I get a pain in the back of the knee when doing leg curls. Should I do stiff-legged deadlifts instead, or would this only aggravate the injury that is building up?
I was taught not to let the leg straighten all the way (lock) on leg curls (or straight-leg deads). You don't want to hyperextend the knee. If you're doing that, it might explain your pain. If it's really bad or doesn't go away, of course see a doc.