There are many great reasons to choose ithlete, so many that we’ve written a blog series looking at why we do things the way we do. Follow the series to learn more about the type and length of measurement, how breathing influences your HRV and much more.

When designing ithlete in 2009, we homed in on a particular HRV measure known as RMSSD. It had the qualities we were looking for and can produce a valid HRV measure in just one minute.

The raw RMSSD HRV numbers are not very friendly though – either to individual users or to the maths we would like to do to create a baseline and identify significant changes.

For example, a healthy adult would have an average RMSSD of 35ms, an older or less healthy person an RMSSD of 20ms, but a triathlete could have an RMSSD of 130ms. The distribution of raw RMSSD is skewed, i.e. the differences on the up side are much greater than the differences on the down side. To correct for this, we take the natural log of the raw number. That gives us a more even or ‘normal’ distribution. The only problem now is that the numbers, e.g. 3.5, 3.0, 4.9 from the previous examples are still not very user friendly, so we chose to multiply by 20, which gives us a couple of nice benefits:

  1. Crossfit HRVAn approximately 100-point scale.

Higher numbers are better and have an immediate impact on the user. Even without knowing exactly what it means users are pleased with anything above 70 (healthy HRV), and they see room for improvement below 60 (less healthy). Numbers above 80 indicate high levels of health and fitness whereas those below 50 are a cause for health concern.

  1. No need for a decimal point.

The difference of one point on the scale is 5%, which corresponds to the smallest worthwhile change for the LnRMSSD measure. Again this makes the value more user friendly.

The ithlete number scale* has been used in other HRV apps, such as Bioforce, ReVita5, Metafit, PUSH Vital Signs.


*Note: lnRMSSDx20 is a patented formula and therefore those interested in using this commercially must acquire a licence from HRV Fit Ltd.