Comparison of Exposure to Repetitive Upper Arm Motions and Non-neutral Upper Arm Postures between Apple Harvesting with Ladders and Mobile Platforms

Abstract

In attempts to improve productivity in agriculture, a harvest-assisting mobile platform has been developed and is being evaluated for use in Washington State apple orchards; however, its ergonomic effect on work postures and repetitive motions has not yet been characterized. The purposes of this study were: 1) to compare physical exposures between two methods of apple harvesting: a conventional ladder and a newly-developed mobile platform, and 2) to develop systematic methods for characterizing work repetitions, specifically in the upper arms. Using self-contained tri-axial inclinometers with built-in memory, upper arm inclinations were continuously monitored from twenty male workers over a full day of apple harvesting. At the beginning and the end of work shift, Borg CR10 scales were used as self-report measures of perceived fatigue in the shoulder. Postural exposures were characterized as the percent of time the upper arm postures exceeded specified angle ranges. Repetition was evaluated using changes in upper arm angles ranging from 5 to 30 degrees. In terms of prolonged postural exposures, repetitive work exposure and perceived fatigue in the shoulders, the workers using the mobile platform had less physical stress compared to the workers using the ladders. In addition, the upper arm repetition rates were high (over 15 repetitions per minute) for both harvesting methods. A more systematic study of the harvesting methods is needed to characterize differences in repetition rates and productivity between the mobile platforms and ladders. However, the results indicate that the mobile platform could improve workability and may enable more diverse workers to participate in harvesting activities.