I feel like the arc trainer works more muscle groups. Maybe that's just psychological, but that's just how it feels to me. Also, I burn more calories (unless the machine is wrong, which is very possible). Anyway, I do have a problem w/ my right knee, but never felt any issues w/ the arc trainer.
First goal: under 180:
Second goal: 175 or below:
Third goal: 168 (no longer overweight):
Fourth goal: 161 (what I weighed before I fell off):
Fifth goal: below 160:
Final goal: 145-155: