A key component in maintaining strong, healthy shoulder joints is understanding how to differentiate between using actual shoulder movement v. other movements to compensate for a lack of shoulder mobility.
As the above photos demonstrate, more than one motion can be used to reach arms overhead. Many of us mistakenly believe we're using shoulder mobility to accomplish this motion.
The first photo shows someone reaching arms overhead to touch the wall behind them. At a glance, this might look like fantastic shoulder mobility, but take a closer look at what is happening at the rib cage. It moved away from the wall to help move the arms further overhead. Once the end of actual shoulder mobility is reached, rib cage thrusting can help us achieve further movement without using the shoulders but using the low back instead.
Is this a problem? Not always. But if you are looking to improve actual shoulder joint mobility, compensating with rib cage thrusting bypasses the shoulder joint and uses the spine to achieve more mobility. We commonly see this happen in those who are trying to improve neck and shoulder mobility.
To assess your own shoulder mobility, stabilize your rib cage to the wall and start to slowly lift your arms straight up and over your head (as in photo 2). STOP when you feel your rib cage start to move away from the wall.
This is the limit of your shoulders and if you are looking to improve shoulder strength, work within this range of motion. The best place to try this is in front of the mirror for visual feedback.
Learning the difference between movement of the shoulder v. using other joints to compensate is the first step toward healthy, happy shoulder joints!