Improved VO2max model for hilly runs

Blog post by Marco Altini

We have just released a new version of HRV4Training for iPhone and Android, which deploys our latest VO2max model. 

In particular, this model better accounts for hilly terrain and provides more accurate VO2max estimates for runners that train on hills.

Normally, the relationship between running speed and heart rate is used to estimate VO2max, as we cover in more detail here. 
Intuitively, a lower heart rate at the same speed, means that you are getting fitter. However, this relationship falls apart when we run on trails, or include much elevation gain in our runs. Below is an example of my own data, where you can see a few things:

• until the end of 2017, I lived in a hilly city (San Francisco). Then, I moved to a flat one (Amsterdam)
• the only real change in VO2max was in 2016-17, when I started with polarized training (details here)

In the last part of the graph you can see how my interest shifted toward trail and ultrarunning (very few flat runs). As a result, VO2max estimates show a large decrease. In fact, little change is present in speed over heart rate when looking only at these flat runs (yellow line).

This makes it hard to track progress in aerobic efficiency or VO2max (or whatever you want to call how your heart rate changes at a given speed). 

With the newly released model, we are able to better account for these changes, and provide a more accurate estimate. 

To build this, we modeled the difference in estimated VO2max for the same person when running flat vs hilly, in relation to the average grade of the runs (N = 10 000).

There are of course still limitations, for example no knowledge of how technical is the terrain, but it should be an improvement.

Below are results showing the original estimate (which was a match with testing in the lab), then the poor performance of the model on hilly runs, and the updated results today, for me (right) and Alessandra (left).

​We both had an accurate estimate when living in The Netherlands, then got a reduction in VO2max simply because of the different efficiency (relationship between pace and heart rate) when running on hills in Italy, and then finally you can see the prediction of the new model, which is close to the original one.

​Enjoy!