Research Of Motor Skill Development Alters Muscle Synergy And Joint Kinematics In Human Infant Crawling

Hands-and-knees crawling is an important motor skill developmental milestone for typical developing infants and a widely used intervention for infants with motor disabilities.Accordingly,quantitative measures of motor function in human infant crawling has an exciting prospect in clinics,such as objectively assessment of developmental progression and early evaluation of the effect of intervention for those atypical developing infants.However,current assessment tools of motor skill development are primarily based on clinical scale measures,which provide few information of muscular activity and joint kinematics controlled by central neural system(CNS).On the other hand,Hands and knees crawling is a typical milestone of motor skill development,which involves the coordination of limbs.In addition,the coordination of limb has been implemented by the CNS-controlled synergistic muscle contraction serving for rhythmic joint movement.That is,the relevant muscle synergies and joint kinematics reflect the infant's motor developmental status.Therefore,the current PhD thesis hypothesized that there's an underlying association between infant's motor developmental status and the relevant muscle synergies and joint kinematics “organized” by CNS.Establishing such relationship is important to develop a quantified metrics for the evaluation of motor skill development,and also helpful to understand the developmental progression during infant's early life.Under the support of National Natural Science Foundation(31470953),the current thesis focused on synergistic contractions of skeletal muscles during infant crawling,and mainly tested the effect of(1)typical developmental progression;(2)atypical developmental status(i.e.motor developmental delay)on the muscle synergies and joint kinematics during infant crawling.The aim of this study was to understand and establish the associations between infant's motor developmental status and the kinetic(i.e.muscular activity)and kinematic(i.e.joint kinematics)output of the central neural system(CNS).The detailed work can be summarized as following:(1)Data collection during Infant crawling.This thesis proposed an experiment protocol,including the inclusion,exclusion,and classification criterion of subjects;protocol of how to collect surface electromyography(sEMG)and movement trajectory of limbs during human infant crawling,and the corresponding experiment standards.Then,this thesis collected surface electromyography(sEMG)and movement trajectory of limbs from 66 infants,which including typical developing infants and infants with developmental delay.(2)Muscle synergy analysis during infant crawling.The current thesis focused on analyzing the characteristics of muscle synergy at different dimension,such as the co-activation between antagonist muscles of single joint,and the synergistic contractions across multiple muscle groups.(1)The results from typical developing infants indicated that the developmental progression can be manifested by the coordinated muscular activities(i.e.co-activation index,CI)of infant crawling.Moreover,the developmental progression facilitated the co-activation level between antagonist muscles,and such changes can be regarded as the improved “origination” performance of CNS on muscle contraction.(2)A non-negative matrix factorization(NMF)algorithm and the corresponding neuromuscular model was applied to extract the inter-limb “muscle synergy” during human infant crawling for the first time.In the analysis of typical developing infants,it was found that two muscle synergies were extracted from the inter-limb eight muscles.Both synergies were recruited alternately during crawling,and the structure of extracted synergy was similar across subjects.In the analysis of infants with motor developmental delay,it was found that the infants with developmental delay demonstrated fewer muscle synergies,prolonged activation time,and more co-activation muscles per synergy.These results suggest the “origination” disabilities of CNS on muscle contraction due to the brain injure during birth.(3)Kinematic analysis during infant crawling.In addition to the analysis of muscle synergy,kinematic analysis during infant crawling was also conducted in the current thesis.Several metrics such as temporal-spatial parameters(crawling velocity,cadence,et al),range of joint angle,power and smoothness of joint movement were extracted from the movement trajectory of each joint.Moreover,this thesis analyzed the kinematic coordination across different joints(i.e.“joint synergy”)for the first time,which is similar to the theory of “muscle synergy”.(1)In the analysis of typical developing infants,it was found that developmental progression facilitated the crawling proficiency,such as increased crawling velocity and cadence,decreased crawling duration and stance phase time.Moreover,the power of joint movement during crawling was also increased with motor skill development progression.These results can be regarded as the kinematic output of the improved “origination” performance of CNS on muscle contraction.That is,the neuromuscular system gradually learned how to organize the muscle contractions with the motor developmental progression,and the performance of joint kinematics improved accordingly;(2)Compared with typical developing infants,infant with developmental delay demonstrated increased power,but the corresponding crawling velocity,cadence.et al did not show any significant changes,which means a decreased transition efficiency of energy cost.Moreover,the movement smoothness of joints decreased in infants with developmental delay,suggesting a rigid and stereotype crawling behavior.Our experimental results demonstrated no effect of motor skill development on the kinematic characteristics of joint angle and “joint synergy”.(4)Correlation analysis between muscle synergies and kinematics.After the analysis of muscle synergy and kinematics,a correlation analysis was conducted between these two metrics.It was found that the co-activation index between quadriceps femoris and hamstrings significantly correlated with the movement power and smoothness of knee joint.In addition,the activation coefficient of inter-limb muscle synergy and inter-limb joint synergy showed a significant correlation,which demonstrate the role of neuromuscular system to modulate the inter-limb coordinated movement.These findings provide a new insight into the neuromuscular strategy of crawling movement.(5)The design of a software used for crawling analysis.Last,this thesis designed a software to fill the gap of crawling analysis in clinics.This software was designed by the LabVIEW platform and tested by the data collected in the current thesis.In summary,this PhD thesis evaluated the effect of motor skill development on the muscle synergy and kinematics during infant crawling for the first time,which offer the potential of kinetic and kinematic measures for early evaluation of motor skill development during infant's early life.