The Effect of Keyboard Key Spacing on Productivity, Usability, and Biomechanics in Touch Typists with Large Hands

International standards that specify the spacing between keys on a keyboard have been guided primarily by design convention. Experienced typists (N=37) with large hands typed on five keyboards with different horizontal and vertical key spacing (19x19, 18x19, 17x19, 16x19, and 17x17mm) while productivity, comfort ratings, left and right extensor carpi ulnaris (ECU) and flexor carpi ulnaris (FCU) muscle forces, and right and left wrist extension and ulnar deviation were recorded. Productivity and usability ratings were significantly worse for the 16x19 keyboard. There was a trend for muscle activity to increase in the left forearm and decrease in the right forearm with decreasing horizontal key spacing. There was also a trend for left wrist extension to increase and left ulnar deviation to decrease with decreasing horizontal key spacing. The study findings support key spacing on a keyboard between 17 and 19mm. These findings may influence keyboard standards and design of keyboards.