I heard an advertisement for sleepwear that will prevent the "impingement position." What is this?

When the arm is lifted overhead, some of the soft tissues in the shoulder can get compressed or pinched. This is called shoulder impingement. Impingement can cause pain in the neck, shoulder, upper back, and even down the arm. There may be numbness and tingling in the arm and hand.

People who sleep at night with a hand under the pillow or with the arm overhead are at risk for impingement. Keeping the arm down by the side is one way to prevent these symptoms. Medical supply companies offer shoulder immobilizers that work for this problem. A simpler method is to place the arm against the body under a snug nightshirt.