Guest article by Didier BOFF 

We often think of stress as something purely mental, almost abstract.
Yet stress is first and foremost a biological response. It is one of the body’s natural ways of adapting to internal and external demands. This is why stress is not always the enemy. What matters most is not whether stress appears, but whether the body can regulate its response and return to balance afterward. That capacity to activate, adapt, and recover is
at the heart of resilience.

For yoga practitioners and teachers, this is where breathing becomes especially meaningful. Breath is one of the rare functions that is both automatic and voluntary. We do not consciously decide our digestion, blood pressure, or heartbeat moment by moment, but we can influence them indirectly through the way we breathe. This makes breathing a powerful bridge between body and mind, and a practical tool for managing stress and building resilience.

Stress is not always harmful

The word stress tends to carry only negative associations, yet not all stress is bad. In fact, a certain amount of stress is necessary for growth and adaptation.

Exercise is a simple example. Muscles become stronger when they are challenged and then allowed to recover. Endurance athletes train under demanding conditions because the body adapts to those challenges over time. In the same way, the nervous system can also become more resilient when it encounters manageable forms of stimulation followed by recovery.

Stress becomes problematic when it is too intense, too frequent, too prolonged, or when recovery is insufficient. So the real question is not how to eliminate all stress, but how to support the body’s ability to regulate itself. This is where stress management breathing techniques and other simple slow, deep breathing practices become so relevant.

We are always regulating

Even when we feel still, the body is never static. Countless physiological processes are constantly being adjusted to maintain stability: temperature, blood pressure, oxygen saturation, digestion, hormonal activity, and more. This relative internal stability is known as homeostasis.

Yet homeostasis is not maintained by rigidity. It is maintained through continuous change and adjustment. Heart rate shifts when we move. Breathing changes depending on oxygen needs and emotional state. Hormones rise or fall depending on whether we are alert, resting, digesting, or recovering. This adaptive process is often described as allostasis.

Seen in that light, stress is part of life. The body is always in dialogue with its environment. The key is whether this dialogue remains flexible.

What is heart rate variability (HRV)?

One of the clearest markers of that flexibility is heart rate variability, or HRV. If you have ever wondered about the heart rate variability meaning, here is the simplest explanation: HRV is the variation in time between one heartbeat and the next. A healthy heart does not beat with perfect mechanical regularity. Even at rest, the interval between beats changes constantly. A heart rate of 65 beats per minute is only an average. Underneath that average, the heart is subtly accelerating and slowing down all the time.

So what is HRV, really measuring? Not simply how fast the heart beats, but how flexibly the autonomic nervous system can regulate the heart in response to internal and external demands.

In general, higher HRV is associated with better adaptability, stronger recovery capacity, and greater physiological resilience. Lower HRV may be seen with fatigue, chronic overload, poor sleep, illness, or prolonged stress. It is not a diagnosis by itself, but it is a useful indicator of the body’s regulatory state.

What is a good HRV? 

A common question is: what is a good HRV? There is no single ideal number for everyone.
Heart rate variability normal values vary according to age, sex, training status, and overall health. In other words, heart rate variability values are personal. Your own trend over time matters more than comparing yourself to another person.

That is why HRV is best understood as a baseline marker. If your HRV drops after a difficult week, emotional strain, illness, or hard training, then recovers with rest, that often
reflects healthy adaptation. If it remains low for a prolonged period, it may signal that more recovery is needed.

How do you measure HRV? 

If you are curious about heart rate variability, how to measure it reliably, consistency matters.

Many smart devices estimate HRV through optical sensors, but chest straps or ECG-based devices are generally more precise.

That is why ECG heart rate variability tracking is often preferred when accuracy matters. The usual recommendation is to take a short reading each morning under the same conditions, ideally lying down and breathing normally, then watch trends over time rather
than obsessing over one number.

The autonomic nervous system: sympathetic vs parasympathetic

To understand why HRV changes, we need to look at the autonomic nervous system. The autonomic nervous system, sympathetic vs parasympathetic balance is one of the body’s core regulatory dynamics. The sympathetic branch is associated with mobilization, alertness, and action. The parasympathetic branch is more associated with slowing down, restoration, digestion, and recovery.

Neither branch is “good” or “bad.” Both are necessary. The goal is not to switch off activation completely, but to move fluidly between activation and calm depending on what life requires.

What happens when this balance is disrupted?

When this regulation becomes less flexible, the body may struggle to move smoothly between activation and recovery. This is one reason we become interested in autonomic nervous system problems: not because every stressful period indicates a disorder, but because dysregulation can show up through fatigue, poor recovery, disturbed sleep, shallow breathing, digestive discomfort, or a lingering sense of being “stuck” in stress.

This is where the vagus nerve becomes central.

The vagus nerve and the parasympathetic system

The vagus nerve and parasympathetic system are closely linked. The vagus nerve is one of the major pathways involved in parasympathetic regulation. It connects the brain with the heart, lungs, digestive organs, and other systems.

When people speak about the parasympathetic and vagus nerve, they are usually referring to this role in calming, restoring, and regulating the body after activation. One especially useful concept here is the vagal brake.

The vagal brake is not a separate anatomical structure, but a helpful way to describe how the vagus nerve slows the heart. On inhalation, that brake partially releases and heart rate speeds up slightly. On exhalation, it re-engages and heart rate slows slightly. This natural rhythm is one of the reasons HRV exists.

So when we speak about breathing and the vagus nerve, or about breathing for vagus nerve support, what we really mean is that breathing changes the way the nervous system regulates the heart and the rest of the body.

How does deep breathing reduce stress?

This leads to one of the most practical questions: how does deep breathing reduce stress?

Breathing is special because it can be both voluntary and involuntary. By slowing and regularizing the breath, we indirectly influence heart rhythm, blood pressure regulation, and nervous system activity. That does not erase the causes of stress, but it can reduce excessive activation and make recovery easier.

This is why deep breathing can be such an effective part of stress management. A slower, steadier breath gives the body a rhythm it can organize around. It can help reduce inner agitation, improve emotional regulation, and support a return to calm after stress.

Can stress cause breathing problems?

Yes, stress can influence the way we breathe.

Many people notice shallow breathing, chest tension, air hunger, or other stress-related breathing issues when anxious or overwhelmed. In that sense, stress and breathing are closely connected: stress can disturb the breath, and a disturbed breath can reinforce the feeling of stress.

This is also why learning how to control stress and anxiety often begins with the breath. Slowing the exhale, softening the ribcage, and restoring a smoother rhythm can help interrupt that loop.

Cardiac coherence: breathing in resonance

One of the clearest practical applications of this physiology is cardiac coherence.

Cardiac coherence is a breathing practice in which the rhythm of the breath, the rhythm of the heart, and blood pressure oscillations become more synchronized. For many people, this happens around five to six breaths per minute, often with an inhale of about five seconds and an exhale of about five seconds. At that pace, the natural relationship between breath and heart becomes more visible and more coherent.

On HRV recordings, this often appears as smooth, wave-like oscillations: the heart rate rises with inhalation and falls with exhalation. This is not an artificial trick. It is an amplification of a natural physiological mechanism.
That is why slow breathing works so well in practice, it does not force the nervous system into relaxation. It creates conditions that support better regulation.

Yogic breathing, pranayama, and mental health

Slow breathing pranayama techniques such as Sama Vritti, Nadi Shodhana, Bhramari, and Sheetali have been highlighted in scientific studies for their positive effects on stress regulation, autonomic balance, vagal activity, and heart rate variability. In that sense, pranayama offers both a traditional yogic discipline and a modern physiological lens through which we can understand how breathing affects the body and mind.

Practiced skillfully, pranayama for mental health is not about forcing calm. It is about refining awareness, attention, and regulation through the breath. This is one of the reasons breathing practices remain central in yoga: they support not only concentration and presence, but also the body’s own capacity to move out of stress and back toward balance.

In that broader sense, slow yogic breathing can also be understood as a practical form of vagus nerve breathing meditation. The practitioner is not directly controlling the nervous system by force, but creating conditions that support parasympathetic regulation, steadier attention, and a more flexible response to stress.

If you can breathe, you can begin

The phrase “if you can breathe, you can do yoga” may sound simple, but here it points to something essential. Breath is one of the most accessible entry points into self-regulation.

Yoga does not begin only with movement. Sometimes it begins with the willingness to sit, feel, and breathe.

Ways to improve vagal tone through practice

People often look for ways to improve vagal tone, and breathing is one of the simplest
places to start.

Regular slow breathing, especially with smooth, unforced exhalations, can help support vagal activity over time. Yoga adds something valuable here because it does not isolate breathing from the rest of experience. In a thoughtful yoga context, breath can be linked with posture, attention, interoception, and a sense of safety.
This is why steady practice can support both stress recovery and resilience. It is not only a tool to use in moments of overwhelm, but also a way of gradually improving the body’s baseline capacity to regulate itself.

Conclusion

Stress is not simply a problem to eliminate. It is part of how the body adapts to life. The real issue is whether the nervous system can respond, recover, and return to equilibrium. HRV gives us a window into that flexibility. The autonomic nervous system, especially the
relationship between sympathetic activation and parasympathetic recovery, helps explain why the body sometimes feels mobilized and sometimes able to rest. The vagus nerve plays a major role in that process. And breathing gives us one of the clearest ways to influence it voluntarily.
For yoga teachers and practitioners, this offers a beautiful meeting point between ancient practice and modern physiology. Cardiac coherence, slow breathing, and pranayama all remind us of the same essential truth: resilience is not the absence of stress, but the ability
to move through activation and come back to balance.

Didier BOFF is a software engineer and nutrition coach specialized in digestive health, certified by Elite HRV and Ecole 5.3. Since 2020 he has been researching science-based evidence supporting natural approaches to healing the brain and gut in irritable bowel syndrome.
→ https://digestibible.com/ 

Sources 

Definition of stress

• Eustress and Distress: Neither Good Nor Bad, but Rather the Same? (BioEssaysVolume 42, Issue 7)
• Allostasis, Homeostats, and the Nature of Stress (The International Journal on the Biology of Stress Volume 5, 2002 – Issue 1)
• The Concept of Allostasis: Coping With a Capricious Environment (The International Journal on the Biology of Stress Volume 5, 2002 – Issue 1)

Heart rate variability as a reliable biomarker of health 

• Relation of High Heart Rate Variability to Healthy Longevity (Neuroscience & Biobehavioral Reviews Volume 143)
• Heart-rate variability: a biomarker to study the influence of nutrition on physiological and psychological health? (Behavioural Pharmacology 29(2 and 3):p 140-151)
• Deep learning with wearable based heart rate variability for prediction of mental and general health (Journal of Biomedical Informatics Volume 112)
• Heart rate variability in the prediction of mortality: A systematic review and meta-analysis of healthy and patient populations (Neuroscience & Biobehavioral Reviews Volume 143)

Stimulating the vagus nerve

• A review of vagus nerve stimulation as a therapeutic intervention (Journal of Inflammation Research Volume 11)

Vagal tone

• Accuracy of assessment of cardiac vagal tone by heart rate variability in normal subjects (Journal of Inflammation Research Volume 11)
• Heart Rate Variability and Cardiac Vagal Tone in Psychophysiological Research – Recommendations for Experiment Planning, Data Analysis, and Data Reporting (Front. Psychol., 20)

Cardiac coherence breathing

• Cardiac coherence, self-regulation, autonomic stability, and psychosocial well-being (Front. Psychol., 29)
• Guiding Breathing at the Resonance Frequency with Haptic Sensors Potentiates Cardiac Coherence (Special Issue, Sensors 2023, 23(9))

Studies on Pranayamas

• Effect of Pranayama On Stress and Cardiovascular Autonomic Tone & Reactivity (Special Issue)
• Integrating Kriya Yoga, Pranayama and Brainwave Entrainment for Stress Reduction: An HRV-Based Exploration (Mymensingh Med J 2025 Jul; 34)
• Effect of Sheetali pranayama on cardiac autonomic function among patients with primary hypertension – A randomized controlled trial (Complementary Therapies in Clinical Practice Volume 39)
• Effects of Nadishodhana and Bhramari Pranayama on heart rate variability, auditory reaction time, and blood pressure: A randomized clinical trial in hypertensive patients (Complementary Therapies in Clinical Practice Volume 39)
• Investigating components of pranayama for effects on heart rate variability (Journal of Psychosomatic Research Volume 148)
• Blood Pressure and Heart Rate Variability during Yoga-Based Alternate Nostril Breathing Practice and Breath Awareness (PMCID: PMC4247229)

Studies on Samavritti pranayama

• The effectiveness of mindfulness based stress reduction and sama vritti pranayama on reducing blood pressure, improving sleep quality and reducing stress levels in the elderly with hypertension (Bali Medical Journal, 11 (1). pp. 302-305. ISSN 2302-2914)
• The Effects Of Slow Breathing Exercise On Heart Rate (ALTERNATIVE THERAPIES, JUL/AUG 2020 VOL. 26 NO. 4)