I find that the limiting factor in doing squats with a bar vs on a machine is that my shoulders begin to hurt when using the bar. Does anyone have any suggestions on how to deal with this? Perhaps I'm just being a pussy. On the bar it usually gets painful around 225 while on the machine I can do around 600 (machine has pads for the shoulders). Granted I understand there is a conversion factor between the two, but I doubt it is 3 to 1. Thanks.