[00:00:00] Welcome friends to the Heart Rate Variability Podcast this week in Heart Rate Variability Edition, each week we explore the latest research and news from the world of hrv. Please consider the information in this podcast for informational purposes only and not as medical advice. Always consult your healthcare provider before applying any strategies we discuss. This week we have a fascinating lineup that spans from female physiology to cutting edge brain body science. We'll kick things off with a comprehensive look at how HRV recorded by wearables changes across the menstrual cycle and other life stages in women. Then we'll dive into a creative new use of breathing, how intentionally sighing on a fixed schedule can act as a mini stress test for your heart. [00:00:38] After that, we'll explore whether yoga practitioners have a secret advantage in how quickly their nervous systems calm down after exercise compared to folks doing traditional cardio or weight training. And finally, we'll wrap up with a groundbreaking study that shows how the heart and brain can sync up during a balancing task, especially when the challenge is just right. It's an eye opening set of insights, so let's get started. [00:00:55] Our first study today is from Sports Medicine and is titled Wearable Derived Heart Rate Variability across the Menstrual Cycle, Hormonal Contraceptive Use and Reproductive Life Stages in a Living Systematic Review. This was conducted by Eline de Jager, Brian Caulfield of Gina Angeliti, Brian McNamee and Sunit Holden. The researchers tackled an important question how do ovarian hormones and different female life stages affect heart rate variability as measured by wearables in real life? We know that HRV reflects autonomic nervous system function, but most HRV norms and guidance don't account for female specific factors such as menstrual cycles or menopause. So this team combed through the scientific literature 299 records initially and pulled together 16 quality studies on women's HRV measured with wearables. They looked at naturally menstruating women across their cycles, women using hormonal contraceptives, and women in other hormone related stages like pregnancy or post menopause. The findings give us a much clearer picture of how HRV fluctuates with female hormonal changes. In women with natural menstrual cycles, HRV was consistently higher at the beginning of the cycle and and lower toward the end. In practical terms, early in the menstrual cycle around menstruation and the follicular phase, HRV was slightly higher. And as women moved into the late luteal phase before the next period, HRV dropped the differences weren't enormous. On the order of a few percentage points, they reported time domain HRV differences of roughly 3% to 9%, but they were consistent across studies. Now, what about women on birth control or other exogenous hormones? The review found that women using hormonal contraceptives had generally lower HRV compared to naturally cycling women, and this effect was notably pronounced in what would be equivalent to the late cycle period for pill users, for example the days leading up to the withdrawal bleed. This suggests that the artificial steady hormone levels or hormone withdrawal associated with contraceptives can influence autonomic tone, often keeping HRV a bit suppressed. They also examine HRV across other life stages. One key insight HRV tends to decline after menopause, especially with advancing age. We know that aging often leads to lower hrv, but this review suggests that the loss of ovarian hormones during menopause may contribute to the downward shift in HRV and in addition to age itself. Interestingly, pregnancy data were a bit scarce in the included studies, but the authors aimed to cover all reproductive life stages, meaning they set the stage for including research on pregnancy and postpartum as it emerges. Hence calling it a living systematic review. They intend to update the review as new studies come out. It's worth noting that the review rated the overall quality of evidence as moderate. A limitation was that different studies defined menstrual phases in different ways. Some used hormone measurements, others just calendar days, others body temperature etc. Others, which made it tricky to conduct a formal meta analysis. But despite those differences, the overarching trends were clear. There are real, measurable HRV variations linked to female hormonal cycles and stages. The conclusion from Dieger and colleagues is that wearable derived HRV isn't one size fits all for women. It ebbs and flows with the menstrual cycle, is affected by birth control and changes after menopause. For women athletes, patients or anyone tracking hrv, this is a big deal. It means if you're a woman looking at your HRV trends, you should consider where you are in your cycle or whether you're on the pill or approaching menopause because those factors could be influencing your numbers. Rather than seeing those normal shifts as random or as progress regress, they could be an expected part of your physiological rhythm. The Takeaway Our tech and our coaches should start accounting for these female specific patterns when interpreting HRV data now from hormones to breathing and not just any breathing, but sighing Our second study is from Psychophysiology and it's titled Dissecting cardiovascular responses to a fixed interval volitional sighing protocol using a mixed modeling approach. This study was led by Neil Mazumdar, Kelly Sun, Samuel Jiang, Kelsey Pearsall, Anthony P. Pollack, R.A. marsha E. Bates, and Jennifer F. Buchman. I know that title is a mouthful, so let's break down what they actually did because it's pretty cool. We often think of sighing as a spontaneous reaction to relief or exhaustion, but here the researchers intentionally use sighs as a tool almost like exercise, to see how the cardiovascular system responds. They created something called the fixed interval volitional sighing protocol, FIVS for short. In plain terms. They had people take deep sighing breaths at regular controlled intervals kind of pacing their size and measured what happened to their hearts and blood vessels. They brought in 250 healthy college students, a nice large sample, 65% of them female, and hooked them up to monitors for heart rate, blood pressure, breathing, et cetera. First, each person did a baseline period of normal breathing, then two rounds of the sighing exercise. In one round they had to sigh once every 30 seconds, a long interval sighing task. And in the next round they upped the pace to one sigh every 15 seconds, a short interval sighing task. So essentially breathe normally, then do slow periodic sighs, then do faster periodic sighs, all while being measured. What happens when you start sighing regularly? It turns out a lot happens and it looks surprisingly like what happens during exercise or a stress response. The research team found that a volitional sigh actually triggers a reliable sympathetic surge in the cardiovascular system. During both the slow and the fast sighing protocols, participants heart rate and blood pressure increased from baseline. The effect was even stronger when the sighs were more frequent as every 15 seconds. It wasn't just heart rate and blood pressure either. They looked at heart rate variability measures too. Specifically, low frequency HRV increased significantly from baseline to sighing. Meanwhile, the high frequency HRV actually decreased during the more intense sighing, the fast 15 second interval size. These findings reflect what happens during an HRV biofeedback practice. They even measured something called pulse transit time variability pttv. Basically variations in how quickly the pulse pressure wave travels which which can relate to blood vessel tone and blood pressure variability in low and high frequencies. Those two shifted with sighing. For example, pulse transit time variability and low frequency variability increased with size, indicating changes in vascular dynamics, again more so with the rapid size. Another interesting angle, they looked at sex differences. It turned out that males had larger responses across many of these measures. The men showed larger increases in heart rate, low frequency HRV and blood pressure variability in response to sighing than the Women did, and where high frequency dropped during fast sighing, that drop was smaller in men than in women. So what does all of this mean? The authors suggest that guided sighing could be used as a simple stress test to reveal how someone's autonomic and cardiovascular system is functioning. We're used to the idea of a treadmill stress test in cardiology. You make the patient exercise and see how the heart performs. Here we have a kind of breath based stress test. Just by having someone sigh at fixed intervals, you put a mild load on their system. In healthy young people, it reliably produced these expected responses, HR, UP, etc. The fact that the responses were systematic and measurable suggests that this method could be used to spot if someone isn't reacting normally. For example, if a person had blunted responses or overly exaggerated responses, it might indicate an underlying autonomic issue before bigger problems appear. And since sighing is something nearly everyone can do safely, it's not physically taxing like exercise, and you can do it sitting in a chair. It could be a very accessible tool. It's also a reminder that not every breathing exercise is relaxing. We often talk about slow breathing to increase HRV and calm down. But a sigh in this protocol is more like a sharp, deep breath, often a double inhale and longer exhale. And doing that repeatedly can actually stimulate the body. In fact, these researchers frame it as moving from passive HRV tracking to active manipulation. By rhythmically loading the system with size, you might uncover differences between people. They demonstrated that the more sighs per minute, the more the greater the sympathetic activation, which is a dose response effect. And with the sex differences, it suggests there are individual fingerprints in how our bodies respond to such breathing loads. Volitional sighing, as odd as it sounds, might become a tool in our toolkit to test autonomic function in a quick and non invasive way. So the next time you heave a sigh, remember you're momentarily nudging your heart and blood vessels, almost like a brief workout. And these researchers are suggesting that controlled size could help detect early autonomic or cardiovascular dysfunction. Since it's physically accessible for most people, as they put it, it's a neat example of thinking outside the box, using the breath not just for relaxation techniques, but as a deliberate stressor to see how strong our heart's responses are. Before we move on to our next story, a quick word from our sponsor, Optimal hrv. Optimal HRV is an app that brings all this exciting HRV science to your fingertips. If you're looking to measure, track, and even improve your heart rate, variability. Optimal HRV has you covered. One of its most popular features is a guided resonance frequency breathing assessment, essentially a personalized breathing test that helps you find the ideal breathing rate to maximize your HRV and calming response. It's like having a personal coach in your pocket. The app walks you through different breathing paces to pinpoint what works best for your nervous system. From there you can train with real time biofeedback, watching your HRV in the moment as you practice slow breathing or even new techniques like slow paced muscle relaxation. Optimal HRV is built for both individuals and health professionals, so whether you're just trying to manage daily stress or you're a clinician tracking client's progress, it provides detailed metrics and easy data sharing. The bottom line Optimal HRV helps you put all this research into practice, guiding you to build resilience and track your wellness. Check it out and take the guesswork out of your HRV training. Alright, back to the research Our third study asks a question many fitness enthusiasts and clinicians have been curious about. Does the type of exercise training you do influence how quickly your autonomic nervous system recovers after a workout? In other words, do yogis bounce back faster than gym rats or runners? This study is titled Autonomic Recovery Following Submaximal Exercise in Yoga Practitioners versus Aerobic and Strength Trained Individuals. It was published in Annals of Physical and Rehabilitation Medicine and the research team includes Srinath N. Pahlavi, L.C. baskaran, Chandrasekaran, Lavya, Shetty, Lavina M. Manu and Shivaprakashka and Gachenaya. These authors point out that rapid autonomic recovery after physical stress like exercise is a sign of good cardiovascular health. If your heart rate and HRV return to baseline quickly after exercise, that generally means you're parasympathetic Calming system is strong. Yoga and traditional exercise like running or weightlifting are both known to affect the autonomic system, but surprisingly few studies have directly compared them head to head for recovery. So this team set up a straightforward experiment. They recruited 51 healthy young adults ages 18 to 35 and divided them into three groups based on their long term exercise habits. One group had long term yoga practitioners, people who practice yoga regularly. The second group was composed of aerobic trainers, think runners, cyclists or people focusing on cardio fitness thinking. And the third group was resistance trainers, folks doing weight training strength training. There were 17 individuals in each group, all similarly young and presumably healthy. All participants then underwent the same controlled exercise challenge, a five minute submaximal Harvard step test. This is a stepping exercise that raises the heart rate but is not an all out maximal effort. It's a moderate standardized test. The idea was to stress everyone's cardiovascular system equally for a short period and then see how they recover. They measured heart rate variability from ECGs at baseline brain before the exercise and throughout a 10 minute recovery period after the step test. If they were particularly interested in vagal reactivation, basically how quickly the parasympathetic activity rest and digest comes back after the exercise ends, here's what they found. The yoga group showed a markedly more efficient autonomic recovery than both the aerobic and the resistance training groups. By more efficient we mean their HRV metrics bounced back faster and to higher levels. When the researchers controlled for small baseline differences between the groups, there was a clear group effect on HRV high frequency AHF power during recovery. HF power is a measure of parasympathetic activity and it was significantly higher in the yoga practitioners during recovery. So much so that the difference had a p value of 0.001 which is quite convincing in practical terms. After the five minute exercise the yoga folks vagal tone as seen in HF HRV recovered strongly whereas in the aerobic and strength groups it was more blunted at the 10 minute mark. They also looked at other HRV measures. PNN 50, the percentage of successive heartbeat intervals that differ by more than 50 milliseconds, another indicator of high vagal tone, recovered better in the yoga group. Sdnn, overall heart rate variability and LF and total power of HRV were also significantly higher in yoga practitioners than in the other two groups post exercise. In all these metrics, yoga outperformed the aerobic and resistance training groups with statistically significant differences in post hoc tests. Interestingly, one common HRV metric, rmssd, a time domain measure of short term vagal hrv, did not show a significant difference between groups in the study's recovery phase. Nor were there significant differences between groups in the recovery of simple heart rate or blood pressure themselves. Those basic vital signs dropped after exercise at a similar rate for everyone. It was the HRV nuances that revealed the difference. The authors conclude that regular yoga practice is associated with more efficient parasympathetic reactivation after exercise. Essentially the yogis nervous systems hit the cool down state faster and more fully. Yoga is often described as an integrative practice combining physical postures, breathing techniques and often a mindfulness or meditative component. The thinking here is that this combination might uniquely challenge and train the autonomic nervous system. Yoga frequently involves slow controlled breathing and periods of relaxation or savasana after exertion, which might condition the body to switch into recovery mode more readily. In contrast, typical aerobic training or weightlifting, while great for fitness, might not emphasize cool down or breathwork to the same extent, possibly leading to a less pronounced immediate vagal rebound. For anyone who's an athlete or a trainer, these results are a heads up. Adding yoga to your routine might improve how quickly your body can relax after other workouts. For clinicians, it suggests that if you have patients who need to improve their autonomic recovery, say cardiac rehab patients or people with high stress, yoga could be a useful component because it seems to strengthen that vagal muscle, so to speak. And for the physiology enthusiasts, it raises cool questions. Are there specific elements of yoga like the breathing or maybe the isometric holds that are driving the autonomic benefits or or is it the whole mind body package? Regardless, this study provides some of the first direct evidence in a controlled comparison that the type of training you do matters for HRV recovery, and that yoga in particular may confer a unique advantage in autonomic resilience. Finally, let's journey into the intersection of brain and heart. Our fourth study is truly at the frontier of mind body research. It comes from the cerebral cortex and is titled the Interplay between Cardiac and Brain Activities within a Balancing Skill Challenge Context During Goal Directed Motor Control. The authors are Hengu Kun, Liyao, Qiao, Yang Zhao Hunting, Xiao, Li Li and He Chen. Now that title is quite dense, but it basically boils down to exploring how the heart and brain interact. When you're performing a balance task that is calibrated to be challenging for your skill level, imagine you're doing something that requires balance and coordination, for example balancing on a board or in a virtual reality game where you have to keep stable. If it's too easy, you're bored. If you if it's way too hard, you're overwhelmed. There's this just right zone, not too easy, not too hard, which in psychology is sometimes called a flow state or optimal challenge. This study sought to understand what's happening physiologically in that sweet spot, particularly how the brain's activity patterns relate to the heart's signals. The researchers set up a goal directed motor control task with a balancing element, and importantly, they made the difficulty level adjustable. They essentially created a system that allowed them to adjust the challenge's difficulty relative to a person's skill level to see how that affected heart brain dynamics. [00:15:23] Participants performed this task while the scientists recorded their brain activity, likely via EEG and their cardiac activity, looking at things like heart rate and heart rate variability, but also something more. Heartbeat evoked potentials or heps. Heps are a really fascinating measure. They're basically EEG signals, time locked to the heartbeat. In other words, it's the brain's electrical response to each heartbeat. Previous research has shown that heps can change across different states of interoception, for example, how aware you are of your heartbeat and and across different emotional states. Here they used heps as a way to gauge heart brain coupling, essentially how strongly or in what way the brain is listening to signals from the heart during the task. They also examined interactions in terms of brainwave patterns. For instance, phase amplitude coupling, which is a measure of how the phase of a slower brain rhythm might influence the amplitude of a faster brain rhythm. That can indicate how different brain circuits are interacting. Why mention this in a heart study? Because some coupling analyses might involve the heartbeat as one of the rhythms or see how brain rhythms sync with the cardiac cycle. So what did they find? A key result was that the coupling between heart and brain signals became more pronounced when the task difficulty was well matched to the participant's skill level when challenge and skill were in balance. In conditions where the task was too easy below the person's skill, or way too hard beyond their skill, the heart brain interactions were different or weaker. But in the just right challenge condition, the brain's response to heartbeats, the hep, showed distinct patterns and certain brain oscillations locked in with the cardiac cycle more strongly. In plain language, when people were in the zone, really focused and working at a comfortable but pushing the edge level, their brain and heart seemed to be in a kind of dialogue or synchrony that wasn't as evident otherwise. The researchers interpret this as evidence that during optimal motor performance like balancing, when it's challenging but achievable, Our central nervous system, brain and autonomic nervous system heart body are highly interconnected. It's as if the brain and heart tune into each other to meet the demands of the task. This makes sense if you think about it. Maintaining balance under challenge isn't purely a brain task or purely a heart task. It requires both cognitive focus, brain controlling muscles, processing sensory input, etc. And autonomic support, heart rate might increase to pump blood to muscles, etc. The interesting bit is that the communication between the two, the timing, the neural signature of the heartbeat and the brain actually got stronger in that balanced challenge context. They even phrase it in terms of skill proficiency and task demands within the same participants. It appears they may have run two experiments, one in which they varied people's skill or examined skill differences, and another in which they varied task difficulty across both. They did some common analyses and found that the sweet spot of balanced demand was where notable heart brain coupling signatures emerged. Specifically, they observed changes in the heartbeat evoked potentials and perhaps certain brainwave couplings that were strongest when the skill level and task difficulty were reasonably matched. Why is this important? Because it suggests a physiological basis for that feeling of being in the zone. When athletes talk about being in flow or rehabilitation specialists try to find the right challenge level for patients. There's always been this intuitive idea that there's an optimal zone for engagement. Now we see that zone reflected in heart brain physiology. It has implications for neuro ergonomics, designing work or training environments to best suit our brain body systems, and for rehabilitation. For example, if you're retraining balance in a patient with a brain injury, you might want to titrate the difficulty to just what they can handle because that might actually induce more beneficial brain body coupling and potentially better learning or adaptation. This study also exemplifies a broader idea. The heart is not just pumping blood. Its activity is closely intertwined with that of the brain, especially during active goal directed behavior. We often measure HRV to infer brain states like stress or relaxation. But here they directly measured brain electrical signals in relation to heartbeats. Finding a stronger signal when the challenge was optimal might even suggest that the brain is using cardiac feedback more efficiently in those moments, possibly monitoring bodily state to maintain focus and posture. It's almost poetic. When we are challenged at the right level, our heart and brain fall into a kind of synchronized rhythm, working together to keep us balanced and on target. [00:19:14] So whether it's athletes training on a balanced board or therapists helping someone regain motor control, paying attention to that skill challenge balance could literally synchronize mind and body in a beneficial way. It's a sophisticated study and it reminds us that performance isn't just in the muscles or or in the mind alone. It's an embodied whole system event. As research like this progresses, we may even see new biofeedback training that provides people with feedback on both brain and heart signals to optimize their learning or rehab exercises. Exciting stuff. Alright, that was a lot of cutting edge research. [00:19:47] Let's distill what we've learned into some practical insights and takeaways. It's great to hear about studies, but how can we apply this knowledge in real life or in our work? I'm going to break this down for a few groups of listeners, for individuals, everyone out there tracking their own health. If you're a woman tracking your hrv, consider tracking your menstrual cycle alongside it. Don't be discouraged if you see your HRV dip at certain times of the month. It might just be your luteal phase doing its thing. You can adjust your expectations, perhaps taking it easier or prioritizing recovery on those lower HRV days. And avoid misinterpreting normal hormonal effects as something wrong. Also, think about adding some yoga or breath focused exercises to your routine. The yoga studies suggest that regularly practicing yoga could help your body calm down faster after any workout or even after daily stressors, which over time can lead to better overall resilience. And speaking of breathing, while slow breathing exercises are great for relaxation, be mindful that techniques like repeated deep sighs can actually ramp you up. That's not a bad thing if used appropriately. For instance, a couple of sighs might wake you up or prepare your body for action, whereas gentle, prolonged exhales might be what you want for winding down. It's fascinating to know that even how we breathe can be a tool, one mode for energizing and testing ourselves, another for calming. Finally, recognize that being in the zone isn't just a mental state, it's physical too. If you're practicing a skill, say learning to surf or even doing balance exercises in the gym, try to find that sweet spot of challenge. You'll know you're there when you're fully engaged but not overwhelmed. In those moments, trust that your heart and brain are cooperating at a peak level to help you learn and perform. [00:21:14] That might encourage you to train smart, not just hard, but at the right level that pushes you just enough. For clinicians and coaches, these studies carry some important clinical pearls. First, when evaluating female patients HRV or designing HRV based interventions, factor in hormonal status. If a patient is premenopausal and not on birth control, her HRV might swing a bit month to month, which is normal. Educating patients about this can prevent confusion and help with more personalized baselines. If you're working with someone on oral contraceptives or who is postmenopausal, be aware their HRV might be consistently a notch lower than expected for a similarly aged male, not because they're unfit or overly stressed, but because of hormonal influences. On the intervention side, consider incorporating yoga or mindfulness based movement into rehab or training programs. The evidence here suggests yoga isn't just flexibility or balance training it actually might fortify the autonomic nervous system. For example, a cardiac rehab program or an athlete's training schedule might benefit from a weekly yoga session to boost vagal tone and recovery. Also, the psy test from the second study is intriguing for assessments. It's simple enough to try in a clinic. You could have a patient take deep sighs and see how their heart rate or blood pressure responds down the line. We may develop protocols to use it as a screening test for autonomic dysfunction, kind of like how we do orthostatic HR or blood pressure tests. Keep an eye on that research because it might give us a quick, office friendly tool to gauge stress reactivity. And for those in neurorehabilitation or sports coaching, the heart brain coupling findings underscore the value of progressive challenge. If you're helping someone relearn balance or a motor skill, don't keep them in the easy zone too long. Introduce challenge and complexity at a level they can handle because their system may actually adapt better when engaged fully. Conversely, if you push someone too hard to the point where they are constantly failing, you might not only discourage them but also miss the optimal physiological state for learning. It's a fine line, but science is giving us backup for finding that flow channel in therapy and training. For researchers, there's a lot to chew on from these studies and a lot of open questions. The systematic review of women's HRV is a living review indicating that this field is evolving. Researchers should take note when designing HRV studies. Consider stratifying or controlling for menstrual cycle phase, contraceptive use or menopausal status. It's clear now that ignoring those factors could wash out important effects or lead to misleading conclusions, especially in studies involving female participants. The Sign Protocol study opens up a novel avenue using controlled breathing interventions as standardized autonomic stress tests. Future research could extend this. For example, what do fixed interval sigh responses look like in populations with known autonomic dysfunction, such as people with diabetes or PTSD or long Covid? Could it serve as an early indicator for overtraining in athletes? It's a relatively easy protocol to implement, so I anticipate follow up studies applying it to different groups. The yoga versus Exercise study highlights a need to unpack the yoga effect. Is it the breathing, the meditation, the physical poses, or some combination that yields better vagal recovery? Researchers might design experiments to isolate those components, say comparing breathwork only versus stretching only versus both, and it'd be interesting to see whether similar benefits occur in other mind body practices such as tai chi or qigong for the heart brain coupling work. That's a sophisticated demonstration which might inspire deeper dives into heart brain interaction. We could ask, for instance, how heartbreak coupling during optimal challenge relates to learning outcomes. Do people who show stronger coupling learn the skill faster or perform better? [00:24:19] Also, does training over time enhance that coupling? [00:24:22] This might lead into the realms of neurofeedback or biofeedback, where perhaps one day individuals could train to consciously improve their heart brain synchrony. A message for the research community is also methodological. These studies demonstrate the power of interdisciplinary approaches that combine physiology, neuroscience and exercise science. There's real value in breaking out of silos. The coolest insights often come when we measure across systems. Here we saw respiration linking to heart and heart linking to brain. So future researchers keep integrating. Measure multiple systems together if you can, because the human organism doesn't operate in isolated compartments. [00:24:52] For businesses and innovators, there are several takeaways that could translate into better products or services for makers of wearables and health apps. Consider integrating menstrual cycle tracking with HRV data, an app that can say, your HRV is a bit low today and we see you're in your late luteal phase. This might be a normal pattern for you would provide much more value to female users. It could prevent unnecessary alarms and encourage personalized coaching, for example, suggesting more recovery activities during certain phases. There's also an opportunity in the corporate wellness or fitness industry to incorporate yoga and breath training as a standard offering not just as a stress reduction class, but to legitimately improve recovery and autonomic health of clients. Gyms might start marketing hybrid programs, for example Cardio plus yoga packages that explicitly state this isn't just for flexibility, it's for your heart's recovery. In the tech sphere, the PSI protocol hints at new biofeedback or self monitoring tools. Imagine a smartphone or smartwatch feature that guides you through a brief sighing test each morning and gives you a read on how reactive your system is, perhaps flagging if your sympathetic jump is unusually high or or low compared to your normal. That could be a daily check in on your stress or fatigue level. It's almost like a quick autonomic fitness test that could tell you, hey, maybe take it easy today. Or conversely, you're well recovered and responsive. Innovative companies might run with that. And how about the heart brain coupling as VR and gaming tech advanced developers could design training games that adapt difficulty in real time by sensing the user's physiological state, maybe using HRV or even EEG if available. The study suggests that when difficulty is just right, engagement and coupling are highest. So a smart system could keep someone in that zone by upping the challenge when they're too comfortable or dialing back when they're overwhelmed. Using HRV and other signals as a guide that could enhance learning, rehabilitation outcomes or just user experience in gaming. Finally, for those in the health tech device market, integrating multi sensor inputs like combining an ECG chest strap with an EEG headband might be an emerging niche for high performance training or clinical assessment tools. It's more complex, but this research shows the rich insights you can get when you measure brain and heart synchronously. There may be a future for devices that help consumers see how in sync their mind and body are during meditation, exercise or work. A new kind of wellness metric, perhaps, as we wrap up the big picture, is that heart rate variability research is touching so many domains now, from understanding basic physiology and cycles to creating new stress tests, to informing exercise and recovery, to delving into neurocardiology. It's an exciting time where each discovery connects the dots between lifestyle, technology and our innate biology. Thank you for joining me for this week in hrv. I hope these insights empower you, whether you're managing your own health, helping others, or building the next innovation in wellness. If you enjoyed the show, please subscribe and share it with anyone who geeks out on this stuff. We'll be back next week with more fascinating findings. Until then, stay healthy and keep your heart in sync.