While you may or may not know that the majority of the rotator cuff muscles help with rotating your shoulder, this is far from their most important job-what they do when they all work TOGETHER.
First a little anatomy. Your shoulder is a ball and socket joint that is very mobile, yet very prone to coming out of place due to its shallow socket. However, while its true that Mother Nature has put our shoulders at a slight mechanical disadvantage, it didn't leave us totally helpless either. Instead of giving the shoulder a nice deep socket, like the hip joint, or lots of strong ligaments to hold the bones together, we've got the next best thing - powerful support from the rotator cuff muscles.
Individually, each of the four rotator cuff muscles have their own jobs. Some help roll the shoulder in, some help roll the shoulder out, and so on. But when all the rotator cuff muscles work together and contract at the same time, their combined pull helps keep the shoulder's ball and socket joint firmly in its place.
Now there are four rotator cuff muscles, the supraspinatus, infraspinatus, teres minor, and subscapularis, and when these muscles all contract AT ONCE, the net result is that the upper arm bone gets pulled snuggly towards the shoulder blade, thus firmly locking the "ball" into the "socket."
And when exactly does this happen, the rotator cuff muscles "kicking in" and contracting all at once to stabilize the shoulder joint? Well, according to the latest research, it occurs immediately before a person starts to move their shoulder around. For example, if you were to reach out right now and wave to someone, your rotator cuff muscles will contract the very instant BEFORE your arm actually starts to move. In this way, the shoulder joint starts out in a safe position and is held tightly in place as you go about using it. Pretty neat, huh?
Scientific-minded readers will also be glad to know that the research has confirmed the stabilizing role of the rotator cuff muscles. A study published in the peer-reviewed journal Clinical Biomechanics involved recording the EMG activity of people's shoulder muscles as they were asked to perform certain motions (David, 2000). Sure enough, researchers found that a "pre-setting" of the rotator cuff muscles occurred before any shoulder motion actually took place.
You can learn more about keeping your rotator cuff strong so you can avoid all the common shoulder problems such as bursitis, impingement, rotator cuff tears, and arthritis in the book Treat Your Own Rotator Cuff.