So what is it with back pain, anyway? If researchers are right, then over 80 percent of working adults are going to have low back pain (LBP) sometime. Is it the worker’s size or height that makes the difference? Or is it personality? The workplace? Mental stress?
Researchers at the Low Back Biomechanics and Workplace Stress Laboratory in Cincinnati are trying to find some answers to these questions. This study looked at 60 college-aged subjects (30 men and 30 women). No one had back pain or a history of back pain. Each person lifted boxes from a conveyor in front to a shelf on one side or the other. The lift rate was two lifts per minute to eight lifts per minute. A lumbar motion monitor measured trunk motion during the lifting. Electrical activity of the muscles was also measured.
There are two kinds of load on the spine: compressive and shear. Compression is the load straight down through the spine from top to bottom. Shear is the side-to-side force of one bone against another.
In this study body size, height, and shape had a big effect on the shear force. Personality and gender also made a difference. Compression load was based on the weigt of the load. The researchers also found that muscle activity is affected most by gender, load weight, and body type. Body size and shape had the greatest influence on trunk motion and posture when lifting. Mental concentration didn’t seem to have an impact on spinal loads or muscle activity.
The authors say the most surprising finding is the effect of load placement as a unique stressor. Load placement refers to where the box is held (close to the body or away from the body) and how it’s lowered to the shelf. They conclude that the worker and workplace need to be a good match. Workplace design such as adjustable shelves may be one place to start. Other adjustable equipment may reduce the effect of different worker heights, sizes, and shapes. Knowing what factors put the greatest load on the spine may lead to better ways to prevent LBP.