A Masterclass in Improving Your HRV - Dr Jay Wiles

In this podcast episode, Dr. Jay Wiles takes a deep dive into heart rate variability (HRV), explaining what it is, what it measures, and why it's gaining so much interest today. From the foundations of the nervous system and autonomic regulation to the practicalities of HRV measurement, its limitations, and innovative interventions like resonance breathing and biofeedback, Dr. Wiles offers a comprehensive masterclass. He also addresses common misconceptions, the nuanced relationship between stress and HRV, and the importance of combining HRV practices with lifestyle factors such as sleep and exercise.

What is HRV?

Dr. Wiles introduces heart rate variability as the most powerful non-invasive biomarker we have for assessing how our nervous system adapts to internal and external stimuli. HRV is essentially the variation in time intervals between successive heartbeats, measured in milliseconds. Rather than the heart beating like a perfect metronome, a healthy heart shows a natural, dynamic fluctuation in those intervals driven by complex nervous system responses. This variability reflects the nervous system's flexibility, adaptability, and resilience to stressors—key factors in our overall well-being.

He emphasizes HRV as a window into nervous system regulation rather than a standalone metric of stress, cautioning against simple assumptions like "high HRV is always good" or "low HRV means stress." Instead, HRV should be understood contextually and longitudinally, recognizing the nervous system as a complex signaling highway with both autonomic and somatic branches.

The Nervous System and Autonomic Balance

To understand HRV's significance, Dr. Wiles breaks down the nervous system into its central (brain and spinal cord) and peripheral components, focusing on the autonomic nervous system (ANS). The ANS regulates involuntary processes such as heart rate, blood pressure, respiration, and digestion to maintain homeostasis. It comprises two primary branches: the sympathetic nervous system, responsible for mobilizing energy (commonly oversimplified as fight, flight, or freeze), and the parasympathetic nervous system, which conserves energy and supports rest and digestion.

Crucially, these branches do not operate as a simple on/off seesaw but rather work in synergy to finely tune physiological responses. HRV reflects this dynamic interplay, showing how well the nervous system can make quick, nuanced adjustments in response to changing demands.

How HRV is Measured and Interpreted

Dr. Wiles explains that HRV measurement focuses on analyzing the time between heartbeats with high precision, registering differences in milliseconds. For instance, a heart rate of 60 beats per minute does not mean one heartbeat per second in a perfectly timed manner; instead, the intervals fluctuate as breathing and nervous system activity vary. Inhalation typically accelerates heart rate shortening the interval, while exhalation slows it down, elongating the interval.

He underscores a key insight that healthy HRV patterns look "chaotic" rather than uniform. This variability is a sign of adaptability, whereas a heart beating like a metronome suggests regulatory issues. In practice, HRV is not a single value but a collection of metrics (12–15 commonly used indices), with time-domain measures like RMSSD (root mean square of successive differences) being prevalent.

Long-term trends in HRV stability are more informative than day-to-day fluctuations. He stresses that a person's HRV should be viewed in relation to their own baseline rather than compared against others. High or low absolute HRV values have limited meaning without personalized context.

Factors Influencing HRV: Non-Modifiable and Modifiable

There are multiple factors influencing HRV, categorized as non-modifiable and modifiable. Age naturally reduces HRV as vascular stiffening and decreased autonomic efficiency occur typically starting in the 30s to 50s. However, this decline does not imply a fixed ceiling—improvements remain possible regardless of age.

Genetics also plays an important role, with twin studies indicating moderate to high heritability in HRV traits. Sex differences are notable as well; men generally have higher HRV than women, partly due to hormonal fluctuations across the menstrual cycle affecting autonomic balance.

Among modifiable factors, cardiorespiratory fitness significantly enhances HRV through improvements in stroke volume, resting heart rate, and vascular health. Chronic health conditions such as diabetes, cardiovascular disease, and chronic pain tend to suppress HRV. Finally, overall stress load, especially chronic psychological stress common in modern life, impairs nervous system flexibility and thus lowers HRV.

What HRV Does Not Measure

Dr. Wiles clarifies that HRV does not measure psychological stress directly, nor is it a one-time snapshot that determines how stressed or relaxed you are at any moment. It reflects physiological adaptability rather than the subjective experience of stress. The nervous system's responses are complex and include many inputs beyond what HRV alone indicates. Thus, using isolated HRV readings to interpret stress or direct momentary mental state can be misleading and create counterproductive reactions.

The Gap Between Measurement and Intervention

With the explosion of wearable technology (Whoop, Oura, Apple Watch), access to HRV data has become widespread. However, understanding and applying that data meaningfully remains a challenge. Many wearers see their HRV scores but lack clear guidance on actionable steps to improve them.

Dr. Wiles highlights that diagnostics—HRV measurement—have outpaced interventional knowledge. People can detect changes but often don't know how to leverage that insight for nervous system health. Education and practical tools to translate HRV insights into daily behavioral and physiological improvements are crucial.

State Changes vs. Trait Changes

A fundamental distinction is drawn between state changes (acute temporary shifts) and trait changes (longer-term adaptations) in nervous system function. Breathing practices like resonance breathing can create fast-acting state changes by regulating nervous system tone, but lasting trait changes require consistent, repeated practice over time—akin to strength training for the nervous system.

State changes can help quickly modulate anxiety or arousal before stressful events. Trait changes remodel the nervous system's baseline resilience and flexibility over weeks or months.

The Physiology of Resonance Breathing

Resonance breathing, also called HRV biofeedback (BOF), is a scientifically validated method to harness breathing's potential to synchronize heart rate variability, respiratory sinus arrhythmia, and baroreflex mechanisms. By breathing at a specific slow frequency (typically between 4.5 and 6.5 breaths per minute), individuals can maximize parasympathetic activation and stabilize blood pressure regulation.

This practice was initially studied by Russian physiologists during the space race to optimize astronaut physiology. It enables the nervous system to achieve a "resonant" state where physiological systems oscillate harmoniously, enhancing autonomic flexibility.

A single session can elicit meaningful changes within 6 to 12 minutes, while consistent practice 4 to 6 days a week over 8 to 12 weeks fosters trait-level improvements, including increases in HRV and baroreflex gain.

Frequency Domains Within HRV

Beyond simple time-domain measures, HRV can be analyzed in the frequency domain, breaking down heart rate signals into low frequency and high frequency components. Low frequency power relates to slow sinusoidal oscillations seen during resonance breathing and reflects baroreflex activity. High frequency power aligns with respiratory sinus arrhythmia related to normal breathing rhythm.

Training resonance breathing predominantly engages low frequency power, which in turn facilitates improvements in high frequency power at rest over time. This interplay reinforces vagal tone and nervous system regulation.

Challenges of Breathwork Trends and Preservation of Scientific Rigor

Dr. Wiles acknowledges the popularity of breathwork but expresses reservations about the mix of evidence-based practices with esoteric or unverified claims prevalent in wellness circles. While various breathwork forms are used mainly for state change or emotional release, resonance breathing uniquely shows robust scientific evidence for trait change and nervous system modulation.

He cautions against conflating breathwork's psychological benefits with physiological remodeling, emphasizing the importance of precision, intention, and consistent practice.

HRV Biofeedback Technology and the M Device

To improve accessibility and adherence to resonance breathing, Dr. Wiles discusses the "M" lamp device, designed to reduce barriers such as the need for multiple wearable sensors and phone interaction. The device guides users to their precise, dynamically adjusted resonance frequency within a session by monitoring real-time physiological signals via a photoplethysmography (PPG) sensor embedded in a warm stone.

This approach optimizes breathing timing with personalized inhale/exhale ratios, adjusts pacing throughout the session, and enables users to practice without the distraction of looking at screens or wearables, promoting better compliance and deeper engagement.

Mindfulness, Attention, and Feedback Integration

Attention and mindfulness enhance resonance breathing benefits. Wandering thoughts activate sympathetic responses that can pull one out of the desired physiological state. Layering mindfulness or meditation with HRV biofeedback is recommended to maximize both nervous system regulation and mental attunement, although some nervous system benefits can still accrue without focused mindfulness.

Practical Applications: Protocols and Lifestyle Integration

A practical regimen for enhancing HRV centers on combining cardiorespiratory fitness (around 120–150 minutes of moderate-intensity exercise weekly, including some high-intensity sessions) with regular resonance breathing practice (ideally 10 to 20 minutes per session, four to six times weekly).

Dr. Wiles emphasizes quality over quantity, noting that sessions longer than 20 minutes yield diminishing returns. Shorter sessions under 10 minutes may induce state changes but are less potent for trait adaptations.

For certain high-performing athletes, timing and dosing may be personalized, sometimes avoiding resonance breathing before competition if it dampens desired arousal but favoring post-exertion recovery.

The Relationship Between Psychological and Physiological Stress

Dr. Wiles explores how stress signals flow bidirectionally between body and brain. Physiological states can influence cognitive-emotional appraisal (bottom-up), and mental interpretations can modulate physiological responses (top-down). Interventions targeting the body's nervous system (e.g., resonance breathing) can complement and potentiate traditional psychotherapies by calming physiological overactivation and enhancing receptivity to cognitive processing.

He shares clinical examples from his work with veterans suffering trauma-related autonomic dysregulation, illustrating how somatic regulation can unlock the mind-body impasse that pure talk therapy may struggle to address.

Sleep: The Foundation of Nervous System Health

Sleep is presented as the cornerstone of nervous system repair and overall wellness. High-quality, efficient sleep corresponds with better autonomic regulation, which is reflected in HRV metrics during overnight monitoring. Disrupted sleep, fragmentation, and sympathetic bursts impair restorative processes and erode HRV.

Advanced medical-grade devices (e.g., Absolute Rest's SleepImage ring) offer granular insights into cardiorespiratory coupling and fragmentation beyond consumer wearables, identifying autonomic dysregulation during sleep. Incorporating resonance breathing before bedtime can improve these sleep metrics and promote deeper, more restorative sleep stages over time.

Limits and Appropriate Uses of HRV

Dr. Wiles cautions against over-reliance on HRV as a singular health metric. It should not be treated as a vanity number or used for cross-person comparisons due to genetic, age, and sex variability. HRV is best interpreted relative to one's own baseline trends and as part of a composite picture incorporating subjective feelings and other physiological markers.

Unlike metrics such as VO2 max, HRV does not provide a direct measure of cardiovascular fitness or longevity risk. Its strength lies in real-time feedback and monitoring dynamic nervous system function, especially when combined with interventions that promote autonomic adaptability.

Resources and Further Exploration

Although the "M" device is still in pre-order phase with expected shipping later in the year, Dr. Wiles encourages listeners to explore resonance breathing and HRV biofeedback as accessible tools for nervous system health. He emphasizes the importance of integrating evidence-based practices alongside existing wellness routines to harness autonomic flexibility and resilience, noting the growing relevance of this field in health optimization.