I am not doing the challenge, but I rode my trainer for maybe the 3d time this year (I have been going to spin classes 1-2X a week). I did half the Chris Carmichael workout that someone posted here, 35 minutes of fast spinning and endurance intervals. I did one set instead of 2 of the endurance intervals, as there is no way I can be on the trainer for an hour unless DH is there to talk to me.