Most Tractors Require More Strength Than Teenagers’ Physical Capabilities

By Jane Fyksen Crops Editor
Thursday, September 11, 2008 6:23 AM CDT

The clutches and brakes on the majority of commonly used farm tractors require more strength than teens 13 to 17 can comfortably and consistently muster. That’s according to a new study published this summer, which, according to one of the primary researchers, “raises serious questions about the ability of children to safely operate tractors in common use on U.S. farms.”

Barbara Marlenga is a research scientist with the National Farm Medicine Center in Marshfield with a PhD in nursing and rural sociology. She grew up on a dairy farm near Catawba, where her brother is now milking cows.

She tells Agri-View that the ergonomic forces required to operate controls on 40 different models of tractors n ones most commonly used on U.S. farms n typically exceed the physical capabilities of most teens n males and females, ages 13 to 17. Most simply aren’t strong enough to safely drive tractor for an extended length of time, notes Marlenga, who is also associated with the National Children’s Center for Rural and Agricultural Health and Safety (part of the National Farm Medicine Center).

This new study provides objective evidence that might result in farm safety experts establishing more restrictive minimum-age recommendations for tractor operation by youths. This research is ongoing and meant to provide a clearer picture of the ability of teens of varying physical capacities to effectively n and safely n drive tractor. Titled "Forces Required to Operate Controls on Farm Tractors: Implications for Young Operators," this groundbreaking study is co-authored by University of California-Davis ergonomic specialists Fadi Fathallah and Ji Hong Chang; Richard Berg, a Marshfield bio-statistician; and William Pickett, an injury epidemiologist in Ontario.

Marlenga explains the reason for the work. In 1999, farm safety experts developed the North American Guidelines for Children’s Agricultural Tasks (www.nagcat.org) that offered parents some advice for assigning jobs around the farm n including driving tractor n to kids, based on expert consensus as to their physical, mental and emotional capacities. The guidelines were based on the “best judgment” of experts and producer reviewers. There was no hard, scientific research-based data n until now.

Further, Marlenga says farm tractors account for the majority of fatal injuries to youth working in agriculture. Her research team wanted to know why. Are adolescents being assigned tractor work they’re not physically able to do? It now appears that may very well be the case.

Working directly with farmers and equipment dealers in California and Wisconsin, this team identified the most commonly used tractors in the U.S. Fifty-eight percent were between 20 and 70 horse, but they all fell between 20 and 156 horsepower. Marlenga says they already knew from other research that it’s the smaller, older tractors that teenagers tend to drive n not the very newest, state-of-the-art tractors (even if their folks own several on the home farm).

In this study, they estimated the activation forces required to operate tractors in common use and compare them with existing estimates of physical strength of teens 13, 15 and 17 (males and females). Marlenga says the medical community already knows the typical maximum leg strength of teens of various ages. They compared that to the force needed to clutch, brake and operate the steering wheels n factoring in a “reasonable exertion level,” determined to be 30 percent of the “maximum strength” necessary. That’s become it’s impossible to “give it all you’ve got” all the time. That 30 percent limit is the level at which they felt the tractors could be comfortably and safely operated for a sustained period of time.

They found that the majority of the brakes and clutches on the 40 tractors studied exceeded that limit for both sexes, ages 13 to 17. Even for 17-year-old males, with presumably the greatest leg strength, the majority of tractors exceeded that reasonable exertion level. Most of the tractors in this study were older than 1985 models, but as noted, they’ve been determined to be ones farmers are still using a lot today.

Kids aren’t “driving the new high-end tractors,” that maybe are easier to operate, Marlenga remarks.

Other studies, in fact, have already shown that the activation force needed to operate tractors exceeds the physical capabilities of 60 percent of the female farm workforce and even up to 20 percent of the adult males on farms.

As for the steering wheels, Marlenga says that was “pretty easy,” and basically, not an issue for teen tractor drivers.

As for the strength needed to clutch and brake, however, their work presumed an optimal position for the young drivers with leg bent and pushing straight to the floor and a back rest. In reality, teens are driving many tractors without backrests, and they have to extend their legs and press forward to clutch and brake. “So we may be overestimating what kids can do,” she remarks.

This research determined that driving some of the most commonly used tractors on farms today “takes more strength” than most kids have to give n at least for longer periods of time. Parents who don’t take that into account may be putting their youngsters in jeopardy. Marlenga says safety experts know that teens are involved in collisions and runovers; she speculates maybe they can’t brake in time.

While kids can take tractor safety at age 12, Marlenga thinks parents should give careful thought to the physical strength needed to brake and clutch. Then when there’s a lot of gear changing required, they should wonder if what they’re asking their younger tends to do in the tractor seat is simply taking too much exertion. Will certain jobs tire them physically and mentally n and jeopardize their safety.

Work is ongoing. Marlenga says they’re also looking at reach distances n how far away the controls are n and kids range of vision at different heights. How well can they see and what are the blind spots? Physical perimeters needed to safely operate tractors will likely be fine-tuned for the farm task guidelines after their work is complete. The guidelines might very well be revised, she notes.

Right now the guidelines suggest kids be at least 12 to drive a tractor, and be 14 for more complex tractor work. In light of these new results, however, maybe parents should consider the physical strength of their teen and the force needed to comfortably brake and clutch the tractors on their farm.

The guidelines also advise kids only operate tractors with rollover protective structures (ROPS), Marlenga adds.

She doesn’t expect tractor manufacturers to make tractors in the future that’ll be easier for kids to drive. They clearly state tractors are for adults.

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