Prolonged standing as a precursor for the development of low back discomfort: an investigation of possible mechanisms.

Low back discomfort (LBD) has been associated with prolonged periods of standing, yet research has shown that the magnitude of spinal loading during standing is relatively minimal. Therefore, the mechanism of this discomfort is not fully understood. Research has monitored numerous variables during prolonged periods of standing; however the focus of this work has been primarily on the comparison of the effect of different floor surfaces on these variables. No study to date has made an attempt to relate these changes to the development of LBD. The purpose of this study was therefore to determine possible mechanisms for the development of LBD during standing by monitoring biological variables. It was hypothesized that during a prolonged standing period, LBD would develop and the measured variables would change over time. Sixteen individuals stood for 2h while activation of torso and hip muscles, lumbar spine posture, back extensor muscle oxygenation, torso skin temperature, and centre of pressure changes under the feet were monitored over time. Thirteen out of sixteen individuals developed LBD as a result of the prolonged standing period, which significantly increased over the 2-h period (p<0.0001). Only three of the 37 variables measured were significantly altered over time. However, a generated regression model incorporating 15 of the 16 individuals (which incorporated how each individual stood in the first 15 min) explained 78% of the variance in LBD at the end of the 2-h standing period. Prolonged standing resulted in LBD, yet few significant changes in the measured variables were observed over time. It is possible that LBD is not linked with alterations in standing over time, but rather associated with how an individual initially stands.