Investigating the effect of experience and time on kinematics during one hour of sign language interpreting

Fischer, S., Johnson, R. Abdoli, M., Woodcock, K., 2014. Investigating the effect of experience and time on kinematics during one hour of sign language interpreting. IIE Transactions on Occupational Ergonomics and Human Factors 2, 60–70.

OCCUPATIONAL APPLICATIONS Upper extremity injuries pose a considerable problem to sign language interpreters. Over 1 hour of interpretation, interpreters experienced a decrease in their mean rate of wrist flexion and extension, while novices also experienced decreases about other wrist and elbow axes as well. It is suspected that interpreters were beginning to fatigue over the 1-hour duration, more so among novices, and that this increasing fatigue may be reducing their ability to “keep-up” with the interpretation. While more research is needed to measure fatigue and the quality of sign output, 1 hour of signing can induce changes in a signer’s movements. In the near term, injury-prevention efforts could focus on helping interpreters (particularly novices) structure their workload to ensure they provide themselves with ample opportunities for recovery. Imposing stricter guidelines regarding the maximum length of a continuous interpretation session is one example of a practical, near-term intervention.

TECHNICAL ABSTRACT Background: Sign language interpreters frequently report pain, and many develop musculoskeletal disorders. Yet, there is limited research quantifying the mechanics of signing independently or how such factors as experience or duration might influence those mechanics. Purpose:The purpose of this study is to determine if duration (within a single session) or experience affected kinematics during a 1-hour simulated classroom interpreting session. Methods: Nine novice (<2 years of experience) and nine experienced (≥5 years of experience) sign language interpreters interpreted for a continuous 60-minute session. Kinematic measures of the left and right upper extremities were recorded and compared between groups (experience) and within participants (time). Results: Duration had a significant effect on the mean angular velocity of right wrist and elbow movements. Novices exhibited decreased velocities between the first and last 15-minute samples for all right limb velocity measures (interaction effect). However, experienced interpreters only exhibited this decrease at the right wrist about the flexion/extension axis (main effect). Additionally, the number of micro-breaks increased between the first and last 15-minute samples about the wrist flexion/extension axis in both groups (main effect) and about the right elbow flexion/extension axis only among novices (interaction effect). Conclusions: Despite anecdotal evidence suggesting that novice interpreters use a less effective signing approach, these data suggest that on the basis of kinematics, novice and experienced sign language interpreters sign using similar kinematics, at least during the initial 15 minutes of an interpreting session. However, over the course of a continuous 1-hour session, differences emerge. It is plausible that novices may be more fatigable than their experienced counterparts or that they have not yet learned strategies to slow the accumulation of fatigue while maintaining the similar signing kinematics.

Author: Kathryn Woodcock

Dr. Kathryn Woodcock is Professor at Toronto's Ryerson University, teaching, researching, and consulting in the area of human factors engineering / ergonomics particularly applied to amusement rides and attractions (, and to broader occupational and public safety issues of performance, error, investigation and inspection, and to disability and accessibility.