I think the cross trainer is the machine that mimics skiing, so you supposedly get a good overall workout (since your arms and legs are all moving). Personally, I don't rate them particularly. I can't see how using one is any better than, for example, doing burpees (see: http://www.warriorforce.com/articles/burpeeclip.htm) or squat thrusts (see: http://www.trainforstrength.com/ex-12.shtml).