The Shoulder Muscles

About Your Shoulder Muscles

When you first get out of bed in the morning, what’s the first thing you do? You probably stand up and spread your arms in a wonderful stretch that usually includes a yawn. You know you’ll be using your back and shoulder muscles all day, so you might as well stretch them out right when you get out of bed!

Your shoulders obviously have a huge number of daily activities, so it’s important to make sure they’re working their best. Stretching and exercising them is important, especially when we start talking about the rotator cuff muscles which all work to stabilize the shoulder joint (anatomically known as the glenohumeral joint).

The Deltoid Muscle

The Deltoids are the largest of the shoulder muscles and are broken up into three distinct parts: the anterior, lateral, and posterior regions. As you know, the deltoid has a very large range of motion. How does it actually work?

Well, as with the other muscles, understanding how it works will involve an understanding of the muscle’s attachment points…

• The Anterior fibers run from the front lateral portion of the clavicle (collar bone) to a point on the humerus (upper arm) called the deltoid tuberosity.

• The Middle fibers run from the acromion of the scapula (the “point” you feel at the top of your shoulder) down to the deltoid tuberosity.

• The Posterior fibers arise from the back of the scapula (near the spine of the scapula) and also inserts into the deltoid tuberosity.

Did you notice any similarities here? All of these fibers insert into the same point on the humerus in the form of a single tendon. So, what’s the action of each orientation of fibers?

• The Anterior fibers are used in pushing sort of movements as in the bench press. In anatomical terms, this is called transverse flexion of the shoulder. A common exercise specifically targeting the anterior fibers is the front dumbbell raise.

• The Middle fibers are involved in all abducting movements (or raising the arm away from the body). The most common exercise for working these fibers is the lateral dumbbell raise.

• The Posterior fibers are involved in extending the shoulder joint as in pulling your arms backwards. A common exercise to work these fibers is the bent-over lateral dumbbell raise (a.k.a. reverse shoulder fly).

The orientations and movements of the shoulder muscles are built to accommodate and house the ball-and-socket joint upon which your arm rotates. This allows you to swing your arm in a circle (as in a throwing motion) without ripping or tearing any muscles or dislocating the joint. The rotator cuffs are no exception! In fact, their main job is to stabilize the joint…

The Rotator Cuff Muscles

The rotator cuff consists of a series of four shoulder muscles that surround the ball-and-socket joint I mentioned above (this is called the glenohumeral joint). The main function of these muscles is to stabilize the joint, help rotate the arm and to assist the deltoid in certain movements. All of the rotator cuff muscles originate on or near the scapula and insert into the humerus (upper arm). This insertion point determines how the muscle will act on the shoulder and arm…

• The Supraspinatus muscle sits in a location known as the supraspinous fossa of the scapula (or the upper portion of the scapula) and runs over the top of the shoulder joint, inserting into the top, lateral portion of the humerus (an anatomical location called the greater tubercle). It’s kind of like a hinge: when the muscle shortens, the arm is pulled directly upward and away from the body. In other words, the supraspinatus abducts the arm. After the first 15 degrees of abduction, the middle fibers of the deltoid take over the rest of the movement.

• The Inftraspinatus muscle, conversely, sits in the infraspinous fossa underneath the supraspinatus muscle. It attaches to the same location as the supraspinatus (the greater tubercle), but on the posterior side. So, when the muscle fibers contract, the arm will rotate externally as in opening your palms to face forward.

• The Teres minor attaches to the lateral side of the scapula and reaches over, once again, to the greater tubercle from the posterior. The muscle also helps to externally rotate the arm.

• The Subscapularis muscle also attaches to the scapula, but closer to the rib cage. In other words, it’s the deepest of the rotator cuff muscles when looking from the back. It originates on the underside of the scapula and proceeds on to the anterior portion of the greater tubercle (the front side of the arm). A contraction of this muscle will cause the arm to rotate internally as in forcing your palms to face backwards.

Avoid Injury!

Injuries to the shoulder muscles, especially the rotator cuff, are extremely common especially in athletes and weight lifters. The main problem is that working out your rotator cuff usually (and unfortunately) takes back seat to the other major muscle groups! In fact, it’s quite easy to injury a rotator cuff muscle if you’re bench pressing too much weight. This results in a destabilization of the shoulder joint that may prove to be too much for the rotator cuff to handle. Injuries are most common, of course, when doing repetitive overhead motions such as throwing a ball and even swinging an object such as a baseball bat or golf club.

The supraspinatus muscle is the most commonly injured of the rotator cuff muscles, especially when the injury is due to wear and tear (like a weight lifting injury). Pitchers may injure a rotator cuff by internally rotating the arm with too much force or too often (like when throwing a curveball). The muscles involved here might be the Teres minor and the infraspinatus muscles.

Don’t Injure Your Rotator Cuff!

Some ways to prevent injuries to your rotator cuff muscles in the gym are…

• Workout your rotator cuff! This is the premier mistake made by most people who sustain such injuries. Weak rotator cuff muscles can cause havoc in any sort of activity. Use dumbbells to work the internal and external rotation abilities of the arm. One way to do this is to lie on your left side with a light dumbbell in your right hand (say 5 lbs). With the arm bent at 90 degrees, slowly rotate your arm upward towards the ceiling. You can use the same motion for internally rotating the arm, just put the dumbbell in the other hand!

• You can do the same exercise by standing on top of a latex band. Start by holding the band in front of you parallel to the ground with your arm bent at a 90 degree angle. Slowly rotate the arm upward until your fist is towards the ceiling. Alternatively, you can also attach the band to a stable object. With the band coming directly from your right, hold the band with your left hand. With your elbow static, externally rotate the arm and pull the band. You can also do the internal rotations by holding the band in your other hand.

• Bands are great for the rotator cuff because you have more control over them than you do dumbbells. You also don’t have to lie on the floor or find a specialized rotator cuff exercise machine to work them. They’re also very smooth and allow you to isolate the rotator cuffs, removing the stress put on other muscles. Furthermore, using bands allows you to put more pressure on the shoulder muscles (including the deltoid) the more you stretch the band along with easing out of each rep. Forcefully jerking back and forth with dumbbells is a recipe for injury to begin with – but bands give more resistance when you need it. Again, working the rotator cuffs with dumbbells with quick movements can result in injuries.

• Using too much weight with the dumbbells may actually cause you to injure the rotator cuff – pick a light weight! Don’t let your ego get in the way of this one; a rotator cuff tear can lead to a life full of shoulder problems.

Whether or not you’re working out your shoulder muscles can either make you or break you. What I mean is, your shoulders are the link between your chest and your arms. If you have weak shoulder muscles, your chest and arms will have much less potential to build. Furthermore, the rotator cuff muscles are an extremely important set of muscles that keep your humerus and scapula locked into place. Having weak rotator cuffs can lead to a shoulder dislocation, shoulder separation, or simply a muscle tear. These sorts of injuries don’t always heal properly, so it’s best just to steer clear of these injuries in the first place!

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