switching from treadmill to the cybex 750A arc trainer ......less stress on the joints and legs and you can get up serious cardio bpm.... been looking at the machines for six months and decided to try it yesterday for 30 mins. did 60 mins. tonite on my rest day and my shirt was soaking wet.....
a lil research to check out
Arc Trainer - The Science Behind the Performance
Both my gyms have this but I've never bothered with it. I stick to the normal elliptical and the treadmill.