High intensity interval training raises your heart rate really high and I was wondering if this is safe. Is it okay for anybody to jump straight into HIIT like obese or people that haven't been training for long?
As I suspected, the common advice is to consult your doctor before doing HIIT:
I believe this is particularly true if you know you are not in good physical health or are at aa high risk for coronary disease. That said, you can get conditioned, as long as you do it a little at a time.
If you talk with your doctor, and they have concerns with the HIIT protocol ask for suggestions of how to work up to it--or what to look for when your body can't handle it any more. If you start light and progressively increase, it gives your cardiovascular system time to beef up and get ready for the real HIIT training.