering from a very intense workout, working your way down from a faster breathing cadence all the way down to a slower cadence is the way to do it. And this is how whenever I train my
athletes, whenever I train my students to train athletes, that's what we teach people how to do. So I love this study because they were really trying to find out which one is better, but they forgot such an important fact that is associated with physiological stress that it's almost comical to see this study out there in the wild. So that was 2025. The link is below if you want to take a look yourself. So was this as surprising for you as it might have been for the researchers? Let me know in the comments below. Thanks so much for watching the Breath Lab today. I'll see you
next week.