21′s consist of 3 parts:
Set Up: Begin with Dumbbells by your side
Part 1: Curl Dumbbells halfway up until your forearms are parallel with the ground. Lower to starting position. Repeat 7 times.
Part 2: Curl the Dumbbells to the top, but lower only halfway, to the midpoint where forearms are parallel to the ground. Repeat 7 times.