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Getting a grip on tractor ergonomics for smaller-stature operators

Melissa Bravo for Progressive Dairyman Published on 11 December 2018
Tractor design can be a struggle for women

Most of us can relate to what happens when a man tries to get behind the steering wheel of a vehicle after a woman’s been driving. He has to slide the seat back.

It doesn’t seem to matter what country you’re from – the average male is several inches taller than the average female.

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Spending 12 hours a day sitting down while doing something with our hands and feet is pretty common, which is why, after an eight-hour day stacking round bales and cleaning the barnyard, I got to wondering how many tractor companies design tractor cab ergonomics for the shorter-statured female, kid and migrant operator.

I was not able to get a direct line to an engineer at One Gehl Way, West Bend, Wisconsin; CNH, Racine, Wisconsin; John Deere, Waterloo, Iowa; Kubota, Gainesville, Georgia; or CAT, Sanford, North Carolina, to answer this question. So I contacted Stuart Birell, Cornell’s professor of agricultural and biosystems engineering.

Birell sent me a copy of Kyle Dooley’s presentation at the Agricultural Equipment Technology Conference in Louisville, Kentucky, titled “Ergonomics and the Development of Agricultural Vehicles (2012).” What Dooley says is pretty straightforward: “The best possible ergonomic match maximizes an operator’s effectiveness, comfort and system safety. For every ergonomic mismatch, you are deducting from your ideal productivity, costing time and money.”

Dooley does not mention if the industry has adapted machinery for female operator comfort. But given the USDA reports more and more women are taking the reins of farming, and Ronald Holden of Forbes says in his Feb. 12, 2018 article, “The future of food is farming, and the future of farming is female,” I think it’s a valid $50,000 to $100,000 dollar question.

A 2012 study on “work-related musculoskeletal discomfort of dairy farmers and employed workers,” in the Journal of Occupational Medical Toxicology is a good example of how ergonomic discomfort manifests differently between men and women. The Swedes in this study reported the most pain in the lower back and shoulders followed by neck, hands, feet and elbows. But women reported more pain in the neck and hands.

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And I can relate to that.

My neighbor has a John Deere right-handed joystick-operated 110 loader backhoe I use to stack round bales. While it’s pretty awesome, it’s not a perfect size for this operator. I am left-handed, which means I am right-mind dominant. It’s a very unnatural adaptation for someone left-handed to use a right-handed tool all day.

I am also only 5 feet 2 inches tall.

After a few hours of bucket work, my right hand hurts – particularly my fingers. Both wrists, my lower back and neck hurt. Even my calf muscles hurt. That is because I have to slide the seat forward to engage the drive pedals. If I don’t, the safety switch kills the engine. Once I slide the seat forward, my right elbow is locked in a right-degree angle, and my left is now on top of the steering wheel.

And while I may be shorter than most Caucasian women, South and Latin American migrant farmworkers are often just as short as their European counterparts. Farming in this country is very dependent on the migrant worker.

For every one of the 3.2 million male farm operators in the 2012 U.S. agriculture census statistics, there are probably a woman, a child and a migrant worker using farm equipment on that farm. According to the National Center for Farmworker Health Inc. fact sheet on demographics, 3 million migrant and seasonal workers are in the U.S. at any given time.

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I wonder if the industry has accounted for the current demographics of tractor operation when they design their cab ergonomics.

Unfortunately, I could not find any industry factoids on the ergonomics of tractor or skid loader operation by women, children and migrant workers. But I did discover astronaut studies. NASA has done quite a bit of work on the “anthropometry and biomechanics” differences between men and women.

I’ve used their figural anthropometric dimensional gender models while seated and wonder how that translates to tractor cab comfort for short people like me.

  • Tractor mirror placement: With an average 3.5 inches difference in eye height in the fifth percentile comparison, you can see how mirror placement and line of sight on tractors can be an issue for shorter-statured people.

  • Seat dimensions: A 4.2-inch difference in sitting height makes a world of difference in these newer skid loader models. Differences in crotch height (5.6), buttock circumference (4.3), buttock-knee length (3.2), buttock-popliteal length (3.6) and knee height (4.3) explains in inch increments why I can’t reach the pedals on this John Deere.

  • Muscular-skeletal strain: It’s easy to see how the differences in scye circumference, biacromial breadth, shoulder-elbow length, elbow rest height, forearm-hand length, hand length, hand breadth, hand circumference, waist height, buttock-popliteal length, thigh clearance, popliteal height and calf height between men and woman operators when seated can lead to a lot of aches and pains at the end of the day.

You’re probably thinking tractor cab designers must take all of this into account. Birell sent me a 1981 publication by Allis Chalmers engineer Larry Stikeleather titled “Operator Seats for Agricultural Equipment” that does a good job summarizing ergonomics. (But it does not appear to be a female depicted in the schematics used to explain ergonomic design.)

  • Grip strength: Joystick comfort and discomfort also differs considerably between men and women. In a different study, by the U.S. National Health and Nutrition Examination Survey on combined grip strength by age and sex (Figure 1), 89 percent of adult men were stronger than the 89 percent of adult women.

    Graph of combined grip strength studyA study of 49,964 participants by British researchers demonstrated grip strength of 20- to 40-year-old women maxes out at around 88.18 pounds, but men of the same age start out at over 80 pounds and go on up to 132.2 pounds. Canadian Suzy L. Wong graphed the mean medium grip strength reference value for selected countries by age and sex with similar results (Figure 2).

Mean/median grip strength reference values

Given these differences, and the awareness that musculoskeletal- related injuries are a real problem for all farm equipment operators (but more so for those of us who measure up on the short end of the stick), perhaps we should be asking our industry sales reps if joystick-operated grip-dependent farm equipment comes in gender-specific S, M, L and XL sizes?  end mark

PHOTO: Tractor design can be an ergonomic struggle for women operators, increasing fatigue and musculoskeletal discomfort. Photo by Courtney Miller, Spencer, Ohio.

Melissa A. Bravo
  • Melissa A. Bravo

  • Certified Crop Adviser – Herd Health Specialist
  • Meadow Lake Farm Consulting
  • Email Melissa A. Bravo

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