Children with developmental coordination disorder (DCD) exhibit marked developmental delays in motor coordination skills.1 In particular, coordinating complex movements such as those required in sports and active play may be difficult for children with DCD.2 Such difficulties may affect the child on several health dimensions, including participation and level of function, as outlined by the framework of the World Health Organization International Classification of Functioning, Disability and Health.3 Despite the effect of poor motor coordination on daily living, participation and how this relates to physical fitness have rarely been investigated in the population with DCD.4
Participation, broadly defined as involvement in life situations, is valuable for the overall well-being and health of children.1 , 5 An important part of participation includes physical activities during leisure time. School-aged children should accumulate at least 60 minutes of physical activity daily for health.6 Children, in general, have become less physically active in recent decades.5 In children with DCD, probably because of their motor coordination deficit, participation in physical activities seems to be even more compromised.7 , 8 Indeed, it has been demonstrated that children with “probable DCD” (children who meet criterion A of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition [DSM-IV] criteria [population-based study]) participate less in organized and free-play activities.2 The study described here focuses on leisure time physical activities (LTPAs), defined as habitual participation in physical activities during leisure time. In children with a “diagnosis of DCD” (children who meet all 4 criterion of the DSM-IV criteria [clinical-based study]), different types and intensities of LTPAs have never been investigated. It is likely that distinguishing different types of LTPAs may provide more insight into the levels and patterns of activities in children with DCD.8 , 9
Lower participation rates in physical activities for children with DCD than those for children developing typically may, in turn, affect their physical fitness level negatively. Physical fitness is defined as a set of attributes that people have or achieve that relate to the ability to perform physical activity.8 The components of health-related physical fitness are body composition, cardiorespiratory fitness, muscle strength and endurance, anaerobic capacity, power, and flexibility.4 Although there are more components of health-related physical fitness, the present study will focus on the most widely accepted cardiorespiratory fitness component, aerobic fitness, measured as maximal oxygen uptake.5 , 10 Aerobic fitness refers to endurance, or the ability to sustain activity for prolonged periods of time. Aerobic fitness is lower in children with probable DCD than in children developing typically.10–12 Aerobic fitness in children with a diagnosis of DCD has been studied only once.13 Chia et al13 used the incremental treadmill protocol to indicate a lower aerobic fitness in children with DCD.
To date, only a few cross-sectional studies focused on the relationship between physical activities and the level of physical fitness in children developing typically. For instance, Hoffman et al14 found an association between seasonal physical activities and the level of anaerobic power and muscular strength in children developing typically, and Zahner et al 15 found participation in organized sports to be particularly associated with a level of endurance fitness in children developing typically and who are not overweight. It is not known whether this positive not-causal relationship between participation in physical activities and physical fitness exists also in children with a diagnosis of DCD. Only 1 previous cross-sectional, population-based study including children with probable DCD led to the conclusion that reduced participation in physical activities resulted in lower cardiorespiratory fitness.11
So far, studies of participation in LTPA or on the relationship between participation in LTPA and aerobic fitness in children with coordination problems have included only children with probable DCD.4 These population-based studies only tested poor motor coordination in relation to chronological age (DSM-IV, criterion A) and ignored the effect of poor motor coordination on daily life (DSM-IV, criterion B). In addition, 31 of 49 children with probable DCD in a 7-year-old population are likely to have a misdiagnosis.16 Therefore, the present study is clinically based and focuses on children with DCD, who met all 4 DSM-IV diagnostic criteria for DCD. The first purpose was to explore participation in LTPA (overall, organized, nonorganized, vigorous, and light) in children with DCD recruited from rehabilitation clinics in comparison to a group of children developing typically. The second purpose was to examine the association between participation in LTPA and aerobic fitness.
The present study was part of a multicenter case-control study in the Netherlands. Ethical approval was obtained from the medical ethics committee of the University Medical Center Groningen. The main outcome measures were assessment of participation in LTPA and aerobic fitness. Additional variables were personal and environmental characteristics of the participants. The environmental characteristics included the parents' sports participation and education level. All participants were measured once by experienced physical therapists and movement scientists. The examiners were trained to standardize measurements. Children in the DCD group were assessed during therapy time and children in the group developing typically were assessed during school time. Written informed consent was gained from the parents before participation of the child in the study. Twelve-year-old children also signed an assent form for participation in the study.
Children with DCD, aged 7 to 12 years, were recruited from 3 rehabilitation centers in the Netherlands. Children developing typically, matched for age and gender, were recruited from 4 mainstream Dutch elementary schools. Children with DCD had to meet the operationalized DSM-IV diagnostic criteria for DCD (see Appendix 1)17 and received less than 2-month treatment. Exclusion criteria were presence of either heart or lung problems. Children developing typically were excluded when they had motor coordination problems according to criterion A of the operationalized DSM-IV diagnostic criteria for DCD or when they were under medical treatment.17
Assessment of Participation in LTPA
The Dutch translation of the Modifiable Activity Questionnaire was used to indicate participation in habitual LTPA.18 The Modifiable Activity Questionnaire, which has been shown to be both valid and reliable, measures the current habitual physical activity of the child (past year and past week), as well as extreme levels of inactivity.19 Parents assisted their children with the questionnaire. The present study focused on the habitual participation in physical activities during the past year. Participation in LTPA was defined as joining at least 10 times a LTPA, like soccer, swimming, cycling, dance, during a year. Not all children walk or cycle to school, and hence, these activities were considered as LPTA. The average participation was investigated for overall, type, and intensity of LTPA (hours per week). Overall LTPA contained all reported activities. Type of LTPA was divided into organized LTPA, defined as participation through a formal club, and nonorganized LTPA, like bicycling, walking, and playing soccer during leisure time. Intensity of LTPA was defined as the ratio of working metabolic rate to a standard resting metabolic rate per activity. The average resting metabolic rate intensities for each activity were allocated to each LTPA according to the compendium of Energy Expenditures for Youth.20 Not all activities (eg, scouting) were reported in the compendium, thus these activities were matched with the most similar activities. Two intensity levels were created, namely light and vigorous LTPA (see Appendix 2). To calculate the frequency of light and vigorous activities, the cutoff point was set at the estimated intensity of 6 resting metabolic rates.9 The average habitual participation in physical activity (hours per week) over the past year was calculated for each activity as follows18:
(months) × (4.3 weeks per month) × (days per week) × (minutes per day) ÷ (60 minutes per hour) ÷ (52 weeks per year);
for each of the 5 LTPA categories, the number of hours spent in activities was summed to determine total time spent in a particular category of LTPA over the past year in hours per week.
Assessment of Aerobic Fitness
The Maximal Multi-stage 20-m Shuttle Run Test was performed to predict maximal aerobic capacity (henceforth called aerobic fitness).21 , 22 Participants were required to run back and forth on a 20-m course ever faster and to touch the 20-m line when a beep was heard. The test is stopped when the participant is no longer able to follow the set pace. To predict aerobic fitness, the final stage reached was converted to estimated aerobic fitness by using the formula from Léger et al21:
31.025 + 3.238 × velocity (km·h−1) − 3.248 × age (y) + 0.1536 × velocity (km·h−1) × age (y);
where velocity was defined as 8 + 0.5 × last gained stage. The Maximal Multistage 20-m Shuttle Run Test has been found to be reliable (test-retest r = 0.89) for children.22 The Maximal Multistage 20-m Shuttle Run Test is a valid predictor of aerobic fitness (correlated at r = 0.71 to cycle ergometer) when the cycle ergometer is not feasible.23
Data were analyzed using SPSS (version 17). To analyze differences between children with DCD and children developing typically, t tests were used. Mann-Whitney U tests were used if data were nonnormally distributed or if the level of measurement was ordinal. Chi-square tests were used to analyze classification levels between groups. Associations between and within the participation in LTPA and aerobic fitness were assessed with partial correlation coefficients. Correlations were considered low (0.26 < r < 0.49), moderate (0.50 < r < 0.69), or high (r > 0.70), using the guidelines provided by Cohen.24 Age was added as a covariate to correct for differences associated with age.10 Hierarchical regression analysis was used to estimate the relationship between the duration of participation in LTPA and aerobic fitness. Associations within participation in LTPA variables determined which LTPAs were used as predictors. The variables were entered into several steps. In step 1, the covariate age was added. The 2 research groups were taken into account in step 2 by the dummy variable group, where children with DCD were compared with the reference category of children developing typically. In step 3 and 4, the independent variable LTPA and the interaction term between group and LTPA were entered in the model, respectively. Interaction terms of participation in LTPA and group were computed by multiplying standardized scores with the dummy variable group, to determine whether the relationship between participation in LTPA and aerobic fitness differed according to participant group. The variables that significantly differed between groups were added in step 5 to control for potential confounding effects of group and participation in LTPA on aerobic fitness. Assumptions for regression analysis were checked and none of the assumptions were violated. The α level was set at .05 to determine statistical significance.
Seventy-six children, 38 with DCD (28 boys, 10 girls; mean age, 9 years) and 38 age- and gender-matched children developing typically (mean age 8 y 11 mo), were included in the study. No significant differences in personal characteristics were found between the groups (Table 1), except for the significantly lower Movement Assessment Battery for Children scores for children with DCD (P < .05) and the educational level of parents, which was significantly lower for the parents of children with DCD (P < .05).
Differences Between Children With DCD and Children Developing Typically
The group with DCD spent an average of 4.5 h/wk in LTPA compared with 5.8 h/wk for the group developing typically (Table 1). Only 31.6% of the group with DCD met global health recommendations to be physically active for 1 h/d, (2 h/wk of obliged physical activity lessons at school were counted), compared with 52.6% in the group developing typically. Children with DCD reported to spend significantly less time in LTPA compared with children developing typically for overall (P = .016), nonorganized (P = .022), and vigorous (P = .004) LTPA.
The group with DCD had an average aerobic fitness of 44.8 mL·kg−1·min−1 compared with 48 mL·kg−1·min−1 for the group developing typically (Table 1). Compared with children developing typically, children with DCD had a significantly lower score on aerobic fitness (P < .001).
Association Between Participation in LTPA and Aerobic Fitness
Correlations between aerobic fitness and all LTPA categories were significant but low (Table 2). Overall LTPA correlated positively with organized (moderate association), nonorganized (high association), light (moderate association), and vigorous (high association) LTPA. Because of the moderate and high associations between the predictors, only overall LTPA was included in the regression analyses. Vigorous and nonorganized LTPA had a high association (correlation = 0.766).
Step 1 of the hierarchical regression analyses (Table 3) shows that aerobic fitness was significantly lower for children who are older (b = −0.98, SE = 0.33, and P = .004). Step 2 shows a significant effect for group, that is, children with DCD had a significantly lower aerobic fitness than children developing typically (b = −3.28, SE = 0.76, and P < .001). Step 3 shows that overall participation in LTPA was a significant and positive predictor of aerobic fitness (b = 1.59, SE = 0.35, and P < .001), indicating that an increment in overall participation in LTPA of 1 unit results in an increment in aerobic fitness of 1.59 units. The interaction between overall participation in LTPA and group in step 4 was not significant (P = .818). Thereby, although both groups differed on parents' educational level, controlling for this variable in step 5 did not lead to a different estimate of the participation in LTPA regression coefficient. The model resulting in the third step is considered to be the best model. This model, including the predictors age, group, and overall participation in LTPA, explained 46.2% of the variance in aerobic fitness. Having DCD or not was the most important in predicting aerobic fitness (18.8%), followed by participation in LTPA (16.4%).
The present study showed that children with DCD participated less hours per week in overall, nonorganized, and vigorous LTPA compared with children developing typically. No differences were found in organized and light LTPA between groups. Only 31.6% of children with DCD met the global recommendations to be physically active for 1 h/d compared with 52.6% in the group developing typically.6 In addition, aerobic fitness was significantly lower in children with DCD. Participation in LTPA is a significant predictor of aerobic fitness in children with DCD and children developing typically.
Regarding our first research aim, to explore the level of participation in LTPA in children with DCD, the present study revealed 3 remarkable findings. First, in line with studies regarding children with probable DCD, children with DCD spent less time in overall LTPA compared with their peers who are healthy.2 , 4 , 7 , 11 Thereby, not all investigated children meet the global health recommendations. These are important findings because sufficient physical activity plays an important role in preserving and enhancing health and quality of life, especially for children with a disability.25 Second, the present study revealed no difference for organized LTPA, whereas a difference for nonorganized LTPA was found between groups. Regarding organized LTPA, our finding is in contrast with previous research, which reported that children with probable DCD spent less time in organized LTPA.2 , 4 , 7 , 11 An explanation for this difference may be the age of the children included. As in the present study, children with DCD were relatively young compared with those in comparative studies, parents may still oblige young children to engage in an organized sport. The lower participation in nonorganized LTPA in children with DCD is in accordance with previous research in children with probable DCD.2 , 4 , 7 , 11 Indeed, it seems that children with DCD are less active when they have to initiate physical activities themselves, in comparison to children developing typically. Third, so far, no previous studies addressed the intensity of LTPA (light LTPA or vigorous LTPA) in children with probable DCD or DCD. A new result of the present study is that children with DCD participate less in vigorous activities. A possible explanation for lower participation rates in vigorous LTPA but equal participation rate in light LTPA is that children with DCD experience strength and power deficits and, therefore, avoid vigorous LTPA.26 A result of this type of classification is that nonorganized and vigorous LTPA are highly associated with overall LTPA and with each other. This is probably caused by some common LTPA and the overlap of these activities, especially for cycling, a typical Dutch nonorganized and vigorous LTPA. All these findings are based on a subjective questionnaire, the Modifiable Activity Questionnaire. Issues associated with this kind of questionnaire for young children may include the tendency to overestimate and give social desirable answers.27 To avoid overestimation, the parents of the children helped to fill in the questionnaire in the present study. Because these issues refer to both the children with DCD and children developing typically, only the proportions should be interpreted. Beyond these limitations, results showed that children with DCD have a lower overall participation rate, which is reflected in lower nonorganized and vigorous LTPA rates.
Regarding the second research aim, to examine the association between participation in LTPA and aerobic fitness, the present study found an effect of group and an effect of LTPA. First, the most important predictor of aerobic fitness was group (18.8%), indicating that children with DCD have a lower aerobic fitness than children developing typically. This finding is in line with earlier research in children with DCD and probable DCD.4 , 13 Second, participation in LTPA explained 16.4% of the variability in aerobic fitness. So, for both children with DCD and children developing typically, the model suggests that aerobic fitness will increase as the duration of participation in LTPA increases, consistent with the study of Faught et al.11 The finding that higher duration of participation in overall LTPA is associated with a higher aerobic fitness in both children developing typically and children with DCD may indicate that the underlying mechanism for aerobic fitness in both groups is equal. However, the fact still remains that even when children with DCD spent the same amount of time in a LTPA, their aerobic fitness level is lower. An explanation for the lower aerobic fitness level might be that children with DCD perform the reported physical activities with a lower intensity and, thus, are less physically active during the same (recess) time compared with children developing typically because of their coordination problems.5 , 12 Our results show that participation in LTPA is associated with aerobic fitness in both children with DCD and children developing typically.
Although LTPA appeared to be associated with aerobic fitness, causality cannot be established. On the basis of the lower aerobic fitness level as well as a lower participation rate in children with DCD, we recommend improving both to promote the child's health. The differences found in vigorous and nonorganized LTPA provides the physical therapist with information on training children with DCD more specifically. The promotion of vigorous activities and fostering playing outdoors, like rowing or cycling, might be examples of tailored advice, where it should be emphasized that participation is more important than winning. In addition, to enable participation, it seems important that children with DCD choose their own functional goals in an area of physical activity in which they feel comfortable, thereby improving competence and becoming more a part of the group.28 Furthermore, it seems important that therapists pay attention to possible personal and environmental mediating factors, such as, social functioning, self-worth, and parental support, that could prevent children with DCD from successful participation.29
A number of limitations should be addressed in future research on participation and aerobic fitness in children with DCD. In the present study, a self-report was used for the assessment of participation in LTPA, which is subjective and may induce recall bias and result in social desirable answers. The use of more objective measurement tools, like accelerometers, are recommended for future studies. Despite the fact that different components of LTPA were distinguished, future research should, in particular, pay more attention to the actual intensity of the performed activities. The present study had a cross-sectional design; in further research, a longitudinal or intervention study is needed to detect possible individual differences in the development of motor coordination skills and to determine a possible causality between participation in LTPA and aerobic fitness.
In comparison with earlier research on children with probable DCD, the present study showed that children with DCD spent less time in overall, nonorganized, and vigorous LTPA compared with children developing typically. Thereby, children with DCD have lower aerobic fitness than children developing typically. Therefore, suitable physical activities should be fostered in children, particularly in children with DCD, who already have a low participation rate as well as aerobic fitness level.
The authors thank the participating children and their parents, Roessingh Center for Rehabilitation (Enschede, the Netherlands), University Medical Center Groningen Center for Rehabilitation (Groningen, the Netherlands), Rehabilitation Center “Revalidatie Friesland” (Beesterzwaag, the Netherlands), Paulusschool (Rutten, the Netherlands), OBS Exel (Laren GLD, the Netherlands), Joh. Calvijn school, (Groningen, the Netherlands), Openbare Jenaplanschool de Petteflet (Groningen, the Netherlands), and Marieke van Hunen for their contributions.
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