Wrist and forearm postures and motions during typing

Awkward upper extremity postures and repetitive wrist motions have been ide ntified by some studies as risk factors for upper extremity musculoskeletal disorders during keyboard work. However, accurate body postures and joint motions of typists typing on standardized workstations are not known. A lab oratory study was conducted to continuously measure wrist and forearm postu res and motions of 25 subjects while they typed for 10 - 15 min at a standa rd computer workstation adjusted to the subjects' anthropometry. Electrogon iometers continuously recorded wrist and forearm angles. Joint angular velo cities and accelerations were calculated from the postural data. The result s indicate that wrist and forearm postures during typing were sustained at non-neutral angles; mean wrist extension angle was 23.4 +/- 10.9 degrees on the left and 19.9 +/- 8.6 degrees on the right. Mean ulnar deviation was 1 4.7 +/- 10.1 degrees on the left and 18.6 +/- 5.8 degrees on the right. Mor e than 73% of subjects typed with the left or right wrist in greater than 1 5 degrees extension and more than 20% typed with the left or right wrist in greater than 20 degrees ulnar deviation. Joint angles and motions while ty ping on an adjusted computer workstation were not predictable based on anth ropometry or typing speed and varied widely between subjects. Wrist motions are rapid and are similar in magnitude to wrist motions of industrial work ers performing jobs having a high risk for developing cumulative trauma dis orders. The magnitude of the dynamic components suggests that wrist joint m otions may need to be evaluated as a risk factor for musculoskeletal disord ers during typing.