“The player uses several joints in a well-defined sequence. If the timing is right, the flowing movement of the upper arm, forearm, hand, and racquet produces a summation of forces. The force generated by the shoulder, the elbow, and the wrist is increased by the force of subsequent joint movement.” – Professor Thomas Schrefl, Excerpt From Winning Formula, Red Bulletin Magazine
(Biomechanics)
The glenohumeral (shoulder) joint is a very unstable joint based on its structure alone.
Adding more mobility to a joint that, based on its nature, is already very mobile equals even less stability.
Efficiency = Muscles + Ligaments
Optimal Stiffness
In order for you to bring your arm straight out to the side, a lot of muscles have to generate a sufficient amount of internal force to overcome gravity.
If you are not familiar with the rotator cuff muscles; the term rotator cuff implies a group of muscles. The group consists of 4 muscles: supraspinatus, infraspinatus, teres minor and subscapularis.
If you are like me, you learned the muscle actions primarily from anatomical position.
The term anatomical position is used to describe a position where “all” movement is initiated.
Since this post is focused on the upper extremity; try to visualize your arms by your side; with the palms of your hands facing the computer.
This is easy to understand up to this point, right?
The anatomy texts have traditionally emphasized the importance of the transverse plane (rotation) as it relates to the majority of the muscles that make up the rotator cuff.
With one arm by your side, keep the palm of your hand facing the computer; then bring your arm straight out to the side and over head.
If you watch the motion of your arm in a mirror, it isn’t visually apparent, but your upper arm (humerus) is gradually laterally rotating (0ut) as you brought your arm overhead.
You can not see it (and probably would not think about it) because the palm of your hand is still facing the same direction.
(Curiosity)
The motion of your arm occurred at the shoulder joint, e.g., Abduction of the arm at the shoulder joint.
If you think back to what you have learned about the rotator cuff, you are probably thinking that the rotator cuff was not involved in that frontal plane motion.
(Perspective)
The truth is, the rotator cuff played an important role in your ability to accomplish that motion at the shoulder joint.
