I've been riding since june. Nothing real hard. Maybe 15 miles per day about 4 days a week. Didn't have any real problems, some minor outside knee pain which went away with some tweaking of the saddle height. I put the bike on the trainer, mother nature letting us know winter is coming, rode twice, each about 30 minutes and have seemed to have pulled the right hamstring. Is there something different about trainer riding that would cause this to happen? Sadlle height is based on the heel on the peddle method with the pedal at 6 o'clock.