Several physical stressors, including repetitive, sustained, and forceful exertions, awkward postures, localized mechanical stress, highly dynamic movements, exposures to low temperatures, and vibration have been linked to increased risk of work-related musculoskeletal disorders. Repetitive exertions have been among the most widely studied of these stressors, but there is no single metric for assessing exposure to repetitive work. A new methodology enables repetitive hand activity to be rated based on observable characteristics of manual work. This method uses a series of 10-cm visual-analog scales with verbal anchors and benchmark examples. Ratings for repetition reflect both the dynamic aspect of hand movements and the amount of recovery or idle hand time. Trained job analysis experts rate the jobs individually and then agree on ratings. For a group of 33 jobs, repetition ratings using this system were compared to measurements of recovery time within the cycle, exertion counts, and cycle time. Amount of recovery time within the job cycle was found to be significantly correlated with the analysis ratings (r2 = 0.58), as were the number of exertions per second (r2 = 0.53). Cycle time was not related to the analyst ratings. Repeated analyses using the new method were performed 1 1/2 to 2 years apart on the same jobs with the same group of raters. Ratings for repetition differed less than 1 point (on the 10-cm scale), on average, among the different sessions. These results indicate that the method is sensitive to exertion level and recovery time, and that the decision criteria and benchmark examples allow for a consistent application of these methods over a period of time. This method of rating repetition can be combined with similar scales for other physical stressors.

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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.

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