Investigation On Hands-and-Knees Crawling In Human Adults By Means Of Muscle Synergy Analysis

As a theory to explain how the central nervous system(CNS)correctly controls the movement of many skeletal muscles of the human body and how they cooperate with each other to complete various movements,muscle synergy hypothesis reasonably solves degree of freedom(DOF)problem of human locomotion.In this theory,muscle synergy is considered to be the smallest unit under control of the central nervous system.Multiple muscle synergies in charge with different functions are recruited in turn to complete a certain task.Muscle synergistic analysis has been widely used in the studies on neuromuscular control mechanisms and neurological diseases.Crawling is the primary manner of human locomotion before walking,playing a vital role in the development of neonates and infants.The study of crawling can help to understand the control mechanisms underlying human crawling,and is valuable in the clinical assessment of the development of infants and neuromuscular disorders in patients.As a whole-body-movement,crawling requires the cooperation of almost all trunk and limb muscles.Present studies on crawling focuses on the coordination patterns between limbs,and the intra-limb coordination pattern is rarely involved.Muscle synergistic analysis can explore both inter and intra-limb coordination of crawling,and has great potential in exploring the underlying neuromuscular control mechanism of crawling.This thesis reports muscle synergistic analysis of hands-and-knees crawling in human adults to offer basis for the further exploration on crawling in children or cerebral palsy.The main work can be summarized as follows:(1)A research program of hands-and-knees crawling based on muscle synergistic analysis was proposed,which included surface electromyography(EMG)data acquisition during crawling,data preprocessing and muscle synergy analysis.Taking into account the muscle distribution,size and depth,sEMG data from 16 most relevant muscles(8 from the arm and 8 from the leg)were recorded on each of both sides of the body.A non-negative matrix decomposition algorithm was used to extract the muscle synergies.A new way to calculate limb phase lag based on muscle synergy was proposed and the change of recruitment pattern was quantified from three aspects:recruitment level,recruitment phase and recruitment time duration.(2)Inter and intra-limb coordination pattern of hands-and-knees crawling were analyzed.In the analysis of intra-limb coordination,it was found that two muscle synergies,one relating to stance phase and another relating to swing phase,were extracted from each limb.Both synergies were recruited alternately during crawling and the similar phenomenon was observed across other subjects.In the analysis of inter limb coordination,it was found that there was a half phase difference in the recruitment of corresponding muscle synergies on both the left and right sides.Recruitment patterns of muscle synergies extracted from the arm muscles of all subjects were approximately the same,but those extracted from the leg muscles varied and depended on the crawling pattern.Intra group similarity was observed among subjects in trot-like or pace-like crawling patterns,but fundamental differences were observed among subjects crawling with mixed limb pairing.Using the recruiting phase differences in muscle synergies between stance phases of the arm and leg,inter limb coordination patterns could be classified effectively.(3)Muscle synergy analysis was performed under different crawling conditions.From the muscle synergy analysis at different speeds and angles,it was found that the change of speed would affect the crawling pattern.Subjects with the mixed limb pairing at low speed tended to use the trot-like or pace-like crawling pattern at a higher speed.However,the change in speed did not affect the synergy structures,but it affected the recruitment level,recruitment phase and recruitment time duration.In addition,the change of angle did not change the crawling pattern,but impacted the synergy structure and the recruitment level.The study of muscle synergy of human crawling with hands and knees is of great significance to understand the underlying control mechanism of crawling,and provides a theoretical basis for two-layer central pattern generator(CPG)model.Under the assumption of a two-layer CPG model,the structure of the muscle synergy can be considered as the production of pattern formation(PF)circuit,and the recruitment pattern can be regarded as the output of the rhythm generator(RG).RG of each limb recruited muscle synergies corresponding to the stance phase and the swing phase alternately to achieve the control of single limb movement,and the coordination of four limbs achieves a crawling movement.Adaptation to crawling speed and angle is done by the central nervous system by adjusting the RG and PF circuits.