Podcast Summary: ZOE Science & Nutrition

Episode: HRV vs. VO2 max vs. ECG: Which wearable metric ACTUALLY matters?
Guest: Prof. Malcolm Findlay
Host: Jonathan Wolf
Date: October 2, 2025

Overview

This episode tackles the value of different wearable health metrics—specifically Heart Rate Variability (HRV), VO2 max, ECG, and more. Prof. Malcolm Findlay, cardiologist and electrophysiologist, offers a deep dive into which wearable metrics genuinely reflect cardiovascular health and how best to use this data to improve well-being. The discussion helps listeners understand the science behind these numbers, practical implications, common misconceptions, and best practices for tracking heart health.

Key Discussion Points & Insights

Quick Fire Myths and Truths (01:51–02:34)

• HRV & Heart Health: HRV does reflect heart health, but it's one of many metrics, not the definitive indicator.
  • Quote [01:54]: “Can HRV tell you something about the health of your heart?”
    Malcolm: “Yes.”
• Wearables’ Utility: Can help you care for your heart if used thoughtfully.
• Focusing on Wrong Metrics: May mislead users into poor health habits.
• Individual Variation: Two people with identical heart rates can have very different HRV readings.
• Biggest Heart Health Myth: “Looking after yourself in a general way doesn't negate the need for proper medical intervention.” (02:38)

Understanding HRV (Heart Rate Variability) (03:24–08:54)

• What HRV Measures: Subtle beat-to-beat variations in heart rhythm, reflecting the balance between the sympathetic (fight-or-flight) and parasympathetic (rest) nervous systems.
  • Quote [03:24]: “It measures the subtle changes in the beat to beat time differences...”
    Malcolm
• High vs. Low HRV: A higher HRV generally indicates a healthy, responsive heart. Flat (very low) HRV can signify issues (e.g., post-heart transplant).
  • Quote [04:39]: “It’s the other way around. Absolutely the other way around.”
    Malcolm (on whether no variability is best)
• Normal Variability: HRV varies by individual, age, and context—average is 50 ms but can range from 30 to 70+.
• Age Effect: HRV decreases with age.

HRV in Health and Disease (06:50–10:07)

• Who Should Watch HRV: Only meaningful in people with ‘normal’ heart rhythms (sinus rhythm), not those with atrial fibrillation or similar arrhythmias.
  • Quote [06:50]: “In patients with an irregular heartbeat...heart rate variability actually is not a valid measure.”
    Malcolm
• Atrial Fibrillation: HRV becomes invalid; wearables can, however, help detect atrial fibrillation early (see ECG section).

What Controls HRV? (09:08–16:26)

• Nervous System: HRV is impacted by both direct nerve signals and hormones (like adrenaline).
• Psychological Influence: Thoughts, emotions, and mental states can affect HRV via brain–heart connections.
  • Quote [13:15]: "Just having these thinking tasks, psychometric tasks, can directly affect the way the heart cells activate and relax..."
    Malcolm
• Day-to-Day Fluctuations: HRV changes with illness, stress, infection, poor sleep, and improves with better lifestyle habits.

HRV & Stress, Illness, Lifestyle (16:39–19:46)

• Decreases With: Illness, psychological stress, inadequate sleep, or chronic health issues.
• Increases With: Sustained healthy changes—good sleep, improved diet, lower stress.
• Clinical Use: Not sensitive enough alone for diagnosis or tracking psychological or physical interventions, but can reflect overall trajectory.

Other Key Heart Metrics in Wearables (19:46–27:15)

ECG (Electrocardiogram) (20:08–22:29)

• What It Is: A direct measure of heart’s electrical activity.
• Accuracy: Wearable ECGs (even low-cost) deliver clinical-grade traces, suitable for diagnosis of many rhythm disorders.
  • Quote [20:50]: “Absolutely right. That is a direct measure of the heart's electrical activity.”
    Malcolm
• Everyday Use: Occasional checks are useful, particularly if symptomatic; wearables may prompt an ECG if irregular rhythms are detected.

Heart Rate (24:05–25:26)

• What It Tells You: General cardiovascular workload, sleep quality, exercise intensity.
• Variability: Track longer-term trends, not one-off changes.

VO2 Max (40:36–41:48)

• What It Is: Maximal oxygen uptake—“gold standard” for aerobic fitness.
• Usefulness: Great for athletic training; less useful as a general health marker for most people; wearable estimates are improving but not yet definitive.

What to Actually Track? Actionable Advice (29:45–41:57)

HRV:

• Compare to Yourself: Don’t compare absolute numbers with others; only your own long-term trends matter.
  • Quote [30:48]: “Really don’t be worried. That's your own number and the changes in one's own number that are going to be the key things to track...”
    Malcolm
• Meaningful Changes: Look for consistent shifts over weeks, not day-to-day fluctuations.
• Use: A feedback metric for general wellness/lifestyle change—encouragement rather than diagnosis.

ECG:

• Who Needs It: Occasional use for healthy people; crucial if you have palpitations or concerning symptoms.

Heart Rate (35:44–38:45):

• Exercise Goal: Aim to raise your heart rate above 110–120 bpm during purposeful activity.
• Duration: Even 1–2 hours per week at this level is beneficial.
• Don’t Over-Obsess: You don’t need to reach “training” (very high) zones for heart health.

Sleep Consistency (38:45–40:33):

• Why It Matters: Directly linked to better HRV and overall health.
• What To Do: Regular sleep/wake times matter more than total hours.

Diet & Alcohol (27:30–29:45):

• Alcohol: Excess intake negatively impacts HRV and heart health; moderate social drinking (up to one glass/day) appears acceptable.
• Diet: Chronic dietary habits impact health over time; improvements can boost wellness/HRV, but no “quick fix” from a single meal.

VO2 Max:

• Best for: Athletes, those interested in structured performance training.
• General Health: Not a primary concern for most wearables users.

Individualization:

• Don’t Compare: Track your own progress, don’t benchmark against others.
  • Quote [41:57]: “This is about you making yourself better for your own health and your own longevity...”
    Malcolm

Notable Quotes & Memorable Moments

• [02:38] Malcolm on the biggest myth: “Just looking after yourself in a general way doesn't negate the need for some proper medical intervention.”
• [04:39] On HRV and health: “It’s the other way around. Absolutely the other way around.” (Higher HRV is healthier.)
• [20:50] On using wearable ECGs in diagnosis: “Absolutely right. That [wearable ECG] is a direct measure of the heart's electrical activity.”
• [30:48] On HRV comparison: “Really don't be worried. That's your own number and the changes in one's own number that are going to be the key things to track...”
• [41:57] On competing with others: “Don't care what other people think... This is about you making yourself better for your own health and your own longevity and your own feeling of, well, being.”

Important Timestamps

• 01:51–02:34: Quick fire myths and clarifications
• 03:24–08:54: Explaining HRV and what it reflects
• 13:15–15:39: Brain-heart connection, psychological impacts on HRV
• 16:56–19:46: Day-to-day HRV influences (illness, stress, well-being)
• 20:08–22:29: ECG—what it is, how accurate, game-changing potential
• 24:05–25:26: Heart rate interpretation
• 29:45–33:20: Actionable advice: what to track, how HRV trends matter
• 35:44–38:45: Exercise, heart rate targets, and longevity
• 38:45–40:33: Sleep consistency importance
• 40:36–41:48: VO2 max—when it matters

Summary Table: Metrics Worth Tracking (Wearables)

| Metric | Usefulness | Who Should Focus | Key Takeaway | |-------------|------------|------------------|---------------------------------| | HRV | Medium | Self-monitoring, wellness | Track long-term trends; don’t compare with others. | | ECG | High | Anyone with symptoms; peace of mind for all | Accurate; can trigger early diagnosis and treatment. | | Heart Rate | High | All users | Target >110–120 bpm in exercise for benefit. | | VO2 Max | Niche | Athletes, performance trainers | Training tool, not general health proxy. | | Sleep Consistency | High | Everyone | Better sleep = better HRV and health outcomes. |

Engaging Takeaways for Listeners

• Use wearables for long-term trends, not for day-to-day anxieties.
• Focus on your own baseline; don’t compete on metrics.
• HRV is a health “output”; lifestyle is the health “input.”
• Wearables offer genuine clinical value—especially ECG—but can also empower self-care and early detection.
• The best path to heart health: regular moderate activity, good sleep, balanced diet, and moderation in all things (especially alcohol).

In Prof. Findlay's own words (41:57):
"This is about you making yourself better for your own health and your own longevity and your own feeling of, well, being."