You can curl until you're blue in the face with traditional biceps exercises, but if you want a fully developed upper arm, more specifically, the "golf ball," you have to include brachialis training.
What it is: The brachialis muscle.
Where it is: The outside of the upper arm, between the biceps and lateral triceps head.
1. Reverse Curls
The key is to maintain a neutral, overhand position and avoid any flexion or extension of the wrist during the lift. Lock your elbows at your sides and only raise the weight three-quarters of the way up to really focus on the brachialis. Pause for a moment and lower back down. Shoot for three sets of 8 to 12 reps.
2. Overhead Curls
Using a lat pull-down or overhead cable, attach a straight bar and sit directly beneath the pulley. With a narrow grip, arms straight overhead and keeping your elbows pointing forward, curl your arms down so that your hands end up behind your head. Try getting three sets with 12 to 15 reps using perfect form.
3. Double Cable Curls
Standing in a cable crossover setup, set the pulley at shoulder height or above. Grab the handles and with palms face up make a T with your body and arms. Keeping your elbows stationary and locked in position with neutral wrists, curl the weight inward so that your fists end up near your ears. I find three sets in the 10 to 12 rep range best.It’s important to remember we’re trying to target the smaller, more elusive brachialis muscle, not the larger biceps. Therefore the emphasize needs to be on perfect form and use of lighter weights. Try alternating traditional bicep workouts with these three movements and you’ll have the golf ball in no time.