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Title: Performance of a dynamic reach-and-grasp task in children with developmental coordination disorder
Authors: Leung, Yuk-wa Eva
Degree: M.Phil.
Issue Date: 2007
Abstract: Introduction: Most of the published data in children with developmental coordination disorder (DCD) examined time and force factors separately, and with force control examined in a static setup. These findings had limitations in explaining their poor performance in sport activities that involve the control of both speed and force. Since playing is an essential domain in the life of children and boys have shown a higher prevalence of DCD than girls, the setup of this study was specially designed to simulate a dynamic ball game, which boys are most commonly involved in. The objective of this study was to investigate the performance of a dynamic reach-and grasp task in children with DCD when compared with a group of healthy children at similar age. We examined the successful rate of completion of the dynamic reach-and grasp task in children with DCD. We also studied whether children with DCD required a longer reaction and movement time as well as greater peak force and rate of force production than healthy children. We further explored whether these children had difficulties in adjusting their time and force to a change of weight and speed of the target. Methods: Twelve healthy children (mean age: 7.8 +- 0.6 years old) and seventeen children with DCD (8.1 +- 0.6 years old) were instructed to use their dominant hand to grasp a toy car, which was allowed to slide down from a slanted board of adjustable slope. All subjects were tested in 4 conditions with different combinations of slope (8o or 15o) and weight (no-weight-added and weight-added), 5 trials for each condition. The sequence of testing conditions was randomized. Reaction time, movement time, peak force and rate of force production were recorded. These variables were analyzed using two-way repeated measures analysis of variance (ANOVA) with group (DCD and control) as the 'between' factor, and slope (8o and 15o) and weight (no-weight-added and weight-added) as 'within' factors. Pearson product-moment correlation coefficient was calculated to establish associations among movement time, peak force and rate of force production. Within-subject standard deviations were calculated to investigate the variations in reaction time, movement time and peak force. A significance level of 0.05 was employed for all analyses. Results: The testing procedure was found reliable with the Intraclass Correlation Coefficients of test-retest reliability valued above 0.83 for reaction time, movement time and peak force. Healthy children completed all trials of reach-and-grasp task successfully. However DCD group failed in 118 out of the total of 340 test trials, i.e. 34.7%, with the highest failure rate found in the fastest condition. The 3 most common failure reasons were 'Child picked the toy car up at the wrong spot', 'Toy car ran off the board without being picked up' and 'Child pressed down the toy car to stop it but did not pick it up as instructed'. Within the successful trials, DCD group had much more within-subject variability in the movement time than control group among the 4 conditions. DCD group took significantly longer reaction times than control group in all 4 conditions (p<0.05), but both groups did not adjust their reaction time in response to change in weight or slope. DCD group tended to use longer movement times than control group, although these differences did not reach a significant level. Both groups used significantly shorter movement time when the slope was increased (p<0.05). Regarding the peak force, DCD group used greater force than control group even when grasping a static toy car, although the difference did not reach a significant level. They used significantly greater peak force than healthy children when grasping a moving toy car (p<0.01). Both groups increased their peak force significantly when the slope was increased (p<0.01). For the rate of force production, there was no between-group difference, and both groups tended to increase their rate of force production when the slope was increased although not to a significant level. In both healthy and DCD groups, their movement time was inversely correlated to their rate of force production. Discussions: Children with DCD appeared to have difficulty in adjusting time and force to complete a dynamic reach-and-grasp task, therefore they had a high failure rate to complete the task in this study. To reach and grasp the toy car successfully, children had to rely on visual information to plan, initiate and monitor the motor response. Children with DCD might have visual perceptual problems, which led to inaccurate prediction of the toy car's motion and planned an inaccurate action. Hence they failed many trials by grasping the toy car at a wrong site. Their high failure rate might also be related to their slowness in developing the capacity to process proprioceptive input and to effectively integrate visual and proprioceptive information. Therefore they required a longer time to plan and to execute the movement. When time was limited; they could not pick up the toy car before it ran off the track. Regarding the prolonged reaction time, children with DCD might have longer tracking delay in detecting the temporal and spatial information about the toy car, and a longer time was required to process and translate this information to plan for an appropriate response. The high within-group variability for the movement time reflected that they had ineffective feed-forward and feedback control for the on-going movement. In the present study, movement time was subdivided into 'reach time' and 'grasp time'. There was a trend of prolonged movement time in children with DCD, and the 'grasp time' showed the similar trend of difference between the two groups. It was possible that the prolonged MT in successful trials was contributed by the prolonged 'grasp time', i.e. the time between initial contact of the toy car to a secured grasp. The trend of prolonged 'grasp time' could be related to their inaccurate proprioceptive sensory system. Therefore, they required longer time to collect information on the weight of the toy car to produce the required force, and information on the position of the fingers involved in the grasp so as to refine the shape of the hand grasp. It might also be related to their ineffective integration between the sensory and motor systems. Children with DCD used significantly greater force than healthy children to pick up the moving toy car. They could have impaired kinaesthetic perception and sensory-motor integration, therefore, they compensated by increasing the peak force. In successful trials, children with DCD could decrease movement time, increase peak force and increase rate of force production when the slope was increased in a similar manner as those of control subjects. But the high failure rate in the DCD group reflected that their adjustment ability was not as effective as that of the control group. Conclusions: The result of this study confirmed that children with DCD were less effective in performing a dynamic reach-and-grasp task with a failure rate of 34.7%. In successful trials, they used significantly longer reaction time and larger peak force, and tended to use longer movement time to perform the fine-tuning phase of the task. They could adjust their movement time, peak force and rate of force production in response to change of slope of the slanted board, hence the speed of the toy car. Findings of this study suggested that their poor performance in sport activities could be related to their prolonged time to plan, prolonged and inconsistent time to fine-tune the motion, excessive force to grasp, and inefficient rate of force production. They could adjust their motion time in a crude reaching phase and their force output in response to a change in speed of the target but were not as effective as the healthy children. This was causing a lot of their failure in a dynamic reach-and-grasp task. In order to improve their performance in dynamic sport activities, training program with timely and quantified feedback may be useful to speed up their reaction time, movement time and to optimise their force output with a greater consistency.
Subjects: Hong Kong Polytechnic University -- Dissertations.
Occupational therapy for children.
Physical therapy for children.
Motor ability in children.
Clumsiness in children.
Pages: xiv, 160 leaves : col. ill. ; 30 cm.
Appears in Collections:Thesis

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