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The aim of the technique is to decrease the rippling of the water, so that your heart beats are disrupting the water minimally — then the reflection becomes cleanest. This is a form of biofeedback, translating your heart rate, heart rate variability and blood pressure into an image.

I love biofeedback, meditation and I love taking baths. Some people combine these in various ways, but I’ve found a particular way that works very effectively, which I want to share with you here. Before reading on, note that I’m a rigorous evidence-driven kinda guy. I have a PhD in neuroscience and while I have a company I’m currently building (Maaind) and aim to promote at most opportunities, people know me for my rigor and empiricism — in other words, this isn’t me trying to sell you something. This isn’t woowoo magic either, but a meditation/biofeedback technique that has good scientific basis behind it. I won’t present concrete data here (yet), but have started to gather heart rate variability and other physiological measures that I’ll share in the near future. As I gather HRV and other data from myself while doing this technique (and comparing it to others), I’ll update this article.

I’ve recently started to explicitly apply this ‘new’ type of biofeedback — though both I and many others probably have used this and use this technique unknowningly. I call it the water-heart rate variability biofeedback technique, or water-HRV. Unlike many other kinds of biofeedback, you don’t need any devices — like biometric wearables tracking your HRV (heart rate variability). All you need is yourself and a filled bathtub to practice this type of biofeedback.

How the technique works

You lie mostly submerged in a filled bathtub, and focus on the visual reflection on the other side of the bathtub that you can see. Typically, if you’re lying with your head away from the bath faucet, you’ll be seeing some reflection of the faucet. That’s great. Focus on that. The aim of the exercise is to make the reflection image as still as possible. That’s it. And it’s ridiculously effective. As you do this for a few minutes, trying different ways of breathing, eventually you’ll hopefully find a way of breathing that keeps the image most still and clear. Do this anywhere between a few minutes to 20 minutes. I feel strong relaxation effects within a few minutes usually.

At this point, there are three things going on to varying degrees, all of which are good for decreasing your stress individually and in combination:

  1. Decreasing your breathing rate — Decreasing your breathing pace increases the parasympathtic tone or activity, which leads to a physiological response of an arousal and stress reduction. If your heart beats faster, there will be more waves and movement in the water, which makes the image less still. So the slower you breath, the calmer you are and this is reflected in a calmer image.
  2. Increasing your heart rate variability (HRV) — this is harder to consciously do, but happens if you breath in a paced and slightly slower way — e.g. as you might during many meditation practices. If your heart is more synced, with each beat of the heart very neatly following the previous one, this is a sign of increased physiological stress and arousal — and low HRV. What you want is higher HRV. The more regular your heart is beating (lower HRV), the more the waves/movement from the water are synced and the larger it will be — this means the image will be less still. So, with higher HRV, the heart beats happen in a less regular way, and the water’s wave movements cancel out, and there is a more still image to focus on.
  3. Decreasing your blood pressure — The hot temperature of the bath is likely to decrease your blood pressure and lead to a general decrease in the sympathetic response. This has been shown in a few studies, most notably one comparing the effects of young people and older people who took hot baths with water at 40 degrees Celsius. The effect here can differ depending on your age and older people seem to respond less favorably to hot baths compared to young people. In other words — the bodies of older people generally cannot respond as effectively to the stress of being submerged in hot water, so to some extent the ultimate health benefits and the physiological reduction in stress effect may be less for older people than younger people. I don’t have concrete data for this claim but I suspect the difference in the response to hot water baths may start at around the ages of 40–45.

Both the slower paced heart rate and increased HRV are well-established and understood as markers of relaxation and healthy signals. I haven’t done rigorous testing of the technique yet but have now started to measure my HRV during the exercise, when I take baths. The effects are strong but I don’t want to over-claim anything just yet. I’ll collect more data using a wearable and then look at longer-term patterns of the effect through my company’s AI assistant app, Aurora. I’ll aim to report back on findings. Single participant studies are not the most convincing, sometimes for good reason, but I’m aiming to more robustly quantify the relative efficacy of this sort of biofeedback as opposed to either meditation with eyes closed, paced breathing eyes open, or biofeedback with numeric feedback.

Another interesting point about this exercise is that it translates sensations and feedback during meditation and other practices which are usually tactile or interoceptive (say — how your chest, nose or heart feel during breathing) to visual, by having the heart beats translate to image movement in the bathtub.

The science suggests that warm baths with this technique should be combining multiple beneficial effects in one exercise. If you try it or already do something like this, I’d be keen to hear how effective you felt the exercise is for you. Note that it might be slightly contraindicated for older people — so please practice with caution.

I’ve written a more technical basis and background on this technique and relevant previous research —in other words, the neuroscientific basis of the technique. In the mean time, I’ve summarized some of my research on the topic, below.

  • From my short review of the literature in prepartion to write this article, almost all of the studies of breathing and stress reduction (through HRV or otherwise) I found seemed to be with males instead of females
  • Many, if not most, seem to be from Japan or Asia
  • Most studies done are with small samples (10 to 30 people) but large effects
  • Most studies looking at stress and breathing in particular are with young people (early 20s) or elderly (~70 years old and up). Where are the middle aged?
  • Very few cited papers from later years, mostly from 1–2 decades back.

I’m building the future of mental wellbeing and AI assistive technology for human augmentation. My vision is to help humans augment our emotional, moral, cognitive capacities — as well as our consciousness, through trustable and safe applications of artificial intelligence, brain computer interfaces and data.

If you’re interested in biofeedback, neurofeedback, mental wellbeing or improving your mental performance, please follow my company Maaind on Facebook, Twitter, LinkedIn.

If you want to help shape the future of AI for human wellbeing join the alpha program for Maaind Aurora.

Thanks to dzera kaytati, Imre Bard, Elias Rut, Donald Clark, Aleksandrs Baskakovs, Kostadin Dinov, Vesselka dinova and, last but not least, Alex Dunsdon — useful feedback on the drafts.

A neurotech startup improving mental wellbeing & cognitive performance using AI, voice & biometrics 💭

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Martin Dinov

Martin Dinov

PhD neuroscience. AI engineer. All around hacker. Space enthusiast. Co-founder of @Maaind_ai and HackTheSenses. Senior data scientist+AI engineer @ Capgemini.

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