Take More Breaks to Avoid Back Injuries, Study Says

A study of workplace back injuries funded by NIOSH and conducted by researchers at Ohio State University has come up with three key findings:

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  Workers who do a lot of lifting need to take longer and more frequent breaks to prevent back injuries.


• Workers who are new to a job involving a lot of lifting should take breaks even more frequently.


• The risk of back injury is higher at the end of a shift.

Study coauthors William Marras and Gang Yang had 10 people lift boxes onto a conveyor for 8 hours while the research team measured how much oxygen was getting to the muscles of the lower back.

Boxes weighed between 2 and 26 pounds, and the test subjects were given only two 15-minute breaks and one 30-minute meal break during the 8-hour period.

Test subjects wore oximeters, which measured oxygen levels in the muscles of their lower back. They were also equipped with lumbar motion monitors, which measured spinal movement.

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Less O2, More Injuries

The researchers discovered that as the workday progressed, the workers’ back muscles needed more and more oxygen. And the more oxygen needed, the more fatigued the back muscles became.

The two short breaks helped a little, but not as much as the longer lunch break. But even though the 30-minute break helped back muscles recover somewhat, once the workers began lifting boxes again after lunch, the demand for oxygen in the back muscles rose sharply and kept climbing for the rest of the workday.

"That was alarming to us,” Marras says, “because it means that their muscles were becoming fatigued much faster during the afternoon, and we know that fatigue increases the risk of back injury. Because the oxygen demand at the end of the day was so much higher, that’s when we’d expect people to get hurt on the job. And the data I see coming out of industry bear that out—people tend to hurt their back toward the end of a shift."

Marras and Yang believe that the only way to counteract the increased risk of injury is with more breaks as the day goes on.

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Tense Muscles Are a Bad Sign

Lumbar motion monitor information was also important to the study’s findings. Marras says the data showed that people use their muscles differently as the muscles get tired. Previous studies have found that when back muscles begin to hurt, they tense up. So people compensate by trying to use less fatigued muscles to lift with.

Muscle tension prevents proper blood flow, so the muscles become even more oxygen deprived. Marras says that using different muscles to lift may lessen pain at first, but it increases stress on the joints and the spine, which over time increases risk of disabling back injury.

"Now because of this study, we have a clinical reason for why that’s happening. It’s because the muscles are becoming fatigued, because they have such a high demand for oxygen," Marras says. “When that happens, it’s like the muscles fight each other. You have back muscles that fight the abdominal muscles, and when they both contract, it’s like a seesaw effect, except you’re pulling down on both ends, and your spine is in the middle."

Ouch! But don’t worry. There’s help on the way for your employees’ beleaguered backs. Tomorrow, we’ll focus on some tips—in addition to taking longer, more frequent work breaks—that can also help prevent back injuries.

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