MHR and Sprints...


Orange Belt
Aug 6, 2003
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OK, with all the talk of interval training lately I dicided to go out and do some sprints today. Now I would say I am in decent shape and do about 10-15 miles of road work (jogging) a week, but havent done much high intensity cardio of late. Anyway, I put on my polar heart rate monitor and proceeded to do tabata intervals of sprints. By the second interval my heart rate was at 93%. Is it dangerous or counterproductive to train in this range (even if only for 4 minutes)? I know that the standard thought is to stay within the 65-85% range, but with HIIT I have a hard time staying that low, I can stay 80-85% just jogging. Now this is according to a cheap HRM so I may have to take the data with a grain of salt.

And I dont want this to turn into an endurance vs interval thread.
you will not stay low with interval training. Period. 65% to 85% is fat burning zone, distance running dogma.
that would depend on whether or not you're a distance runner.
I've heard a few people (one, including my wife) mention that in order for a person to burn fat they need to be doing cardio for about 20 minutes. I called work, but is there any truth to this?
I've heard closer to 40 actually. but consider this, interval training (which can be done in under 20 minutes) will elevate your metabolism for hours, whereas it will return to normal shortly after a jog (most commonly prescribed for fat burning). So, you can jog for 40 minutes and burn fat while you do it, or run some intervals in as little as 4 minutes and burn fat while you watch some TV afterwards. Don't kid yourself though, you WILL work for it with interval training.
It's not dangerous, in fact it's the only way to condition your lactic acid energy system, and very beneficial. But, I would consider 93% to be near the low-end, with MAX (or near max) being the goal. Tabata was aiming for 170% of VO2 max (i.e. oxygen debt), so yeah they hurt. Also, even the low-end Polar monitors are very accurate, the high-end models just have more bells and whistles, that you probably don't even need.