Abstract:
The relationship between the many potential risk factors and the development of work-related upper extremity musculoskeletal morbidity has not been fully defined (NIOSH, 1997; NAS, 1998). Current exposure measurement methods need to be better defined and refined with regards to their accuracy and precision before they will be able to distinguish between incremental increases in physical exposure variables. This study refined state of the art field measurement methods and tools in order to perform an inter-method comparison between the three primary methods of risk factor exposure assessment: Self-Report Questionnaires, Expert Observation and Direct Measurement.
Tools and procedures were defined for the three methods which may be employed in any type of work, including repetitive and unstructured work environments. A self-report questionnaire was developed, a video analysis method was derived from previous research, and more accurate techniques of using electrogoniometers were developed to measure wrist posture and motion. Eighteen subjects in two western Washington tree nurseries participated in the study. Each participant performed three different jobs for a measurement period of 20 minutes, during which time direct measurements, video, and self-reports were recorded.
Results indicate that self-reports were the least accurate and precise assessment method, consistently over-estimated exposures for all risk factors. Wrist flexion/extension duration and repetition were best measured by electrogoniometer. Wrist deviation duration and repetition were more precisely measured by expert observation from video. Forearm rotation duration and repetition appeared to be best measured by electrogoniometer. Grip force was best measured by electromyography and movement velocity was best measured by electrogoniometer. The use of calibration procedures allowed the calculation of confidence interval bounds for electrogoniometer measures and more accurate group measurement by self-reports.
The results indicate that present and past studies using any of these field-based measure may have significant levels of inaccuracy. All exposure measures did not appear to be accurate on an individual subject level but were more reliable on a group level. The described levels of precision and accuracy for each measure and method should be considered when designing future upper extremity exposure assessments and epidemiological studies.