Here’s a quick and fun look at the human muscle anatomy. Every week we focus on one particular muscle that is commonly injured or has some unique features that go underappreciated. Enjoy!
Name of muscle?
Supraspinatus: Supraspinatus is Latin for “above the spine” because it is located above the bony ridge in the back of the shoulder blade.
Where am I?
It is located in the top of the shoulder blade, or scapula, and attaches on the ball (or head) of the humerus.
What do I do?
The supraspinatus keeps the ball of the humerus centered in the shoulder when you lift your arm or you reach and lift objects. Technically, I depress the ball so it does not rub on the roof the shoulder, or the acromion. There is also a portion of the muscle that can assist with external rotation of the shoulder.
What nerve innervates me?
Typically, this muscle innervated by the cervical root C5 but gets its direct input from the suprascapular nerve.
Why am I important?
The tendon of the supraspinatus is one of the more common tendons to tear in the body. This is one of four “rotator cuff” muscles that supports the shoulder inside the glenohumeral joint. This is an extremely important muscle in most shoulder stability programs in physical therapy.
This muscle is more complex that most people realize, and is not illustrated in detail in most anatomy books. I can’t add the appropriate images to demonstrate this on our blog because of copyright restrictions, but you can find some images here.
This muscle has a bipennate architecture, or in other words, two sets of muscle fiber alignments onto a single central tendon. The advantage of this architecture is that allow for the muscle to generate a great deal of force and occupy a small area, and to allow different sets of muscles perform different actions onto the shoulder. Considering how much you can move your shoulder (think gymnast or a baseball picture), this type of arrangement comes in handy to keep the joint stabile and healthy.
There is a critical zone where the tendon loses its vascularity. Injuries to the tendon in this area heal very slowly and are also the area with the tendon tears frequently. This makes some of the tendon injuries in this area heal much more slowly that other areas of the shoulder and explains of the variety of time frames you can expect with any tendinitis or tendinopathy to the area.
The supraspinatus physiologically is considered to be a phasic muscle. These muscles have a predominant fast twitch muscle, or prone to inhibition, and is easily fatigued.