A Comparative Evaluation of Job Techniques in the Tree Nursery Industry

Abstract

A pilot study was conducted as part of a larger project to assist a labor/management ergonomics team at a bareroot tree nursery in Washington State in developing potential solutions for reducing or eliminating risk factors for work-related musculoskeletal disorders (WMSDs). Measurements were collected of employees performing the jobs of Bin Unloading, Grading/Counting and Bag Closing using two different work techniques and workstation settings. Muscle activity (electromyography) of the distal upper extremity and back motion (Lumbar Motion Monitor) on three axes were recorded to determine differences in the WMSD risk factors between techniques. Bin unloading was performed with a bin flat on the stand and with the bin raised and tilted towards the worker. For grading/counting, the conveyor belts used to move trees were arranged in a stacked configuration and a side-by-side configuration. Closing the bags was performed by rolling the bag with two people and by folding the bags with one person. Paired t-tests were used to compare EMG data between methods and a mixed model was used to analyze LMM data. In general, grading/counting trees from a side-by-side conveyor configuration appeared to have slightly higher levels of finger flexor muscle activity, higher deltoid EMG static levels and back velocity and acceleration than grading from an over-under configuration. However, the differences were significant only for acceleration on the side bending and rotational axis and velocity on the sagittal and rotational axis. Workers unloading seedlings from bins that were raised and tilted forward experienced higher static, median and peak muscle levels, but slightly lower back velocity and acceleration. However, these results were not statistically significant. Bag folding appeared to have significantly higher levels of musculoskeletal risk factors, including higher deltoid, flexor and extensor muscle activity and higher ranges of movement, velocities and accelerations of the back. However, the number of workers exposed is less than for bag rolling.