Development and validation of work movement task analysis: part 2

Abstract

This paper elucidates the second part of the development of Work Movement Task Analysis (WMTA). This part involves improvements of the WMTA previous version and validation test using experimental approach. Methods: Current study comprises of three main objectives; (1) to investigate specific muscle activity subject to the WMTA risk rating (combination of Posture and Load, (2) to determine differences of perceived exertion (Posture and Movement) subject to the WMTA risk rating, (3) to determine differences of perceived exertion (Load and Load size) subject to the WMTA risk rating. A total 14 participants with no previous history of musculoskeletal injuries handled a load (5kg and 10kg) from the low risk to the high risk workstation setting on three simulation trials. For objective (1), Electromyography (EMG) data was recorded during the tasks then demeaned, high band-pass filtered using sixth order Butterworth filter at 25-30Hz then full-wave rectification. Subsequently low-pass filtered using fourth order Butterworth filter at 4Hz and mean absolute values (MAV) were obtained. MAV were applied for normalizing the EMG data with respect to the percentage of maximal voluntary contraction (MVC) for every muscle involves. For objective (2) & (3), perceived effort determined using the Borg's scale. Results: Experiment I: Workstation height and load variations significantly affected EMG. There was a trend of increasing of muscles activity from Task 1 to Task 3 relative to the WMTA scores; Left anterior deltoid p<0.000, Right anterior deltoid p<0.001, Right upper trapezius p<0.005, Left upper trapezius p<0.001, Right erector spinae p<0.001 and Left erector spinae p<0.000. Experiment II-simulation 1: there was a trend of increasing of muscles activity from Task 1 to Task 3 relative to the WMTA scores. Significant different (p<0.007) perceived effort of the participant for Task 1, Task 2 and Task 3. Experiment II - simulation 2: : there was a trend of increasing of muscles activity from Task 1 to Task 3 relative to the WMTA scores. Significant different (p<0.016) perceived effort of the participant for Task 1, Task 2 and Task 3. Conclusions: The study provides evidence to support the validity of the WMTA tools that focused on the combination of ergonomic risk factors; Postures and Loads, Posture and Movement & Load and Load Size. This tool is expected to provide new workplace ergonomic observational tool with solid experimental validation to assess WMSDs for the next stage of the case study.