Date of Award


Document Type

Scholarly Project

Degree Name

Master of Physical Therapy (MPT)


Physical Therapy

First Advisor

Beverly Johnson


Computer Terminals; Cumulative Trauma Disorders; Electromyography


Purpose: Ergonomics involves adapting the job and work environment to fit the worker and maximize safety and efficiency in the workplace. To mimimize the stresses on the musculoskeletal system, ergonomic guidelines have been established for visual display terminal workstations. The 90 degree angle position of the elbow is considered an industry standard, however available literature has not adequately established that this angle represents the optimal elbow position. The purpose of this study is to add to the current knowledge of ergonomics and reduce the risk of upper extremity cumulative trauma disorders in the workplace by determining the optimal elbow position during typing.

Methods: Thirteen female employees of a regional insurance company participated in the study. Surface electromyograpy (sEMG) was used to examine muscle activity in four upper extremity muscle groups (upper trapezius, extensor digitorum, extensor carpi radialis brevis and longus, and flexor superficial during typing at three different angles of elbow flexion (70, 90, and 110 degrees). Analysis of the data was performed using two different methods: 1) using the maximum voluntary contraction as the normative value, and 2) using the 90 degree angle trial as a reference. A repeated measures analysis of variance was used to compare the muscle activity of the four muscles between the three positions. Post-hoc analysis was examined by applying the Scheffe's test.

Results: Significance was established between elbow position in the extensor digitorum and extensor carpi radialis brevis and longus muscles. However, muscle groups that do not display significance at varying positions should not be ruled out because of the repetitive nature of the typing activity.

Conclusion: The 90 degree angle of elbow flexion while typing may indeed represent the overall optimal position. However, the 70 and 110 degree angles may be considered for workers who would benefit from less tension or load on a particular muscle group.