Palms-Down Wrist Curl Over A Bench

Muscles worked

Filled = primary · Outlined = secondary

Source: Free Exercise DB (public domain)

Start out by placing a barbell on one side of a flat bench.
Kneel down on both of your knees so that your body is facing the flat bench.
Use your arms to grab the barbell with a pronated grip (palms down) and bring them up so that your forearms are resting against the flat bench. Your wrists should be hanging over the edge.
Start out by curling your wrist upwards and exhaling.
Slowly lower your wrists back down to the starting position while inhaling.
Your forearms should be stationary as your wrist is the only movement needed to perform this exercise.
Repeat for the recommended amount of repetitions.