Development of postural adjustments during reaching in typically developing infants from 4 to 18 months

Knowledge on the development of postural adjustments during infancy, in particular on the development of postural muscle coordination, is limited. This study aimed at the evaluation of the development of postural control during reaching in a supported sitting condition. Eleven typically developing infants participated in the study and were assessed at the ages of 4, 6, 10 and 18 months. We elicited reaching movements by presenting small toys at an arm’s length distance, whilst activity of multiple arm, neck and trunk muscles was recorded using surface EMG. A model-based computer algorithm was used to detect the onset of phasic muscle activity. The results indicated that postural muscle activity during reaching whilst sitting supported is highly variable. Direction-specific postural activity was inconsistently present from early age onwards and increased between 10 and 18 months without reaching a 100 % consistency. The dominant pattern of activation at all ages was the ‘complete pattern’, in which all direction-specific muscles were recruited. At 4 months, a slight preference for top-down recruitment existed, which was gradually replaced by a preference for bottom-up recruitment. We conclude that postural control during the ecological task of reaching during supported sitting between 4 and 18 months of age is primarily characterized by variation. Already from 4 months onwards, infants are—within the variation—sometimes able to select muscle recruitment strategies that are optimal to the task at hand

The relationship between a child's postural stability and manual dexterity

The neural systems responsible for postural control are separate from the neural substrates that underpin control of the hand. Nonetheless, postural control and eye-hand coordination are linked functionally. For example, a stable platform is required for precise manual control tasks (e.g. handwriting) and thus such skills often cannot develop until the child is able to sit or stand upright. This raises the question of the strength of the empirical relationship between measures of postural stability and manual motor control. We recorded objective computerised measures of postural stability in stance and manual control in sitting in a sample of school children (n = 278) aged 3–11 years in order to explore the extent to which measures of manual skill could be predicted by measures of postural stability. A strong correlation was found across the whole sample between separate measures of postural stability and manual control taken on different days. Following correction for age, a significant but modest correlation was found. Regression analysis with age correction revealed that postural stability accounted for between 1 and 10 % of the variance in manual performance, dependent on the specific manual task. These data reflect an interdependent functional relationship between manual control and postural stability development. Nevertheless, the relatively small proportion of the explained variance is consistent with the anatomically distinct neural architecture that exists for ‘gross’ and ‘fine’ motor control. These data justify the approach of motor batteries that provide separate assessments of postural stability and manual dexterity and have implications for therapeutic intervention in developmental disorders

The development of postural response patterns during reaching in healthy infants

Reaching movements in adults are accompanied by complex postural adjustments which are controlled by spatial, temporal, and quantitative parameters. The basic postural adjustments are selected on the basis of the spatial parameter, whereas fine tuning of the pattern is guided by temporal and quantitative parameters. In specific conditions, such as during fast arm movements, postural adjustments have an anticipatory character.Recently, the development of postural adjustments during reaching was studied longitudinally in infants aged 3-18 months, placed in supine and sitting positions. The data revealed that already at 4 months, the age at which successful reaching emerges, reaching movements are accompanied by complex postural adjustments. The early postural patterns resembled the adult ones in spatial features (dorso-ventral ordering), temporal characteristics (top-down recruitment), and position dependency. With increasing age the postural patterns changed considerably, including a transient period of less extensive postural activity at 6-8 months, the age at which rolling, sitting up and crawling develops. Postural anticipation during reaching was not consistently present at any age. (C) 1998 Elsevier Science Ltd. All rights reserved.</p

The development of postural adjustments during reaching in 6-to 18-month-old infants - Evidence for two transitions

The present study focused on the developmental changes of postural adjustments accompanying reaching movements in healthy infants. We made a longitudinal study of ten infants between 6 and 18 months of age. During each session multiple surface electromyograms of arm, neck, trunk and leg muscles at the right side of the body were recorded during right-handed reaching movements in two positions ("upright sitting" in an infant chair and "long-leg" sitting without support). Simultaneously the whole session was recorded on video, Comparable data were present from the same infants at 3-5 months. Additionally, 18 infants (8-15 months) were assessed once during similar reaching tasks, but in these infants electromyographic activity of the trunk and neck muscles at both sides of the body were recorded. Our data revealed two transitions in the development of postural adjustments. The first transition was present around 6 months of age. At this age the postural muscles were infrequently activated during reaching movements. At 8 months ample postural activity reappeared and the infants developed the ability to adapt the postural adjustments to task-specific constraints such as arm movement velocity or the sitting position at the onset of the reaching movement. The second transition occurred between 12 and 15 months. Before 15 months the infants did not show consistent anticipatory postural activity, but from 15 months onwards they did, particularly in the neck muscles

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