The muscles involved in increasing arm size are the biceps, triceps and forearms. To get bigger arms, do a workout that targets those muscle groups. Allow a rest period of two days between workouts. This is an ongoing process that will likely take weeks or months for visible results.
Do four sets of spider curls for biceps
Set a weight bench at a 45-degree angle. Lean chest-first against the bench with a curl bar within reach. Grab the curl bar and curl the arms up without raising the elbows. Repeat between six to 15 curls per set.
Perform three sets of triceps presses
Sit on a bench with back support. Use a dumbbell as heavy as you can lift. Grasp the dumbbell with both hands and hold it over the head so that the palms are top-most and the weight rests on them. Lower the dumbbell behind the head and back up in a smooth motion. Repeat eight to 10 presses per set.
Do three sets of reverse barbell curls for the forearms
Start by standing with a barbell held at a shoulder-width apart. Keep the elbows close to the torso and the palms facing down. Keep the upper arms stationary while curling the barbell up. Contract the biceps and breathe out. Make sure only the forearms are moving. Repeat 15 curls per set.
Add chin-ups for all-over arm work
Perform three sets of four to eight chin-ups with the hands only 8 inches apart. This works all the major arm muscles, in addition to back and shoulder muscles.