Deep Dive: HRV Training—Protocols and Interpretation¶

Reading time: ~6 minutes
Prerequisite: Chapter 2.12 (Stress and Mental Health)

The Big Picture¶

Heart rate variability (HRV) has become a mainstream health metric. Your clients may have wearables that track it, apps that analyze it, and questions about what it means.

HRV provides a window into autonomic nervous system function, reflecting the balance between "fight or flight" (sympathetic) and "rest and digest" (parasympathetic) states. Understanding HRV can help you guide recovery, stress management, and training decisions.

What HRV Actually Measures¶

Your heart doesn't beat like a metronome. Even at a steady heart rate of 60 bpm, the interval between beats varies, maybe 1.02 seconds, then 0.98 seconds, then 1.01 seconds.

HRV quantifies this variation. Common metrics include:

RMSSD (Root Mean Square of Successive Differences): The most common metric. Higher values generally indicate better parasympathetic tone.

SDNN (Standard Deviation of NN intervals): Reflects overall variability. Used in research but less common in consumer apps.

HF Power (High Frequency): Specifically reflects parasympathetic activity.

LF/HF Ratio: Traditionally thought to reflect sympathetic/parasympathetic balance, but this interpretation is now considered oversimplified.

For coaching purposes, RMSSD is usually what your clients' devices report.

What Higher and Lower HRV Mean¶

Higher HRV generally indicates:
- Good parasympathetic tone
- Well-recovered state
- Lower stress levels
- Better cardiovascular health
- Capacity for training and challenging activities

Lower HRV generally indicates:
- Sympathetic dominance
- Incomplete recovery
- Stress (physical, mental, or emotional)
- Illness or overtraining
- Need for rest or reduced intensity

Important caveats:
- HRV is highly individual, your "low" might be someone else's "high"
- Day-to-day variation is normal
- Trends matter more than single readings
- Context matters enormously

Interpreting Your Client's HRV¶

Track Personal Baselines

The most useful approach is establishing each client's personal baseline over 2-4 weeks, then tracking deviations.

Context Always Matters

A low HRV reading could mean:
- Poor sleep last night
- Fighting off illness
- Emotional stress
- Overtraining
- Dehydration
- Alcohol the night before
- Normal variation

Don't overreact to single readings. Look for patterns and context.

HRV-Guided Training¶

One practical application is using HRV to guide training intensity:

High HRV Day: Client is recovered; good day for:
- High-intensity intervals
- Heavy strength training
- Challenging workouts

Low HRV Day: Client needs recovery; better for:
- Light movement (walking, yoga)
- Mobility work
- Rest day
- Lower intensity aerobic work

This isn't rigid. Some clients do fine training through low HRV days. But it provides useful information for decision-making.

HRV Biofeedback Training¶

Beyond passive tracking, HRV can be actively trained through biofeedback, using real-time feedback to shift into parasympathetic states.

Resonance Frequency Breathing

Each person has a breathing rate (typically 4-7 breaths per minute) at which HRV is maximized. This is called resonance frequency.

Protocol:
1. Use biofeedback app to find personal resonance frequency
2. Practice breathing at that rate for 10-20 minutes daily
3. Watch HRV increase in real-time as feedback

Research shows this can increase resting HRV over weeks of practice.

Simple Protocol (Without Biofeedback)

For most people, breathing at 6 breaths per minute (5 seconds in, 5 seconds out) is close to resonance frequency.

Practice:
- 10 minutes daily
- Slow, smooth breaths
- Focus on extending exhale slightly
- Relaxed, not forced

What Wearables Get Right and Wrong¶

Generally Accurate:
- Trends over time
- Relative changes within an individual
- Morning resting measurements

Less Reliable:
- Absolute numbers (varies by device and algorithm)
- Real-time readings during activity
- Single-point measurements
- Comparing numbers between different devices

Best Practices for Clients Using Wearables:
- Measure at the same time daily (ideally morning, upon waking)
- Track trends over weeks, not daily fluctuations
- Don't obsess over single readings
- Use the same device consistently
- Understand your personal baseline

Common HRV Mistakes¶

1. Overreacting to Single Readings

One low reading isn't a crisis. Look at 7-day rolling averages.

2. Comparing Numbers to Others

HRV is highly individual. A 25-year-old athlete and a 50-year-old sedentary person will have very different baselines. Both can be healthy.

3. Ignoring Context

Did they drink alcohol? Sleep poorly? Feel stressed? Numbers without context are meaningless.

4. Using HRV to Override How They Feel

If someone feels great but has low HRV, they might be fine to train. If they feel terrible with high HRV, something's off. Subjective feel matters.

5. Measuring at Inconsistent Times

HRV varies throughout the day. Morning readings are most reliable for tracking trends.

Factors That Improve HRV¶

What This Means for Coaches¶

• HRV is useful, not magical: It provides one data point about recovery and stress, not a complete picture.
• Trends over points: Track patterns over weeks, not daily readings.
• Context is everything: A low reading without context tells you little.
• Individual baselines: Help clients establish their personal normal before interpreting deviations.
• Don't let data override intuition: HRV informs decisions; it doesn't make them.
• Biofeedback can help: For stressed clients, HRV training through resonance breathing is evidence-based.

Key Takeaway¶

HRV provides a window into autonomic nervous system balance and recovery status. It is useful for guiding training and stress management when tracked as trends against personal baselines, but it is easily misinterpreted when taken as single data points or compared between individuals.

References¶

1. Shaffer F, Ginsberg JP. An Overview of Heart Rate Variability Metrics and Norms. Front Public Health. 2017.
2. Plews DJ, et al. Training Adaptation and Heart Rate Variability in Elite Endurance Athletes. Int J Sports Physiol Perform. 2013.
3. Lehrer PM, Gevirtz R. Heart Rate Variability Biofeedback: How and Why Does It Work? Front Psychol. 2014.
4. Fatisson J, et al. Influence Diagram of Physiological and Environmental Factors Affecting Heart Rate Variability. Heart Int. 2016.
5. Kim HG, et al. Stress and Heart Rate Variability: A Meta-Analysis. Psychiatry Investig. 2018.
6. Laborde S, et al. Heart Rate Variability and Cardiac Vagal Tone in Psychophysiological Research. Front Psychol. 2017.