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 posts
A Singular Workout
If you're a bodybuilder and you've spent your weightlifting life doing sets of 8,10, 12, etc., doing singles will absolutely blow you up. A terrific idea and a terrific program that'll raise you head and shoulders above the competition.
Tip: Build Your Back by Stretching Your Pecs
Do this drill before training your back. It'll fix those tight pecs which make it difficult to recruit your upper back muscles.
Violent Variations - Part 2
High Stimulation Training Methods for Enhanced Growth
Tip: The PPL Training Split
If your goal is hypertrophy, this is one of the smartest splits to follow. Here's why and how to set it up.