The forearms are composed of several flexion and extension muscles. For a quick anatomy of forearms, go to www.wikipedia.org and look up "forearms".
Here are simple exercises for wrist flexion and extension.
Wrist flexion - use a barbell:
It is best to sit. Keep your body stable. Wrest your elbows on your thighs. Grasp bar with an underhand grip. Let the barbell to roll out of the palms down to the fingers. Grip the barbell back up and flex your wrists. Lower steadily and repeat. Do four sets of ten repetitions.
Reverse wrist curl - use a barbell:
Use the same arm and body position. Grasp bar with narrow to shoulder width overhand grip. Rest forearms on thighs with wrists just beyond knees. Hyperextend your wrist and return until wrist are fully flexed. Repeat for four sets of ten repetitions.
The information from this blog was obtained from http://www.exrx.net/WeightExercises/WristFlexors/BBWristCurl.html .
Disclaimer: The information on this blog is not intended to replace medical diagnosis, advice or treatment.