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Heart rate variability - HRV - has gone from a tool used by elite athletes and cardiologists to something measurable on a consumer wearable in under a decade. But most men who see an HRV number on their watch or ring don't fully understand what they're looking at.
HRV is the metric I check before I decide whether to push or pull back on a training day. Once you understand it, the number on your ring stops being abstract and starts driving better decisions.
Here's what HRV actually measures, why it's one of the most informative health metrics available, and what you can do to improve it. HRV is one node in the larger picture I cover in continuous health monitoring for men over 40.
What HRV Actually Measures
Your heart doesn't beat like a metronome. Even at rest, the time between consecutive heartbeats varies from beat to beat - sometimes by just a few milliseconds, sometimes by tens of milliseconds. This variation is heart rate variability.
A high HRV means there's significant variation between beats - the intervals are irregular. A low HRV means the beats are highly regular, almost metronomic.
Counterintuitively, high variability is better. Here's why.
The Autonomic Nervous System Connection
Your heart rate is regulated by the autonomic nervous system (ANS), which operates on two opposing branches:
Sympathetic nervous system (fight-or-flight): When activated, it increases heart rate and reduces variability. The heart beats faster and more regularly. Stress, illness, overtraining, sleep deprivation, and alcohol all activate the sympathetic branch.
Parasympathetic nervous system (rest-and-digest): When activated, it slows heart rate and increases variability. The vagus nerve releases acetylcholine that causes beat-to-beat variation in heart rate. Recovery, sleep, meditation, and good nutrition promote parasympathetic dominance.
High HRV reflects a nervous system that can rapidly shift between sympathetic and parasympathetic states - it's responsive, adaptable, and resilient. Low HRV reflects a nervous system that's under sustained stress and has lost some of its ability to regulate itself.
HRV is therefore not just a measure of cardiac function - it's a window into the state of your entire nervous system and your body's capacity to handle stress.
Why HRV Declines With Age (And What You Can Do About It)
Average HRV declines significantly with age. A 20-year-old male might have an HRV of 60–70ms (RMSSD, the most commonly used metric). By 40, the average has typically dropped to 40–55ms. By 60, it's often below 35ms.
This decline reflects genuine physiological changes: reduced vagal tone, reduced cardiac autonomic flexibility, and cumulative lifestyle factors. But age is only one contributor. Research consistently shows that lifestyle variables - chronic stress, poor sleep, sedentary behaviour, excess alcohol, inflammation - accelerate the decline. And these are all modifiable.
Men who exercise regularly, sleep well, manage stress, and minimise alcohol consumption in their 40s often maintain HRV levels comparable to averages 15–20 years younger.
What HRV Predicts
HRV's relevance extends well beyond athletic recovery. Population studies have linked low HRV to:
Cardiovascular disease. A meta-analysis of 21 studies published in the European Heart Journal found that low HRV was independently associated with increased mortality from cardiovascular disease. The relationship holds even after adjusting for age, blood pressure, and established cardiovascular risk factors.
All-cause mortality. Low resting HRV is a significant predictor of all-cause mortality in men over 40, independent of cardiovascular disease status.
Testosterone. Research has found positive correlations between HRV and testosterone levels in men, mediated through the HPA axis. Chronic sympathetic activation (low HRV state) is associated with elevated cortisol and suppressed GnRH, which in turn reduces testosterone production.
Mental health. Reduced HRV is associated with anxiety disorders, depression, and reduced cognitive resilience. The vagus nerve has direct connections to the limbic system and prefrontal cortex, and vagal tone influences emotional regulation.
Metabolic health. Low HRV correlates with insulin resistance and metabolic syndrome markers.
How HRV Is Measured
Most consumer wearables now measure HRV using photoplethysmography (PPG) - an optical sensor on the wrist or finger that detects changes in blood volume with each heartbeat. This is less accurate than an ECG-based measurement but sufficient for tracking trends over time.
More accurate measurement uses a chest strap with an ECG sensor (Polar H10 is considered the consumer gold standard) connected to an app like HRV4Training.
What to look at:
- RMSSD is the most commonly reported metric. It reflects high-frequency HRV driven by parasympathetic activity and is the most reliable indicator of recovery status and vagal tone.
- Don't compare your number to other people's. HRV varies enormously between individuals based on genetics, age, and cardiac anatomy. What matters is your personal baseline trend.
- Measure consistently. Take your reading at the same time every day (typically first thing in the morning, before getting up) for meaningful data. Single readings are noisy; trends over weeks are informative.
How to Know What Your HRV Is Telling You
Track your HRV daily for 3–4 weeks to establish your personal baseline. Once you have a baseline, interpret daily deviations:
HRV well above baseline: You're recovered. Adaptations from previous training are taking hold. This is a good day for high-intensity work.
HRV slightly below baseline: Normal day-to-day variation. Train as planned but monitor.
HRV significantly below baseline (more than 1–2 standard deviations): Your body is under stress. This could be from training, illness, alcohol, poor sleep, or high psychological stress. This is not a day to add further physiological stress. Prioritise sleep, light movement, and parasympathetic recovery activities.
How to Improve HRV
The interventions with the strongest evidence base for improving HRV in men over 40:
Aerobic exercise (zone 2 in particular). Consistent aerobic training is the single most effective intervention for improving resting HRV. Zone 2 training - sustainable, conversational-pace cardio - directly improves vagal tone. Aim for 150+ minutes per week.
Sleep duration and quality. Even a single night of poor sleep measurably reduces next-day HRV. Sleep quality is the most powerful overnight driver of HRV. Prioritise 7–9 hours, consistent sleep and wake times, and a cool, dark room.
Alcohol reduction. Alcohol is one of the most reliable suppressors of HRV. Even moderate consumption the night before causes measurable reductions in morning HRV. This effect is dose-dependent and cumulative.
Cold exposure. Brief cold water exposure (cold shower, cold immersion) activates the vagus nerve and acutely improves parasympathetic tone. Research on long-term HRV improvement from regular cold exposure is preliminary but promising.
Slow, controlled breathing. Resonance frequency breathing - typically 5–6 breath cycles per minute - directly stimulates vagal tone and produces acute HRV improvements. 10–20 minutes of this practice before bed improves both sleep HRV and resting HRV over time.
Omega-3 fatty acids. Meta-analyses of omega-3 supplementation consistently show modest but significant improvements in HRV markers. EPA and DHA at 2–4g daily are the doses used in most positive trials.
HRV is a window into your nervous system, not just your heart. Track your personal baseline for a month, then use deviations to guide training, sleep and stress decisions. Aerobic work, sleep, less alcohol and slow breathing move the dial more than any supplement.
Connecting HRV to Your Full Health Picture
HRV is one piece of the picture. To understand the full context - whether low HRV reflects high cortisol, low testosterone, chronic inflammation, thyroid dysfunction, or simply a heavy training load - you need blood data alongside wearable data.
A comprehensive blood panel from a service like Lola Health covers cortisol, testosterone, inflammatory markers (hsCRP), thyroid function, and nutrient status - the internal markers that most directly influence HRV. Pairing wearable HRV data with biannual blood testing gives you a genuinely complete picture of what's driving your recovery capacity and where the interventions will have the most impact.
HRV norms vary significantly between individuals. Track your personal baseline rather than comparing against population averages.
