Trunk and head stabilization during the first months of independent walking

Postural control during reaching while sitting and general motor behaviour when learning to walk

AIM

To study changes in muscular postural strategies and general motor behaviour during the transition to independent walking. Postural control was assessed at its two functional levels: (1) direction specificity, in which dorsal muscles are primarily activated when reaching forward; and (2) fine-tuning of direction specificity.

METHOD

In an explorative longitudinal study, surface electromyograms of the arm, trunk, and neck muscles of 28 typically developing infants were recorded during reaching while sitting. Each infant was assessed in three developmental phases: during pull-to-stand (T0), first independent steps (T1), and 1 month after T1 (T2). Motor behaviour was assessed using the Infant Motor Profile (IMP). The effect on developmental outcome measures (postural parameters and IMP) of the developmental phases (T0, T1, T2) was estimated using linear mixed-effects models.

RESULTS

None of the postural parameters changed significantly over time. However, individual developmental trajectories showed infant-specific postural reorganizational changes. Total IMP score decreased between T0 and T1 (mean IMP score 95% and 91% respectively; p<0.001); between T1 and T2 IMP scores did not change (91% and 93%; p=0.073).

INTERPRETATION

Typically developing infants do not show consistent patterns of postural reorganization but show individual muscular strategies during the transition to independent walking. However, signs of reorganization of general motor behaviour are present.

WHAT THIS PAPER ADDS

Infants show signs of reorganization of motor behaviour when learning to walk. Infants show individual strategies of postural reorganization when learning to walk.

Early human motor development: From variation to the ability to vary and adapt

This review summarizes early human motor development. From early fetal age motor behavior is based on spontaneous neural activity: activity of networks in the brainstem and spinal cord that is modulated by supraspinal activity. The supraspinal activity, first primarily brought about by the cortical subplate, later by the cortical plate, induces movement variation. Initially, movement variation especially serves exploration; its associated afferent information is primarily used to sculpt the developing nervous system, and less to adapt motor behavior. In the next phase, beginning at function-specific ages, movement variation starts to serve adaptation. In sucking and swallowing, this phase emerges shortly before term age. In speech, gross and fine motor development, it emerges from 3 to 4 months post-term onwards, i.e., when developmental focus in the primary sensory and motor cortices has shifted to the permanent cortical circuitries. With increasing age and increasing trial-and-error exploration, the infant improves its ability to use adaptive and efficicient forms of upright gross motor behavior, manual activities and vocalizations belonging to the native language.

Deliberately Light Interpersonal Contact Affects the Control of Head Stability During Walking in Children and Adolescents With Cerebral Palsy

OBJECTIVE

To evaluate the potential of deliberately light interpersonal touch (IPT) for reducing excessive head and trunk sway during self-paced walking in children and adolescents with cerebral palsy (CP).

DESIGN

Quasi-experimental, proof-of-concept study with between-groups comparison.

SETTING

Ambulant care facility, community center.

PARTICIPANTS

Children and adolescents (N=65), consisting of those with CP (spastic and ataxic, n=26; Gross Motor Function Classification System I-III; mean age, 9.8y; 11 girls, 15 boys) and those who were typically developed (TD, n=39; mean age, 10.0y; 23 girls, 16 boys).

INTERVENTIONS

IPT applied by a therapist to locations at the back and the head.

MAIN OUTCOME MEASURES

As primary outcomes, head and trunk sway during self-paced walking were assessed by inertial measurement units. Secondary outcomes were average step length and gait speed.

RESULTS

CP group: apex and occiput IPT reduced head velocity sway compared with thoracic IPT (both P=.04) irrespective of individuals' specific clinical symptoms. TD group: all testing conditions reduced head velocity sway compared with walking alone (all P≤.03), as well as in apex and occiput IPT compared with paired walking (both P≤.02).

CONCLUSIONS

Deliberately light IPT at the apex of the head alters control of head sway in children and adolescents with CP. The effect of IPT varies as a function of contact location and acts differently in TD individuals.

Evaluation of toddler different strategies during the first six-months of independent walking: a longitudinal study

Twenty infants (age 10-16 month) were analyzed using inertial sensors over a 6-month period after the onset of independent walking. Changes in gait temporal parameters, coordination and gait strategies were evaluated. Gait temporal parameters showed a developmental shift at 2 months of walking experience: after this period, a change in the developmental trend was present in most of the analyzed parameters. Cadence results showed that the increased velocity is more due to an increase in step length than to an increase in cadence, after the first two months of independent walking. Different gait strategies were identified during the first month of independent gait based on collected data; after one month, characteristics of the pendulum mechanism were present in each examined toddler.

Three-dimensional head and trunk movement characteristics during gait in children with spastic diplegia

This study uses a recently developed trunk model to determine which head and trunk kinematic parameters differentiate children with spastic diplegia from typically developing (TD) children while walking. Differences in head and trunk parameters in relation to the severity of the motor involvement (GMFCS levels) were additionally examined. The trunk model consisted of five segments (pelvis, thorax, head, shoulder line, spine). Discrete kinematic parameters (ROM, mean position) and angular waveforms were compared between 20 children with spastic diplegia (age 9.8 years±2.9 years; GMFCS I: n=10, GMFCS II: n=10) and 20 individually age-matched TD children (9.7 years±3 years). A new measure for overall trunk pathology, the trunk profile score (TPS), was proposed and included in the comparative analysis. Compared to TD children, children with GMFCS II showed a significantly higher TPS and increased ROM for pelvis tilt, for thorax and head in nearly all planes, and the angle of kyphosis. In children with GMFCS I, only ROM of thorax lateral bending was significantly increased. Sagittal ROM differentiated best between GMFCS levels, with higher ROM found in children with GMFCS II. Current results provide new insights into head and trunk kinematics during gait in children with spastic diplegia.

Head stability during quiet sitting in children with cerebral palsy: effect of vision and trunk support

Deficits in postural control are one of the hallmarks of disability in children with cerebral palsy (CP). Yet, much remains unknown regarding the etiology of postural deficits in these children. Here we evaluated postural control at a simplified task level by measuring head stability during quiet sitting while systematically manipulating the level of trunk support and vision in 15 children with CP (6-16 years), 26 typically developing (TD) children (4-14 years), and 11 adults. While TD children did not differ significantly from adults, children with CP had greater head movement than adults in both the sagittal and frontal planes under all conditions except frontal plane movement with Torso Support. Vision did not affect head stability in the sagittal plane for any group while it had differential effects on head stability in the frontal plane. Lack of vision improved head stability in adults and older TD children while destabilizing the head in young children (TD and CP) during the most unstable sitting position. Moreover, vision affected children with CP differently depending on their movement disorder. Children with spastic CP performed worse with eyes closed while those with dyskinetic CP had improved head stability with eyes closed. Our results demonstrate that children with mild to moderate CP have deficits in head stability even during quiet sitting.

Early stage of walking: development of control in mediolateral and anteroposterior directions

The authors examined the changes in bipedal gait of toddlers in the anteroposterior (AP) and mediolateral (ML) directions, as a set, at the onset of independent gait and 1 month after onset. Two groups with distinctly different dynamic resources were studied: 8 toddlers with typical development (TD) and 8 toddlers with Down syndrome (DS). Three-dimensional kinematic data were collected, and gait parameters, such as walking speed, stride length, and stride frequency, as well as the ratio of exchange between potential energy and kinetic energy of the center of mass (COM), were calculated. Displacement of the COM in the AP and ML directions were also analyzed. For some gait variables, toddlers with DS seemed to show more mature values at walking onset than their peers with TD. Those group differences reversed and increased by Visit 2. When the authors considered the motion of the COM of the system, it became clear that the qualitative differences between those groups were characterized primarily by constraints in the ML direction. The authors propose that establishment of coupling between AP and ML oscillations is a key component for the emergence of independent bipedal walking for both populations.

Gait control in spinal palsy

Developmental motor impairment with lower limb spasticity most commonly corresponds to cerebral palsy of the spastic diplegia type. Here we describe a 4-year-old girl whose locomotor phenotype reflects early cortico-spinal lesion at the spinal level. This child has developmental spastic paraparesis secondary to D4-D8 cord compression. We analysed her gait using the ELITE optoelectronic system and compared it to that of six normal age-matched controls and six age-matched children with leucomalacic spastic diplegia. Gait characteristics of the patient included preservation of head orientation and arm swing similar to findings in normal controls and contrasting with children with spastic diplegia. She also had truncal instability and displayed lack of selectivity in lower limb movement as in spastic diplegia and in contrast with normal controls. This may reflect differences in locomotor control between developmental spasticity of cerebral and spinal origin. The latter might correspond to spinal palsy defined as abnormal movement and posture secondary to non-progressive pathological processes affecting the immature spinal cord.

Head movements during locomotion in a gibbon and Japanese macaques

Kinematic analysis of head and body movements during locomotion in Macaca fuscata and Hylobates lar revealed that coordinated head rotation and translation that have been reported to play an important role in stabilizing gaze during locomotion for humans are also observed in non-human primates. The fact that well-coordinated head movements were observed in two species, and during both bipedal and quadrupedal walking, suggests that the head orientation during locomotion is well regulated in the manner of top-down control over the species and modes of locomotion. The result validates the monkey model and enables us to explore the underlying mechanisms for gaze, head, and postural control during locomotion.

Muscle synergies during shifts of the center of pressure by standing persons

Movements by a standing person are commonly associated with adjustments in the activity of postural muscles to cause a desired shift of the center of pressure (COP) and keep balance. We hypothesize that such COP shifts are controlled (stabilized) using a small set of central variables (muscle modes, M-modes), while each M-mode induces changes in the activity of a subgroup of postural muscles. The main purpose of this study has been to explore the possibility of identification of muscle synergies in a postural task using the framework of the uncontrolled manifold (UCM) hypothesis employing the following three steps in data analysis: (i) Identification of M-modes: Subjects were asked to release a load from extended arms through a pulley system, resulting in a COP shift forward prior to load release. Electromyographic (EMG) activity of eleven postural muscles on one side of the body was integrated over a 100 ms interval corresponding to the early stage of the COP shift, and subjected to a principal component (PC) analysis across multiple repetitions of each task. Three PCs were identified and associated with a 'push-back M-mode', a 'push-forward M-mode' and a 'mixed M-mode'. (ii) Calculation of the Jacobian of the system, which relates changes in the magnitude of M-modes to COP shifts using regression techniques: Subjects performed three different tasks (releasing different loads at the back, voluntarily shifting body weight forward and backward, at different speeds) to verify if the relationship between magnitudes of M-modes and COP shifts is task or direction specific. (iii) UCM analysis: Three tasks were chosen (load release in the front, arm movement forward and backward) which were associated with an early shift in COP. A manifold was identified in the M-mode space corresponding to a certain average (across trials) shift of the COP and variance per degree of freedom within the UCM (V(UCM)) and orthogonal (V(ORT)) to the UCM was computed. Across subjects, V(UCM) was significantly higher than V(ORT) when analysis at the third step was performed using a Jacobian computed based on a set of tasks associated with a COP shift in the same direction but not in the opposite direction. This result confirms our hypothesis that the M-modes work together as a synergy to stabilize a desired shift of the COP. Forward and backward COP shifts are associated with different synergies based on the same three M-modes.

Acquirement of stability and mobility in infant gait

We examined gait development in a longitudinal and cross-sectional study in 35 infants, age range 7-70 months. We estimated walking stability from mediolateral motion of body segments and mobility from the angular displacement of joints. Motion at the shoulder, hip, knee and ankle decreased significantly over several months after the onset of walking and thereafter changed gradually. The remarkable decrease began distally. The trunk-thigh and thigh-shank angles changed significantly until 9 months after the onset of walking. These results indicate that lateral stability, which develops earlier than mobility, is the most important factor in gait development in infants.

Distinct multi-joint control strategies in spastic diplegia associated with prematurity or Angelman syndrome

Spastic diplegia is commonly due to periventricular leucomalacia associated with premature birth. It is also a feature of Angelman syndrome (AS), a neurogenetic disorder with developmental delay, absent speech and mirthful behaviour. We studied the kinematics and kinetics of the squatting movement and associated electromyographic (EMG) activities in 20 children with spastic diplegia associated with periventricular leucomalacia (SDPL) or AS and 18 unimpaired children. While movement of normal subjects consisted of vertical translation of most body segments, the movement of SDPL children was operated around the fixed knee with backward shift of the hip, and AS children performed a forward flexion of the trunk over the thigh. Trunk stability was correlated with movement velocity in both pathological groups. In normal subjects, anticipatory EMG pattern consisted of silencing of hamstring muscle tonic activity prior to movement onset. This deactivation was not present in spastic diplegia. In SDPL, anticipatory overactivation of ankle joint actuators was recorded and tonic co-contraction persisted throughout the movement. In AS, rhythmic EMG bursting was seen during the movement. Shoulder, hip and knee trajectories in the sagittal plane showed marked within-group stereotypies in orientation, shape and length. The patterns in both pathological groups were therefore distinctive. We speculate that they reflect corticospinal impairment in SDPL and combined corticospinal and cerebellar dysfunction in AS.

Early emergence of temporal co-ordination of lower limb segments elevation angles in human locomotion

We analysed the co-ordination of the elevation angles of the thigh (alpha(t)), shank (alpha(s)) and foot (alpha(f)) during walking in 19 adults and 21 children (aged 11--144 months), including the very first unsupported steps in four. Cross-correlation functions (CCF) maturation of pairs of elevation angles was quantified by a global error parameter (Et((CCF))) reflecting the difference between particular CCF value of toddlers and mean adult value (Ea((CCF))). During the very first step, Et((CCF)) could be five times higher than Ea((CCF)). With walking experience, Et((CCF)) for both alpha(t)-alpha(s) and alpha(s)-alpha(f) pairs evolved following a biexponential profile, with a fast time constant below 6 months. Adult-like CCF parameters were reached earlier for alpha(s)-alpha(f) than alpha(t)-alpha(s), indicating disto-proximal maturation of the temporal co-ordination of the lower limb segments in human locomotion.

Coordination between arm and leg movements during locomotion

To evaluate the contrasting dynamical and biomechanical interpretations of the 2:1 frequency coordination between arm and leg movements that occurs at low walking velocities and the 1:1 frequency coordination that occurs at higher walking velocities, the authors conducted an experiment in which they quantified the effect of walking velocity on the stability of the frequency and phase coordination between the individual limb movements. Spectral analyses revealed the presence of 2:1 frequency coordination as a constant feature of the data in only 3 out of 8 participants at walking velocities ranging from 1.0 to 2.0 km/h, in spite of the fact that the eigenfrequencies of the arms were rather similar across participants. The degree of interlimb coupling, as indexed by weighted coherence and variability of relative phase, was lower for the arm movements and for ipsilateral and diagonal combinations of arm and leg movements than for the leg movements. Furthermore, the coupling between all pairs of limb movements was found to increase with walking velocity, whereas no clear signs were observed that the switches from 2:1 to 1:1 frequency coordination and vice versa were preceded by loss of stability. Therefore, neither a purely biomechanical nor a purely dynamical model is optimally suited to explain these results. Instead, an integrative model involving elements of both approaches seems to be required.

Acquisition of upper body stability during walking in toddlers

This study examines the development of head and trunk movements in toddlers as they begin to walk independently. The data are from a longitudinal study of 7 infants observed from the onset of walking over a period of 46-80 weeks. Head and trunk rotations were measured in the frontal and sagittal planes together with global gait parameters (progression velocity, step cadence, length and width, duration of double support phase). The results showed that during the first weeks of walking head and trunk oscillations significantly decreased, indicating that considerable progress is made in upper body stabilization. Dramatic changes in global gait parameters also occurred at this time. After this first period of rapid changes, gait parameters continued the same developmental trend but with slower changes. The close relation between gain in head and trunk stability and improvement in walking efficacy is discussed on the basis of the individual developmental trends.

Head coordination as a means to assist sensory integration in learning to walk

After a brief presentation of the development of free walking interpreted as learning dynamical equilibrium, the problem of sensory integration in the process of walking development is discussed. A critical review of the role of vision in the development of posturo-locomotor task is presented, along with recent test results on the development of the vestibular system. A final section presents the development of head stabilization and coordination as a necessary means to assist sensory integration. It is suggested that if sensory information is necessary to enhance posturo-locomotor skills, a good mastery of walking is in turn necessary to increase the efficiency of sensory integration.

Development of anticipatory orienting strategies during locomotor tasks in children

Some basic problems related to the development of goal-directed locomotion in humans are reviewed here. A preliminary study is presented which was aimed at investigating the emergence of anticipatory head orienting strategies during goal-directed locomotion in children. Eight children ranging from 3.5 to 8 years had to walk along a 90 degrees right corner trajectory to reach a goal, both in light and in darkness. The instantaneous orientation in space of the head, trunk, hips and left foot antero/posterior axes was computed by means of an ELITE four-TV camera, 100 Hz system. The results showed that predictive head orienting movements can occur also in the youngest children. The head starts to rotate toward the goal before the corner point of the trajectory is reached. In children, the head peak rotation coincides with the trajectory corner while in adults the peak is attained before. In children, the walking speed is largely decreased in darkness. The results suggest that feedforward control of goal-directed locomotion appears very early in gait development and becomes increasingly important afterwards.

Ocular counterrolling in response to asymmetric radial acceleration

The fact that the labyrinths are positioned at approx. 3.5 cm from the head-centric axis leads to the generation of systematic radial acceleratory, or centrifugal, forces during physiological head rotations. Under physiological conditions, the forces exerted on the right and left maculae are generally assumed to be equal and opposite. In the present test, however, the subject was displaced eccentrically during constant angular velocity so that one labyrinth was aligned concentrically with the rotatory axis, whilst the other was exposed to the radial acceleration component generated by the chair rotation. In comparison with previous testing based on subjective setting of the visual vertical, three-dimensional eye movements were recorded in order to obtain an objective measure of the otolith-ocular response mechanisms in the brainstem. The results obtained from normal subjects demonstrate a predominant ocular counterroll (OCR) response to this asymmetric, or unilateral application of linear acceleration. The direction of the OCR response proved to be independent of direction of rotation. The findings demonstrate a symmetrical response magnitude for stimulation of the left and right maculae. In comparison with the OCR response to head-tilt, which can be described as critically damped, the time course of the present response appeared to be underdamped.

Head coordination in the sagittal plane in toddlers during walking: preliminary results

In adults, head rotations in the pitch plane are highly synchronized with vertical head translations during different locomotor tasks as walking, running, and hopping. The head is rotating up then down in the pitch plane as stepping movement drives the head down then up, respectively. The purpose of our study was to determine at which period of the motor control development this fine head coordination occurred. The organization of head movements was analyzed in four normal children observed longitudinally from the onset of walking up to 80 weeks of independent walking (IW). The degree of synchronization between vertical head translations and head rotations in the pitch plane was used to define an index of head coordination for 15 to 25 steps per child per session. Our results show that the coordination of head rotations in the pitch plane improves continually in toddlers but does not reach the optimal level during the first year of IW experience. We showed previously that head stabilization in space was achieved during the first weeks of IW. Both head stabilization in space and fine head coordination during walking are considered as directly involved in gaze stabilization, but in toddlers head stabilization in space is completed earlier than head coordination. Head stabilization appears to be a necessary motor control to acquire prior to the development of head movement coordination.