Relationship between Computer Keyboard Slope and Wrist Extension Angle

Abstract

The literature has shown that sloping the keyboard downward reduces extension angle of the wrist, which is a risk factor for work-related musculoskeletal disorders (WMSDs) of the wrist. However, the slope angle of the keyboards tested and reported in the literature were adjusted by the individual or preset to only one angle. Therefore, it is difficult to infer from these studies' results the effect of the magnitude of keyboard slope on wrist extension angle. The goal of the study presented in this paper was to determine the effect that varying the slope angle of a keyboard has on wrist extension angle. Ten subjects typed on a keyboard whose slope was adjusted to +15⁰, +7.5⁰, 0⁰, −7.5⁰, and −15⁰. (Positive keyboard slope indicates the keyboard was sloped upward toward the VDT, and negative keyboard slope indicates a downward sloping keyboard.) As keyboard slope angle moved downward 30⁰ (+15⁰to −15⁰), wrist extension decreased approximately 14⁰. Mean wrist extension for the left wrist decreased monotonically from 22.5⁰ at 15⁰ positive slope to 7.8⁰ in the 15⁰ negative slope condition. Likewise, the right wrist's mean extension decreased monotonically from 23.8⁰ to 9.9⁰ when the keyboard was sloped downward from +15⁰ to −15⁰ Keyboard slope angle did not impair typing performance. Based on carpal tunnel pressure studies, histologic studies of tendons, and modeling of the wrist, it appears that keyboards that can be sloped downward are beneficial with respect to etiology of WMSDs of the wrist.