A friend who always spots me pointed out then on my last few heavy reps, my back begins to jerk and come an inch or two off the pads. I've realized its better off to go lighter and follow super strict form. However, when I throw on 275 and jerk the back a little, my chest gets absolutely fried, amazing pump. So my two questions are, how much "cheating" am I doing with moving the back and how dangerous is it?