| Purpose: to investigate if there is an effect of prolonged trunk axial twisting on thedevelopment of low back disorder. We hypothesized that if prolonged trunk axialtwisting elicits significant trunk rational creep and spinal shrinkage. If it causes theVAS to have a significant increase in low back area, and causes erector spinae musclesto become active longer during anterior flexion as well as extension, indicating a higherrisk in developing low back disorder.Background: Trunk axial twisting is thought to be strongly associated with low backdisorder in industrial environment work. However, it is not clear if prolonged trunk30axial twisting could induce spinal shrinkage. The time dependent spinal rotationalcreep elicited by prolonged trunk axial twisting has not been demonstrated in healthyindividuals either.Methods:16male university students volunteered for this study. The trunk axialtwisting was created with a torsion moment of50Nm in10min. The spinal shrinkagewas measurement before and after twisting by a precision stadiometer.The axialrotational creep was estimated by the transverse camera view directly on the top of thehead and estimated by a Performance Analysis System. The visual analog scale in lowback area was examined both in the initial and at the end of twisting. Each performedthree trials of lumbar flexion-extension with the cycle of5s flexion and5s extension instanding before and after shrinkage. Surface electromyography from bilateral erectorspinae muscles as well as trunk flexion performance was recorded synchronously invideo camera. A one-way ANOVA with repeated measures was used to evaluate theeffect of twist.Before twisting, maximal voluntary contractions (MVC) were obtainedfor left and right ES through applying resistance in the Beiring–Sorensen position.Thevideo data both from transverse and sagittal view were digitized and transformed totwo-dimensional space using the APAS (Ariel Performance Analysis System, USA) software. The Kinematic data were smoothed using a zero lag fourth order Butterworthdigital low-pass filter with a cut-off frequency of1Hz.Results: The result showed that after10min static axial spinal twisting with50Nmtwisting moment, there were significant changes (p<0.01) both on spinal shrinkage androtational angle with the normalized value4.7(2.1)mm and10.4(4.5)°respectively aftertwisting and the VAS increase with a mean value45mm. The erector spinae was activein a larger angle during flexion as well as extension after trunk axial twisting.Significant changes were found in flexion period both at EMG-Off flexion and atEMG-Off inclination after twisting. At EMG-Off flexion, the absolute value increasessignificantly (p<0.01) from41.5°before to53.1°after whereas the normalized valueincreases significantly (p<0.01) from67.5%before to83.4%after twisting. AtEMG-Off inclination, the absolute value increases significantly (p<0.01) from59.0°before to68.5°after whereas the normalized value increases significantly (p<0.05)from64.8%before to75.3%after twisting.Obvious increases were also found in the extension period both at EMG-Onflexion and EMG-On inclination. At EMG-On flexion, though not significantly, theabsolute value increases obviously (p<0.05) from50.4°before to56.4°after whereasthe normalized value increases obviously (p<0.05) from81.9%before to88.5%aftertwisting. At EMG-On inclination, the absolute value increases significantly (p<0.05)from66.7°before to77.0°after whereas the normalized value increases significantly(p<0.01) from72.5%before to84.2%after twisting.Conclusions: Prolonged trunk twisting induces a significant spinal shrinkage a causesthe trunk to have a time dependent axial rotational creep. It causes the VASto have a significant increase in low back area, and causes erector spinae muscles tobecome active longer during anterior flexion as well as extension, indicating a higherrisk in developing low back disorder. |
PDF Full Text Request