Balance control of children with developmental coordination disorder: clinical applications.

Children with Developmental Coordination Disorder (DCD), often referred to as clumsy or awkward, exhibit movement difficulties in the presence of normal intelligence and no known neurological disorders (American Psychiatric Association, 1994). In addition to experiencing difficulty in other skills, appropriate balance control is a critical contributor to the less than optimal involvement of these children in physical activities taking place during physical education class and recess (Cermak & Larkin 2002). Generally, the examination of balance control is based on statistical differences involving some measures of balance (sway, EMG, kinematics). However, at the behavioral level of analysis, the effectiveness of these patterns can be inferred from the functionality of emerging movement behaviors in the context of specific task demands. For example, in the case of static balance, different ways of controlling COP (centre of pressure) within the base of support in order to maintain stance on a moving bus or elevator may be viewed as effective, as long as they prevent falling, staggering, or taking a step. In terms of dynamic balance, voluntary adjustments of COP outside the base of support may also be viewed as effective, as long as they afford successful completion of a task, such as reaching for an object, catching an upcoming ball, or walking and running on, over, under, or through environmental features.

The postural adaptations/ balance control strategies exhibited by children with DCD are expected to differ from those used by typically developing peers (Williams, 2002). However, in line with the functionality perspective, these strategies could be viewed as atypical yet adaptive, rather than pathological and demanding intervention, if they afford the completion of the task goal (Latash & Anson, 1994). To date the primary focus of balance research involving children with DCD has been on their abilities to detect the body's deviation from vertical alignment and to match it with an appropriate muscular response to maintain (static) stance. More recent investigations suggest that balance control strategies exhibited by children with DCD, although possibly different, may be as effective and functional as those exhibited by their typically developing peers (Geuze, de Jong & Taylor, 1999; Williams, 2002). To verify this hypothesis, the balance control of boys with and without DCD was examined and described based on a number of different measures of postural sway. Also, as the hypothesis that children with DCD over-rely on visual input to maintain stance has been questioned recently (e.g., Geuze et al., 1999), a secondary purpose was to examine the ability of both groups to maintain stance with eyes open and closed.

Method

A three-part procedure was used to screen the participants. With assistance of principals and teachers in the local school system a preliminary evaluation of movement characteristics was carried out by the homeroom teacher using the Motor Behavior Checklist (MBC) (Weir, 1992). The MBC is composed of 10 questions pertaining to general motor abilities, simple everyday activities, and behavioral patterns of children. The next stage involved a formal assessment using the Movement Assessment Battery for Children (MABC) (Henderson & Sugden, 1982). The MABC was incorporated to obtain information regarding each child's overall motor skill level reflected in a Total Impairment Score (TIS), as well as his balance control abilities inferred from the Total Balance Score (TBS).

As a result, forty boys were recruited and subsequently divided into two even groups, one consisting of boys with DCD and balance difficulties ([M.bar] = 8 years, 7 months, [SD.bar] = 2 years, 1 month), and a comparison group of boys without DCD and balance difficulties ([M.bar] = 8 years, 6 months, [SD.bar] = 2 years). All boys in the DCD group had visible movement difficulties and scored at or below the 5th percentile on the TIS and TBS. The comparison group did not demonstrate general movement difficulties and had scores above the 15th percentile on both the TIS and TBS. The groups differed significantly on TIS ([t.bar] (38) = -11.609, [p.bar] < .001), and the TBS scores ([t.bar] (38) = -9.939, [p.bar] < .001). Also, there were no significant differences in height (t(38) = -.475, [p.bar] < .638) or size of support (foot length) ([t.bar](38) = -.900, [p.bar] < .374).

Data Collection

Participants were asked to stand on an AMTI strain gauge force platform which quantified the amount of displacement of center of pressure (COP), at a sampling rate of .01 seconds (100 HZ). The testing session lasted approximately 15 minutes, including pre-testing measurements and two twenty-second trials (one with eyes open and the second with eyes closed). In the eyes open task the children were asked to look at a point located at eye height 5 meters away while standing as still as possible with arms crossed at the chest. The same procedure was followed in the eyes closed task, except participants were asked to close their eyes just prior to commencement of the trial.

Data Analysis

The data were analyzed through the AMTI AccuSway Plus system, which provided sway displacement measures of path length (L) (cm), anterior-posterior (AP) (cm), lateral sway (LAT) (cm), and area of sway (Ao) ([cm.sup.2]). Generally, a lesser amount of sway is indicative of more efficient balance control. Whereas the first three variables path length, AR and Lat) describe the amount of COP displacement, the Ao indicates the range and size of the area created during the COP migration. All four variables were translated into Romberg's quotient (RQ) (eyes closed/eyes open x 100%) to determine whether a) the balance control of both groups was affected when visual information was removed, and if b) this effect was proportionally similar for both groups. The larger the deviation from 100%, the more pronounced the effect of removing vision on balance performance during stance (e.g., Elliott, FitzGerald & Murray, 1998).

A series of 2 by 2, group (DCD vs. no DCD) by condition (eyes open or eyes closed) ANOVAs with a repeated measure on the second variable were performed for AR LAT sway, area and path length. To determine whether both groups reacted similarly to the removal of visual information, a multivariate analysis of variance (Hotteling's [T.sup.2]) was carried out on the four measures transformed into Romberg's (RQ) ratios. All statistical procedures were carried out at a = .05. The analysis of interclass correlation coefficients confirmed adequate reliability of the measures used.

Results/Discussion

The results provided no clear evidence to suggest that the status of feedback-based control, underlying balance strategies in quiet stance, is less effective for children with DCD than without DCD. Children with DCD exhibited more sway in the AP plane ([M.bar] = 2.14, [SD.bar] = .68) and a larger area of sway ([M.bar] = .52, [SD.bar] = .28) than children without DCD ([M.bar] = 1.66, [SD.bar] = .52; [M.bar] = .33, [SD.bar] =. 19, respectively). However, there were no significant differences between children with and without DCD in LAT sway ([M.bar] = 2.12, [SD.bar] = .74 vs. [M.bar] = 1.90, [SD.bar] = .70) and in the total amount of COP displacement (path length) ([M.bar] = 35.39, [SD.bar] = 11.98 vs. [M.bar] = 30.63, [SD.bar] = 6.58). While seemingly contradictory at first, closer examination of the data indicated that boys with DCD exhibited a tendency to settle in the anterior-posterior plane of sway, while their typically developing peers did not appear to show any directional bias in their sway patterns. When considering the shape of the COP migration pattern (area of sway), children without balance difficulties converged onto a fixed point around the initial location of COR a safer strategy that may have allowed them to avoid any extreme excursions from the vertical, stable position. On the other hand, children with DCD tended to settle predominantly into large, pendulum-like anterior-posterior cycles of displacement. This tendency positioned their COP closer to their stability limits, running a greater risk of losing balance. Despite the differences in (balance) strategies used, both groups were able to complete the task successfully without falling, staggering, or taking a step.

In terms of the role of sensory information, it is generally easier to maintain stance with vision than without it. Children with DCD were expected to over-rely on visual information to maintain balance, suggesting that its removal would be more detrimental to their ability to maintain stance as compared to children without DCD (Wann, Mon-Williams, & Rushton, 1998). Results of the present investigation did not support this hypothesis. There were no significant differences between the groups on any of the measures involved. The increase in amount of sway, due to the removal of visual input, was found to be proportionally similar for both groups. Thus, while the nature of sensory information used to maintain stance is not known, both groups appeared to compensate adequately for the lack of visual input, supporting the findings of Geuze and colleagues (2002) and Jung-Potter and colleagues (2002).

While the groups differed on some measures of balance control, the strategies incorporated by all children were equally effective in maintaining stance. Thus, if functionality is considered the bench mark against which the effectiveness of the emerging behaviour is inferred, the strategies exhibited by children with DCD could be considered as adaptive and different, rather than delayed and requiring intervention. Do children with DCD have balance difficulties? Clearly many do. However, it is likely these problems may not be due to the status of balance control used in static tasks (Williams, 2002), but rather are nested within mechanisms underlying feedforward/feedback type of control (Przysucha & Taylor, manuscript in preparation). This mode of control is relied upon when the system is required to anticipate limb position in space and carry out the necessary adjustments to the emerging pattern during the ongoing action (e.g., catching, batting).

Practical Implications

The idea that children with DCD are able to develop strategies that, while deviating from what is seen as typical, could be considered as functional and adaptive, (Latash & Anson, 1992), has important implications for identification and instructional strategies. In relation to the difficulties in dynamic postural adaptations, they may be identified in the laboratory through various methodologies (e.g., EMG) and assessment tools (e.g., MABC). However, professionals who operate in the field (e.g., physical education teachers) generally do not have access to these resources.

In keeping with the idea that different can be considered as adaptive, Ecological Task Analysis (ETA) (Burton & Davis, 1996) may be a useful instructional/intervention tool to detect difficulties in the postural adaptations underlying behaviors (e.g., catching, kicking) occurring in natural settings (e.g., physical education class, recess). Here, the manipulation of relevant individual, task, and environmental constraints allows the detection of these problems and helps determine the factors that may afford or limit meaningful, and above all, functional participation of a child in a particular activity. The implicit assumption, in this approach, is that there is no one way of accomplishing a movement task. Therefore, the different movement strategies a performer may choose to accomplish a task may be considered as effective as long as they are functional.

The role of the teacher, coach, or practitioner is not to impose on the performer a particular movement form that is considered normal or typical for a given age group. Rather, it is to seek and strengthen those patterns leading to functional outcomes and which may be optimal given the characteristics of the performer and task at hand. In fact, due to the neuro-physiological make up of children with movement difficulties, expecting their movement patterns to resemble those generated by the majority of typically developing individuals may simply be unrealistic.

Encouraging exploration of alternate strategies to achieve outcomes both meaningful and successful is critical when promoting the active participation of children with movement difficulties in physical activity settings.

Complete Details

Eryk Przysucha, Faculty of Physical Education and Recreation, University of Alberta, Van Vliet Center E-436, Edmonton, AB, CANADA T6G 2HJ; [phone]; [e-mail]. Co-authors include Nancy Cavaliere and M. Jane Taylor.

Selected References

American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed). Washington, DC: Author.

Cermak, S.A., & Larkin, D. (2002). Developmental Coordination Disorder. Albany, NY: Delmar.

Elliott, C., FitzGerald, J.E., & Murray, A. (1998). Postural stability of normal subjects measured by sway magnometry: Path length and area for the age range 15 to 64 years. Physiological Measurement. 19(1), 103-109.

Geuze, R., de Jong, F.J., & Reitsma, E.M. (2002, May). Developmental Coordination Disorder and static balance. Paper presented at the 5th Biennial Workshop on Children with DCD, Banff, Alberta.

Geuze, H.R., de Jong, F.J., & Taylor, J. (1999, October). Balance control of children with DCD. Poster session presented at the Biennial Conference on Children with a Developmental Coordination Disorder, Groningen, Netherlands.

Henderson, S., & Sugden, D. (1982). Movement assessment battery for children. New York: Harcourt, Brace & Jovanovich (The Psychological Corporation).

Jung-Potter, J.O., Kim S.J., Metcalfe, J.S., Horn, C., Wilms-Floet, A.. McMenamin, S., Whitall, J., & Clark, J.E. (2002, May). Somatosensorymotor coupling in children with Developmental Coordination Disorder. Paper presented at the 5th Biennial Workshop on Children with DCD, Banff, Alberta.

Latash, M. L., & Anson, J.G. (1996). What are "normal movements" in atypical populations? Behavioral & Brain Science. 19, 55-106.

Przysucha, E.P., & Taylor, M.J. Postural adaptations Of boys with and without DCD in dynamic balance tasks (manuscript in preparation).

Wann, J. P., Mon-Williams, M., & Rushton, K. (1998). Postural control and co-ordination disorders: The swinging room revisited. Human Movement Science, 17, 491-513.

Weir, J. (1992). Teacher identification of physically awkward school children. Unpublished master's thesis, University of Alberta, Edmonton, Alberta, Canada.

Williams, H.G. (2002). Motor control in children with Developmental Coordination Disorder. In S.A. Cermak & D. Larkin (Eds.). Developmental Coordination Disorder (pp. 117-131). Albany, NY: Delmar.

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