The first time I did lowmax I wasn't that excited about it. It didn't get my heartrate up as high as I had hoped. The second time I did it, I put the step up to the 8 inch height and gave it a little more my all and there was a big difference. The first time, my HRM gave me 255 (a low normal calories burned reading for a 1 hour step workout) The second time I got 334, which ranks it up above IMAXes for me. Being a little more familiar with the choreo I'm sure also factored into it.
By the way, I am real jealous of you folks getting these real high calorie count on their HRM! I have a very low resting heartrate so I guess that's why my calorie burned numbers are low. I have to have a real sweatfest like a terminator or the like to get above 400.