Nonlinear Dynamics Analysis Of Standing Balance Control On Sloped Surfaces Under The Influence Of Aging And Lumbar Disc Herniation

Standing balance control is to effectively keep the movement of the center of gravity of the body within the support of surface.Aging and diseases can change one or several systems in sensory,nervous and motor,affecting standing balance.The elderly is a group with high incidence of falls.The fall has become the first cause of death due to injuries among elderly people over 65 years old in China.In-depth understanding of balance performance decline associated with aging is essential for the prevention of falls in elderly people.Lumbar disc herniation(LDH)affects the patient's nerves and muscles,and makes the patients have different characteristics of standing balance control.In-depth understanding of the changes in LDH-related balance control mechanisms can help to find a more convenient,real-time and accurate quantitative assessment method.This article mainly completes the following work:(1)Research on dynamical coordination of the elderly people during standing on sloped surfaces.Center of pressure(COP)is closely related to the movement of the body's center of mass and can be used as an effective indicator of balance control.The dynamical coordination of the COP signal in anterior-posterior(AP)and medial-lateral(ML)directions,and in the same direction between two lower limbs during standing is of great significance for the deep understanding of the standing balance control mechanism.In this study,18 healthy elderly subjects and 18 gender-matched healthy young subjects were required to standing on sloped surface with 5 different angles.The cross recurrence quantification analysis(CRQA)was applied to quantify the dynamical coordination of intra-and inter-limb COP signal pairs.The elderly group presented more deterministic components in the COP coordination of the left limb than the young subjects.The aging led to tighter inter-limb COP coupling in AP direction and increased restriction on balance control between limbs.The effects of sensorimotor deficits due to aging could be more obviously exhibited as standing on declined rather than inclined surfaces.Standing on a sloped surface and removing the visual feedback could result in increased randomness but decreased complexity in the intra-and inter-limb coupling of COP components.(2)Research on neural control loop of the elderly people during standing on sloped surfaces.The neural control loop,as the front end of the balance control system,is crucial to the performance of balance control.In order to quantitatively analyzing the changes of neural control loop in the elderly,the frequency-specific fractal analysis(FsFA)algorithm was used to process the COP trajectory signal and COP velocity signal in specific frequency band.The results showed that aging significantly reduced the control flexibility of the neural control loop related to proprioception.Two neural control loops—one related to proprioception and another related to visual-vestibular system,cooperated with and complemented each other in the process of balance control.(3)Research on multi-muscle synergy of lower limb in elderly people during standing on sloped surfaces.As a source of power for the musculoskeletal system,muscles provide power for balance control system.Multiple muscles work in synergistic or antagonistic mode.In this study,the surface electromyography(sEMG)signals of anterior tibia,soleus,medial head of gastrocnemius and lateral head of gastrocnemius muscles were recorded.The multi-muscle synergy of synergistic muscles and of antagonistic muscles were quantified by joint recurrence quantification analysis(JRQA).The results showed that aging increased the synergy of the synergistic and antagonistic muscle groups.When subjects stood on a sloped surface,the effects of sensory motor defects caused by aging on standing balance were exhibited more obviously.Cut off the visual feedback,the multi-muscle synergy modes would be more rigid.(4)Nonlinear dynamics analysis of standing balance control mechanism in patients with lumbar disc herniation during standing on sloped surfaces.At this stage,there is little research on the effects of LDH on standing balance control.In this study,10 patients with LDH and 10 age-and gender-matched healthy subjects were asked to stand on sloped surfaces with 3 different angles.The CRQA was applied to quantify the dynamic coordination of COP,FsFA was used to explore the changes of neural control loop in patients with LDH,and CRQA was applied to quantify the dynamical coupling of antagonistic muscles in the thighs and calves.The patients with LDH presented magnified inter-limb load asymmetry and had more deterministic components in the COP coordination of the non-paretic limb and of the full-body than the healthy subjects.The LDH reduced the flexibility of neural control loop related to proprioception and enhanced the strength of coupling of antagonistic muscles in the paretic limb.The parameters of FsFA for neural control loop and of CRQA for muscle coupling showed a certain correlation with dysfunction scale scores.