I was a phys ed major about 1 million years ago. One of the interesting things we learned is the researchers who did the infamous heart rate charts basically guessed at the maximum rates for training.


Superbly trained athletes will train in the high 190's but their recovery is the thing that sets them apart from us "mortals." I can push my heart rate up there but as I am getting oler my recovery is taking slightly longer. I used to be able to get up to 180 and down to 100 within 1 minute. Now I get up to 180 and 1 minute recovery is 112.

For some other bit of information. No such place as fat burning mode. If you train at "sprint" conditions for 20 minutes you will burn x calories. Now if you train at a lower, more comfortable rate without pushing for 40 minutes you will probably burn the same amount of calories you burned in 20 minutes at high level. I would much prefer to do the 20 minutes cardio at high levels myself.