Correct me if I'm wrong, but this looks like the answer to that mystery. Why would your beats per minute reliably equal itself divided by four plus a hundred? Just multiply the quarter minute pulse by four. If you're getting 140-150 by the method you described, then you would get 160-200 by doing it properly. I'm no health expert but I do know my algebra.

Another thing that's relevant here is that HIIT is definitely not safe for people who aren't experienced runners. I think that needs to be made more clear on this site. The HIIT program listed in the sticky for "beginners" is not for people who aren't used to running. It's specifically for experienced runners new to HIIT. I seriously injured my leg because I didn't know that.

What do you mean experienced runners? I'm not a track athlete and was new to HIIT and I've never had any problems with it. I'm routinely switching between different HIIT templates and I've made my own to push myself or draw back a little on certain days and I've never had any issues.

If you've never ran before or haven't ran in years then maybe you might want to get some regular pace cardio done before you start doing HIIT, but I think for most individuals HIIT shouldn't be a problem. Besides you don't necessarily have to follow a certain scheme, just the general pattern is the idea, don't push yourself to the point that you will injure yourself.

I feel the best time is based off of the study of Dr. Tabata. If you havent read the article/thread here it is.

In the study, the group of athletes did 6-8 intervals of 20 sec FULL OUT pedaling as well as 10 second resting. Similiar to what I did today, I prefer a FULL OUT sprint along with a 10 second medium jog. You realize that your done because by the 8th interval, you sprint as fast as you started jogging in the 1st one (roughly).

If you have ever had a heart disease (even though I have one, I still break my limits), it is not really recommended. If you have high cholesterol, ever been a serious smoker or have ever experienced a heart attack, see a doctor and ask about it. Also, if you are considered obese (25% for men and 30% for women), it is recommended that you do not participate in this until you drop your weight through regular cardio and weight lifting. See your doctor before participating in it, unless your like me and feel your in good enough condition to do HIIT.

As far as heart rate goes. I am 37 years old and get my heart rate up to 170-175 on the sprint portion. I'm not dead yet!
Seriously, if you are concerned about heart rate, get a decent heart rate monitor with the band around your chest (ala Polar). estimating your pulse accurately while sprinting/jogging is impossible.

Please listen to this man, he knows what he is talking about here.