While general weightlifting and upper body training will work your forearms, some exercises focus on the forearms alone. Of course the "best" exercise depends on what you want to achieve -- whether flexibility, bulk or tone. Forearm exercises fall into two main types: flexor exercises and exercises that work the extensors. You use flexor muscles when curling your hand toward the inside of your wrist and extensor muscles when moving in the opposite direction.
Barbell Wrist Curls
One of the most straightforward, and most effective, forearm exercises is the barbell wrist curl. You can perform the exercise sitting down with your arms resting on your thighs and pointing straight out. Hold a barbell from the underside with your palms facing up and and let your hands drop down over the edge of your knees, about 4-inches apart. Keep your arms in position and curl the barbell up moving only your wrists. This works the flexor muscles.
Palm-Down Bench Wrist Curl
Doing the palm-down wrist curl while kneeling over a bench is the best way to develop the muscles on top and on the outside of your forearm. For this you need to position a barbell weight in front of a workout bench. Kneel behind the bench and lean into it with your midriff. Hold the barbell in an overhand grab with your palms facing down. Bring the barbell up and rest your forearms on the bench. Pull the bar up toward your chest using only your wrists. This works your extensor muscles. Exhale as you lift and breath in as you lower.
Dumbbell Wrist Curl
Using dumbbells allows you to focus on one arm at a time, spending longer on your weaker side. The wrist curl requires a solid bench. Sit with the bench between your legs and bend over so that your forearm rests on the bench with your hand just over the edge. Hold the dumbbell in that hand. Pull the dumbell up toward your elbow, but keep your arm still. To work your extensor forearm muscles bring your arm around 90 degrees to hold the dumbbell off the side of the bench with your palm faced down. This is the reverse wrist curl.
Forearm endurance is something that athletes such as rock climbers, swimmers or boxers need to develop. The website Indoorrockclimbing.com suggests that a hanging routine is one of the best forearm exercises to build endurance. You'll need a pull-up bar with enough height to hang with your legs off the ground. Start by hanging with both arms, then lower one arm and shake it out. Switch arms after five seconds. Do this for as long as you can before tiring.