Variability in mechanical exposure within and between individuals performing a highly constrained industrial work task

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Variability in mechanical exposure within and between individuals performing a highly constrained industrial work task. / Mathiassen, Svend Erik; Moller, T; Forsman, M.

I: Ergonomics, Vol. 46, Nr. 8, 2003, s. 800-824.

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Mathiassen, Svend Erik ; Moller, T ; Forsman, M. / Variability in mechanical exposure within and between individuals performing a highly constrained industrial work task. I: Ergonomics. 2003 ; Vol. 46, Nr. 8. s. 800-824.

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TY - JOUR

T1 - Variability in mechanical exposure within and between individuals performing a highly constrained industrial work task

AU - Mathiassen, Svend Erik

AU - Moller, T

AU - Forsman, M

PY - 2003

Y1 - 2003

N2 - Data on exposure variability is an important remedy for designing and interpreting studies of occupational ergonomics. The present study aimed at retrieving the within- and between-subjects variance of several mechanical exposure parameters in a repeated, short-cycle task. Seven experienced operators repeatedly secured joints using two types of hand-held nutrunners. The joints were placed in three different locations on a rack, simulating automotive assembly. Bilateral muscle activity from the upper trapezius and the lower arm extensors, as well as head and upper arm inclination was continuously monitored. Exposure levels and their variance components were assessed in several data subsets using ANOVA. The results were interpreted in terms of statistical precision and power, and discussed as markers of important ergonomic qualities. A substantial exposure variability was found within and between subjects in all joint locations and for both tools. For mixed work across tools and locations, the necessary number of subjects to arrive at a group mean exposure with 95% confidence limits corresponding to +/- 10% of the mean ranged between 8 and 158, with posture recordings tending to require smaller populations than muscle activity recordings. Within-subject variance increased 2- to 37-fold, depending on exposure parameter, when work was 'enlarged' from securings with a specified location and tool to a mix of all locations and tools. Systematic differences between subjects in variability and responsiveness to 'work enlargement' indicated individualized motor control strategies. The results illustrate the importance of exposure variability data to the design of proper measurement strategies. They also suggest that the sizes of exposure variability per se can be interpreted as operational indices of what is thought to be important ergonomic risk indicators, such as the 'sameness' of repeated operations and the allowance for flexible working techniques.

AB - Data on exposure variability is an important remedy for designing and interpreting studies of occupational ergonomics. The present study aimed at retrieving the within- and between-subjects variance of several mechanical exposure parameters in a repeated, short-cycle task. Seven experienced operators repeatedly secured joints using two types of hand-held nutrunners. The joints were placed in three different locations on a rack, simulating automotive assembly. Bilateral muscle activity from the upper trapezius and the lower arm extensors, as well as head and upper arm inclination was continuously monitored. Exposure levels and their variance components were assessed in several data subsets using ANOVA. The results were interpreted in terms of statistical precision and power, and discussed as markers of important ergonomic qualities. A substantial exposure variability was found within and between subjects in all joint locations and for both tools. For mixed work across tools and locations, the necessary number of subjects to arrive at a group mean exposure with 95% confidence limits corresponding to +/- 10% of the mean ranged between 8 and 158, with posture recordings tending to require smaller populations than muscle activity recordings. Within-subject variance increased 2- to 37-fold, depending on exposure parameter, when work was 'enlarged' from securings with a specified location and tool to a mix of all locations and tools. Systematic differences between subjects in variability and responsiveness to 'work enlargement' indicated individualized motor control strategies. The results illustrate the importance of exposure variability data to the design of proper measurement strategies. They also suggest that the sizes of exposure variability per se can be interpreted as operational indices of what is thought to be important ergonomic risk indicators, such as the 'sameness' of repeated operations and the allowance for flexible working techniques.

KW - study design

KW - statistical power

KW - shoulder

KW - neck

KW - inclinometry

KW - tools

KW - hand-held

KW - exposure variability

KW - electromyography

KW - arm

KW - assembly work

U2 - 10.1080/0014013031000090125

DO - 10.1080/0014013031000090125

M3 - Article

VL - 46

SP - 800

EP - 824

JO - Ergonomics

JF - Ergonomics

SN - 0014-0139

IS - 8

ER -