Originally Posted by Rajah
Curls are probably the one area that you can cheat with good benefits. It's no good doing a heavy bench and using your back and shoulders to lift the weight. You see people arching their backs and their legs flopping all over the place. That has no benefit at all.
As long as your glutes and head are touching the bench, arching your back is actually proper powerlifting form.
It all depends on what your goals are. But I tend not to cheat, I even retract my shoulder blades when I bench to deactivate the shoulder fibers even more. I bench to get my chest larger, so I don't bother cheating unless its something minor like a baby bounce on my last rep.
I am more in to the aesthetics of lifting than anything. But I am not a bodybuilder, or a powerlifter, I am a weight lifter.