Developmental coordination disorder: a developmental delay?

The first criterion for Developmental Coordination Disorder (DCD), according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) (APA, 1994), specifies that the motor performance of children with DCD should be below that expected given the person's chronological age. The inability of these children to perform motor skills at a level of competence equal to that of age-matched peers is the most prominent aspect of the disorder. Children with DCD are by definition delayed on the results of norm-referenced motor tests, such as the Bruininks Oseretsky Test of Motor Proficiency (BOTMP) (Bruininks, 1978) or the Movement Assessment Battery for Children (Movement-ABC) (Henderson & Sugden, 1992). The DSM-IV, however, does not describe an awkward style of performance. This is an aspect clinicians can observe and agree on, but which is difficult to assess with objectivity (Henderson & Henderson, 2002). Many of the current motor tests for children with DCD, such as the Movement-ABC (Henderson & Sugden, 1992) or the BOTMP (Bruininks, 1978), provide a record of the quantitative level of performance. The score depends upon factors such as the number of balls caught, the number of steps made on a balance beam, or the time needed to perform a movement task. These tests measure the outcome of the movement rather than how the movement was performed. Generally, chronological age is the yardstick against which performance is evaluated. The outcome of the assessment allows comparison with same-aged typically developing children (Burton & Miller, 1998). However, a teacher or therapist who uses a test will want to know why the child failed it and what they should do about it. They will want to know how the child performed the task and will focus on its qualitative aspects, form, style, or strategies.

Computer-based movement analysis, describing the kinematics, kinetics, and EMG patterns of the movements of children with DCD, compared to same-aged children without DCD allowed researchers to identify the clinical features of influence, awkwardness and poor coordination in the children with DCD. These studies revealed significant differences between children with DCD and same-age control children in the strategies used for performing tasks. However, they do not make it possible to determine whether the altered properties of a movement pattern should be attributed to a delay in development or to a deficient neuromotor system. The Smits-Engelsman and Van Galen (1997) study, which investigated the skill of handwriting, also used younger control children. In this study, children with DCD seemed to apply different strategies to various handwriting tasks, compared to younger children. The authors interpret these differences as being adaptations to the children's deficiency (Smits-Engelsman & Van Galen, 1997).

Some standardized motor test scores offer a motor age equivalent to performance (Folio & Fewell, 2000; Bruininks, 1978; Ulrich, 2000). This could encourage remedial teachers and therapists to interpret the disorder from a neuro-maturational lag perspective. However, if the movement patterns of children with DCD are different from those of younger children, the abnormal movement patterns could be interpreted as the optimal task solution given the altered properties of a deficient neuro-motor system. This point of view has important implications for the development of theory-based intervention programs.

In this study, ball catching was chosen as an activity for investigating whether movement strategies of children with DCD can be compared to the strategies of younger, typically developing children.

Method

Participants

To compare children with DCD to younger, typically developing children, we matched twenty-nine children with DCD, aged 7.5 to 9.5 years, to typically developing children of the same gender who were two years younger and who had caught a similar number of balls in the ball catching test. To compare children with DCD to same-age peers, we matched 27 children with DCD, aged 7.5 to 9.5 years, with typically developing children of the same gender and age.

Instrumentation

Long ball catching test. A long ball catching test was constructed that consisted of catching 10 consecutive tennis balls in eight different series. To standardize the throwing component, a tennis ball machine was used. The test comprised catching the ball in a pouch, catching the ball using two hands, and using one hand. The children's ball-catching performance was scored by viewing a video of the test. The total number of appropriately caught balls was used as the quantitative measure of ball catching performance. The last five series of the long ball catching test (catching the ball with one or both hands) were used to calculate the ratio of grasping errors. If the child did not catch the ball but touched it, this was categorized as a grasping error. A grasping error was not possible when the ball was not touched. As a measure of the amount of grasping errors, we used the ratio of the total number touched but not caught balls to the total number of touched balls.

Modified ball catching item of the Test of Gross Motor Development. A modification of the ball catching item of the Test of Gross Motor Development (TGMD) (Ulrich, 1985), was used to evaluate the strategies used to catch the ball. The item consists of catching a foam ball with a diameter of 20 cm, thrown from a distance of 4.5 m, 3 times. The performance criteria for ball catching are: (a) preparation phase: elbows flexed and hands in front of the body; (b) arms extend in preparation for ball contact; (c) ball is caught and controlled by hands only; (d) elbows bent to absorb force. Each criterion was scored with a one or zero score, the criterion being present or not. The child received 10 trials and each catch was scored afterwards from a video.

Procedure

All children were assessed with the modified item of the Test of Gross Motor Development (Ulrich, 1985), followed by the long ball catching test. All assessments took place in quiet rooms in the children's schools or rehabilitation centers.

Results

Children with DCD, compared to same-age control children for the number of caught balls, the modified TGMD-item score, and the ratio of grasping errors, performed significantly worse for the three dependent variables (p<.001). Moreover, effect sizes were large for all variables.

Children with DCD did not perform significantly differently with regard to the number of balls caught because children from both groups were matched to each other for this variable. However, the children with DCD had a significantly lower modified TGMD-score (p = .044) and a significantly higher ratio of grasping errors (p = .009). Effect sizes were low, but as the children were matched for a similar number of caught balls, no large effect sizes were to be expected.

Discussion

By definition, children with DCD do not perform as well as same-age typically developing children on various motor task outcome measures. As would be expected, the quantitative and qualitative performance on all ball catching measures were significantly poorer for the group of children with DCD compared to same-age peers. When children with DCD were compared to typically developing younger children who were able to catch a similar number of balls in the ball catching test, the children with DCD still had a significantly poorer qualitative ball catching performance.

Grasping error involves measuring the frequency of a well defined ball catching error, which is supposed to measure difficulties in the timing of the catching movement. When compared to younger peers, children with DCD had a significantly higher ratio of grasping errors. Even if they could touch the ball, children with DCD did not succeed in catching it. Though both groups caught a similar number of balls cleanly, the younger control children caught more balls by trapping them against the chest or by bobbling the ball, and then catching it. Fewer of the touched balls fell to the floor in the group of younger typically developing children. It could be that movement timing problems in children with DCD were manifesting themselves in an increased number of grasping errors. Conversely, typically developing children who are not able to catch a ball properly are better able to switch their strategies so they catch the ball, even if they have to clutch the ball against the body or bobble and then catch it.

While not measured in this study it is possible that a substantial number of the children with DCD maintain an inefficient anticipatory position of the arms, a strategy of keeping both hands together in order to catch with hands cupped (see Figure 1). Typically developing children who realized the ball catching strategy they used was not efficient, could have changed hand position in a next trial. These children seemed to learn more from the experience of previous catches, Other studies have described that children with DCD appeared to repeatedly perform a task the same way, whether or not it was successful. Missiuna (1994) showed that children with DCD have difficulties with learning and generalizing motor skills. It might be interesting to study whether or not children with DCD, missing several balls, continue to use the same catching strategies despite there ineffectiveness, compared to younger typically developing children.

[FIGURE 1 OMITTED]

The modified TGMD-item score was significantly lower for children with DCD. Since both groups of children were matched according to the number of properly caught balls in the long ball catching test, we can suppose that both groups could also catch a similar number of balls by hands only in the modified TGMD-item (third criterion of the TGMD). In conclusion, the preparation phase of catching of the children with DCD showed less elbow flexion and hands in front of the body, less ann extension in preparation for ball contact, and less bending of the elbows to absorb force when compared to younger typically developing children with the same level of ball catching proficiency. The children with DCD were able to catch a similar number of balls cleanly, even though they did not exhibit a proficient preparation phase. It may be that they learned to use other strategies, more appropriate for their inefficient motor control system.

In summary, this study revealed that children with DCD who had poor ball catching performance used different strategies than younger children with the same quantitative level of performance. The children with DCD prepared to catch the ball in a different way and had more catching problems, especially if they were not able to catch it cleanly.

Practical Applications

These findings are important for teachers and therapists. It seems that methods used to teach ball catching cannot simply be transposed from younger typically developing children to children with DCD. As a result, movement strategy instructions given to typically developing children may not necessarily be the best instructions for children with DCD.

Effective intervention for children with DCD cannot be confined to a single principle within one conceptual framework. A useful distinction is to separate intervention approaches into process-oriented and task-oriented. If a child has difficulty in catching a ball, one can intervene by giving ball-catching experiences of various types, a task-oriented approach, or one could break the act of ball catching into its underlying processes and try to improve these, which would be a process-oriented approach (Sugden & Chambers, 2005). Although the task-specific intervention programs are relatively new, the first results regarding their effectiveness are promising (Pless & Carlsson, 2000). However, any task-specific program should always start from task analysis and task adaptation to be successful. Both are crucial steps and are very much dependent on the skill of the professional. Results of this study show that task analysis and task adaptation should not adhere necessarily to an analysis of typical motor development. Children with DCD move with a slightly different neuro-motor system and the best strategy for typical developing children is not necessarily suitable for the child with DCD. For example, in the typical teaching of writing, children are told to sit up and leave space between the table and their tummys. However, many children with DCD are hypotonic and write better if they are allowed to lean to the table.

This study was not focused on the adaptation of the catching strategy of children with DCD in a series of catching identical balls. Do children with DCD change movement strategies into more efficient strategies in the same way as younger typically developing children? This clinically relevant question still remains to be answered. However, in the context of teaching an individual child, teachers or therapists can observe the learning strategies of a child. They cannot only help the child to discover the most efficient movement strategy but also the strategys to discover this most efficient movement strategy. This is also known as a meta-cognitive perspective to movement teaching and is a principle applied in the CO-OP approach: Cognitive Orientation to daily Occupation Performance (Mandich & Polatajko, 2005).

Selected references

American Psychiatric Association. (1994). Diagnostic and Statistical Manual of Mental Disorders (4th ed.). Washington DC: Author.

Bruininks, R.H. (1978). Bruininks-Oseretsky test of Motor Proficiency. Minnesota: American Guidance Service. Circle Pines.

Burton, A.W., & Miller, D.E. (1998). Movement Skill Assessment. Champaign: Human Kinetics.

Folio, M.R., & Fewell, R.R. (2000). Peabody Developmental Motor Scales. Austin, TX: PRO-ED.

Henderson, S., & Henderson L. (2002). Toward an understanding of Developmental Coordination Disorder. Adapted Physical Activity Quarterly, 19, 12-31.

Henderson, S.E., & Sugden, D.A. (1992). Movement Assessment Battery for Children: Manual. London: Psychological Corporation.

Mandich, A.D., & Polatajko, H. (2005). A cognitive perspective on intervention for children with Developmental Coordination Disorder: the CO-OP experience. In: Sugden, D., & Chambers, M., eds. Children with Developmental Coordination Disorder London & Philadelphia, Whurr Publishers.

Missiuna, C. (1994). Motor skill acquisition in children with developmental coordination disorder. Adapted Physical Activity Quarterly, 11, 214-235.

Pless, M., & Carlsson, M. (2000). Effects of motor skill intervention on Developmental Coordination Disorder: a meta-analysis. Adapted Physical Activity Quarterly, 17, 381-401.

Smits-Engelsman, B.C., & van Galen, G.P. (1997). Dysgraphia in children: Lasting psychomotor deficiency or transient developmental delay? Journal of Experimental Child Psychology, 67,164-184.

Sugden, D.A., & Chambers, M.E. (2005). Models of intervention: towards an eco-developmental approach. In: Sugden, D., & Chambers, M., eds. Children with Developmental Coordination Disorder London & Philadelphia, Whurr Publishers.

Ulrich, D.A. (2000). Test of Gross Motor Development-2. Austin, TX: PRO-ED.

Complete Details

Contact Hilde Van Waelvelde, Department of Rehabilitation Sciences, Faculty of Physical Education and Physiotherapy, K.U.Leuven, Belgium; Physiotherapy Department; Arteveldehogeschool, University Hospital 1K4, De Pintestraat 185, 9000 B-Gent, Belgium.

E-mail: [e-mail]

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