How to Work Your Biceps & Not Your Forearms

Many exercises believed to isolate the biceps, or the biceps brachii, build up the muscles in forearms as well. However, a few variations of the traditional biceps curl isolate the bicep muscle. When working out the biceps, you must lift enough weight to cause fatigue after 12 repetitions, according to the Mayo Clinic. The Mayo Clinic also recommends taking at least one day off in between working out specific muscle groups.

The biceps run along the front of the upper arms. These muscles help bend the elbows and flex the forearms, which is why many biceps exercises also strengthen forearm muscles such as the brachioradialis. Although it may be difficult to completely isolate the biceps from the muscles of the forearm, certain types of biceps curls target the biceps to help define, shape and strengthen them.

Preacher curls are effective in isolating the lower part of the biceps. To perform a preacher curl, sit at a preacher bench and place the back of your forearms on the padded support. With an underhand grip, grab the barbell roughly shoulder width apart. Slowly lift the barbell until the forearms are vertical. Lower the barbell slowly until the arms are totally extended. Try not to bend your wrists throughout the entire movement. Using a straight barbell instead of an EZ curl bar helps isolate the biceps.

Standing barbell curls isolate the biceps muscles, particularly if a straight barbell is used instead of an EZ curl bar. Start with your feet shoulder-width apart and the barbell resting against your thighs; your palms should be facing out. Slowly curl the barbell up and toward your shoulders, keeping your elbows in and near your body. At the top of the movement, squeeze your biceps, then slowly lower the barbell until it rests against your thighs.

Concentration curls target the head of the bicep muscle, rather than the muscles of the forearm. Begin by sitting on the end of a workout bench or a chair, with one elbow resting against your inner thigh; your legs should be spread apart and the dumbbell should be between your legs. Lean forward and slowly curl the dumbbell upward to your shoulder. As you curl the dumbbell up, keep your thumb pointing outward. Slowly lower the dumbbell until your arm is again completely extended.