Abstract: A universal arm board for hand and forearm fixation is provided for exposing part of the forearm at the wrist for the attachment of electrodes for stimulating the ulnar nerve. The palm of the person being tested rests on the arm board and is fixed in position by a lock assuring immobility of the palm and fingers and leaving free only movement of the thumb which is positioned in a thumb ring. The wrist is immobilized by a belt with a Velcro lock leaving free the exposed part of the palmar side of the forearm at the wrist for ulnar nerve stimulation. The proximal part of the forearm rests on a foam arm protector and is immobilized by a belt with a Velcro lock. A force-transducer positioner is attached to the arm board. The positioner allows adjustments to any position required by the anatomical differences of the thumb-hand angle and allows changes in the resting tension of the adductor pollicis muscle.