Muscle Group: Forearms 

Behind the Back Wrist Curls develop the flexor muscles of the forearm. This is the best power exercise for the forearm flexors, and you can go for the heaviest possible weight.

Back up to a barbell rack and grab a bar. Take it off the rack and hold it down at arm’s length behind you, hands shoulder width apart, palms facing behind you.

Keeping your arms stable, open your fingers and let the bar roll down out of your palms. Close your fingers, roll the bar back up into your hands, and then lift it up and back behind you as much as you can, flexing your forearms. Concentrate so that only the wrist moves in this exercise.