Try this for fun:
Stand about three feet away from a wall and assume the position of Attention.
Put your hands on the wall and lean foward until your forehead touches the wall.
Return your hands to your sides and stand (lean) rigidly at Attention with your neck held straight and your forehead holding your weight against the wall.
If you don’t get it right the first time the DI yelling in your ear will offer helpful suggestions while commenting about your manhood and parentage. Don’t be concerned - he only looks like his arteries are ready to explode with rage at your very presence - he’s really going to be fine once you are out of his life.
Do not slouch or allow your neck or back to bend unless you want the DI to take violent corrective action.
Continue until your muscles give out and you slide slowly into and down the wall, ending as a quivering puddle of nerve and muscle.
Force yourself back up, assume the position of Attention, and do it all over again. If you have trouble rising the DI will give you a boost with a few well placed kicks.
After several hours of this you will be determined not to falter or fail in carrying out the DI’s slightest wish.
How about the barbell squat in the SDI’s office...
They had a barbell, (two huge coffee cans cemented to a bar), you'd have to bend over at the waist and pick it up, with your back against the wall, slide down the wall into the squat position while holding the barbell straight out
(about fifty pounds) and maintain that position until he says UP! You repeat on command, and don't dare lower the barbell.