Every time I wake up, my knuckles are stiff.

Stiffness of finger joints after waking up every time is caused by deficiency of qi and blood, and fingers will become stiff without qi and blood nourishment.

Either the constitution is poor, the qi and blood are insufficient, or the meridians and blood vessels in the body are blocked due to frequent sedentary, or the body is cold and wet, which leads to the slow movement of qi and blood.

When sleeping, the qi and blood in the body run slower than normal, and the fingers are the peripheral parts of the body, so first of all, the lack of qi and blood nourishment will produce a stiff feeling.

To recover, it is necessary to strengthen the body, nourish qi and blood, speed up the circulation of qi and blood in the whole body, clear the blockage, drive away cold and dampness, and make the whole body qi and blood accessible, and then recover.

How? You can search this article, "Six reasons for physical stiffness and strain, why do people who practice traditional martial arts relax, be flexible and approachable?" The article tells the story of a recovery method of traditional sports, hoping to help you and adopt it.