Understanding Smartwatch Health Metrics: SpO2, HRV, and Stress Scores

Your COLMI smartwatch or smart ring tracks SpO2, HRV, and stress scores every day — but unless you know what these metrics actually mean, the numbers are just noise. This guide gives you a complete, jargon-free explanation of each metric: what it measures, why it matters, what a healthy range looks like, and how to use the data your wearable provides to make meaningful improvements to your health.

SpO2: Blood Oxygen Saturation

What It Measures

SpO2 stands for peripheral oxygen saturation — the percentage of your haemoglobin molecules that are carrying oxygen. Your red blood cells use haemoglobin to transport oxygen from your lungs to every tissue in your body. SpO2 tells you how effectively this process is working at any given moment.

A reading of 98% means 98% of your haemoglobin is saturated with oxygen. A reading of 92% means 8% of your haemoglobin is delivering less oxygen than it could. Small percentages have significant physiological consequences — the relationship between SpO2 and oxygen delivery is not linear.

How Your COLMI Device Measures It

COLMI smartwatches and smart rings use photoplethysmography (PPG) with dual-wavelength light (red and infrared) to estimate SpO2. Oxygenated haemoglobin and deoxygenated haemoglobin absorb these wavelengths differently, and the ratio of absorption is used to calculate saturation. The sensor is on the back of the watch (against your wrist) or on the inner surface of the ring (against your finger).

Normal Ranges and What They Mean

• 97–100%: Normal and healthy. No action needed.
• 95–96%: Slightly below average but generally acceptable. Worth monitoring if persistent.
• 92–94%: Below normal. Consult your GP if readings consistently fall here, especially if accompanied by breathlessness or fatigue.
• Below 92%: Concerning — seek medical advice promptly if you see this consistently, particularly during rest.

When SpO2 Naturally Drops

Brief SpO2 dips are normal during intense exercise, at altitude, or during certain sleep stages. A reading of 94–96% immediately after peak exertion is not concerning. What matters is your baseline during rest and the patterns you see in the Da Fit app's historical data.

Persistent nocturnal SpO2 dips (below 90% repeatedly during sleep) can indicate sleep-disordered breathing worth discussing with your GP.

Tips for Accurate SpO2 Readings

• Remain completely still during the 30-second measurement
• Measure at rest, not immediately after exercise
• Warm your hands first — cold fingers reduce peripheral blood flow and degrade sensor accuracy
• Ensure your ring or watch is correctly fitted and sensors are in good contact with skin

HRV: Heart Rate Variability

What It Measures

Heart rate variability is a measure of the variation in time intervals between consecutive heartbeats. Despite what the name might suggest, a healthy heart does not beat with perfect clockwork regularity — the time between beats naturally varies from one beat to the next. This variability is controlled by the autonomic nervous system (ANS), which has two branches:

• Parasympathetic (rest and digest): Promotes recovery, relaxation, and restoration. Associated with high HRV.
• Sympathetic (fight or flight): Activates in response to stress, exercise, illness, and perceived threat. Associated with low HRV.

High HRV indicates that your parasympathetic system is dominant — your body is recovered, relaxed, and resilient. Low HRV indicates sympathetic dominance — your body is under stress, still recovering from exertion, fighting illness, or sleep-deprived.

How Your COLMI Device Uses HRV

COLMI devices measure HRV-derived data to generate the stress score you see in the Da Fit app. Rather than displaying raw HRV numbers (which require context to interpret), the app translates HRV into a stress score on a simple scale. Low stress score = high HRV = good recovery. High stress score = low HRV = physiological or psychological stress.

HRV is also used to derive the sleep quality components related to recovery and restoration visible in your sleep reports.

What Is a Healthy HRV?

HRV is highly individual — population norms vary enormously with age, fitness level, sex, and genetics. A young fit athlete might have resting HRV values of 60–80ms (RMSSD, a common HRV metric), while a healthy sedentary 60-year-old might average 20–30ms. Both can be entirely normal for their individual profiles.

This is why your personal baseline matters far more than any external benchmark. After 2–4 weeks of consistent wearing, your Da Fit app establishes your typical HRV range. Deviations from your personal baseline are the meaningful signals:

• Morning HRV higher than your baseline: You're well recovered. This is a good day for a hard workout or demanding cognitive work.
• Morning HRV lower than your baseline: Your body is under stress. Consider a lighter training day, prioritise sleep, and watch for developing illness.

What Affects HRV?

• Exercise: Acute exercise lowers HRV temporarily; chronic aerobic fitness raises long-term baseline HRV
• Sleep quality and quantity: Poor sleep dramatically reduces HRV
• Alcohol: Even moderate alcohol significantly reduces overnight HRV and suppresses recovery
• Stress: Psychological stress activates the sympathetic system and reduces HRV
• Illness: Immune activation lowers HRV, often before symptoms appear
• Breathing: Deep, slow breathing (especially 6 breaths per minute, or 0.1Hz) maximally increases HRV by activating baroreflex sensitivity

Stress Score: Turning HRV Into Actionable Insight

What It Measures

The stress score displayed on your COLMI device and in the Da Fit app is an algorithm-derived number based primarily on HRV analysis, combined with heart rate context. It translates complex physiological data into a simple, actionable scale — typically 0–100, with low numbers indicating low stress (high HRV, parasympathetic dominance) and high numbers indicating high stress (low HRV, sympathetic dominance).

Interpreting Your Stress Score

• 0–24: Relaxed state. Your body is in good recovery mode.
• 25–49: Normal, mild stress. Typical for most of the working day.
• 50–74: Elevated stress. Consider taking a break, practising breathing, or identifying the stressor.
• 75+: High stress. Your body's sympathetic system is heavily activated. Prioritise rest, recovery, and stress management.

Note that the stress score cannot distinguish between physical stress (hard workout), psychological stress (difficult meeting), and physiological stress (fighting a cold) — all produce similar HRV patterns. Context matters when interpreting the number.

Using Breathing Exercises to Lower Stress Scores

One of the most evidence-based interventions for quickly improving HRV and reducing stress scores is controlled slow breathing. Breathing at approximately 6 breaths per minute (5 seconds in, 5 seconds out) maximally activates the baroreflex and rapidly shifts the autonomic nervous system toward parasympathetic dominance.

Your COLMI smartwatch includes guided breathing exercises accessible directly from the device. Most breathing sessions last 1–5 minutes and produce measurable reductions in heart rate and stress score within a single session. Using this tool when you see an elevated stress score is one of the most immediately effective stress management interventions available.

Using SpO2, HRV, and Stress Together

The most powerful approach to health monitoring with your COLMI device is to use these metrics together rather than in isolation:

• Consistently low SpO2 + consistently high stress score overnight may indicate sleep-disordered breathing
• High stress score + elevated resting heart rate + good sleep score suggests psychological or work stress rather than illness
• High stress score + elevated resting heart rate + poor sleep score + recent hard workout = classic overtraining signature; prioritise recovery
• Elevated resting heart rate + lower than usual HRV + normal stress score (no obvious reason) = early illness indicator; watch for symptoms

These combinations give you a holistic picture that no single metric can provide. Review all three alongside your sleep data weekly to build genuine health intelligence from your wearable.