Psychological Expected Effect of Lumbar Stabilizer Rapid Responses to Sudden Trunk Unloading imbalance

Objective:Sudden trunk unloading is the important reason to cause lumbar spine instability,acute lumbar muscle injury and low back pain.In this study,sudden trunk unloading imbalance paradigm was used to study the effects of psychological unloading expectation on rapid response latency(RRL) and rapid response intensity(RRI) of lumbar stabilizer muscles to sudden trunk unloading imbalance and to investigate the physiological mechanism of subjective expectation to reduce lumbar muscle injury in condition of sudden unloading imbalance.Methods:Sudden unloading imbalance trials on trunk muscles of left and right side were implemented in expected and unexpected unloading conditions on 11 healthy young male subjects respectively.Surface Electromyography(sEMG) signals from bilateral lumbar multifidus(LMF) muscles,lumbar erector spinae(LES) and external oblique(EO) muscles were measured simultaneously to calculate RRI and RRL of the investigated muscles,and to investigate the influences of sudden trunk unloading on RRI and RRL of them and the physiological effects of psychological unloading expectation.Results:Compared with resting situation,average electromyography(AEMG) of LMF,LES and EO all significantly increased.There were no noticeable differences between AEMG of ipsilateral and contralateral LMF and LES while RRI of ipsilateral EO was noticeably lager than that of the contralateral.Psychological unloading expectation had a trend of a certain degree of less significance on AEMG responses of ipsilateral LMF,LES and EO,but it could noticeably weaken AEMG responses of contralateral LES and EO.Psychological unloading expectation could accelerate RRL of ipsilateral and contralateral LMF,LES and EO,among which the effect on RRL of contralateral LMF was statistically significant.Conclusions:Sudden trunk unloading imbalance could significantly activate the activities of global and local lumbar stabilizer muscles.Psychological unloading expectation could significantly accelerate RRL of contralateral LMF and weaken RRI of lumbar stabilizer muscles and then enhance lumbar spine stability without increasing lumbar loading.The possible mechanism was related to the feed-forward control caused by subjective expectation.