Pulling your chin over the bar requires assistance from your forearms.
When you work out, you may not think much about your forearm, but this area between your elbow and wrist contains dozens of muscles essential to daily activity. Working your forearm strengthens your elbow joint and improves the strength of your grip. Pulling exercises such as pullups do work muscles in the forearm, but pushing exercises such as pushups do not.
The forearm is made up of more than 20 small muscles. These include muscles that extend and flex your fingers and elbow as well as help you make a fist. You use these muscles when doing things like opening a jar, typing on the computer or folding laundry. Other forearm muscles enable you to turn your palm face up and down. Sports such as tennis and golf, as well as any that involve throwing a ball, benefit from strong forearms.
Pullups Work Your Forearms
During pullups, the forearm muscles that extend the elbow, the brachialis and brachioradialis, assist the latissimus dorsi, the broad back muscle that is the primary mover during the exercise. These muscles assist the elbow joint as it bends when you pull up. The extensors and flexors of your fingers work to help you grip the bar.
Pushups, Not So Much
Classic pushups use the forearms for stabilization, but don't actively train them. The pushup emphasizes the pectoralis major of the chest, the triceps at the back of the upper arm and the anterior deltoid at the front of the shoulders. The abdominal muscles, biceps and erector spinae stabilize during the exercise.
You can alter pushups slightly to make them emphasize the forearms more. Do pushups with your hands on a balancing device, such as a half ball or a full stability ball. Use your fists for wrists, meaning you form fists with your hands and place those on the mat as you push your body weight up and down. This substitution trains the forearms more significantly than when you do pushups with your palms flat. It also neutralizes the wrist joint, potentially alleviating pain in this sensitive area. Pushups done on your fingertips, with the palm of the hand lifted out of the floor, or plyometric pushups in which you "jump" your hands up as you rise, also work the forearms.
If your goal is to build forearm strength, opt for exercises designed to target these muscles. For example, biceps curls done with the palms facing down, called reverse curls, or hammer curls with the palms facing each other target the brachioradialis. If you seek greater strength in the wrist extensors and flexors, try overhand and underhand wrist curls. To work the muscles that enable you to rotate your palm, lie on your left side, holding a dumbbell in your right hand, and place your right elbow at a 90 degree angle with the upper arm supported on your ribs. Rotate the dumbbell so your thumb faces up and down.