Arm movement is always the result of a complex interplay between the shoulder blade (scapula), the upper arm bone (humerus) and the collarbone (clavicle). The bones involved move in a precisely coordinated rhythm, which is also known as the "scapulohumeral rhythm" due to the joint partners involved.

In order to maintain the stability and functionality of the shoulder, it is important to train the joint regularly over the full range of motion and to ensure that the movement is biomechanically correct.

When the arm is raised, not only the arm moves, but also the shoulder blade. First the humerus moves, then the scapula and then the humerus again.

According to the scapulohumeral rhythm, the scapula and humerus move in a ratio of 1:2 when the arm is raised. So if the arm is abducted (raised sideways) 180°, the scapula is rotated 60° and the humerus 120°.

If your shoulder blade can move freely, you should see the inner edge of your shoulder blade parallel to your spine when you look at the back of your shoulder. When you raise your arm, the lower angle of the shoulder blade should end in your armpit.

If you cannot see this, the first thing to do is to find out whether your muscles are too tight and the shoulder blade can no longer be released or whether your muscles are too weak to lift the shoulder blade.

Muscles that are often tight include the latissimus dorsi muscle (broad back muscle) and the levator scapulae muscle (shoulder blade lifter).

Muscles that are often too weak include the serratus anterior muscle (anterior saw muscle) and the trapezius pars transversa muscle (middle hood muscle).

Injuries, one-sided strain or incorrect training can affect the position of the joint partners involved and lead to a disruption of the scapulohumeral rhythm.

If, for example, the shoulder blade does not move during arm movement, the upper arm has to perform the entire movement in a way that the joint is not designed for. The restricted mobility of the shoulder blade can usually be compensated for a long time with the help of small evasive movements. In the long term, however, consequential damage can also occur in the form of excessive wear and tear of the joint structures; the diagnoses are then often bursitis, impingement syndrome or tendonitis of the rotator cuff.

However, with biomechanically correct training exercises, the scapulohumeral rhythm can usually be corrected and the shoulder's ability to function can be restored and maintained in the long term.

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