I posted this on the ladies who lift forum but I thought you girls and guys might be able to give me an answer as well!

I went to the local gym today and they did not have an elliptical trainer so I got on the arc trainer. It seems to work you a lot more on the legs. I guess it is because there is no hand motion? Also the movement of the legs seemed different and I was wondering if it actually works different muscles on the legs because of the way you move.

I could only do about ten minute sessions on the arc so I switched from the recumbant bike for 10 minutes to the arc for ten minutes. I did this twice. I was sweating like crazy when I was done.

I also have to be really conscienous of standing up straight on the arc even more than the elliptical.

I cannot give you any specific answer, but I would assume that there would be at least a subtle difference - and sometimes those subtle differences can feel really big!.

My gym recently up-graded about 80% of their weight machines. I very quickly found out that although the major group muscles for each machine were being used in basically the same way, there were all of these little muscles near them that weren't being used so much in the old machines but were in the new (or maybe were being used in a slightly different way). While using the machines, all I could tell was that the exercises "felt different" it wasn't until later that night that I came to realize the full brunt of that difference. OUCH!

I'd suggest approaching the machine like it is completely new to you, pull back on the intensity a bit and work your way back up. Those little muscles in your legs will thank you.

I can't be specific either, but agree with andoreth that a slight change in muscle use can produce big results. Just going backwards on the eliptical works the muscles in a completely different way than forwards.

I use a cardio wave at my gym, which is a bit like an eliptical, but you don't use your arms and your legs go side ways, imagine speed skating. On this machine my heart rate used to sky rocket, and I would be a puddle of sweat after 5 minutes (I had been exercising for a year when I first got on it) It's the same set of muscles, just another cardio exercise, but amazing how much work it took to get proficient at it.