The push-back push-up forces your shoulders to work hard to drive your body back using a natural arc and push angle.
Just drop down, explode straight back, and return to push-up position. To take it up a notch, put your feet up on a bench. Your abs will be begging for mercy too.
The Voyer Shrug is for anybody that has a slouched posture, shoulder problems, is preparing for an intense strength phase, or just wants to tap into some new growth.