I don't think I'm doing HIIT but its some form of modified interval training. I warm up for 5 minutes by cycling pretty slowly and then I cycle as fast as I can for two minutes, followed by walking speed for a minute. All in all it ends up close to 30 min (5 min warm up, 20 min interval, 5 min cooldown). I am 20 yrs old and my heart rate during the two min interval is 155-160 (according to machine) and during the one minute rest it is 140-150. Is this safe to do daily, or should I only do it 2-3 times a week and do 40 min steady state cardio the rest of the week? Thanks for a response.