thank you for your fast reply!
I have already found the function and the object and I have already added hrmAvg and hrmMax to my fork of the add-on, but I would like to add the actual heart rate value too (the actual heart beatings) this is what I have referred to in my first post.
I have found neither UpdateContainer nor TrackStats contains this value this is why I think I should extend they with this value. But the question is how can I obtain the actual heart rate value. Is it supported by Locus API?