I work out 2 or 3 times a week by lifting a little and then hitting the bike for 30 to 40 minutes. The bikes I use have Heart Rate monitors which constantly update. I think the listing on the bike says 170 is the max for my age group, but it's usually above that. Often it nears 200 and once it went over. Sometimes when it gets high, it suddenly drops to just below 100... I don't understand much about this, but I'm starting to wonder if there's some sort of danger with it getting high?