Postural adjustments accompanying fast pointing movements in standing, sitting and lying adults

The present study evaluated the effect of different positions, which varied in the amount of bodily support, on postural control during fast pointing movements. Fourteen adult subjects were studied in standing, various sitting and lying positions. Multiple surface electromyograms (EMGs) of arm, neck, trunk and upper leg muscles and kinematics were recorded during a standard series of unilateral arm movements. Two additional series, consisting of bilateral arm movements and unilateral arm movements with an additional weight, were performed to assess whether additional task-load affected postural adjustments differently in a sitting and standing position. Two pointing strategies were used – despite identical instructions. Seven subjects showed an elbow extension throughout the movements. They used the deltoid (DE) as the prime mover (DE group). The other seven subjects performed the movement with a slight elbow flexion and used the biceps brachii (BB) as the prime mover (BB group). The two strategies had a differential effect on the postural adjustments: postural activity was less and substantially later in the BB-group than in the DE group. Anticipatory postural muscle activity was only present in the DE group during stance. In all positions and task-load conditions the dorsal postural muscles were activated before their ventral antagonists. The activation rate, the timing and – to a lesser extent – the amplitude of the dorsal muscle activity was position dependent. The position dependency was mainly found in the caudally located lumbar extensor (LE) and hamstrings (HAM) muscles. The EMG amplitude of LE and HAM was also affected by body geometry (trunk and pelvis position). Position and body geometry had only a minor effect on the activity of the neck and thoracic extensor muscles. This difference in behaviour of lower and upper postural muscles suggests that they could serve different postural tasks: the lower muscles being more involved in keeping the centre of mass within the limits of the support surface, and the upper ones in counteracting the reaction forces generated by movement onset. Increasing task-load by performing bilateral movements and – to a minor extent – during loaded unilateral movements affected the temporal and quantitative characteristics of the postural adjustments during standing and sitting in a similar way. The effect was present mainly during the early part of the response (within 100 ms after prime mover onset). This suggests that feedforward or anticipatory mechanisms play a major role in the task-specific modulation of postural adjustments. Received: 9 April 1997 / Accepted: 9 October 1997     

Reliability and concurrent validity of the Infant Motor Profile

Aim

The Infant Motor Profile (IMP) is a qualitative assessment of motor behaviour in infancy. It consists of five domains: movement variation, variability, fluency, symmetry, and performance. The aim of this study was to assess interobserver reliability and concurrent validity of the IMP with the Alberta Infant Motor Scale (AIMS) and an age‐specific neurological examination.

Method

Fifty‐nine preterm infants (25 females, 34 males; median gestational age 29.7wks, median birthweight 1285g) and 146 term infants (74 females, 72 males; median gestational age 40.1wks, birthweight 3500g) were included. Assessments were performed at corrected ages of 4, 6, 10, 12, and 18 months and consisted of the IMP, AIMS, and an age‐specific neurological examination. Interobserver reliability was investigated on a sample of 25 video recordings. Non‐parametric statistics were used to analyse the data.

Results

Interobserver reliability was high (intraclass correlation coefficient 0.95). At all ages, AIMS scores correlated weakly to fairly with total IMP scores (Spearman's ρ 0.36–0.55), but moderately to strongly with scores on the performance domain of the IMP (Spearman's ρ 0.47–0.84). A clear relation was found between total IMP score and outcome of the neurological examination (Kruskal–Wallis p<0.001 at all ages).

Interpretation

Interobserver reliability of the IMP is good. Concurrent validity with the AIMS is best for the IMP performance domain. Concurrent validity with age‐specific neurological examination is very good.     

Postural adjustments and reaching in 4- and 6-month-old infants: an EMG and kinematical study

Adequate postural control is a prerequisite for daily activities such as reaching for an object. However, knowledge on the relationship between postural adjustments and the quality of reaching movements during human ontogeny is scarce. Therefore we evaluated the development of the relationship between the kinematic features of reaching movements and the accompanying postural adjustments in young infants. Twelve typically developing (TD) infants were assessed twice, i.e. at 4 and 6 months of age, in supine and supported sitting position. Reaching was elicited by presenting toys in the midline at an arm-length distance while simultaneously surface EMG-activity was recorded from multiple arm-, neck-, trunk- and leg muscles. Concurrently kinematics of reaching were recorded with an ELITE system; kinematic analysis was restricted to the behaviour of so-called movement units, which are sub movements of reaching determined with the help of peaks in the velocity profile of the hand, maximum movement velocity and movement duration. A computer-algorithm determined significant phasic muscle activity. Activity in neck and trunk muscles (postural activity) was related to the onset of the prime mover, which was the arm muscle being activated first. The results indicated that about 50% of reaching movements in lying and sitting infants aged 4 and 6 months were accompanied by direction-specific postural adjustments. At 4 months variation dominated, but at 6 months a preference to recruit muscles in a top-down order (during sitting) and in the configuration of the complete pattern, i.e. the pattern in which all dorsal neck- and trunk muscles are activated in concert, (both conditions) emerged. Interestingly, the postural characteristics such as the presence of direction-specificity, recruitment of the complete pattern and top-down recruitment, were related to how successful the reaching was and the kinematics of reaching. It was concluded that the presence of direction-specific activity is not a prerequisite for the emergence of reaching movements. Nevertheless, already from 4 months onwards a better postural control is associated with a larger success and a better quality of reaching.     

Prenatal and early postnatal fatty acid status and neurodevelopmental outcome

The present review addresses the effect of pre- and postnatal supplementation of nutrition with long-chain polyunsaturated fatty acids (LCPUFA) on neurodevelopmental outcome. The few studies which addressed the effect of prenatal LCPUFA status or prenatal LCPUFA supplementation suggest that a better prenatal arachidonic acid (AA) and doxosahexaenoic acid (DHA) status might be related to a better neurodevelopmental outcome until at least 18 months of age. A review of the few randomized controlled trials on formula supplementation with LCPUFA in preterm infants did not provide evidence for a significant beneficial effect of LCPUFA on developmental outcome. A review of the trials on formula supplementation with LCPUFA in term infants revealed that supplementation with LCPUFA, in particularly supplementation with >or=0.30% DHA, has a beneficial effect on neurodevelopmental outcome until 4 months. The studies could not demonstrate a consistent positive effect beyond that age. It was concluded that the relatively subtle effects of LCPUFA supplementation on neurodevelopmental outcome do not only depend on dosage but also on the gestational period during which the nutritional components are supplied: supplementation prior to term seems to have more effect than that after term.     

Body measurements, neurological and behavioural development in six-year-old children born preterm and/or small-for-gestational-age

In three groups of low birth weight (LBW) infants: full term, small-for-gestational-age (FT-SGA, N = 142); preterm, appropriate-for-gestational-age (PT-AGA, N = 47); preterm, small-for-gestational-age (PT-SGA, N = 20); and a reference group of FT-AGA infants (N = 185) the relationship between body weight, body length and head circumference and the presence of minor neurological dysfunction (MND) was studied. Non-caucasian and handicapped children were excluded from the analysis. Data were collected on behaviour and school achievement. The parameters of physical growth in the three LBW groups were reduced significantly compared to the FT-AGA group. In both preterms and full-terms body measurements were related to weight at term age; in the preterm groups no relation with gestational age at birth was found. MND was not related to body weight or length. In the group of FT severely growth retarded infants a relation was found between a skull circumference below the third centile and the presence of MND. Body measurements, behaviour at home and at school and school achievement were not related. The significance of severe intrauterine growth retardation for developmental disorders is emphasized. The data suggest a different aetiology and clinical significance of small head size for AGA and SGA born children.     

Deficient coordination of associated postural adjustments during a lifting task in children with neurodevelopmental disorders

Precision grip and concomitant anticipatory postural adjustments were investigated in 11 children (three females, eight males; mean age 9 years 1 month, SD 11 months) with attention-deficit-hyperactivity disorder (ADHD); 12 children (three females, nine males; mean age 9 years, SD 7 months) with developmental coordination disorder (DCD), and 13 children (two females, 11 males; mean age 9 years 9 months, SD 11 months) with a combination of ADHD and DCD (ADHD+). There were two comparison groups: an age-matched group (four females, 11 males; mean age 9 years 1 month, SD 14 months) and a younger age group (five females, six males; mean age 6 years 5 months, SD 8 months). Adaptation to different weights was evaluated by lifting a specialized grip instrument monitoring grip force, load force, and centre of foot pressure displacements. Children with ADHD+ showed: (1) excessive grip forces, (2) decreased amplitude and prolonged onset of postural adjustments, and (3) reduced ability to adapt the motor output. Children with ADHD and DCD did not scale manual and postural forces in amplitude and time domains. Children with DCD also differed in delayed timing of postural adjustments. Results indicate that children with ADHD and DCD show a spectrum of neural dysfunctions underlying poor motor coordination, which are not specific to the clinical disorder.