Understanding Heart Rate, Heart Rate Variability and Respiration Rate for Improving Fatigue and Chronic Illness

Kate Duder
4 days ago
7 min read

If you are navigating persistent fatigue, burnout, or a chronic illness like long COVID or ME/CFS, understanding three simple metrics: Heart Rate (HR), Heart Rate Variability (HRV), and Respiration Rate (RR), can give you more control over your energy and recovery.

Heart Rate (HR) and the Anaerobic Threshold (AT)

Managing your heart rate can be a key component to pacing and preventing debilitating energy crashes or Post-Exertional Malaise (PEM) in burnout, ME/CFS or Long COVID.

The Concept of the Anaerobic Threshold

The Anaerobic Threshold (AT) is a specific heart rate (HR) level that marks the boundary between aerobic (with oxygen and sustainable) and anaerobic (without oxygen quick burn) energy production.

When you keep your HR below this AT, your body uses oxygen efficiently, and the activity is sustainable.
When you cross the AT, your body quickly builds up metabolic byproducts (like lactic acid), triggering an overwhelming biological stress response that, for someone with burnout or chronic illness, can lead directly to ongoing fatigue or PEM for an extended period of time afterwards.

The goal for daily activity is to consciously keep your heart rate under this personal ceiling.

Two Ways to Calculate the Anaerobic Threshold

AT is highly individual, and is calculated differently for a healthy individual vs someone dealing with burnout, ME/CFS, Long COVID or other fatigue conditions. For individuals with the traditional max heart rate calculations can lead to over exertion and the triggering of fatigue or post exertional malaise (PEM) symptoms, therefore you can either calculate:

50-65 % of your max heart rate = estimated as 220 - age x 0.6 (or 0.65) eg. for a 48 year old this would be 220-48 = 172 x 0.6 = 103.

Whether you use 50 or 65% will depend on your level of fatigue and functionality and you may need to refine this accordingly.

Average resting heart rate + 15. E.g. if your RHR is 60 BPM, your suggested upper limit for activity would be 60-15 = 75 BPM.

How: Determine your average resting heart rate (RHR) by either checking your wearable or smart watch or taking your heart rate first thing in the morning, while still lying flat in bed, for at least 7 days and calculate an average.

Important: This is a starting point. You need to monitor your symptoms closely and adjust this limit downwards if you experience PEM.

If your heart rate goes over this limit try to reduce it within 2 minutes and if needed you can use breathing and other relaxation activities to bring it down again.

2. Heart Rate Variability (HRV): Your Body’s Adaptability Score

HRV is the tiny variation in time between your heartbeats, measured in milliseconds. Your heart doesn’t beat like a metronome; it adjusts to the environment and the greater variation the better the body is able to adapt and switch between sympathetic and parasympathetic nervous system activation.

High HRV: Indicates your Parasympathetic ("Rest-and-Digest") system is dominant. This means your body is resilient, adapting well to stress, and actively recovering.

Low HRV: Suggests your Sympathetic ("Fight-or-Flight") system is dominant. This is a sign of stress, strain, fatigue, or illness, and indicates that your body's resources are depleted.

Tracking your HRV will help you understand and improve how your body responds to sleep, exercise, stress and daily activities.

By providing concrete data, HRV tracking reduces the guesswork with changes you are making as often subtle changes are visible in the data before we feel the effects physically.

Most wearables enable you to record your HRV at specific times, however there are only a few devices (Garmin and Firstbeat) which continuously monitor HRV throughout the day and night, which enables you to see when your body is in a sympathetic vs para sympathetic state and when rest or recovery is required. Others measure it on demand or throughout the night to get a picture of your resting HRV which can be tracked over time to see changes. Continuous HRV tracking with detailed reporting is a tool gives you greater understanding of what’s happening day and night to enable you to make changes with more confidence and control.

More information:

3. Respiration Rate (RR): The Nervous System Reset

Respiration Rate (RR) is simply the number of breaths you take per minute and has a direct impact on your nervous system, stress and fatigue.

Fast, Shallow Breathing (often 16-20+ breaths per minute) is typical when under stress. This mimics and drives the Sympathetic ("Fight-or-Flight") response and when consistent can contribute to burnout, fatigue and chronic illness.

Slow, Deep Breathing actively stimulates the Vagus Nerve and shifts your body into the Parasympathetic ("Rest-and-Digest") state. This promotes calm, lowers stress hormones, and aids healing and recovery.

The Aim for Recovery

Slow deep breaths often referred to as Resonance Frequency (RF) breathing, actively stimulates the Vagus Nerve to engage the Parasympathetic Nervous System (the "rest and digest" mode), which promotes calm, reduces stress, and enhances recovery.

Aim to practice a slow, diaphragmatic breath at a rate of approximately 5-7 breaths per minute (a full breath cycle of around 10 seconds = 4 second inhale and 6 second inhale) for several minutes a day. This simple practice is one of the most effective ways to foster recovery and combat fatigue.

Your smart watch should be able to tell you your lowest, average and highest breaths per minute each day.

Other Key Principles for Activity and Heart Rate Management:

Pacing (Energy Management): The primary strategy is pacing, which involves carefully managing all forms of energy (physical, mental, emotional, social) to stay within your individual energy envelope and avoid PEM. Heart rate monitoring and HRV tracking are key tools for pacing.
Avoid "Pushing Through": Unlike traditional fitness advice, pushing into or through fatigue or symptoms can be detrimental and worsen your condition.
Listen to Your Body (Subjective & Objective): Track your symptoms and pay close attention to you feel, while using your heart rate monitor and HRV Tracking as an objective guide. Learn what your warning symptoms and if an activity feels "hard" or you notice early symptoms, stop and rest, regardless of your heart rate.
Daily Fluctuation: Your AT and tolerance can vary day by day depending on your symptom severity, sleep, stress levels, and prior activity. Be prepared to adjust your activity levels accordingly. If your morning RHR or body battery (on Garmin wearables) is elevated, it's often a sign you need to reduce activity for that day.
Conservative Approach: Always start with a very conservative heart rate limit and gradually, cautiously, and incrementally explore if you can tolerate more activity without triggering PEM. The goal is to minimize PEM, not necessarily to increase activity levels quickly.

Tracking your symptoms, activities and data can help you see patterns and recognise what is helping or hindering your recovery.

For anyone with burnout, Long COVID or ME/CFS, it's highly recommended to work with a healthcare professional experienced in these conditions who can help you develop a personalized pacing strategy, potentially including heart rate monitoring.

Wondering how HRV Tracking with Health and Nutrition Coaching could help you?

As a health coach, I specialise in helping people navigate burnout or complex health challenges, something I understand deeply from personal experience.

My approach is collaborative, compassionate, strategic and focused on you! I use HRV Tracking as a tool to give you concrete data on what's working or not working.

I’m a good listener who meets you where you are, and together, we’ll find simple, realistic next steps and practical tools that give back a sense of control, so you can move toward improved energy and living your best life.

Health Coaching can provide:

Tools and strategies to help you understand and manage symptoms and energy - including heart rate variability tracking
Nutrition, exercise, sleep and stress management guidance
Tips, tricks and resources for making sustainable lifestyle changes
Advocacy guidance
Accountability to help you stay on track

About Firstbeat Life

Inside Matters works with Reclaibrate NZ to bring you Firstbeat life technology.

Firstbeat Life is a pioneer in the HRV space with over 20 years experience in the HRV tracking for sports performance and improving wellbeing. They have made significant contributions to scientific research and operate in over 70 countries.

The technology includes a chest device and app available through health professionals like Health Coaches, Exercise Physiologists or Personal Trainers.

The HRV tracking data connects the dots between what’s happening in your body and your daily activities/stress. It shows how you react to the different demands in your life, what your daily (or longer) recovery looks like, how you sleep, your fitness and if your days include enough movement or physical activity to provide you with the positive health effects that are right for you.

It is not easy to identify the factors that cause stress, and these factors vary greatly between individuals and their respective life situations - that’s where HRV tracking and Firstbeat combined with Health Coaching can be so powerful for you. HRV tracking provides

reliable, objective data that enables you to see what works and doesn't work helping you make informed decisions about positive lifestyle changes to improve your health and well-being and reduce your chances of burnout or chronic illness.

If you have a chronic illness, HRV tracking can help you manage your recovery and tweak or finetune activities and recovery strategies to improve your health and wellbeing faster.

Firstbeat is designed to be used for period of 3-5 days at a time and provides a full report with scores on sleep, stress/recovery and exercise/movement.

Looking at heart rate heart rate variability and respiration rate using a Firstbeat device or your own wearable alongside health coaching can help you reduce the guesswork, balance your activities and improve your health and wellbeing.