I ride it anywhere from 30 minutes to two hours. It all depends on what workout I have scheduled for that day. For base miles I just do 2/3's as much time on the trainer as I would do on the road. I figure that equals about the same since on the trainer I never get to coast.
To pass time I try to put in a good adventure movie. Something that takes my mind off of the time. Either that or I'll put in a copy of a bike race or something like that. For the 30 minute to one hour days I just watch a sit com or something.
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I may be fat but I'm slow enough to make up for it.