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.
Thick, strong forearms not only complete the physique, they help you move more weight and perform better. Here's everything you need to know about grip training.