I'm sorry, maybe I don't know much about powerlifting, but are you saying that in powerlifting you are supposed to arch your back the way you do in that video?
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P.S. Hedgy, chip in on this one, for as I thought that his form, with the back arched as high as he does, would seriously cause him to hurt his back or potentially snap some of his vertebrae..
P.S.S. Doesn't the arching of your back cause you to further reduce any true distance during the lift, thereby not allowing you to assess what your true strength is?
Powerlifting is about lifting the biggest amount of weight within the rules allowed.
Some are of the opinion that using a slight incline is better than a flat bench when training to build mass or strength.
But if you compete in powerlifting, or any sport for that matter, sport-specific training, ie excersises that resembles the actual sport you compete in, are generally considered to be most effective.
Eg, a lot of soccer conditioning drills can be done with a ball, this will make the conditioning drills more game-like, and aid in training balance and agility towards the SPECIFIC SPORT.
A bit of a long post, eh?
-Hedge
edit: Some of the greatest benchpressers of all time, James Henderson comes to mind, as well as the man himself, Kazmaier, and Ted Arcidi, and other greats, used little or no arch.
But still, not tweaking your technique so you're able to get the most out of the current rules, isn't gonna get you bonus pounds.