The lateral deltoids are positioned on the top of the shoulders, between the anterior and posterior deltoids. This muscle is responsible for abducting the arm and assists in internal and external rotation. It is also the muscle that gives the shoulder the rounded and full appearance many people find attractive and strive to achieve. Lift a weight heavy enough to fatigue your muscle within a specific repetition range. The National Strength and Conditioning Association recommends lifting heavier weights between six and 10 repetitions for strength gains, between 10 and 15 repetitions for muscle growth and toning, and over 15 repetitions for endurance.
Smith Machine Press
Most gyms have a Smith Machine, which is a barbell that is attached to a support unit so you control the weight, but the barbell moves in a fixed fashion. Sit on a bench with vertical back support. Adjust the barbell so it is positioned slightly above shoulder level. Grab the barbell with your hands slightly wider than shoulder-width apart, palms facing forward. Press the bar overhead and then slowly lower it back down. This exercise targets the lateral deltoids and allows you to lift a heavier weight, because the machine helps you control the bar.
Grab a 5- to 15-pound dumbbell in each hand. Stand in front of a mirror to check your form with the dumbbells down at your sides, palms facing the mid-line of your body. With a slight bend in the elbows, raise the dumbbells laterally out to each side until your arms are horizontal. Slowly lower them back down to the starting position. Your arms should rise on the sides of your body but be slightly forward so you can see both arms in your peripheral vision. This position helps prevent shoulder injuries.
The Arnold press involves a slight shoulder rotation to exercise the entire deltoid muscle but primarily the lateral deltoid. Sit on a bench with vertical back support. Hold a 10- to 20-pound dumbbell in each hand. Press the dumbbells overhead with palms facing forward, but as you bring them down, internally rotate your arms so when the dumbbells reach chest level, your palms face your body. Keep your elbows tucked in close to your sides. Press the dumbbells back up and externally rotate your arms as the weights move upward, finishing with arms extended and palms forward.
Grab a barbell with hands about shoulder-width apart and hold it with arms straight down in front of your body. Keeping the bar close to your body, bend your arms and lift up the bar. Allow your elbows to lead the movement. Finish with the barbell at shoulder level but with your elbows positioned higher than the bar. Slowly lower the bar back down. Upright rows can also be done on a Smith Machine to lift a heavier weight while still remaining in control of the bar.