Biomechanical analysis of upper extremity risk in Sign Langauge Interpreting

Abstract

Upper extremity cumulative trauma distorders (UECTD) have been identified as an occupational health problem in professional Sign Language Interpreters (SLI). A previous study of UECTD in SLI has indicated significant differences between interpreters working with pain and those working without pain. This earlier research focused on gross measures of hand/wrist movement, work/rest cycles, and deviations from an optimal work envelope. The present paper describes a detailed biomechanical analysis of wrist and forearm activity associated with SLI. This assessment included forearm (flexion and extension) and wrist (flexion/extension and radial/ulnar deviation) measures of movement frequency, counts of individual motion, joint movement velocities and accelerations as well as range of motion. The analyses revealed that the postures required for interpreting result in the signing hand frequently held in a fully pronated position, with the palm facing out. The wrist was most frequently in an ulnar deviation and/or extension while the elbow was flexed more than 90° and held in close to the body with the fingers pointing up. The frequency of motions for the forearm and wrist were observed to be 270 per minute (4.5 Hz), which is equivalent to 13,600 per 50 minute lecture hour. The mean absolute joint movement velocity and acceleration values were relatively high in contrast to industrial jobs with wrist and forearm accelerations between 34,754 degreees/sec(2) and 36,046 degrees/sec(2), respectively. The findings from this biomechanical analysis indicates that SLI can involve highly repetitive, awkward movements with significant accelerations of the hand and wrist. Such job characteristics may predispose interpreters to upper extremity CTD-related disorders.

The effects of two interventions on persistent pain: A multiple single-case study among sign language interpreters

“…From the physical exposure point of view SLIs represent an interesting group to study because no external forces are exerted during their work; strictly upper limb motions are involved, which simplify the number of physical factors to consider. A semi-quantitative analysis revealed that a typical 50 min work assignment involved 13,600 wrist motions (Shealy et al, 1991). Such a high frequency of wrist motions might explain part of the WMSDs among SLIs, considering that dynamic wrist motions have been reported as a risk factor for MSDs of the wrist (Malchaire et al, 1997;Marras and Schoenmarklin, 1993).…”

Investigating the Effect of Experience and Duration on Kinematics During 1 Hour of Sign Language Interpreting

“…As in previous research (Shealy et al, 1991;Delisle et al, 2005;Qin et al, 2008), this study focused on interpreting in a lecture-based environment, and thus the results may not be applicable to other settings. In Canada, approximately 35% of interpreters reported working in a full-time employment situation (such as an institutional setting), 15% split time between full-time and freelance work (i.e., interpreting for medical or legal proceedings), while the remainder work primarily as freelance interpreters .…”

Physical exposure of sign language interpreters: baseline measures and reliability analysis

“…Signing clearly exposes interpreters to these postural characteristics. Furthermore, a semi-quantitative analysis revealed that a typical 50-min signing assignment involved 13,600 wrist movements (Shealy et al 1991). Such a high motion rate also supports a possible link between sign language interpreting and MSDs, considering that highly dynamic wrist movements have been reported as a risk factor for wrist disorders (Malchaire et al 1997;Marras and Schoenmarklin 1993).…”