The purpose of this study is to analyze the coordination patterns of the elevation angles of lower limb segments following the onset of unsupported walking in children and to look for the existence of a planar covariation rule as previously described in adult human locomotion. The kinematic patterns of locomotion were recorded in 21 children (11-144 months of age) and 19 adults. In 4 children we monitored the very first unsupported steps. The extent to which the covariation of thigh, shank, and foot angles was constrained on a plane in 3D space was assessed by means of orthogonal regression and statistically quantified by means of principal component analysis. The orientation of the covariation plane of the children was compared with the mean value of the adults' plane. Trunk stability with respect to the vertical was assessed in both the frontal (roll) and sagittal (pitch) planes. The evolution with walking experience of the plane orientation and trunk oscillations demonstrated biexponential profiles with a relatively fast time constant (<6 months after the onset of unsupported locomotion) followed by a much slower progression toward adult values. The initial fast changes of these walking parameters did not parallel the slow, monotonic maturation of anthropometric parameters. The early emergence of the covariation plane orientation and its correlation with trunk vertical stability reflect the dynamic integration of postural equilibrium and forward propulsion in a gravity-centered frame. The results support the view that the planar covariation reflects a coordinated, centrally controlled behavior, in addition to biomechanical constraints. The refinement of the planar covariation while morphological variables drastically change as the child grows implies a continuous update of the neural command.

The covariation between thigh, shank and foot elevation angles during locomotion was analysed by means of orthogonal planar regression in a patient with pure hereditary spastic paraparesis before and after an intrathecal bolus of baclofen and in seven healthy subjects. The size, shape and spatial orientation of the loop de®ning patient's planar covariation (thigh angle vs. shank angle vs. foot angle) signi®cantly differed from the controls' before baclofen, whereas these features resumed normal characteristics after baclofen injection. This shows that alteration of the control of phase coupling for the co-ordination of lower limb segments in human gait by increased spinal re¯exes can be reversed by intrathecal baclofen injection. q 2000 Elsevier Science Ireland Ltd. All rights reserved.Keywords: Human; Locomotion; Co-ordination; Planar covariation; Baclofen; Hereditary spastic paraparesis As a GABA B agonist [14], baclofen reduces the release by primary afferent terminals in laminae II and III of excitatory neurotransmitters onto ventral horn motoneurons in the spinal cord [5,17]. Although intrathecal baclofen (ITB) is becoming a standard treatment of spinal origin spasticity [15], its effect on locomotor control is unclear. A recent approach has revealed a speci®c covariation of elevation angles of the lower limb segments along an attractor plane during locomotion in healthy humans [2±4,10]. The plane orientation and the shape of the loop that de®nes it re¯ect the phase relationships between these angles and therefore intersegmental co-ordination, on which postural stability with respect to gravity and dynamic equilibrium for forward progression depend. Recently, the features of this covariation in Parkinson's disease before and after therapeutic intervention gave insights into basal ganglia function [11]. In this study, we analysed this covariation in a patient with uncomplicated autosomal dominant hereditary spastic paraparesis (HSP) [9] before and after an ITB bolus.The studied patient, aged 41, has normal muscle power, increased tone and re¯exes in the lower limbs, extensor plantar responses and a spastic gait. Seven healthy subjects (aged 38.2^4.6) participated as controls.Using the ELITE system [8], four sessions of ten trials of the patient's self-paced locomotion over ten meters were recorded with a 100 Hz sampling rate, respectively before ITB of 75 mg (0.77 mg/kg) via lumbar puncture and 2, 4 and 6 h after it. Ten trials were recorded for each control subject. Markers over the anterior-superior iliac spine, trochanter, lateral knee condyle, lateral malleolus and 5th metatarsal, de®ned the segments of the thigh, shank and foot.Statistical analysis of the angle covariation was based on principal component (PC) analysis (see [2]). PCs were computed by pooling the sample of time-varying angles after subtracting the mean. PCs are linear combinations of variates which are the covariance matrix eigenvectors. The ith PC is given by: PCi u i T a where u i is the eigenvector and a the variates. The norm...

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 ®xed knee with backward shift of the hip, and AS children performed a forward¯exion 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 cocontraction 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 re¯ect corticospinal impairment in SDPL and combined corticospinal and cerebellar dysfunction in AS. q

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We analysed the co-ordination of the elevation angles of the thigh (a t ), shank (a s ) and foot (a f ) during walking in 19 adults and 21 children (aged 11±144 months), including the very ®rst unsupported steps in four. Cross-correlation functions (CCF) maturation of pairs of elevation angles was quanti®ed by a global error parameter (Et (CCF) ) re¯ecting the difference between particular CCF value of toddlers and mean adult value (Ea (CCF) ). During the very ®rst step, Et (CCF) could be ®ve times higher than Ea (CCF) . With walking experience, Et (CCF) for both a t -a s and a s -a f pairs evolved following a biexponential pro®le, with a fast time constant below 6 months. Adult-like CCF parameters were reached earlier for a s -a f than a t -a s , indicating disto-proximal maturation of the temporal co-ordination of the lower limb segments in human locomotion. q 2001 Elsevier Science Ireland Ltd. All rights reserved.Keywords: Locomotion; Development; Temporal co-ordination; Lower limb Studies in motor control have increasingly concentrated on the emergence of co-ordinative rules and integration of sensorimotor experiences into prewired neural networks [11]. In this context, the role of maturation in such a fundamental behaviour as locomotion appears critical but has received sparse attention until recently. Several parameters of postural and dynamical control have been studied with respect to early gait development, including head, trunk and hip stabilisation, intralimb co-ordination and centre of mass parameters [1,2,4,5,7,8,16].In adults, a series of experimental studies of locomotion have demonstrated that the elevation angles of the lower limb segments provide a kinematic template revealing a motor organisation rule [3], which is related to minimisation of mechanical energy expenditure [14]. When the elevation angles of the thigh, shank and foot are plotted one versus the others, they describe a regular loop which lies close to a plane. Recently, we found that this planar covariation rule emerges early in toddler locomotion [7], suggesting a rapid dynamical integration of forward propulsion and postural control into the motor command. Two important aspects of the co-ordination of angular evolution of the lower limb segments, namely excursion amplitudes and timing, are expected to in¯uence the planar covariation. The temporal relationships between these angles evolution appear particularly crucial for locomotor co-ordination. Statistical approaches such as cross-correlation function (CCF) have proved to be adequate for deciphering consistent temporal relationships between kinematics signals during free-form movements [1,6]. In this study we introduce a global parameter based on CCF of lower limb segments elevation to quantify the gait kinematic maturation of children from the very ®rst step through adolescence.Twenty-one healthy children (13 girls and 8 boys, aged 11±144 months) and 19 healthy adults (9 females and 10 males, aged 25^4 (mean^SD) years) participated in this study. The procedures were...