We use our "position sense" when we have to quickly adapt our body to changing or unexpected demands. It's the body's way of helping us stay upright when we run on uneven ground or jump into a floating canoe. It also helps keep our joints steady and safe from injury.
We use the position sense of our spines when we lift and carry heavy items. These researchers were interested in seeing how good the spine's position sense is in situations when it is at highest risk of injury. The spine is especially likely to be injured when it is twisted to the side or when it is bent far forward. (This is why we're supposed to lift with our legs, using a straight back.)
Eleven people were tested to see how well they could sense and control the position of their backs. The subjects did pretty well with bending to one side or the other. But the further they had to bend over, the more difficult it was for them to match the test posture. If this is true of most people, it would help explain why lifting with the back stooped over seems to cause so many spine injuries.
The authors recommend that people take extra precautions when they need to bend down deeply to lift objects or do their daily tasks. They say if someone needs to stoop over, they should be make sure they have firm footing and to be especially careful of shifting loads.
Sara E. Wilson, PhD, and Kevin P. Granata, PhD. Reposition Sense of Lumbar Curvature with Flexed and Asymmetric Lifting Postures. In Spine. March 1, 2003. Vol. 18. No. 5. Pp. 513-518.