Elsevier

Human Movement Science

Volume 61, October 2018, Pages 42-51
Human Movement Science

Full Length Article
Investigating motor planning in children with DCD: Evidence from simple and complex grip-selection tasks

https://doi.org/10.1016/j.humov.2018.07.006Get rights and content

Highlights

  • Motor planning was assessed using simple and complex tasks in school aged children.

  • Boys with DCD planned simple movements as efficiently as their peers.

  • Motor planning ability decreased as task complexity increased in boys with DCD.

  • Poorer motor planning in boys with DCD suggests a deficit in internal modelling.

Abstract

Several studies suggest that children with Developmental Coordination Disorder (DCD) may be able to plan simple movements as well as their peers, but experience increasing difficulties as the movements become complex. The present study aimed to clarify the nature of motor planning in DCD, including a putative deficit, by being the first to investigate motor planning using converging measures of simple and complex motor planning in a single sample of children with DCD. Boys aged between 8 and 12 years with (n = 10) and without DCD (n = 17) completed three commonly used ‘simple’ (bar grasping, sword, and bar transport tasks) measures and one ‘complex’ (octagon task) measure of end-state-comfort (ESC), a classic measurement of motor planning ability. To achieve ESC when manipulating an object, a person may choose to start with an uncomfortable grip in order to end the movement in a comfortable position. Results indicate that the participants with DCD planned for ESC as efficiently as their peers when performing the ‘simple’ measures of ESC but were significantly less likely to end their performances in ESC than those without DCD for the more ‘complex’ octagon task. Taken together, our data suggest that school-aged children with DCD may be able to plan simple movements as efficiently as their peers, but have more difficulty doing so for multi-movement or complex sequences. Based on the assumption that the efficiency of such motor planning is dependent on the integrity of internal modelling systems, we argue that our study provides indirect support for the internal modelling deficit hypothesis.

Introduction

Developmental Coordination Disorder (DCD) is a neurodevelopmental condition that affects a person’s ability to perform coordinated movements and significantly interferes with their academic performance and activities of daily living (American Psychiatric Association, 2013). These difficulties become apparent from an early age and persist into adulthood in up to 75% of those diagnosed at an early age (Kirby, Sugden, & Purcell, 2014). The motor difficulties cannot be explained by other neurodevelopmental disorders such as cerebral palsy. A growing number of researchers have found that poor planning of movements is commonly identified in children with DCD (see Adams, Lust, Wilson, & Steenbergen, 2014 for a review).

Many of the simple tasks we perform in our daily life require complex motor planning skills, for instance, picking up a pencil and writing or grasping house keys to lock or unlock a door. Since any given action can be performed using an almost infinite series of motor commands [known as the degrees of freedom problem (Bernstein, 1967)], consideration of the best way to perform a task given the environmental and biomechanical constraints is important to allow efficient completion of the actions. For example, if the end of the house key to be inserted in the lock lies in the same direction a person is facing, then that person is likely to pick up the key using a comfortable hand position: this allows them to also end the movement comfortably. However, if the key lies in the opposite direction then to complete the movement comfortably the individual must sacrifice a comfortable start grip in order to lock/unlock the door in a comfortable way. This is known as the ‘end-state-comfort’ (ESC) effect (Rosenbaum et al., 2014, Rosenbaum et al., 1992, Stöckel et al., 2012). It has been observed that the tendency for individuals to end their movements in ESC increases into early adulthood in typically developing individuals (Jongbloed-Pereboom et al., 2013, Stöckel et al., 2012, Thibaut and Toussaint, 2010, van Swieten et al., 2010, Wilmut and Byrne, 2014b). However, clinical populations with difficulties planning movement, such as those with cerebral palsy, are often less likely to complete movements in ESC than healthy individuals (Crajé et al., 2010, Steenbergen et al., 2013). Accordingly, it is generally accepted that a greater tendency to terminate movements in ESC reflects optimization of motor planning (Rosenbaum et al., 1992).

Motor planning in individuals with DCD may also be compromised as those with DCD have reported an inability to perform many activities of daily living (e.g., brushing teeth, dressing and using utensils) that require complex motor planning skills (Zwicker, Harris, & Klassen, 2013). Consequently, investigations of motor planning in individuals with DCD have become common in recent years, with most studies using ‘grip-selection’ tasks. These tasks require that an individual grasps an object using an uncomfortable initial position to enable completion of the movement in a comfortable end position known as ESC (Rosenbaum et al., 1990). Results are mixed, which could be due to the variety of grip selection tasks used that place varying demands on motor planning (Adams et al., 2017, Fuelscher et al., 2016). To date, the majority of studies using ‘simple’ grip-selection tasks to investigate motor planning in children with DCD have found no differences between their DCD and control groups. For example, Smyth and Mason (1997) assessed children aged between 4 and 8 years with and without DCD on a bar transport and a handle rotation task. The bar transport task required children to simply pick up a wooden bar and place it so that the indicated end was facing them when placed to either their right or left. To complete this with a comfortable end state, participants had to reach and grasp a wooden bar using an overhand grip to place the right end facing them, or using an underhand grip to place the left end facing them. For the handle rotation task, participants had to grasp a handle and rotate it to 180° so that a tab covered a picture. To complete this task in ESC, the participant’s thumb should point towards the tab when the handle is grasped. For both tasks, the initial grip was noted to assess for ESC. The authors found no difference in performance between those with and without DCD suggesting that children with DCD could plan for ESC. This finding has been replicated in studies using tasks of similar design. For instance, Noten, Wilson, Ruddock, and Steenbergen (2014) used a bar rotation task where children with and without DCD aged between 7 and 12 years grasped a bar and placed the specified end into a cup. To complete this task comfortably, participants had to end their movements with their thumb pointing in an upwards direction. Again, no significant group differences between individuals with and without DCD were observed. In another study, Adams, Ferguson, Lust, Steenbergen, and Smits-Engelsman (2016) used the same bar rotation task (low precision) and the sword task (high precision) with 6–11 years old children with and without DCD to address whether task complexity affected motor planning in this population. The bar rotation task was as described above and to complete the sword task in ESC, participants had to grasp the handle of the sword which was oriented differently each time and insert it into a hole making sure their thumb pointed towards the hole. The authors found significant group differences for the latter only and concluded that children with DCD planned less for ESC when the task required precision on completion. Interestingly, when the same participants were tested on the sword task two years later, no group differences were observed (Adams et al., 2017). This suggests a possible lag in the development of motor planning skills for ESC in children with DCD and that the sword task which was of high complexity for younger children was no longer as complex for those aged 8–13 years. Of note, all the above tasks had two grip choices (reach-to-grasp the bar with a thump up/thumb down or using an underhand/overhand grip) and consisted of two movement sequences (reach-to-grasp – place/turn). Given the simplicity of these task parameters, it is likely that demands on motor planning were low for certain age groups, which may explain why those with DCD consistently performed at the same level as those without DCD. This view is supported by findings from other studies using similar grip-selection tasks that have reported that individuals with DCD are able to perform simple movements as effectively as their same age peers (Adams et al., 2016, Adams et al., 2017, Noten et al., 2014, Smyth and Mason, 1997).

A recent meta-analysis reported that impaired motor planning in those with DCD become more apparent with an increase in task complexity (Wilson et al., 2017). For grip selection tasks, complexity increases when the number of initial grip choices and/or possible movement sequences increase. Studies using a more ‘complex’ octagon grip selection task have found significant differences between children with DCD and their typically developing peers aged 8- to 12-years (Fuelscher et al., 2016) and 7- to 11-years (Wilmut & Byrne, 2014a). To complete this task, participants select a grip and turn a pointer which is initially at 0° to the colored stripes arrayed around the eight-sided dial in one, two or three color sequences. Studies found that healthy adults show a decreased propensity to terminate movements in ESC as the number of colors involved in a trial increases, with accuracy falling as low as 55% for the three color sequences (Wilmut and Byrne, 2014a, Wilmut and Byrne, 2014b). Fuelscher et al., 2016, Wilmut and Byrne, 2014a also found that all participants were more likely to choose ESC for the one color sequence than for the other color sequences. At the between group level, Wilmut and Byrne (2014a) found that children with DCD ended significantly fewer trials in ESC than their typically developing peers on the one and three color sequences. Interestingly, for the three color sequences both the typically developing children and those with DCD terminated less than 50% of their trials in ESC. Fuelscher et al. (2016) also showed that children with DCD are less likely to terminate their movements in ESC while performing the octagon task providing further support to the idea that children with DCD are less able to plan complex movements than their typically developing peers.

Taken together, the available evidence indicates that performances on simple motor planning tasks are similar for those with and without DCD, and that both groups are able to plan movements at age appropriate levels (Adams et al., 2016, Adams et al., 2017, Noten et al., 2014, Smyth and Mason, 1997). This could indicate that the tasks were insufficiently complex to discriminate between the two groups. A decrease in performance efficiency is consistently observed on complex tasks indicating that a deficit in motor planning may become more pronounced when task demands are high (Fuelscher et al., 2016, Wilmut and Byrne, 2014a). While this view is consistent with the clinical profile of many with DCD, results to-date do not provide a clear understanding about the motor planning deficit in children with DCD based on the differences in methodology in each study (e.g., screening procedures, age groups and tasks). Therefore, an empirical investigation administering both simple and complex tasks to a single sample of children with and without DCD is necessary in order to draw conclusions about the nature of the putative motor planning deficit in children with DCD.

The purpose of the study is to assess 8–12 year old children with and without DCD on three ‘simple’ (bar rotation, sword task, bar transport) and one ‘complex’ (octagon) motor planning tasks. As described, each has different task demands and levels of complexity. We hypothesised there would be no group differences between children with and without DCD on the simpler tasks of ESC; the bar grasping, sword and bar transport tasks. ESC would become less evident when planning demands increased in the complex octagon tasks. Accordingly, we expected group performance differences to be observed on all the three color sequences of the octagon task.

Section snippets

Participants

Participants were recruited from local schools, advertisements in the local newspaper and on websites for professional Occupational Therapist, Physiotherapist and Disability associations. The final sample comprised 27 boys aged 8- to 12 years. Only boys were included in order to eliminate any potential gender differences given the small sample size. All participants were screened on the four criteria for DCD (A, B, C, and D) described in the Diagnostic and Statistical Manual of Mental Disorders

Participant characteristics

There were no significant differences between the two groups for age and SNAP scores (Table 1). As expected, the DCD group scored significantly lower than the TD group for the NDI.

End state comfort for simple measures of motor planning

The Mann-Whitney U test revealed no significant group differences in the percentage of trials ending in ESC for the bar grasping, sword and bar transport tasks. For these tasks, both groups ended their performances in comfortable end states more often with mean percentage ESC levels ranging between 61% and 75%. There

Discussion

The current study aimed to clarify the nature of motor planning in children with DCD, by comparing performances on three simple (the bar grasping, sword and bar transport tasks) and one complex measure of motor planning (the octagon task) in children with and without DCD. As predicted, we found that both groups performed at similar levels for the simple tasks, regardless of non-critical or critical conditions. However, the participants with DCD ended less trials in ESC compared to their

Conclusion

The present study investigated the putative motor planning deficit in 8–12-year-old boys with and without DCD by administering a series of commonly used ‘simple’ and ‘complex’ motor planning tasks. We extend previous findings by indicating that school-aged children with DCD plan for ESC for simple tasks as efficiently as their peers however this ability decreases as task complexity increases. We found that the three sequence octagon task was too complex for this age group regardless of the

Declaration of interest

None.

Acknowledgements

We would like to thank the Collaborative Research Network for funding this research. Heartfelt thanks to all participants and parents and schools for their support.

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