Last Updated: Mon, February 4, 2019
A researcher with the Washington State Department of Labor and Industries teamed up with researchers from North Carolina State University to put to the test something that most truck drivers do every day … sometimes several times a day.
Their goal was to find out what is the safest, least injurious way to crank the landing gear on a trailer. Their research, using a mock up of a landing gear, led to findings and recommendations for a different cranking method depending on whether the driver is raising or lowering the landing gear.
Something as mundane and common as cranking the gear has never been studied before, notes Washington State researcher Jia-Hua Lin. "There was nothing in the literature about it. There's nothing about these kinds of cranking actions," he said, adding that this action is responsible for pain and injury if done improperly.
There are statistics pointing to the importance of awareness of the cost to the trucking industry when drivers do injure themselves in the course of doing their job.
According to a 2010 National Institute for Occupational Safety and Health Survey of some 1,300 drivers at 32 truck stops across the country, 26.3 percent of the injuries reported by truck drivers were to their arms, while 21.1 percent were related to their necks or backs.
That's almost half of all musculoskeletal injuries – sprains and strains -- reported by drivers.
Statistics from the Bureau of Labor Statistics show that long-haul truck drivers report injuries requiring days away from work at the rate of 355.4 incidents per 10,000 full-time workers. That's more than double the number of injuries reported for other dangerous professions like construction, farming, fishing and forestry.
To find out what can be done to help drivers reduce injuries -- and lost work days -- while cranking landing gears Lin and the North Carolina State University researchers rigged 12 male drivers with an apparatus loaded with sensors to measure their muscle activity and shoulder's range of motion. They then positioned them in various positions to crank the gear.
Findings showed that for raising the trailer there was less strain on the shoulder and muscles when the driver stands parallel to the trailer and cranks the gear in a forward motion rather than facing the trailer and cranking in a rotating motion. The correct position, as shown in the photo, is for the driver to stand with the trailer next to his left side.
That's because raising the trailer needs to overcome more resistance. We've all been there. Nobody enjoys lowering the gear on a trailer with a 45,000-pound load of bottled water. The resistance is considerably more than a 4,000-pound load of bubble wrap. The parallel position makes for less strain on the shoulder and muscles, and allows the driver to use more of his body strength to crank up all that weight.
Conversely, in lowering the trailer, researches recommend standing facing the gear. Although this position would put undo strain on the shoulders and muscles if raising the trailer, must of the resistance is overcome by the weight of the trailer wanting to seek a lower level. The shoulder can handle the much-reduced torque for lowering the trailer.
The mechanics of both actions is simple. Lin explains:
"When you face the trailer and crank, as shown in the photo, you throw a circle with your whole arm in front of you; you are rotating your shoulder. When the resistance is low, it's OK. The shoulder can handle that kind of torque. But when the resistance is high the shoulder joint itself is not as powerful," Lin said.
"This goes to the biomechanics of the shoulder joint. It's harder to throw a circle in front of you. When you rotate the shoulder in front of you, then the elbow is useless. You have to use your shoulder joint mostly to throw this circle in front of you. The shoulder muscles are not that good at generating this kind of torque."
Forcing the issue, especially by facing the trailer and trying to lower the landing gear of a heavily-loaded trailer results in an unsafe and high-strain condition.
Another downside to using the wrong cranking position for raising or lowering the landing gear is safety.
Lin notes that drivers could injure themselves in the facing-trailer position if their hand happens to slip off of the crank handle while straining to raise the trailer with a heavy load. The resistance of the weight could force the crank to snap back and injure the driver.
As part of research for this project Lin asked drivers what other common tasks would lend themselves to research for safety and efficiency. Besides cranking, drivers suggested they would be interested in research on pulling the fifth-wheel pin, raising the hood and pulling down the rolling door.
Lin chose the cranking experiment first because it was easier to build a mock up for that project to simulate the action in a laboratory setting. "We wanted to do a controlled study. Some of the other tasks were not easy for us to produce in the lab," he said.
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