squat

[SHMENT]

hi coach.
when i came to the squat rack and understand that it will be not available for the next 30 minutes (damn people) i decided to do squat on smith machine.
when i do that my lower back hurt.
is there a specific reason why my lower back hurt on smith machine and not when i squat with free weight?

[Mark Rippetoe]

Yes, there is. A Smith machine makes your back do what IT wants your back to do. An actual squat allows your back to do what it is supposed to do.