Take more breaks to avoid back injury on the job

By Megan Rauscher

NEW YORK (Reuters Health) - People who lift boxes and packages all day need to take longer and more frequent breaks to avoid suffering a back injury, research suggests. This is especially true for people new to the job.

Confirming prior research, the study also indicates that the risk of back injury is greatest towards the end of a work shift when fatigue sets in.

With funding from the National Institute for Occupational Safety and Health, Dr. William Marras and colleagues in the Biodynamics Laboratory at Ohio State University had four new and six experienced workers lift boxes onto conveyor belts for 8 hours, as one would do working in a shipping center. The boxes weighed 2, 11, and 26 pounds. The workers took a half hour lunch break and two 15-minute breaks.

During their shift, the workers wore oximeters on their lower back -- a device that measures through the skin the amount of oxygen reaching the muscles, an indicator of how hard the muscles are working and whether they are becoming fatigued.

Marras and colleagues found that the back muscles needed more oxygen as the workday progressed. During the first two hours of lifting, the workers oxygen level rose to 11 percent above their resting level. During the next two hours, the oxygen level rose to 13 percent above resting.

Taking a half-hour lunch break helped the muscles recover from the morning exertion, with oxygen levels returning to resting level, but once back on the job, the workers' oxygen needs rose steeply and kept climbing throughout the afternoon, reaching a peak level of 16 percent above resting level during the last two hours of the work day.

"Their muscles were becoming fatigued much faster during the afternoon and we known that fatigue increases the risk of back injury," Marras said. "The only way to counteract that effect is with more breaks as the day goes on."

The two 15-minute breaks, one mid-morning and one mid-afternoon, helped the back muscles recover somewhat, but not as much as the 30-minute lunch break.

The researchers also noticed that novice workers, when they got tired, tended to tense up their muscles, preventing proper blood flow and oxygenation. Their muscles also needed more oxygen than the muscles of the experienced workers.

"The bottom line is that it's much more costly from a physiological standpoint for novices to do the same work as experienced people," Marras said.

SOURCE: Clinical Biomechanics, January 2007.