Muscle activity and postural control in individuals with and without non-specific chronic low back pain
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Background: Earlier findings suggest that low back pain (LBP) subjects show less postural alterations and less sway during prolonged standing (PS) compared to that of healthy subjects. Greater fatigability, impaired lumbar proprioception and increased muscle activation are proposed to contribute to this altered behavior during PS. So far, these properties have not been assessed prior and after PS in LBP subjects. Objectives: The purpose of the present study was to investigate muscle activity and postural control during PS, and the effect of standing on postural sway, muscle activation, fatigue, proprioception, pain and perceived exertion in non-specific chronic low back pain (NSCLBP) subjects in comparison to healthy subjects. Methods: Participants underwent a prolonged standing trial (15 minutes) and a set of pre and post prolonged standing tests consisting of; quiet standing trials (60 seconds), perceived pain and exertion ratings and flexion-relaxation-, reposition error- and maximal voluntary contraction (MVC) tests. Results: During PS NSCLBP subjects swayed more, and showed more variation in low back muscle activation. No difference in body weight shift was found between groups. After PS the NSCLBP group showed higher ratings of perceived exertion compared to that of healthy. Both groups showed deterioration in flexion-relaxation ratio and MVC after PS, however, there were no significant differences between groups in these measures. No change was shown on reposition error after PS in either group. Also, results showed no difference in body sway between groups after PS. Conclusion: These results suggest that NSCLBP subjects do not present an impaired postural strategy compared to healthy subjects during PS. Furthermore, PS does not seem to have a negative effect on NSCLBP subjects in a greater extent than that of healthy subjects. Key words: Non-specific chronic low back pain, prolonged standing, center of pressure, maximal voluntary contraction, proprioception, muscle activation, fatigue.