I think for most people your maximum heart rate is your maximum heart rate.  That is,  there is a certain rate you can reach and there is not any problem with that.<p>If there is a question about your heart you go to the cardiologist and get a stress test where you have an ECG attached and maybe also they look at your heart with ultrasound and if your are healthy nothing untoward happens.<p>If you are not healthy there is a risk of arrhythmia and other things that can go wrong.  The risk of this is certainly higher if you are older,  but young people,  even teens,  sometimes have sudden cardiac death under stress.<p>Anyway,  I have seen the old electrical types of heart rate monitors do something like this,  where the heart rate seems to bounce back and forth between the true rate and 1&#x2F;2 the true rate and probably there are situations where the monitor picks up every other beat for some reason.