Relationships between Upper Limb Loading, Physical Findings, and Discomfort Associated with Keyboard Use

Abstract

This paper presents findings of a preliminary investigation of the relationship between upper limb muscle loading, reported discomfort, and clinical findings associated with keyboard use. Surface electromyography (SEMG) was recorded bilaterally from the digit flexors (FDS), digit extensors (EDC), and m. trapezius of 52 employees of a large insurance company during their normal work activities involving keyboarding.Normalized SEMG amplitude served as a measure of loading on the relevant muscle groups. Physical examinations were conducted on these employees within 14 days of the EMG recording session, as was the administration of a discomfort questionnaire.The EMG measures of upper limb muscle loading did not predict MSD cases as well as the presence of current symptoms for forearm extensor cases (OR = 9.66), the duration of symptoms for neck/shoulder cases (OR = 2.5), or the intensity of symptoms for forearm flexor cases (OR = 3.72). However, the prediction of forearm extensor case status was improved by including the median EDC normalized EMG (OR = 1.39). The prediction of forearm flexor and neck/shoulder cases was not appreciably improved by including the FDS and trapezius EMG loading variables.

Effects of a Multitouch Keyboard on Wrist Posture, Typing Performance and Comfort

“…Hagberg and Sundelin (1986) used EMG to reliably correlate muscular load to subjective measures of discomfort, such as Borg scales of perceived exertion, on the upper trapezius muscle for 6 female VDT workers. Lowe, Moore, Swanson, Perez, and Alderson (2001) investigated the relationship between upper limb muscle loading, reported discomfort and keyboard use and found that EMG measures of upper limb loading did not predict MSDs as well as the presence of existing symptoms.…”