Dumbbell Wrist Extension

Sit and rest your forearm on your thigh or a bench, wrist and hand hanging just past the edge, palm facing down. Hold a light dumbbell and let your wrist drop toward the floor under its weight, then curl your hand upward as far as it comfortably goes, squeezing the muscles on top of your forearm at the top. Keep your forearm pinned in place throughout, only your wrist should move. This is a small joint doing all the work, so a lighter weight than you would expect is usually the right call; strict form matters far more than load here.