The whole point of high intensity interval training is to push yourself so hard that your heart rate goes sky high instantly. Just try a few tabata rounds and see if you don't notice a faster pulse. "With tabata, you go at maximum effort for 20 seconds, rest for 10 seconds, and do eight cycles," says Iwaniuk. "The key is pushing yourself hard in those 20 seconds. If you're willing to put yourself through the ringer, your heart is going to be pumping a ton of blood through it and you'll stay in the zone of an elevated heart rate the whole time, even during the rests." A good goal: Try not to slack off as the rounds go on — if you did 18 air squats in round one, get 18 in round eight.
