There is a possibility that the cause of persistent stiffness in your neck and shoulder is malfunction of the brain.
Simple checking method to know if your persistent stiff neck and shoulder is caused by malfunction of the brain is checking if your body tilts or not. (Fig. 1) If there is stiff neck and shoulder caused by malfunction of the brain, there are some kinds of tilt of the body. (Fig. 2)
Dopamine The most important function of dopamine is to order to move muscles. When you lift the arm, dopamine is secreted from the brain. Dopamine becomes a signal and the muscles are contracted, resulting in being able to lift the arm. Dopamine controls the muscles of the whole body.
If malfunction of the brain occurs, dopamine is always secreted even if it is not necessary. --> Signals to contract the muscles are always transmitted. --> The muscles are always in a state of tension. --> The body is tilted. --> As a result, chronic stiffness in the neck and shoulders occurs. (Fig. 3)