Workers who lift for a living need to take longer or more frequent breaks than they now do to avoid back injury, according to a new study at Ohio State University.
The study also suggests that people who are new on the job need to take breaks even more often than experienced workers, and that the risk of injury is higher at the end of a work shift.
People who participated in the study lifted boxes onto conveyor belts for eight hours, while researchers measured the amount of oxygen that was reaching the muscles in their lower back.
The oxygen level indicated how hard the muscles were working, and whether they were becoming fatigued, explained William Marras, professor of industrial welding and systems engineering at Ohio State. His research and others’ has shown that muscle fatigue is linked to back injury.
The study, which appeared in a recent issue of the journal Clinical Biomechanics, is the first to examine what happens to muscle oxygenation over a full workday.
Despite the fact that the study participants were performing the same job at the same pace all day, their back muscles needed more oxygen as the day went on. Taking a half-hour lunch break helped their muscles recover from the morning’s exertion, but once they started working again, their oxygen needs rose steeply and kept climbing throughout the afternoon.
“That was alarming to us, 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,” Marras said.
Two 15-minute breaks, one mid-morning and the other mid-afternoon, helped muscles recover a little, but not as much as the half-hour lunch.
“This tells us two things,” Marras said. “First, rest is good — a half-hour break does a good job of helping muscles recover. But it also tells us that people are especially at risk for back injury at the end of the day, and the only way to counteract that effect is with more breaks as the day goes on.”