I've recently added an aerobic routine to my exercise. It's treadmill, but alternating inclines.. My HR goes as high as 140 on the steeper portions. I've figured my maximum HR to be 153 based on the formula of 220 minus my age. I've read that a vigorous routine takes HR to 85% of maximum.. I'm at 91% using this number. Anyone else pay attention to HR when working out?