The most that I can really stand on my cycle ops magnetic trainer is about an hour at a time. I do not really have a system or any power measurement. I just hold about the middle of my cassette (not sure how many teeth) and add in intervals where I click up a gear for 2-5 minutes at a time every 10-15 minutes or so. Not really scientific, but it deos at least maintain my fitness level. I use a box fan pointed directly at me on high, and I still leave 2 puddles on my mat in a chilly basement. The only good thing about the trainer is I get to watch DVDs and Netflix. I always prefer doing all of my rides outside. Even cold chilly rain soaked rides beat the trainer in my opinion. Actually going somewhere and changing your scenery has a lot to do with it.