HRV, Resting Heart Rate, and What Your Wearable Is Actually Telling You About Your Hormones

Millions of Canadians wear devices that record heart rate variability (HRV), resting heart rate, and sleep staging every night. The data accumulates. Trends emerge. The numbers go up and down, and the apps provide colour-coded assessments of readiness and recovery.

Most users know that higher HRV and lower resting heart rate are generally better. Fewer know what these metrics actually reflect physiologically or how they connect to the hormonal and metabolic changes that occur in midlife.

Your wearable is collecting meaningful biological data. Understanding what it means changes how you use it.

What HRV Actually Measures

Heart rate variability is the variation in time between successive heartbeats. A heart that beats at exactly 60 beats per minute does not produce one beat every 1.000 seconds. The intervals vary: 0.95 seconds, then 1.05, then 0.98, then 1.03. This variability is normal and desirable.

HRV reflects the balance between the two branches of the autonomic nervous system. The sympathetic branch (fight or flight) accelerates the heart and reduces variability. The parasympathetic branch (rest and digest), mediated primarily through the vagus nerve, decelerates the heart and increases variability.

Higher HRV indicates greater parasympathetic tone: a nervous system with more capacity to recover, adapt, and respond to stress. Lower HRV indicates sympathetic dominance: a system that is already stressed, recovering, or depleted. But HRV is more than a snapshot of the nervous system. It is a proxy for the living force—the Vis Viva—of the organism. A person with high HRV has physiological resilience. The cardiovascular system is not just pumping adequately; it is adapting dynamically to moment-to-moment demands. This adaptive capacity is present in young, healthy individuals and diminishes predictably with age and chronic disease. When HRV rises, it signals that the body’s foundational capacity for adaptation is improving.

What Resting Heart Rate Reflects

Resting heart rate (RHR) measured overnight or upon waking reflects cardiovascular efficiency and autonomic tone. A lower RHR generally indicates a stronger, more efficient heart that pumps more blood per beat (higher stroke volume) and a well-regulated autonomic system. This relationship between cardiac efficiency and mortality risk is profound: cardiovascular fitness, as measured by maximal aerobic capacity (VO2 max), shows one of the strongest dose-response relationships to all-cause mortality. While resting heart rate is not a direct measure of VO2 max, it reflects the same underlying trait—how efficiently the cardiovascular system works at rest, which is a reflection of aerobic fitness.

RHR trends over weeks and months are more informative than single readings. A gradual rise in RHR may indicate overtraining, inadequate recovery, chronic stress, illness onset, or hormonal changes. A gradual decline typically reflects improving fitness, better recovery, and favourable adaptation. A persistent elevation in RHR of 3 to 5 beats above your baseline, maintained over weeks, warrants investigation. It signals that the cardiovascular system is working harder at rest—whether from poor recovery, metabolic dysregulation, or hormonal imbalance—and precedes many symptoms that patients only later recognize.

The Hormonal Connections

Testosterone

Men with optimized testosterone levels tend to show higher HRV and lower RHR compared to their hypogonadal baseline. Testosterone supports cardiac efficiency (stroke volume), reduces systemic inflammation, and improves body composition, all of which are reflected in autonomic metrics.

A man who starts testosterone therapy and tracks his wearable data over months will often observe a gradual improvement in HRV trends and a decline in resting heart rate as the therapy takes effect. This is not a coincidence. It is the cardiovascular system responding to a more favourable hormonal environment.

Conversely, declining testosterone in untreated men is associated with increasing RHR and declining HRV over time, often attributed to aging when it is at least partly hormonal.

Estrogen and Progesterone

Estrogen supports parasympathetic tone and vascular compliance. Women with adequate estrogen levels tend to have higher HRV than estrogen-depleted women. The decline in HRV observed through perimenopause and menopause correlates with estrogen decline and is partially reversible with estrogen replacement.

Progesterone influences HRV through its effects on the autonomic nervous system and sleep. Women often notice that their HRV is lower during the luteal phase (when progesterone is elevated) and higher during the follicular phase. This is a normal physiological pattern. However, the absence of any luteal HRV variation in a premenopausal woman may indicate anovulation and progesterone deficiency.

Menstrual cycle-linked HRV patterns are increasingly recognized as a potential biomarker for ovulatory status, though this application is still emerging.

Thyroid

Hypothyroidism reduces HRV and can paradoxically either increase or decrease resting heart rate depending on the severity and the compensatory response. Subclinical hypothyroidism is often associated with reduced HRV before TSH moves out of the standard reference range, making HRV a potential early signal.

Hyperthyroidism increases resting heart rate and reduces HRV through sympathetic activation. A sudden and sustained rise in RHR with declining HRV in the absence of other explanations warrants thyroid assessment.

Cortisol and Stress

Chronic stress, whether psychological, physiological, or both, suppresses HRV by maintaining sympathetic dominance. A person with elevated cortisol will show persistently low HRV and elevated RHR, particularly during sleep, when parasympathetic recovery should be at its peak.

If your wearable shows consistently low overnight HRV despite adequate sleep duration, the problem may not be sleep itself but the cortisol environment in which sleep is occurring.

What to Do with the Data

Establish Your Baseline

HRV is highly individual. A healthy 45-year-old might have a baseline HRV of 30 ms (measured as RMSSD), while another healthy 45-year-old might baseline at 55 ms. The absolute number matters less than the trend over time and the consistency within your own range.

Track your morning HRV and RHR daily for at least 30 days to establish your personal baseline. Most wearable apps provide 7-day and 30-day rolling averages that smooth out daily noise.

Watch for Persistent Shifts

A sustained decline in HRV over weeks (not just a bad night or two) is meaningful. It may indicate overtraining, inadequate recovery, worsening sleep, escalating stress, or hormonal changes that warrant investigation.

Similarly, a sustained rise in RHR of 3 to 5 beats above your established baseline is a signal worth investigating. If it coincides with other symptoms (fatigue, mood changes, weight gain), hormonal and metabolic assessment is warranted.

Correlate with Blood Work

Wearable data becomes most powerful when correlated with laboratory findings. A declining HRV trend in a man who also has low free testosterone and elevated fasting insulin tells a coherent story. The wearable provides the longitudinal signal; the blood work identifies the mechanism.

At Manus Solis, wearable data is part of the Virtus domain. HRV, resting heart rate, and sleep staging are reviewed alongside VO2 max, grip strength, and body composition. When these metrics are correlated with Pulsus (blood work) and Sensus (symptom assessment), the clinical picture has three independent dimensions of confirmation.

Do Not Over-React to Daily Variation

Single-day HRV readings are noisy. Alcohol the night before, a late meal, a stressful email before bed, or mild dehydration can suppress HRV for a night without reflecting any meaningful change in health status.

Respond to trends, not datapoints. A 7-day rolling average that has been declining for three consecutive weeks is worth investigating. A single morning with a low HRV number is worth noting and nothing more.

The Wearable as a Partner

Your wearable is not a diagnostic tool. It does not replace blood work, clinical assessment, or physician interpretation. But it provides something blood work cannot: continuous, longitudinal data collected over months and years.

Used well, wearable data becomes an early warning system that prompts investigation before symptoms become severe. It transforms a once-a-year snapshot into a real-time signal. And when combined with comprehensive hormonal and metabolic assessment, it adds a dimension of understanding that makes treatment more precise and outcomes more visible.

Continue Reading

If you found this useful, these related articles may deepen your understanding:

• VO2 Max: The Single Best Predictor of Longevity
• Data-Driven Medicine: Why We Measure Everything
• Can’t Sleep? The Hormonal Explanation

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Dr. Handsun Xiao is a McGill trained physician (MD, CCFP) practicing functional medicine and bioidentical hormone therapy in Toronto, with virtual consultations available to patients across Ontario. He holds advanced BHRT certification through WorldLink Medical and IFM AFMCP training. Manus Solis offers physician led BHRT consultations with custom compounding through a dedicated Ontario pharmacy partner. To learn more or book a virtual consultation, visit manussolis.ca.