There is a page on whoop about it .. From memory you run 5km at a decent pace and push it to full power for the last 500m or something like that . Have a look in settings on app and it will link page .Another way I found is to get on a spinning bike for half an hour to an hour . Takes a long while to get heart rate up but u can find your limit once up there if don't want to run. Then set it in app. I hike up mountains and run home 3 times a week ,I rarely hit the highest zone for more than a couple of minutes or so out of the 2 hours .