I'm a fan and user of elliptical trainer. I had to use it because of my knee. had a sports accident and my sports doctor told me to use it instead of the treadmill (but that's besides the point)..... i used to run and sprint alot, now i rarely do , anyhoo, i'd do 1 to 2hrs straight on high. i'm thin and lean as is and got thinner when using it! so now, i had to tone it down to 1 hr. straight on 50 to 60 --quick button and eat McDonalds Whopper or Big Mac meals or something to put weight on afterwards on the advice of my doc. lol because if i dont i'd look anorexic. B)