To develop that big flexor/pronator belly, you need to use wrist flexion. Really heavy wrist curls bother a lot of my lifters' wrists, so we usually go for sets of 8-plus and seek a pump rather than maximal strength.

Wrist rollers are better suited for heavy wrist flexion, and this version is especially challenging since the resistance increases as you roll.

Related:  Big Forearms, Crushing Grip

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