As you know, we calculate the stress level based on HRV data. For determining stress, we use not some proprietary algorithms, but the Baevsky Stress Index (BSI), which was developed several decades ago and is applied in space medicine.
Professor R.M. Baevsky was a pioneer in space medicine and heart rate variability (HRV) analysis. In the 1960s, he led the development of telemedicine systems for monitoring astronauts’ health and was the first to conduct long-term ECG (Holter) recordings in space aboard the “Salyut” and “Mir” stations.
Baevsky introduced a scientific approach to assessing stress by analyzing heart rhythm patterns under physical and psychological load. His method, now known as the Baevsky Stress Index, helps evaluate how the body’s regulatory systems respond to stress. It has been used for real-time health monitoring in both space and clinical settings.
Baevsky also developed early systems for public health screening and introduced the concept of pre-nosological diagnosis—a way to detect early signs of imbalance before disease occurs. His work remains a foundation in stress physiology and HRV-based health assessment.
There were no issues with the actual calculation of the index, and we have always provided and continue to provide the correct absolute value.
However, after analyzing numerous measurements, we concluded that our norms for interpreting this value were very strict. After processing hundreds of thousands of measurements, we decided to change the norms and the calculation of the percentage value.
As with the index itself, we decided not to reinvent the wheel but to use existing standards and align our norms with the Kubios app.
Kubios is a truly excellent (and probably one of the best) applications used by professional athletes worldwide. Although Kubios displays the square root of the Baevsky Stress Index for stress levels, we continue to show the original value.
So now, if you train professionally and use Kubios, Wellhero’s norms will match it.
Here are our current BSI norms:
0 – 30: Rest
30 – 50: Low Stress
50 – 150: Normal Stress
150 – 500: Elevated Stress
500 – 900: High Stress
900+: Very High Stress
Additionally, we have updated all past calculations and norms for previous records. All past posts in the news feed will show a slightly lower stress level percentage than before, while the original value will remain unchanged.