An unnatural rotation of the hands, called Pronation, is required when typing on a keyboard. Pronation ensures that the hands are level over the keyboard with the thumbs in a central position. It is typically achieved by the pronator teres muscles in the forearm.

The median nerve is the main nerve to the hand and forearm. It passes between the two heads of the pronator teres muscle and beneath the bulk of the muscle mass. The ulnar artery transfers blood to the forearm and also passes through these two heads in the muscle mass above the nerve.

Sustained pronation can cause serious problems such as straining the muscle. It can also put the median nerve under serious pressure and can stress the ulnar artery, reducing blood flow to the forearm and hand.