What New Biomarkers Can Wearables Measure Accurately?

What Is a Biomarker?

A biomarker is a measurable biological indicator of health or disease. Traditionally, biomarkers like blood glucose, cholesterol, or VO₂max could only be measured in clinical settings using specialized equipment. Now, wearable devices are bringing many of these measurements into everyday life — continuously and non-invasively.

1. Heart Rate (Resting and Active)

One of the most reliable biomarkers wearables have measured for years is heart rate — both at rest and during activity. Using optical sensors like photoplethysmography (PPG), devices can track heart rate changes throughout the day and night with high accuracy, especially in rested conditions.

✔ Why it matters:
Resting heart rate is linked to cardiovascular health and stress levels.

2. Heart Rate Variability (HRV)

Heart rate variability — the variation between heartbeats — is another important biomarker wearables can track. Wearables like smart rings and some advanced smartwatches measure HRV to assess autonomic nervous system function, stress, and recovery status.

✔ Why it matters:
HRV can indicate how the body responds to stress, exercise load, and sleep quality.

3. Sleep Biomarkers

Modern wearables can estimate:

• Sleep duration

• Sleep stages (light, deep, REM)

• Sleep quality scores

These metrics come from a combination of heart rate, movement, and sometimes skin temperature. While not as precise as polysomnography (a lab sleep study), wearables provide practical, continuous sleep insight.

✔ Why it matters:
Poor sleep biomarkers can signal stress, health issues, or recovery needs.

4. VO₂max and Cardiorespiratory Fitness

VO₂max — the gold standard measure of aerobic fitness — used to require lab conditions like a treadmill and oxygen mask. Now, machine learning algorithms on wearables can estimate VO₂max accurately during everyday activity without specialized equipment.

✔ Why it matters:
VO₂max is a key predictor of endurance performance and cardiac health.

5. Respiratory Rate

Wearables can estimate breathing rate during rest and sleep by analyzing heart rate patterns and movement data. This respiratory biomarker is useful for detecting changes in fitness or respiratory stress.

✔ Why it matters:
Atypical respiratory rates can signal stress, illness, or sleep disturbance.

6. Skin Temperature and Body Temperature

Wearables that include temperature sensors can monitor changes in body and skin temperature. These changes can correlate with circadian rhythms, infection, menstrual cycles, or environmental responses.

✔ Why it matters:
Temperature shifts can be early indicators of illness or recovery needs.

7. Oxygen Saturation (SpO₂)

Many devices now include pulse oximetry sensors that estimate blood oxygen saturation. This metric is useful for tracking respiratory health, sleep apnea risk, and high-altitude adaptation.

✔ Why it matters:
Low SpO₂ can indicate breathing issues or reduced oxygen delivery to tissues.

8. Activity, Movement, and Gait Biomarkers

Wearables capture:

• Step count

• Movement intensity

• Gait patterns

• Activity duration

These act as digital biomarkers for metabolic health and cardiometabolic risk. Research shows daily movement patterns correlate with clinical biomarkers such as HDL cholesterol, triglycerides, BMI, and waist circumference.

✔ Why it matters:
Consistent physical activity is linked to better cardiovascular and metabolic health.

The Next Frontier: Emerging Wearable Biomarkers

Electrodermal & Electrophysiological Signals

Research is exploring biomarkers like:

• Electrodermal activity (EDA) — linked to emotional arousal and stress responses

• Electrooculography (EOG) — eye movement signals for anxiety and cognitive state detection

These signals expand wearables beyond physical health into emotional and neurological monitoring.

Limitations & Accuracy Considerations

While wearables are advancing rapidly, the accuracy of some biomarkers can vary depending on:

• Sensor quality

• Device placement

• Algorithms used

• Movement and environmental influences

Wearables are generally very good at trends and daily monitoring, but some metrics (especially derived ones like stress scores or sleep stages) still need clinical validation for diagnosis.

Conclusion: Wearables Are Expanding What Can Be Measured Outside the Lab

Wearables have moved well beyond basic fitness tracking. Today, they offer continuous, non-invasive insights into a wide range of biomarkers, including heart rate, HRV, VO₂max, respiratory rate, SpO₂, temperature, sleep metrics, and movement patterns. Emerging research also points toward even more advanced biomarkers — like stress-related signals — being measurable outside clinical settings.

As sensor technology and AI algorithms continue to improve, wearables will become even more accurate and useful in both personal health and clinical research contexts.

Sources

1. Wearable biosensors and digital biomarkers for health monitoring
   https://www.mdpi.com/1424-8220/21/6/2130

2. Making sense of wearable data: accuracy, strengths, and limitations (Gatorade Sports Science Institute)
   https://www.gssiweb.org/en/sports-science-exchange/Article/making-sense-of-wearables-data

3. Fitness levels can be accurately predicted using wearable devices (VO₂max estimation) – University of Cambridge
   https://www.cam.ac.uk/research/news/fitness-levels-can-be-accurately-predicted-using-wearable-devices-no-exercise-required

4. Association of activity tracker metrics with cardiometabolic health biomarkers
   https://pubmed.ncbi.nlm.nih.gov/32012098/

5. Systematic review: Validity and reliability of wearable health devices
   https://link.springer.com/article/10.1007/s40279-024-02077-2

6. Emerging physiological and stress biomarkers from wearable sensors
   https://arxiv.org/abs/2411.17935

7. How accurate are wearables for health and fitness tracking?
   https://www.the-well.com/editorial/how-accurate-are-wearables