Tree-fruit activities such as pruning, structural cutting, and green fruit thinning, are high-intensity labor activities traditionally performed on the ground or on ladders. To explore the impact of new technology on worker strain and injury, this project conducted a comparison between three different treatment groups: ground, ladder, and harvest-assisted mobile platforms.
Tree fruit production activities – such as pruning and structural cutting, green fruit thinning, and harvesting – require high-intensity physical labor. Traditionally, these activities are performed from the ground and on ladders. Now, new innovations are being introduced, such as apple collection systems (vacuums and conveyors) and ladder replacements (harvest assisted mobile technology). These new technologies are designed to increase productivity and reduce injury risk for workers (e.g. ladder falls). However, new practices also have the potential to introduce new ergonomic and safety hazards. This field study conducted ergonomic evaluations of harvesting that compared the use of ladders with the use of harvest-assist mobile technology (a platform). In collaboration with an innovative manufacturer and with growers, our field study comparatively evaluated these methods for ergonomic stressors, including kinematic (arm movements) and physiological (muscle fatigue and muscle activity).
Principal Investigator: Peter Johnson, PhD, MS
Professor, Environmental and Occupational Health Sciences
University of Washington
WA State MAAF 2009-2011 and NIOSH 2011-2016
Aim 1. With current traditional pruning, thinning, and harvesting methods, identify safety hazards and measure and characterize the physical demands along with measures of productivity. The intention is to establish baseline metrics for the traditional tasks to enable comparisons to tasks performed with the existing and emerging assistive tools and technologies collected in Aim 2.
Aim 2. With existing and emerging assistive pruning, thinning, and harvesting technologies, identify safety hazards, as well as measure and characterize the physical demands along with measures of productivity, and compare to traditional tasks collected in Aim 1.
Aim 3. In collaboration with our Technical Advisory Group, develop and evaluate modifications to traditional, existing, and emerging assistive technologies to minimize musculoskeletal discomfort and injury.
Aim 4. Translate and communicate the study findings (Research to Practice) to the tree fruit industry.
In 2014, we conducted an ergonomic field study by comparing apple harvesting using Bandit Xpress harvest-assist mobile platform to harvesting using the conventional orchard ladder. A study group was established through a new partnership with a large apple producer that adopted the new technology and whose workers had at least three months harvesting experience. A rigorous field study assessed three treatment groups, which included harvesting from 1) ground, 2) ladder, and 3) harvest-assisted mobile platforms. Overall, workers using the harvest-assist mobile platform had lower ergonomic stressors than those picking from ladders.
Whole body exertion and body area fatigue
Time-of-day was the primary factor for increases in whole body exertion and body area fatigue, with significant increases in both the monitored and self-reported measures at the end of the workday. Ladder harvesters had the greatest increase in heart rate over the work periods and the greatest decrease in heart rate over lunch (figure x). There was not a significant difference in heart rate among the three harvest methods. Moving the major break (lunch) from 2 hours after starting work to mid-day would create work periods of equal duration, which may help reduce the exertion and fatigue levels experienced by the end of the day. In comparison to the other groups, ladder workers overall worked at the highest exercise levels; therefore, using a harvest-assist mobile platform could reduce harvester fatigue levels.
Lower back and shoulder posture and fatigue
Harvesting from the platform provided workers with a more comfortable upright posture than picking from the ground or ladders. Harvesting from the platform also reduced the right arm extension compared to the right arm extension among workers in the ladder and ground groups. Ladder workers in this study used their non-dominate arm more frequently than the workers in the other two groups. When using platforms for harvesting, it is important to rotate workers between the ground and platform to distribute the impact on the musculoskeletal system over to different body areas.
Comparison of objective and subjective measures
An aspect of this study was to determine if the subjective measures, such as the Borg RPE and Borg CR10, could be used in place of the objective measures for whole body exertion (heart rate) and shoulder fatigue (arm inclination), respectively. The objective measures used in this study required instrumentation with one heart rate monitor and three inclinometers per participant, a relatively costly and time-intensive approach. In this study, the correlations between objective and subjective measures were weak and did not provide sufficient evidence to support substituting the objective measures with the subjective rating scales. The subjective scores still provide important information on a worker’s experience of whole body and body area fatigue.
A Technical Advisory Group (TAG) was established that included, ergonomists, agricultural engineers, extension faculty, physical therapists, representatives from industry (including employees with a farmworker history), and equipment manufacturers. They provided recommendations including industry relevant methods for measuring productivity and additional tools for collecting information on the worker-related musculoskeletal health factors. Results were shared with participating employers and manufacturers and at the annual meetings of the Washington Tree Fruit Association in years 2015 and 2016. The “Best Ergonomic Practices for Tree Fruit Harvesting" pamphlet (Spanish and English) is currently being developed and will be disseminated to orchards through the PNASH Outreach and Education Core.
Best practice safety and health recommendations related to harvesting:
1. Ensure that ground workers do not work in front of the harvest-assist platform.
2. Rotate workers between the ground and platform when using harvest assist mobile technology. By providing different work positions and movement, impact on the musculoskeletal system is more evenly distributed among different body areas.
3. Adjust platform height and vertical area for harvesting to minimize the amount of time workers pick with arms higher-than-shoulder and to maximize the amount of time they are in an upright posture.
4. Provide adequate and appropriately spaced breaks during the workday.
5. Determine the number of pickers on the platform crew based on the density of fruit available for harvesting.
6. Provide safe steps for climbing on and off platforms to prevent climbing on tires and other moving parts.
Partnerships and Advisories
Washington State University
Thamsuwan O. Objective Methods for Characterizing Physical Exposures Which May Contribute to Work-related Musculoskeletal Disorders in Agricultural Workers. 2016 PhD Dissertation, University of Washington.