A Study On The Effect Of Human Inversion On Bending And Relaxation

Objective：: Low back pain (LBP) has been a common disease in modern society,which affects people’s life greatly. Meanwhile, it causes hugely economic loss for themajority of countries. Fourteen male college students volunteered need to take lumbarflexion-extension motion with cycle of5s flexion and5s extension in standing andheadstand on the basis of making surface electromyographic (EMG) and kinematicdata synchronized. The objective of this report is to further study the influence causedby changing motional ways of body on LBP. It is expected to find difference oferector spinae（ES） muscles and biceps femoris (BF) between standingflexion-extension and headstand flexion-extension and to analyze properties of EMGof ES and BF as well as the kinematic parameters. This may offer more evidence tothe mechanism of LBP.Subjects：Fourteen male college students volunteered to participate in a protocol. Themean age,height and body mass of the participants were25±0.85years,175±5cm,weight64.8±4.4kg, respectively. None of the participants reported previous episodesof spinal disorders or low back pain.Methods：A special stool was designed to help participants taking headstand posture.A wooden frame, which includes four legs, could put participants’ head into andcontact with participants’ shoulders. Participants rely on the support of shoulders,assistance of others and the security of bandage to make body headstand, in the sametime, put the feet shoulder width apart, keep arms relax and put them at the front ofeach subject’s chest, and keep the knee straight during the test. Then, participants starttaking lumbar flexion-extension motion with cycle of5s flexion and5s extension.During the standing performance, each subject was required to put the feet shoulderwidth apart, and keep the knee straight during the test [68], and make finger nailscontacting toes of feet in full flexion. Each trial consisted of10s total time:5s fromupright posture to full anterior flexion, and5s from full flexion back to upright posture[69].The EMG signals were amplified1000with a frequency band-pass of10–500Hz,1mV noise referred to input, and CMRR of120dB. The Input impedancewas109kV. The resulting signal was sampled at1000Hz via a14-bit data acquisitionsystem and stored for later processing. Kinematic of the trunk and pelvis segmentswere monitored by a single camera (Sony-DCR-TRV17E) positioned3.0m away fromthe participant with a direct view of the data at50frames per second. The timing foreach trial was set by a metronome with one beat per second. Each subject performedthree full flexion trials, with30s rest between them.Results：1) During the headstand flexion-extension, compared with standing posture,obvious difference of ES motional pattern is observed. ES activity was ceased laterobviously than the cessation of ES during the standing flexion-extension (the closetiming of EMG in standing position is35.09%(10.51), the close timing of EMG inheadstand position is45.94%（5.42）; P<0.01)； ES activity was re-initiated earlierthan it in standing flexion-extension (the re-initiated timing of EMG in standingposition is56.13%（5.24）, the re-initiated timing of EMG in headstand position is68.46%（4.75）;P<0.01）. It is affirmative that the time of ES activity is longer duringheadstand performance.2) The intensity of EMG of ES is increased at the phase of flexion-relaxationphenomena (FRP) during headstand flexion and extension (the average intensity ofEMG signal is0.04(0.01) in standing position and the average intensity of EMGsignal is0.05(0.02) in headstand position; P<0.05)Conclusions： Due to the change of180°of body position during headstandflexion-extension, the vestibular apparatus participate as one of the most importantfactors to regulate the activity of relevant muscles, especially for ES. The time of ESactivity become longer and it’s relax time is shorter. Meanwhile the intensity of EMGof ES is greater at the phase of FRP during headstand flexion and extension. Thesechanges make ES overloaded and cause fatigue of ES. Thus, if people, such as gymnasts, astronauts and acrobats, etc. take headstand flexion-extension often, theyare risk of getting LBP caused by ES fatigue.