Kinematic and Gait Similarities between Crawling Human Infants and Other Quadruped Mammals

Abnormal interlimb coordination of motor developmental delay during infant crawling based on kinematic synergy analysis

BACKGROUND

Previous studies have reported that abnormal interlimb coordination is a typical characteristic of motor developmental delay (MDD) during human movement, which can be visually manifested as abnormal motor postures. Clinically, the scale assessments are usually used to evaluate interlimb coordination, but they rely heavily on the subjective judgements of therapists and lack quantitative analysis. In addition, although abnormal interlimb coordination of MDD have been studied, it is still unclear how this abnormality is manifested in physiology-related kinematic features.

OBJECTIVES

This study aimed to evaluate how abnormal interlimb coordination of MDD during infant crawling was manifested in the stability of joints and limbs, activation levels of synergies and intrasubject consistency from the kinematic synergies of tangential velocities of joints perspective.

METHODS

Tangential velocities of bilateral shoulder, elbow, wrist, hip, knee and ankle over time were computed from recorded three-dimensional joint trajectories in 40 infants with MDD [16 infants at risk of developmental delay, 11 infants at high risk of developmental delay, 13 infants with confirmed developmental delay (CDD group)] and 20 typically developing infants during hands-and-knees crawling. Kinematic synergies and corresponding activation coefficients were derived from those joint velocities using the non-negative matrix factorization algorithm. The variability accounted for yielded by those synergies and activation coefficients, and the synergy weightings in those synergies were used to measure the stability of joints and limbs. To quantify the activation levels of those synergies, the full width at half maximum and center of activity of activation coefficients were calculated. In addition, the intrasubject consistency was measured by the cosine similarity of those synergies and activation coefficients.

RESULTS

Interlimb coordination patterns during infant crawling were the combinations of four types of single-limb movements, which represent the dominance of each of the four limbs. MDD mainly reduced the stability of joints and limbs, and induced the abnormal activation levels of those synergies. Meanwhile, MDD generally reduced the intrasubject consistency, especially in CDD group.

CONCLUSIONS

These features have the potential for quantitatively evaluating abnormal interlimb coordination in assisting the clinical diagnosis and motor rehabilitation of MDD.

Reduced corticospinal drive to antagonist muscles of upper and lower limbs during hands-and-knees crawling in infants with cerebral palsy: Evidence from intermuscular EMG-EMG coherence

BACKGROUND

There is growing interest in understanding the central control of hands-and-knees crawling, especially as a significant motor developmental milestone for early assessment of motor dysfunction in infants with cerebral palsy (CP) who have not yet acquired walking ability. In particular, CP is known to be associated with walking dysfunctions caused by early damage and incomplete maturation of the corticospinal tract. However, the extent of damage to the corticospinal connections during crawling in infants with CP has not been fully clarified. Therefore, this study aimed to investigate the disparities in intermuscular EMG-EMG coherence, which serve as indicators of corticospinal drives to antagonist muscles in the upper and lower limbs during crawling, between infants with and without CP.

METHODS

This study involved 15 infants diagnosed with CP and 20 typically developing (TD) infants. Surface EMG recordings were obtained from two pairs of antagonist muscles in the upper limbs (triceps brachii (TB) and biceps brachii (BB)) and lower limbs (quadriceps femoris (QF) and hamstrings (HS)), while the infants performed hands-and-knees crawling at their self-selected velocity. Intermuscular EMG-EMG coherence was computed in two frequency bands, the beta band (15-30 Hz) and gamma band (30-60 Hz), which indicate corticospinal drive. Additionally, spatiotemporal parameters, including crawling velocity, cadence, duration, and the percentage of stance phase time, were calculated for comparison. Spearman rank correlations were conducted to assess the relationship between EMG-EMG coherence and crawling spatiotemporal parameters.

RESULTS

Infants with CP exhibited significantly reduced crawling velocity, decreased cadence, longer cycle duration, and a higher percentage of stance phase time compared to TD infants. Furthermore, CP infants demonstrated decreased coherence in the beta and gamma frequency bands (indicators of corticospinal drive) in both upper and lower limb muscles. Regarding limb-related differences in the beta and gamma coherence, significant disparities were found between upper and lower limb muscles in TD infants (p < 0.05), but not in infants with CP (p > 0.05). Additionally, significant correlations between coherence metrics and crawling spatiotemporal parameters were identified in the TD group (p < 0.05), while such correlations were not evident in the CP group.

CONCLUSIONS

Our findings suggest that the corticospinal drive may functionally influence the central control of antagonist muscles in the limbs during typical infant crawling. This functional role could be impaired by neurological conditions such as cerebral palsy. The neurophysiological markers of corticospinal drive, specifically intermuscular EMG-EMG coherence during crawling in infants with cerebral palsy, could potentially serve as a tool to assess developmental response to therapy.

The Kinematic-Muscle Synergies during Infant Crawling: A Pilot Study

Many feature extraction algorithms have been separately used for kinematic or muscle synergy analysis during human movement. However, very few studies focus on the co-extraction of kinematic and muscle synergies. Therefore, the aim of this study was to propose a novel and efficient approach for extracting the kinematic-muscle synergies during infant crawling. Surface electromyography signals and three-dimensional joint trajectories were collected from 20 typically developing infants during self-paced hands-and-knees crawling. Angular accelerations of shoulder, elbow, hip and knee flexion/extension computing from those joint trajectories were divided into two independent directional positive degrees-of-freedom. The kinematic-muscle synergies and corresponding activation coefficients were extracted using the non-negative matrix factorization algorithm based on two selection criteria of synergy number (i.e., criterion 1: the total constraint, criterion 2: a combination of the total constraint and a local constraint for each joint/muscle). Then, the data of each joint/muscle were reconstructed by those synergies and corresponding activation coefficients. Our results indicated that the minimum number of kinematic-muscle synergies based on criterion 1 is less than that based on criterion 2. The data reconstruction of joint flexion/extension based on criterion 2 is better than that based on criterion 1, whereas the data reconstruction of muscles is similar between criterion 1 and 2. These promising results show the feasibility of applying the proposed approach to clinical assessments of motor function for infants.Clinical Relevance- Extracting kinematic-muscle synergies during infant crawling has the potential for professional therapists or rehabilitation physicians to conduct the early assessment and rehabilitation treatment of infants with the central nervous system disorders.

Muscle synergy analysis of eight inter-limb coordination modes during human hands-knees crawling movement

In order to reveal in-depth the neuromuscular control mechanism of human crawling, this study carries out muscle synergy extraction and analysis on human hands-knees crawling under eight specific inter-limb coordination modes, which are defined according to the swing sequence of limbs and includes two-limb swing crawling modes and six single-limb swing crawling modes. Ten healthy adults participate in crawling data collection, and surface electromyography (sEMG) signals are recorded from 30 muscles of limbs and trunk. Non-negative matrix factorization (NNMF) algorithm is adopted for muscle synergy extraction, and a three-step muscle synergy analysis scheme is implemented by using the hierarchical clustering method. Based on results of muscle synergy extraction, 4 to 7 synergies are extracted from each participant in each inter-limb coordination mode, which supports the muscle synergy hypothesis to some extent, namely, central nervous system (CNS) controls the inter-limb coordination modes during crawling movement by recruiting a certain amount of muscle synergies, rather than a single muscle. In addition, when different participants crawl in the same inter-limb coordination mode, they share more temporal features in recruiting muscle synergies. Further, by extracting and analyzing intra-mode shared synergies among participants and inter-mode shared synergies among the eight inter-limb coordination modes, the CNS is found to realize single-limb swing crawling modes by recruiting the four inter-mode shared synergy structures related to the swing function of each limb in different orders, and realize the two-limb swing crawling modes by recruiting synchronously two intra-mode shared synergy structures. The research results of the muscle synergy analysis on the eight specific inter-limb coordination modes, on the one hand, provide a basis for muscle synergy hypothesis from the perspective of crawling motion, on the other hand, also provide a possible explanation for the choice of the inter-limb coordination mode in human crawling.

Impacts of Motor Developmental Delay on the Inter-Joint Coordination Using Kinematic Synergies of Joint Angles During Infant Crawling

Motor developmental delay (MDD) usually affects the inter-joint coordination for limb movement. However, the mechanism between the abnormal inter-joint coordination and MDD is still unclear, which poses a challenge for clinical diagnosis and motor rehabilitation of MDD in infant's early life. This study aimed to explore whether the joint activities of limbs during infant crawling are represented with kinematic synergies of joint angles, and evaluate the impacts of MDD on the inter-joint coordination using those synergies. 20 typically developing infants, 16 infants at risk of developmental delay, 11 infants at high risk of developmental delay and 13 infants with confirmed developmental delay were recruited for self-paced crawling on hands and knees. A motion capture system was employed to trace infants' limbs in space, and angles of shoulder, elbow, hip and knee over time were computed. Kinematic synergies were derived from joint angles using principal component analysis. Sample entropy and Spearman's rank correlation coefficients were calculated among those synergies to evaluate the crawling complexity and the symmetry of bilateral limbs, respectively. We found that the first two synergies with different contributions to the crawling movements sufficiently represented the joint angular profiles of limbs. MDD further delayed the development of motor function for lower limbs and mainly increased the crawling complexity of joint flexion/extension to some extent, but did not obviously change the symmetry of bilateral limbs. These results suggest that the time-varying kinematic synergy of joint angles is a potential index for objectively evaluating the abnormal inter-joint coordination affected by MDD.

Overground gait kinematics and muscle activation patterns in the Yucatan mini pig

Objective The objectives of this study were to assess gait biomechanics and the effect of overground walking speed on gait parameters, kinematics, and electromyographic (EMG) activity in the hindlimb muscles of Yucatan Minipigs (YMPs). Approach Nine neurologically-intact, adult YMPs were trained to walk overground in a straight line. Whole-body kinematics and EMG activity of hindlimb muscles were recorded and analyzed at 6 different speed ranges (0.4-0.59, 0.6-0.79, 0.8-0.99, 1.0-1.19, 1.2-1.39, and 1.4-1.6 m/s). A MATLAB program was developed to detect strides and gait events automatically from motion-captured data. The kinematics and EMG activity were analyzed for each stride based on the detected events. Main results Significant decreases in stride duration, stance and swing times and an increase in stride length were observed with increasing speed. A transition in gait pattern occurred at the 1.0m/s walking speed. Significant increases in the range of motion of the knee and ankle joints were observed at higher speeds. Also, the points of minimum and maximum joint angles occurred earlier in the gait cycle as the walking speed increased. The onset of EMG activity in the biceps femoris muscle occurred significantly earlier in the gait cycle with increasing speed. Significance YMPs are becoming frequently used as large animal models for preclinical testing and translation of novel interventions to humans. A comprehensive characterization of overground walking in neurologically-intact YMPs is provided in this study. These normative measures set the basis against which the effects of future interventions on locomotor capacity in YMPs can be compared.

Different flooring surfaces affect infants' crawling performance

This study assessed the influence of different types of flooring on infants' crawling motion patterns and performance. Each participating infant (range: 8.7-12.4 months) was encouraged to crawl on a tatami mat made of woven straw as well as other flooring types such as hardwood, carpet, and joint mat. Material tests were conducted to quantify the friction and shock absorption of the flooring. A three-dimensional motion capture system was used to measure spatiotemporal and kinematic variables during hands-and-knees crawling. An increased crawling rate was associated with a faster cadence of cyclic arm movements, but not with crawling stride length. Hardwood flooring had a significantly lower crawling rate and longer duration of hand-floor contact than tatami, while the crawling stride length and range of motion of joint movements were hardly affected by flooring type. The results of this study suggest a drawback of hardwood flooring in terms of infants' effective quadrupedal locomotion.

Crawl Position Depends on Specific Earlier Motor Skills

Early assessment of motor performance should allow not only the detection of disturbances but also create a starting point for the therapy. Unfortunately, a commonly recognised method that should combine these two aspects is still missing. The aim of the study is to analyse the relationship between the qualitative assessment of motor development at the age of 3 months and the acquisition of the crawl position in the 7th month of life. A total of 135 children were enrolled (66 females). The analysis was based on physiotherapeutic and neurological assessment and was performed in the 3rd, 7th and 9th months of life in children, who were classified according to whether they attained the crawl position or not in the 7th month. Children who did not attain the crawl position in the 7th month did not show distal elements of motor performance at the age of 3 months and thus achieved a lower sum in the qualitative assessment. Proper position of the pelvis at the age of 3 months proved to be very important for the achievement of the proper crawl position at the 7th month. Failure to attain the crawl position in the 7th month delays further motor development. The proximal-distal development must be achieved before a child is able to assume the crawl position. Supine position in the 3rd month seemed more strongly related to achieving the crawl position than assessment in the prone position.

Measurement and Analysis of Human Infant Crawling for Rehabilitation: A Narrative Review

When a child shows signs of potential motor developmental disorders, early diagnosis of central nervous system (CNS) impairment is beneficial. Known as the first CNS-controlled mobility for most of infants, mobility during crawling usually has been used in clinical assessments to identify motor development disorders. The current clinical scales of motor development during crawling stage are relatively subjective. Objective and quantitative measures of infant crawling afford the possibilities to identify those infants who might benefit from early intervention, as well as the evaluation of intervention progress. Thus, increasing researchers have explored objective measurements of infant crawling in typical and atypical developing infants. However, there is a lack of comprehensive review on infant-crawling measurement and analysis toward bridging the gap between research crawling analysis and potential clinical applications. In this narrative review, we provide a practical overview of the most relevant measurements in human infant crawling, including acquisition techniques, data processing methods, features extraction, and the potential value in objective assessment of motor function in infancy; meanwhile, the possibilities to develop crawling training as early intervention to promote the locomotor function for infants with locomotor delays are also discussed.

Analysis of the Inter-Joints Synergistic Patterns of Limbs in Infant Crawling

Hands and knees crawling is an important motor developmental milestone, which is characterized by diagonal coordination between upper and lower limbs. However, the features of inter-joint synergy within each limb in infant crawling is still not clear. Therefore, the aim of this study was to extract the inter-joint synergistic patterns during infant crawling and to test the possibilities of using the extracted inter-joint synergy to distinguish developmental delayed (DD) infants from typical developing (TD) infants. In this paper, kinematic data were collected from the shoulder, elbow, wrist, hip, knee, and ankle joints when 9 TD infants and 9 DD infants were crawling on hands and knees at their self-selected velocity. Tangential velocity was firstly calculated from the three-dimensional (3D) trajectory of each joint. Then, the non-negative matrix factorization (NMF) method was used to extract the joints synergistic patterns of each limb from the tangential velocity data. Our preliminary results showed that the crawling movement could be represented by a joint synergistic pattern, which consisted of three joints' data. In addition, we observed that the distal joint had a greater impact than the proximal joints during infant crawling. Moreover, it was found that the DD infants could be preliminarily distinguished from the TD infants by the features of inter-joint synergy during their crawling stage.

Human crawling performance and technique revealed by inertial measurement units

Human crawling performance and technique are of broad interest to roboticists, biomechanists, and military personnel. This study explores the variables that define crawling performance in the context of an outdoor obstacle course used by military organizations worldwide to evaluate the effects of load and personal equipment on warfighter performance. Crawling kinematics, measured from four body-worn inertial measurement units (IMUs) attached to the upper arms and thighs, are recorded for thirty-three participants. The IMU data is distilled to four metrics of crawling performance; namely, crawl speed, crawl stride time, ipsilateral limb coordination, and contralateral limb coordination. We hypothesize that higher performance (as identified by higher crawl speeds) is associated with more coordinated limbs and lower stride times. A cluster analysis groups participants into high and low performers exhibiting statistically significant differences across the four performance metrics. In particular, high performers exhibit superior limb coordination associated with a "diagonal gait" in which contralateral limbs move largely in-phase to produce faster crawl speeds and shorter crawl stride times. In contrast, low performers crawl at slower speeds with longer crawl stride times and less limb coordination. Beyond these conclusions, a major contribution of this study is a method for deploying wearable IMUs to study crawling in contextually relevant (i.e. non-laboratory) environments.

Intensive Neuromotor Therapy improves motor skills of children with Cornelia de Lange Syndrome: case report

Abstract Introduction: The Cornelia de Lange Syndrome (CdLS) is a rare genetic syndrome. Children with CdLS usually require physical therapy, however the efficacy of physical therapy intervention in this population is lacking in the research literature. Objective: The aim of this study was to report the effect of Intensive Neuromotor Therapy (INMT) on gross motor function and participation of a child with CdLS using the International Classification of Functioning, Disabilities and Health (ICF) model. Method: A Brazilian child with CdLS was followed for over seven months while undergoing three modules of INMT. Results: The child demonstrated an evolution of gross motor function with gains of 11.28% in the first module, 9.22% in the second module, and 10.29% in the third module of INMT. Conclusion: INMT resulted in improvements in gross motor function and participation during daily activities in a child with CDLS. Further studies of larger cohorts are needed to investigate the efficacy of INMT in children with CdLS.

A kinematic synergy for terrestrial locomotion shared by mammals and birds

Locomotion of tetrapods on land adapted to different environments and needs resulting in a variety of different gait styles. However, comparative analyses reveal common principles of limb movement control. Here, we report that a kinematic synergy involving the planar covariation of limb segment motion holds in 54 different animal species (10 birds and 44 mammals), despite large differences in body size, mass (ranging from 30 g to 4 tonnes), limb configuration, and amplitude of movements. This kinematic synergy lies at the interface between the neural command signals output by locomotor pattern generators, the mechanics of the body center of mass and the external environment, and it may represent one neuromechanical principle conserved in evolution to save mechanical energy.

Animals have evolved very different body shapes and styles of movement that are adapted to their needs in the habitats they live in. For example, mice, lions and many other animals use four limbs to walk, while humans and birds only use two limbs.

The styles animals use to walk also differ in terms of how long each foot is on the ground during a single stride, and for four-legged animals, in how long a forefoot lags behind the hindfoot on the same side of the body during the stride. Yet, there are general principles in how walking is organized that are shared between animals of vastly different shapes and sizes. Many animals save energy during walking by swinging the center of their body mass back and forth like a pendulum.

Networks of neurons are responsible for controlling how and when animals move, and these networks have similar architectures and patterns of activity in many different mammals and birds. How do signals from the nervous system regulate the position of the center of body mass while an animal walks?

Here, Catavitello et al. addressed this question by analyzing how over 50 different species of birds and mammals walked around in zoo enclosures and other semi-natural or natural environments. The species studied ranged in size from mice weighing around 30 grams to elephants weighing around 4 tonnes. The team also studied human volunteers walking on treadmills.

The experiments show that all the species studied coordinate their limbs in the same way, so that the angle to which a particular segment of a limb can bend varies together with the angles that the other limb segments bend. This coordination implies that the movement of the center of body mass is regulated and energy is saved.

Along with providing new insight into how walking evolved, these findings may aid research into new approaches to treat walking impairments in humans and other animals.

Degraded Synergistic Recruitment of sEMG Oscillations for Cerebral Palsy Infants Crawling

Background: Synergistic recruitment of muscular activities is a generally accepted mechanism for motor function control, and motor dysfunction, such as cerebral palsy (CP), destroyed the synergistic electromyography activities of muscle group for limb movement. However, very little is known how motor dysfunction of CP affects the organization of the myoelectric frequency components due to the abnormal motor unit recruiting patterns. Objectives: Exploring whether the myoelectric activity can be represented with synergistic recruitment of surface electromyography (sEMG) frequency components; evaluating the effect of CP motor dysfunction on the synergistic recruitment of sEMG oscillations. Methods: Twelve CP infants and 17 typically developed (TD) infants are recruited for self-paced crawling on hands and knees. sEMG signals have been recorded from bilateral biceps brachii (BB) and triceps brachii (TB) muscles. Multi-scale oscillations are extracted via multivariate empirical mode decomposition (MEMD), and non-negative matrix factorization (NMF) method is employed to obtain synergistic pattern of these sEMG oscillations. The coefficient curve of sEMG oscillation synergies are adopted to quantify the time-varying recruitment of BB and TB myoelectric activity during infants crawling. Results: Three patterns of sEMG oscillation synergies with specific frequency ranges are extracted in BB and TB of CP or TD infants. The contribution of low-frequency oscillation synergy of BB in CP group is significantly less than that in TD group (p < 0.05) during forward swing phase for slow contraction; however, this low-frequency oscillation synergy keep higher level during the backward swing phase crawling. For the myoelectric activities of TB, there is not enough high-frequency oscillation recruitment of sEMG for the fast contraction in propulsive phase of CP infants crawling. Conclusion: Our results reveal that, the myoelectric activities of a muscle can be manifested as sEMG oscillation synergies, and motor dysfunction of CP degrade the synergistic recruitment of sEMG oscillations due to the impaired CNS regulation and destroyed MU/muscle fiber. Our preliminary work suggests that time-varying coefficient curve of sEMG oscillation synergies is a potential index to evaluate the abnormal recruitment of electromyography activities affected by CP disorders.

The origin of bipedality as the result of a developmental by-product: The case study of the olive baboon (Papio anubis)

In this paper, we point to the importance of considering infancy in the emergence of new locomotor modes during evolution, and particularly when considering bipedal walking. Indeed, because infant primates commonly exhibit a more diverse posturo-locomotor repertoire than adults, the developmental processes of locomotion represent an important source of variation upon which natural selection may act. We have had the opportunity to follow the development of locomotion in captive individuals of a committed quadrupedal primate, the olive baboon (Papio anubis). We observed six infants at two different stages of their development. In total, we were able to analyze the temporal parameters of 65 bipedal steps, as well as their behavioral components. Our results show that while the basic temporal aspects of the bipedal walking gait (i.e., duty factor, dimensionless frequency, and hind lag) do not change during development, the baboon is able to significantly improve the coordination pattern between hind limbs. This probably influences the bout duration of spontaneous bipedal walking. During the same developmental stage, the interlimb coordination in quadrupedal walking is improved and the proportion of quadrupedal behaviors increases significantly. Therefore, the quadrupedal pattern of primates does not impede the developmental acquisition of bipedal behaviors. This may suggest that the same basic mechanism is responsible for controlling bipedal and quadrupedal locomotion, i.e., that in non-human primates, the neural networks for quadrupedal locomotion are also employed to perform (occasional) bipedal walking. In this context, a secondary locomotor mode (e.g., bipedalism) experienced during infancy as a by-product of locomotor development may lead to evolutionary novelties when under appropriate selective pressures.

Planar covariance of upper and lower limb elevation angles during hand-foot crawling in healthy young adults

Habitual quadrupeds have been shown to display a planar covariance of segment elevation angle waveforms in the fore and hind limbs during many forms of locomotion. The purpose of the current study was to determine if humans generate similar patterns in the upper and lower limbs during hand-foot crawling. Nine healthy young adults performed hand-foot crawling on a treadmill at speeds of 1, 2, and 3 km/h. A principal component analysis (PCA) was applied to the segment elevation angle waveforms for the upper (upper arm, lower arm, and hand) and lower (thigh, shank, and foot) limbs separately. The planarity of the elevation angle waveforms was determined using the sum of the variance explained by the first two PCs and the orientation of the covariance plane was quantified using the direction cosines of the eigenvector orthogonal to the plane, projected upon each of the segmental semi-axes. Results showed that planarity of segment elevation angles was maintained in the upper and lower limbs (explained variance >97%), although a slight decrease was present in the upper limb when crawling at 3 km/h. The orientation of the covariance plane was highly limb-specific, consistent with animal studies and possibly related to the functional neural control differences between the upper and lower limbs. These results may suggest that the motor patterns stored in the central nervous system for quadrupedal locomotion may be retained through evolution and may still be exploited when humans perform such tasks.

The neural control of interlimb coordination during mammalian locomotion

Neuronal networks within the spinal cord directly control rhythmic movements of the arms/forelimbs and legs/hindlimbs during locomotion in mammals. For an effective locomotion, these networks must be flexibly coordinated to allow for various gait patterns and independent use of the arms/forelimbs. This coordination can be accomplished by mechanisms intrinsic to the spinal cord, somatosensory feedback from the limbs, and various supraspinal pathways. Incomplete spinal cord injury disrupts some of the pathways and structures involved in interlimb coordination, often leading to a disruption in the coordination between the arms/forelimbs and legs/hindlimbs in animal models and in humans. However, experimental spinal lesions in animal models to uncover the mechanisms coordinating the limbs have limitations due to compensatory mechanisms and strategies, redundant systems of control, and plasticity within remaining circuits. The purpose of this review is to provide a general overview and critical discussion of experimental studies that have investigated the neural mechanisms involved in coordinating the arms/forelimbs and legs/hindlimbs during mammalian locomotion.

The variability of co-activation pattern of antagonist muscles in human infant crawling

Infant crawling is part of normal human gross motor development, and a 4-beat gait that involves rhythmical flexion and extension of limbs and the underlying muscle co-activation of antagonist muscle around the joint. However, detection the co-activation pattern of antagonist muscle are sparse due to the general difficulty of measuring locomotion in human infants. In this paper, sEMG of antagonist muscles and the corresponding kinematics data of limbs were collected when infants were crawling on hands and knees at their self-selected speed. The infant's gross motor developmental status was assessed by the global Gross Motor Function Measure Scale (GMFM-88) as well. The method based on EMG-EMG plots was used to quantify the variability of co-activation pattern of antagonist muscle. After that, we observed that antagonist muscles of upper limb (triceps brachii and biceps brachii) showed less variability of co-activation pattern of muscles than lower limb(quadriceps femoris and hamstrings) during crawling, and this variability was also varied in different crawling phases (stance and swing). Furthermore, we found some varied behaviors in the co-activation patterns of antagonist muscles when gross motor developmental level increased. The preliminary work suggests that such adaptive changes may be related to the adjustment of neuromuscular in the early stage of gross motor development.

Computational modeling of spinal circuits controlling limb coordination and gaits in quadrupeds

Interactions between cervical and lumbar spinal circuits are mediated by long propriospinal neurons (LPNs). Ablation of descending LPNs in mice disturbs left-right coordination at high speeds without affecting fore-hind alternation. We developed a computational model of spinal circuits consisting of four rhythm generators coupled by commissural interneurons (CINs), providing left-right interactions, and LPNs, mediating homolateral and diagonal interactions. The proposed CIN and diagonal LPN connections contribute to speed-dependent gait transition from walk, to trot, and then to gallop and bound; the homolateral LPN connections ensure fore-hind alternation in all gaits. The model reproduces speed-dependent gait expression in intact and genetically transformed mice and the disruption of hindlimb coordination following ablation of descending LPNs. Inputs to CINs and LPNs can affect interlimb coordination and change gait independent of speed. We suggest that these interneurons represent the main targets for supraspinal and sensory afferent signals adjusting gait.

Growth of the pectoral girdle in a sample of juveniles from the kellis 2 cemetery, Dakhleh Oasis, Egypt

OBJECTIVES

This study investigates growth patterns in the scapula and clavicle in a cross-sectional juvenile skeletal sample ranging from 20 weeks gestation to 8.5 years of age from the Kellis 2 cemetery, Dakhleh Oasis, Egypt. The primary goal is to quantify growth patterns and growth velocities in the scapula and clavicle to better understand the development of the pectoral girdle.

METHODS

A series of low-order polynomial regression models was used to examine growth curves in clavicle diaphyseal length, scapular height, and scapular width. Incremental growth and relative percent increase were examined among successive age groups as a proxy measure of growth velocity. Scapular body proportions were assessed with the scapular index and compared across age groups using a Kruskal-Wallis test with post-hoc tests.

RESULTS

A third-order polynomial best describes growth in clavicle diaphyseal length and scapular height, and a second-order polynomial best describes growth in scapular width. Growth velocity patterns are similar among clavicle diaphyseal length, scapular height, and scapular width particularly from birth until the end of early childhood. Clavicle diaphyseal length decelerates during middle childhood while scapular height and width accelerate during this time. With increasing age, the scapular body proportionately increases more in height than in width. The relatively narrow scapular body characteristic of adult scapulae is first evident during early childhood.

CONCLUSIONS

Changes in scapular body shape during ontogeny may be a reflection of the greater alterations taking place in the integrated morphology of the pectoral girdle during the biomechanical shift from crawling to bipedalism. Am. J. Hum. Biol. 28:636-645, 2016. © 2016 Wiley Periodicals, Inc.

Antagonist muscle co-activation of limbs in human infant crawling: A pilot study

Muscle Co-activation (MCo) is the simultaneous muscular activation of agonist and antagonist muscle groups, which provides adequate joint stability, movement accuracy during movement. Infant crawling is an important stage of motor function development that manifests non-synchronization growth and development of upper and lower limbs due to the well-known gross motor development principle of head to toe. However, the effect of MCo level for agonist and antagonist muscle groups on motor function development of limbs has not been previously reported. In this paper, sEMG signals were collected from triceps brachii (TB) and biceps brachii (BB), quadriceps femoris (QF) and hamstrings (HS) of limbs when fourteen infants were crawling at their self-selected speed. Antagonist muscle co-activation was evaluated by measuring two common indexes (co-activation index and Pearson's correlation coefficient).A significant difference was observed between upper limbs and lower limbs, but the relationship between MCo and speed of crawling was poor. This study is an opening for further investigation including a longitudinal study and compare against infant with CNS disorders.