ISPGR International Conference edition:19 location:Bologna date:21-25 June 2009
It has been demonstrated that persons with non-specific low back pain (NSLBP) exhibit a rigid postural control strategy in static circumstances (e.g. quiet standing), even in postural conditions when this ankle-steered strategy is not the most appropriate such as standing on an unstable support surface . It remains unclear whether this altered postural control strategy is used in more dynamic tasks on unstable support surfaces. Therefore, the aim of this study was to examine the differences in proprioceptive postural control strategy during the sit-to-stand-to-sit (STSTS) movement on an unstable support surface (“foam”) in people with NSLBP and healthy controls.
Methods: The total duration of five consecutive STSTS movements performed on “foam” as well as the duration of each stance, sitting and movement phase of 47 young subjects with NSLBP and 9 young pain-free subjects was recorded. Postural sway characteristics were evaluated with a six-channel force plate during the five consecutive STSTS movements. In addition, muscle vibration on triceps surae muscles and lumbar multifidus muscles was used to appraise the relative proprioceptive weighting (RPW) . A score equal to 1 corresponds to 100% reliance on afferent input from triceps surae muscles for postural control, a score equal to 0 corresponds to 100% reliance on back muscle afferent input.
Results: Persons with NSLBP need significantly more time to perform five consecutive STSTS movements on an unstable support surface than pain-free subjects (p<0.005). This longer performance is caused by both longer stance phases (p<0.05) and longer sitting phases (p<0.05), while the sit-to-stand and stand-to-sit movements have equal durations in people with NSLBP and healthy controls. Furthermore, the postural sways during the stance phases are significantly larger in persons with NSLBP compared to healthy controls (p<0.05). In addition, persons with NSLBP have significantly higher RPW values compared to healthy controls on an unstable support surface (NSLBP: 0.49±0.19; Healthy: 0.38±0.12; p<0.05).
Conclusion: Despite the adoption of a more multi-segmental proprioceptive postural control strategy (still less than the healthy controls) during the unstable support surface condition, these young persons with NSLBP still seemed to have more problems performing a dynamic postural task such as STSTS. For the performance of complex postural tasks optimal co-ordination of producing mobility while also preserving stability is necessary [2,3]. However, the persons with NSLBP showed longer durations of both the stance and sitting phases and larger sways during standing, indicating mainly impairments in the preparatory postural adjustments but not in the focal movement. Preparatory postural adjustments via pelvic control might be impaired in these persons with NSLBP. Further research will be required to elucidate the role of proprioceptive control of the pelvis in complex axial movements and ultimately in the mechanisms of NSLBP.
Acknowledgements: This work was supported by grants from the Fund for Scientific Research-Flanders (1.5.104.03 and G.0674.09)
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