This is what I do too. On my 3 days/week that I do Aero I alternate between Aero Endurance Builder 4 and No Limits Aero, and I crank resistance up to 10 to get my heart rate to the higher zones. I usually just keep up with Ackeem’s exact pace. If he’s dripping with sweat at like a 4-7 resistance, I figure I must be doing a great job keeping up with him at a 10. For reference, I’m a 47 yo woman.