Posture variation and maximal acceptable work pace during repetitive work
2016 (English)Conference paper, Abstract (Refereed)
Aim. It is generally agreed that work postures can lead to musculoskeletal disorders in the neck and shoulders. We investigated the extent to which more variation of upper arm postures in a repetitive task influences maximal acceptable work pace (MAWP), muscle activity, and perceived exertion.
Methods. Thirteen healthy subjects (6F/7M; age 26 (SD 3) years) performed a repetitive pick-and-place task using their dominant hand in four one-hour conditions. In three conditions the average upper arm elevation was 30°, and the hand was moved (1) horizontally (H30), (2) diagonally with upper arm elevation between 20° and 40° (D20/40), (3) vertically, with upper arm elevation between 10° and 50° (V10/50). In the fourth condition, the hand was moved horizontally at 50° average upper arm elevation angle (H50). The travelled distance of the hand was the same for all conditions. Using a psychophysical approach with imposed work paces changing every two minutes (7-13 cycles/min), we arrived at the MAWP of each participant after 50 minutes. Postures of the arm were recorded throughout, as well as dominant upper trapezius muscle activity. Participants reported their perceived exertion (Borg CR-10) just after each protocol.
Results. Kinematic analyses showed that we successfully designed protocols (Figure) differing in posture variation but not in average upper arm elevation angle (H30, D20/40, V10/50), and differing in average upper arm elevation angle but not in posture variation (H30, H50). MAWP was comparable in the conditions with differing posture variation (10.7 cycles/min), but lower in H50, although not significant (9.3 cycles/min). Subjects worked at MAWP with an upper trapezius activity level that did not significantly differ between experimental conditions (median 54% RVE). Dominant trapezius muscle activity at MAWP in H50 (78% RVE) was higher than in H30 (47% RVE), but not significant. Perceived exertion of the upper arm was higher in H50 (2.5) than H30 (1.5), but also not significant.
Conclusion. Variation in upper arm elevation within the investigated limits did not affect MAWP although upper trapezius activity showed a tendency to increase with more variation. Increased working height tended to increase especially upper trapezius muscle activity and decrease MAWP. Thus, our results indicate that posture variation as applied in the current setting did not lead to significant differences in MAWP or muscle activity variables. More thorough workplace redesigns are apparently needed than those investigated by us to accomplish any major changes in psychophysical outcomes as measured by MAWP. Our results do show that engineers should pay attention to working height when advising companies on work pace.
Place, publisher, year, edition, pages
2016. 183- p., O.8.6
Environmental Health and Occupational Health
IdentifiersURN: urn:nbn:se:hig:diva-22359OAI: oai:DiVA.org:hig-22359DiVA: diva2:958352
21st Congress of the International Society of Electrophysiology and Kinesiology, Bridges to innovation,5-8 July 2016, Chicago, Illinois,USA