Heart Rate Variability and Cardiovascular Health

Longevity and How That Relates to Heart Rate Variability

Wearables to monitory your health give you a daily window onto all your days. It is no more important than in the use of measuring Heart rate variability (HRV). HRV refers to the variation in the time interval between heartbeats. It is an essential marker of autonomic nervous system function and overall cardiovascular health. HRV reflects the balance between the sympathetic nervous system (“fight or flight”) and the parasympathetic nervous system (“rest and digest”), making it a valuable metric for understanding body responds to stress, exercise, yoga, and recovery.

There is a variety of ways your WHOOP, Oura Ring, Fitbit, Apple Watch, or Garmin measures your HRV and other physiological aspects of heart heath. Wearables measure heart rate, HRV, and blood oxygen, using photoplethysmography

Photoplethysmography (PPG) is a non-invasive optical technique used to measure changes in blood volume in tissues. It works by shining light (usually infrared or red) onto skin and detecting quantity of light is absorbed or reflected by the blood in the underlying vessels.

Blood absorbs light differently depending on its volume and flow. When blood volume increases (during a heartbeat), more light is absorbed. Slower HRs decreases flow (between beats) and less light is absorbed. A photodetector captures the reflected or transmitted light and converts it into an electrical signal. This signal corresponds to the rhythmic blood flow changes in the underlying vessels.

This post explores first the cardiac factors that influence HRV, and next more about HRV itself. While HRV itself is a measure of these time differences, it is closely tied to a range of cardiovascular parameters that reflect the heart’s performance, blood flow, and vascular resistance. Here’s a breakdown of the key factors and relevance to HRV:


1. Heart Rate (HR)

  • Definition: The number of beats per minute (BPM). It’s what you mostly monitor during exercise with your wearables.
  • Relevance: HR and HRV are inversely related—higher HR often correlates with lower HRV. Variability in HR is a sign of a healthy cardiovascular system capable of adapting to physiological demands.

2. Stroke Index (SI)

  • Definition: The amount of blood ejected by the heart in one beat relative to body surface area (mL/m²).
  • Relevance: Changes in SI can influence HRV by altering the heart’s workload and its ability to adjust to autonomic inputs. It takes very sophisticated machinery to monitor this!

3. Cardiac Index (CI)

  • Definition: Cardiac output (the volume of blood the heart pumps per minute) normalized for body surface area (L/min/m²).
  • Relevance: Higher variability in cardiac output aligns with better HRV, as it reflects dynamic heart performance.

4. End Diastolic Index (EDI)

  • Definition: The amount of blood in the ventricles at the end of diastole, adjusted for body surface area.
  • Relevance: A healthy heart optimally fills during diastole, contributing to efficient HRV patterns.

5. Peak Flow

  • Definition: The maximum velocity of blood ejection during systole.
  • Relevance: Peak flow variability may reflect the heart’s capacity to adapt to stress, linking it to HRV.

6. Ejection Fraction (EF)

  • Definition: The percentage of blood ejected from the ventricles with each beat. Definitely reflects a training effect.
  • Relevance: A higher ejection fraction reflects efficient cardiac function, supporting better HRV.

7. Thoracic Fluid Index (TFI)

  • Definition: A measure of fluid accumulation in the thoracic cavity.
  • Relevance: High thoracic fluid levels can impair HRV by stressing the heart and limiting autonomic regulation.

8. Index of Contractility

  • Definition: A measure of the heart muscle’s strength during contraction.
  • Relevance: Greater contractility supports improved HRV by enhancing the heart’s responsiveness to autonomic signals.

9. Ejection Ratio

  • Definition: The ratio of stroke volume to end-diastolic volume.
  • Relevance: Variability in ejection ratio correlates with the heart’s ability to adapt dynamically, influencing HRV.

10. Systolic Time Ratio

  • Definition: The proportion of time spent in systole versus the total cardiac cycle.
  • Relevance: Alterations in systolic timing can affect HRV by disrupting the balance between filling and ejection phases.

11. Acceleration Index

  • Definition: The rate of pressure increase in the ventricles during systole.
  • Relevance: Higher acceleration variability reflects greater adaptability of the heart to changing demands, supporting HRV.

12. Blood Pressure Metrics

  • Systolic, Diastolic, and Mean Arterial Pressures (MAP):
    • Systolic: Peak pressure during heartbeats.
    • Diastolic: Pressure when the heart rests between beats.
    • MAP: Average arterial pressure during one cardiac cycle.
  • Relevance: Blood pressure variability ties directly to HRV, as it reflects autonomic control over vascular tone.

13. Left Stroke Work Index (LSWI)

  • Definition: The work done by the left ventricle per beat, normalized for body size.
  • Relevance: Efficient left ventricular function supports optimal HRV by improving circulation and autonomic balance.

14. Systemic Vascular Resistance Index (SVRI)

  • Definition: The resistance the heart must overcome to pump blood through systemic circulation, adjusted for body size.
  • Relevance: Variability in vascular resistance is an indicator of autonomic flexibility and closely relates to HRV.

HRV Norms by Gender and Age

Appropriate Heart Rate Variability (HRV) for Men and Women

Heart rate variability (HRV) is a key indicator of autonomic nervous system function and overall health. A However, HRV is highly individualized and influenced by factors such as age, fitness level, and overall health status  There is no research that exactly correlates training to changes in HRV. High intensity exercise might lead to long term gains, but shortterm stress that makes you measure less healthy It measures the variation in time between consecutive heartbeats, with higher variability generally indicating better cardiovascular and nervous system health. However,


HRV Norms by Gender and Age

HRV is often measured using the root mean square of successive differences (RMSSD) or standard deviation of normal-to-normal intervals (SDNN). Below are typical HRV values for men and women based on research and wearable device data:

Age Group Men (ms) Women (ms)
18–25 years 55–105 50–100
26–35 years 50–95 45–95
36–45 years 45–85 40–85
46–55 years 40–75 35–75
56–65 years 35–65 30–65
65+ years 30–55 25–55
  • Men tend to have slightly higher HRV than women, likely due to hormonal differences, particularly testosterone, which is associated with better vagal tone.
  • HRV naturally declines with age due to decreased autonomic flexibility.
  • Athletes or highly fit individuals often have HRV values above 100 ms.

What Influences HRV?

Several factors can impact HRV, including:

  • Physical Fitness: Regular exercise, particularly aerobic and resistance training, increases HRV.
  • Sleep Quality: Poor sleep lowers HRV, while deep, restorative sleep improves it.
  • Stress and Mental Health: Chronic stress reduces HRV due to prolonged activation of the sympathetic nervous system.
  • Hydration and Nutrition: Proper hydration and a balanced diet rich in electrolytes support healthy HRV.
  • Alcohol and Stimulants: Alcohol and caffeine consumption can temporarily lower HRV.
  • Medical Conditions: Hypertension, diabetes, and cardiovascular disease often correlate with lower HRV.

Interpreting Your HRV

  • Higher HRV: Generally indicates better autonomic nervous system function, good recovery, and adaptability to stress.
  • Lower HRV: May suggest stress, fatigue, dehydration, overtraining, or underlying health concerns.

How to Improve HRV

  1. Engage in Regular Exercise – Both aerobic and resistance training improve HRV over time.
  2. Prioritize Sleep – Aim for 7–9 hours of quality sleep each night.
  3. Practice Mindfulness & Stress Reduction – Meditation, yoga, and deep breathing exercises can increase HRV.
  4. Stay Hydrated – Proper fluid intake supports cardiovascular efficiency.
  5. Optimize Nutrition – A diet rich in omega-3s, magnesium, and antioxidants supports heart health.
  6. Limit Alcohol and Caffeine – Reducing consumption can help maintain stable HRV levels.
  7. Track HRV Trends – Wearables like WHOOP, Oura Ring, or Garmin devices provide insights into HRV patterns.

When to Be Concerned

If your HRV suddenly drops and stays low for several weeks, or if it is consistently below 30 ms, consult a healthcare provider. Persistent low HRV may indicate cardiovascular issues, high stress levels, or poor recovery.


What Influences HRV?

Several factors can impact HRV, including:

  • Physical Fitness: Regular exercise, particularly aerobic and resistance training, increases HRV.
  • Sleep Quality: Poor sleep lowers HRV, while deep, restorative sleep improves it. Many trackers only record HRV during sleep, so errors can creep in if you have very poor sleep.
  • Stress and Mental Health: Chronic stress reduces HRV due to prolonged activation of the sympathetic nervous system.
  • Hydration and Nutrition: Proper hydration and a balanced diet rich in electrolytes support healthy HRV.
  • Alcohol and Stimulants: Alcohol and caffeine consumption can temporarily lower HRV.
  • Medical Conditions: Hypertension, diabetes, and cardiovascular disease often correlate with lower HRV.

Interpreting Your HRV

  • Higher HRV: Generally indicates better autonomic nervous system function, good recovery, and adaptability to stress.
  • Lower HRV: May suggest stress, fatigue, dehydration, overtraining, or underlying health concerns.

How to Improve HRV

  1. Engage in Regular Exercise – Both aerobic and resistance training improve HRV over time.
  2. Prioritize Sleep – Aim for 7–9 hours of quality sleep each night.
  3. Practice Mindfulness & Stress Reduction – Meditation, yoga, and deep breathing exercises can increase HRV.
  4. Stay Hydrated – Proper fluid intake supports cardiovascular efficiency.
  5. Optimize Nutrition – A diet rich in omega-3s, magnesium, and antioxidants supports heart health.
  6. Limit Alcohol and Caffeine – Reducing consumption can help maintain stable HRV levels.
  7. Track HRV Trends – Wearables like WHOOP, Oura Ring, or Garmin devices provide insights into HRV patterns.

When to Be Concerned

If your HRV suddenly drops and stays low for several weeks, or if it is consistently below 30 ms, consult a healthcare provider. Persistent low HRV may indicate cardiovascular issues, high stress levels, or poor recovery.

By understanding and tracking your HRV, you can gain valuable insights into your overall health and recovery capacity, making adjustments to optimize long-term well-being.

HRV and Gut Health: The Emerging Connection

HRV isn’t just tied to cardiovascular metrics—it’s also influenced by gut health. The gut-brain axis, mediated by the vagus nerve, plays a critical role in autonomic regulation. Healthy gut microbiota improves HRV by:

  • Reducing systemic inflammation.
  • Enhancing parasympathetic activity.
  • Improving metabolic health, which indirectly benefits cardiac function.

Takeaway

Heart rate variability is a powerful indicator of overall health, reflecting the heart’s ability to adapt to physiological demands. Parameters like stroke index, cardiac index, ejection fraction, and vascular resistance all contribute to HRV, providing a comprehensive view of cardiovascular efficiency. Beyond the heart, HRV is influenced by systemic factors like gut health, stress, sleep, fitness, hormones, and metabolic function, making it a valuable tool for holistic health monitoring.

By understanding these metrics, you can better appreciate how HRV ties into your broader health and work toward optimizing it through lifestyle, nutrition, and medical care when necessary. If HR variability is decreasing and resting pulse is elevating, or oxygen levels are creeping down simple home interventions are to improve hydration, sleep, nutrition, decrease alcohol (and smoking if you smoke), and stress management. Evaluate your exercise: is it too little or perhaps too much, or too imbalanced between cardio and strength.  If these steps are not improving your numbers, consult your health care provider.