RESEARCH: Team Work Leads to a Successful Ergonomic Control

Following a participatory approach within the Maine blueberry industry, a manual-use blueberry harvesting rake was designed which increased productivity, required less force, generated less worker pain and was favorably accepted by employees compared to a traditionally used rake, according to a recent study.

The blueberry harvesting industry, long associated with a high incidence of musculoskeletal injury, was provided an engineering solution by the National Institute for Occupation Safety and Health (NIOSH) in 2001 – a wheeled rake. This device was not well accepted.

Faced with the need to manually pick millions of pounds of blueberries in a safe manner, a Maine community-based endeavor (participatory process) was pursued. Key study findings included:

• Significantly less worker pain was associated with a longer handle rake
• Significantly less worker force was needed with a longer handle rake
• A longer handle rake with 80 tines was significantly preferred by workers
• Productivity was significantly greater with a longer handle rake and greater (but not statistically significant) with 80 tine rakes

A group composed of farmworkers and growers was formed. Assistance was provided by an ergonomist and industry focus groups.

A 3.5 to 10 pound metal rake with a single, short, centrally attached handle and collection box is used to maneuver through plant foliage to manually remove blueberries from plants. Operation of the rake requires radial/ulnar deviation of the wrist and upward pulling by the upper extremity. This motion could be performed more than 30 cycles per minute. 

After gathering input from stakeholders and reviewing rakes that workers had modified, three rake handle models were designed and tested in comparison to the commonly used rake handle. The three trial models included:

• A double handle rake with handle extensions
• A currently used rake with a side grip for collection box stabilization
• A semi-circular steering wheel handle rake

Further, four different rake widths were tested: 60, 70, 80, and 90 tines.

A pilot test was conducted with the 12 designs (three handle options and four tine options) over a 12-day period. Workers were interviewed to identify muscle/joint pain and functional capability relative to each rake. Blueberry harvesting volume and berry damage for each trial rake was assessed.

Pilot test findings reduced the trial rake options to six designs:

• the center handle rake with 10, 14 and 16 inch extension modifications
• fixed rake head width with 70 or 80 tines

After using a traditional rake for one work day, 29 workers were randomly assigned a different trial rake on each of five subsequent work days to use while performing morning work tasks. A worker never tested the same trial rake twice.

Workers subjectively rated a trail rake for general liking (on a scale of 1 to 5), force compared to the traditional rake (less, same, more), and pain (yes/no). Productivity was assessed subjectively by worker reporting of the number of standard blueberry boxes filled. 

Although eliminated in the pilot study, the two-handled rake with extensions created greater productivity than the traditional rake.

Other worker suggestions for rake improvement that went beyond the scope of this study included:

• longer rake handle
• larger rake attached berry holding boxes
• lighter rake weight
• different handle grip size
• different handle angle
• different handle location  

The authors point out that the longer rake handle requires greater motion through the shoulder than the traditional rake. The net impact (this loss versus reduced force in other upper extremity regions, less overall pain, preferred use) is unknown.

Also, this study was composed of Hispanic workers and excluded other races (such as Native American) that are involved in the Maine blueberry industry. It is unknown if this produced a selection basis.