Give it a try to throw a ball.

Wind-up period

Cocking period

Acceleration period

Release period

Follow-through period

Before throwing a ball

The shoulder is turning to the maximum outward with a ball.

Until releasing a ball off a hand from beginning to throw a ball

A ball separates from a hand and a motion of an arm is lost.

Finish throwing a ball, and movement is over

When throwing a ball, what happens to a motion of a shoulder joint?
Let’s think about it over the video.。

Cocking period

The shoulder is turning to maximum outward.

Let’s see the animation
When an arm raises above the shoulder and moves to the back, what happens to a supraspinatus muscle (muscle in green)?

It shrinks tightly.

Triangle-shaped deltoid muscle and the long tendon shown in red are pulled outwardly.

And, the muscle shown in green in the above animation is caught between the bone of scapula and humerus, and will be in a tight condition.

In addition, the bag under the scapula (blue in the animation below) will be also sandwiched appearance.

The sports disorders called the baseball shoulder occurs in supraspinalis muscle, deltoid muscle, the long tendon (long head tendon of the biceps brachii muscle) and bag (acromion lower bursa) and so on shown in this green.

The baseball shoulder is the disorders of shoulder which happens by the sports activities which resembles pitching motion of baseball.

In sports other than baseball, it happens during activities of volleyball, a handball, a basketball, badminton, the javelin throw, tennis, etc.
It is work that the muscle shrinks and extends, but inflammation is caused when these are overdone.
If the bag which plays the role of oil is sandwiched and it becomes difficult to move , it will become hard and a pain will come out of it.

Inflammation of the muscle and the bag become supraspinalis muscle, deltoid muscle, long tendon (long head tendon of the biceps brachii muscle) inflammation or the subacromial bursitis.

From acceleration period to release period

The motion of muscles seen from back

The part which has a triangular line among the blue muscles shown by animation is extended,

:and other muscles are similarly extended from the state which had shrunk.

In other four muscles shown under other than a deltoid muscle, the tendon adhering to a humerus is gathered up.These tendons are especially named a rotator cuff.
The rotator cuff is in the narrow hollow between the scapular bone and humerus, and is sandwiched between a bag and the ligament and pressed down strongly in the release period from the acceleration period.

 

The baseball shoulder which arises at this time occurs in a deltoid muscle and a tendon and a bag etc. as seen in the cocking period.

The deltoid muscle inflammation by the overuse, the rotator cuff which was pressed down and caused inflammation or subacromial bursitis

Sports disorders peculiar to children occur at this time.


Little league shoulder (proximal humerus epiphysiolysis)

In the children of the period of growth, there is a cartilaginous tissue for epiphyseal line that is an arm to grow. This fails by the overdoing of the pitching.

Follow through period

The muscle shown in red is called triceps brachii muscle, and it has adhered to the backside of the upper arm (arm extended from the shoulder). If these muscles are shrunk, an arm will be extended to a front.
Since an arm is shaken out by contraction of triceps brachii to the front, a rotator cuff and the rear surface of the shoulder is extended

For this, a triceps brachii inflammation and the bag which wraps the joint on the backside of a shoulder joint and so on (Bennet lesion) get damaged.

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