A couple of years ago I blogged about the 4 rotator cuff muscles. It's worth focussing in on 1 in particular that can cause you problems if you're a gym rat.
The supraspinatus muscle lies along the top edge of the shoulder blade, facing up, as it were.
Pic by wikicommons.org
As I mentioned before, the job of supraspinatus is to start the movement of abduction - moving your arm sideways away from your body. In fact, it's responsible for the 1st 15⁰ of movement outwards, though it continues to help out the larger deltoid which takes over as far as 30⁰ out.
You can see from the pic that the supraspinatus lies in the top dip, or fossa of the shoulder blade (scapula). It runs across underneath the bony prominence called the acromion to attach to the very top of the arm bone.
So when the muscle contracts, it pulls on the top of the arm bone, causing the arm to rise up sideways away from the body.
Supraspinatus is one of the few muscles of the body that doesn't really vary betwen people. It's known in the trade as the "singularly invariable muscle".
It's also the only one of the 4 rotator cuff muscles that doesn't actually rotate the shoulder.
As if that wasn't bad enough, and to add to confusion, physiotherapists often refer to supraspinatus as The rotator cuff, even though there are actually for of them, and this one doesn't rotate anything!
You can see in the pic, that the muscle runs underneath the acromion. The gap is actually quite small.
If you do a lot of actions that raise your arm out sideways, especially under load (like doing dumbell lat raises), then the supraspinatus muscle will grow quite large. In fact, it can grow so large that it starts to rub against the acromion. This is known as an impingement.
In fact any activity where you're repeatedly moving your arm out to the side (e.g. golf) can have the same effect.
If the activity continues, then there's a danger not just of the muscle fraying (which is the impingment) but of a full blown rupture.
There are simple tests that your physio or remedial sports massage therapist can do see if there's an impingement or rupture - but you can usually tell yourself. If your shoulder joint hurts when you abduct your arm, you probably need to get it seen to.
Supraspinatus impingements become more likely once you're over 40.
To be honest, it's not the end of the world if you've got a supraspinatus impingement: the deltoid is big old muscle on the side of your arm, and it can do the job that supraspinatus is meant to do. Admitedly it's not as efficient or refined as supraspinatus, but deltoid can be recruited to do the job well enough.
There are 2 problems, though:
In both cases, the triage is stop the movement!
If you're a golfer, take a rest from golf. If you're a gym-rat, start and end your lat raises with the weights away from your body by 15-20 degrees each side - that way supraspinatus won't be working so hard.
Then go get yourself some treatment, and continue to rest from the activity until it's better.
As ever, if you think I can help, give me a call.