COLUMBUS, Ohio -- In the first study of its kind, Ohio State University researchers believe they have found an important factor in recurring back injury: our natural tendency to avoid using hurt muscles.
The findings, to appear in the December 1 issue of the journal Spine, point to new forms of physical therapy and new safety standards for physical labor in the workplace. This work could potentially affect the incidence of severe back injury and reduce the millions of dollars in health costs and lost workdays created by these injuries every year.
William Marras, professor of industrial, welding, and systems engineering, and his colleagues discovered that people tend to compensate for back injuries by using many inappropriate muscles in place of the muscles that hurt.
"People with back pain guard the injured area by using more muscles than they need to," Marras said. "The more muscles they use, the greater the load there is on the spine."
For instance, injured people may employ muscles in their abdomen or sides, or other, uninjured back muscles, even though these muscles are not necessary for lifting.
The study revealed that people with back injuries unknowingly inflict twice as much twisting force on their spine, and 1.5 times as much compressive force as uninjured people, when lifting the same object.
Over time, greater loads on the spine lead to more serious back injuries, such as disc degeneration, which require surgery. What's more, lifting objects slowly, as injured people also tend to do, only intensifies the harm. "Moving slowly just increases the length of time the spine has to endure those extra forces," Marras said.
Marras directs Ohio State's Biodynamics Laboratory, where he and his colleagues conducted this study to compare how people with and without back injuries use their muscles.
His colleagues included Sue Ferguson, a research scientist, Benjamin Lucas, a graduate student, and Kermit Davis, a former graduate student who is now an assistant professor of environmental health at the University of Cincinnati.
The Ohio Bureau of Workers Compensation funded this research to combat back injury -- the number one reason Americans miss work, after the common cold. Across the country in 1999, more than 420,000 people missed work because of back injury. Each lost an average of 6 days on the job, according to the U.S. Bureau of Labor Statistics.
The Ohio State study compared the lifting activity of 22 uninjured adults to that of 22 people who were suffering from lower pack pain (LBP). The LBP participants were recruited from the practice of Purnendu Gupta, an orthopaedic surgeon formerly at Ohio State, and now at the University of Chicago.
No other studies have been able to make such a comparison, because injured people are often unwilling or unable to perform the physical exertions necessary for these tests, Marras said.
To solve this problem, the researchers created a mathematical technique to obtain needed information from the partial exertions an injured person can comfortably provide.
The technique takes data from an injured person's electromyogram (EMG), a measure of a muscle's electrical activity, and calibrates it to provide a basis for comparison with an uninjured person's EMG. The researchers were then able to calculate what the forces on the spine would be if an injured person were able to exert the full power of their muscles.
For the same exertion, LBP participants used many more muscles in the back, creating much larger forces on the spine.
Marras likened the forces on the spine to a seesaw: "When people apply all those extra muscles, it's as if they're pushing down on the short end of a seesaw, and trying to lift something on the far end," Marras said. "They exert more force, and to little effect."
On average, the LBP participants weighed more than their uninjured counterparts, and weight also increases force on the spine. That's why losing weight can help people recover from back injury, Marras said.
Another route to recovery, physical therapy, may have to change to prevent recurring back injuries, he added.
Typical therapy for back injury involves helping the patient regain strength. But just as important as strength is learning to use back muscles appropriately.
"After a back injury, people need to re-learn how to use their muscles naturally. The timing of the muscles working together needs to return to normalcy," Marras said.
The study suggests that this new rehabilitation strategy, combined with weight loss and a redesign of the workplace, could reduce the possibility of repeat back injuries.
The U.S. Occupational Health and Safety Administration maintains strict guidelines for preventing healthy people from becoming injured, but not for preventing injured people from becoming injured again.
Marras said the guidelines for injured workers would have to be even more strict. "There are some motions, such as bending to lift far away from the body, or lifting something off the floor, that a normal person can do once in a while without serious harm. Those are the kinds of motions an injured person should never do at all," Marras said. "Bottom line -- you can send people back to work after a back injury, but you have to be very careful about what you have them do."
Recurring back injuries debilitate workers, and create massive health care costs. In Ohio, for example, 16 percent of people with back injuries account for 80 percent of the total health care costs for this injury. That's because the recurring injuries suffered by this 16 percent cost so much more to treat than first-time injuries.
For a first-time back injury, the cost of drugs, doctor's visits, and physical therapy can add up to as much as $10,000. But for more severe cases -- the kind that result when a person is hurt over and over again -- the costs can climb as high as $300,000, Marras said.