The deltoid muscle lies just above the main shoulder joint -- and is divided into three parts -- the anterior deltoid in front, the middle deltoid and the posterior deltoid in back. Performing strength-training exercises that target the deltoid helps build the muscle, enabling it to function effectively and potentially preventing injuries.
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Working the Anterior Delts
The anterior deltoid attaches to the outer third of the clavicle bone on one end and to the humerus bone of your upper arm, just outside your shoulder joint, on the other. This portion of the deltoid contracts to lift your arm forward from your hip, to pull your arm in front of your chest from the side, and to inwardly rotate the humerus bone within the shoulder socket. The front raise, which involves lifting a dumbbell forward to shoulder height from your hip, is a traditional exercise that targets the anterior deltoid. Others include the military press and overhead shoulder press, which you can perform using a barbell, dumbbells, a kettlebell, a resistance band or a specialized weight machine.
Middle Deltoid Exercises
The middle deltoid shares the attachment to the humerus bone with the anterior portion, but attaches to the top of the acromion -- the bony protrusion just above your shoulder joint -- on the inside. The middle deltoid facilitates shoulder abduction, which occurs when your move your arm away from the center of your body, either vertically or horizontally. The lateral raise and upright row are examples of exercises that target the middle deltoid. The first exercise involves repeatedly lifting dumbbells sideways, away from your body, to shoulder height, and the second requires lifting a barbell along the front of your body, from your thighs to your chin, by flexing your elbows and abducting your upper arms.
Posterior Deltoid Workouts
The posterior deltoid attaches to the scapula bone within your upper back on one end and to the humerus bone, combining with the other two segments, on the other. This muscle produces shoulder extension, external, or outward, rotation and horizontal abduction. Most reverse fly and rowing-type exercises work the posterior deltoid. The lying reverse fly, for example, involves holding dumbbells and lying face down on a bench with your arms hanging below your chest and repeatedly arcing them away from each other until they're parallel to the floor. The bent-over row, for another example, requires pulling a barbell to the bottom of your chest from a standing, bent-over position.
How to Progress Your Program
Performing exercises as part of a progressive strength-training program is essential for building deltoid muscle mass and strength. Train each part of the deltoid muscle two to three times per week on nonconsecutive days. Complete three sets of 12 to 15 repetitions at first, then progressively increase the number of sets and the amount of weight and decrease the number of repetitions every two to three weeks until you're performing six sets of six repetitions at the end of your program. Decrease the amount of weight if you're not able to complete all the prescribed sets and repetitions with perfect technique. Consult your doctor if you feel any discomfort other than mild muscle soreness.