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Plate wrist curls done in this style will not be strict. Use a bench instead.
The plate wrist curl places a similar stress on the fingers, wrist, and thumb as the plate curl, but with the added benefit of providing dynamic resistance for the wrist. To perform this exercise, stand a plate up on its edge. Grasp the plate over the top, with the finger tips spread on the flat back of the plate (not in the hole) and the thumb hooked over the rim of the plate. Sit on a bench and rest the forearm on the thigh, with the palm facing up, plate parallel to the ground. Slowly relax the wrist, letting the hand drop to an inch or two below parallel, then flex the weight up until the plate is almost perpendicular to the ground. Lower the weight in a controlled fashion.
Progression for the plate wrist curl is achieved using clamps to affix additional weights to the plate, similar as to in the plate curl. The big difference here is that due to the dynamic motion of the wrist, weights that are manageable on the plate curl will prove to be quite a challenge on the plate wrist curl.