Adaptation of reaching movements in children and young adults with myelomeningocele.

AIM: To investigate the ability to adapt reaching movements to new visuomotor gain conditions in subjects with myelomeningocele (MMC) and subjects without disabilities. In addition, differences in movement error within the MMC group were investigated. METHODS: Thirty subjects with myelomeningocele, 9-19 y, and 30 subjects without disabilities were included in the study. Data were collected with a digitizing tablet linked to a computer. The subjects made reaching movements towards three targets at different distances displayed on the computer screen, and movements were carried out under two different gain conditions-a base condition and an altered condition. Adaptation was quantified from the extent error and expressed in percentage of the target distances. For statistical analysis, ANOVA and t-tests were used. RESULTS: Under the base condition, no statistically significant difference between the groups was found, but after the first gain change, the MMC group evinced larger percentage error compared to the control group (p = 0.005). Analysis showed that the subjects in the MMC group did not fully adapt their movements under the altered condition after several trials of practice, but in the control group movements were rapidly adapted to the new gain. Subjects with early and severe symptoms of brainstem dysfunction showed a dramatic increase in error variability under the altered condition, while subjects who had shunt-treated hydrocephalus did not have larger percentage error compared to the others. CONCLUSION: Motor adaptation of reaching movements was impaired in subjects with MMC, but short-term motor learning did also occur in the MMC group.

Norms for grip strength in children aged 4-16 years.

UNLABELLED: The aim of this study was to provide norms for grip strength in children. A total of 530 Swedish 4-16-y-olds was tested with the instrument Grippit. The instrument estimates peak grip strength over a 10s period, and sustained grip strength averaged across the 10s. The increase in grip strength with age was approximately parallel for boys and girls until 10 y of age, after which boys were significantly stronger than girls. Strong correlations existed between grip strength and the anthropometric measures weight, height and, in particular, hand length. Right-handed children were significantly stronger in their dominant hand, while left-handers did not show any strength difference between the hands. It is therefore suggested that when evaluating grip strength in left-handed children both hands should be assumed to be about equally strong, while right-handed children are expected to be up to 10% stronger with their right hand. Sustained grip strength was consistently about 80-85% of peak grip strength, with somewhat lower values in younger children. The present normative data for peak grip strength were slightly lower than 1980s' data from the USA and Australia, probably because of divergences in age grouping and in instruments used. CONCLUSION: Norms for grip strength including estimates of variation were provided for children aged 4-16 y. These data will enable therapists and physicians to compare a patient's score with the scores of normally developed children according to age, gender, handedness and body measures.

Roles of Visual Information for Control of Reaching Movements in Children.

What visual information do children normally require for the control of reaching movements? How is performance affected when children do not have access to the preferred mode of perceptual information? These questions were studied in 28 children who were tested on 3 occasions: at 6, 7, and 8 years of age. The task was to pick beads, 1 at a time, from 1 cup and carry them to another cup. With the aid of a mirror arrangement and a curtain, the amount of visual information was manipulated with regard to both the target and the performing hand. The movements were monitored with an optoelectronic device (SELSPOT II) and analyzed in terms of transport and object-handling phases. Results showed that object handling required visual information on both hand and target. For the transport phase of the movement, visual information on the spatial location of the target was sufficient, and sight of the hand did not improve performance. In contrast to adult subjects, when children did not have access to the required visual information, their performances deteriorated markedly. These results indicate that from the age of 6, children use visual information for control of arm movements in a manner like that of adults, although with less accuracy and speed. However, even 8-year-old children are limited in their ability to use alternative perceptual strategies for movement control, and they therefore become less flexible and more dependent on visual information.

Relation between muscle response onset and body segmental movements during postural perturbations in humans.

This study has examined the individual movements of the body segments of a group of 10 standing adults during anterior and posterior platform displacements (3 and 6 cm amplitudes), and compared body movements to neck and ankle muscle response onset times. Differences in the kinematics of movement were observed for anterior vs. posterior platform displacements: hip, shoulder, and head began to move much earlier for posterior compared to anterior platform movements. This could explain differences in postural muscle temporal response organization for the two directions of body movement. Though anterior/posterior neck and head displacements were late in comparison to neck flexor muscle response onset, small vertical movements of the shoulder and head occurred early (40 and 67 ms after platform movement onset). These movements were consistently directed upward for anterior platform displacements and downward for posterior platform displacements. In order to determine whether neck proprioceptors were responsible for response activation in the neck we repeated the experiment using a neck stabilization device, on one of our subjects. In this condition, we found normal neck muscle response latencies. This suggests that neck proprioceptors are not the primary contributors to the early neck muscle responses seen during horizontal support surface displacements. In studying the effect of repeated exposure to horizontal platform displacements we found a diminution in the amplitude and an increase in onset latencies in neck and antagonist ankle muscle responses over the sequence of 16 trials, in many of the subjects tested. This corresponded to smaller head accelerations, and smaller displacements of the head and shoulder in later trials in the experimental sequence. The result implies that these subjects changed their postural "set" during the course of the experiment, possibly by relaxing the muscles of the body to allow the viscoelastic properties of the lower body segments to absorb more of the impact of platform displacement.

The integration of sensory information in the development of precise manual pointing.

The development of manual pointing was studied in 270 children from 4 yr of age to 12 yr of age. Fifteen boys and 15 girls were included in each age group. The task was to place pins underneath a table-top at positions seen or felt on the table-top. Each child was tested in four different conditions: both visual and proprioceptive information about the position of the dot to be pointed at could be provided, just one of these two sources of information could be provided, or none of them. Errors were analysed in terms of systematic and random error. The results show that in all age groups, performance was superior when visual information about the position of the dot was provided. The ability to utilize visual information was found to be rather good already at the youngest ages. In the visual conditions the random error decreased with age in a gradual and linear fashion but the systematic error did not, it decreased and increased and decreased again. Errors were substantially smaller at 7 and 11 yr of age. The ability to use information from the proprioceptors improved remarkably during the youngest ages. All the improvement of the random error between 4 and 5 yr of age could be attributed to this factor. The systematic error in all conditions was found to be displaced towards the contralateral side of the body, but this effect was strongest in the proprioceptive condition. A strong interaction between sex and hand used in pointing was found in the systematic errors but none in the random errors. The interaction could be described as a nondominant hand disadvantage of the girls.