@Rob84 Right now the workout player in SYSTM doesn’t capture HRM for the yoga and strength videos - just the cycling and running videos. As a workaround many people dual record - record the workout in SYSTM and also record on a fitness watch or an app such as Strava.
As an example, I have a Suunto watch and pair the HRM with the watch and then record the workout at the same time that the SYSTM workout is running. I then consolidate the records in Training Peaks. I upload the SYSTM workout (either strength or yoga) and then upload the HR data from my Suunto watch.
Hope that helps!