1. Introduction
Developmental coordination disorder (DCD) is a neurodevelopmental condition that is associated with difficulties participating in physical activity and affects approximately 5–6% of school-aged children [
1,
2]. Children with DCD commonly experience difficulties participating in play and sports activities due to a lack of motor competence and performance, including fundamental-motor and motor-coordination skills [
3,
4]. These difficulties can contribute to avoidance of motor activity, a higher incidence of obesity-related chronic diseases, negative cardiovascular-related health outcomes, and lower levels of physical activity in adulthood [
5,
6,
7,
8,
9]. Furthermore, avoidance of physical activity in school-aged children may negatively affect aspects of a child’s social inclusion and self-concept formation, potentially leading to emotional and behavioral issues [
10,
11]. Therefore, providing effective intervention that improves the motor performance and health-related physical fitness level of children with DCD is important.
Children with DCD have difficulties participating in physical activities and activities of daily living (ADL) [
1,
2]. Adequate performance of ADL relies on continuous and sequential movements with appropriate reaction times to achieve motor task completion [
12,
13,
14]. Thus, timing ability, which is one of the motor performances, plays an important role in the development of motor skills and achievement of satisfactory functional performance [
15]. Timing ability relies on the interactions of motor and cognitive functions with the environment and is, therefore, reduced in children with DCD [
16,
17]. This impairment of timing ability in children with DCD, such as uncorrected or slow reactions, can have a negative effect on their ADL [
14,
18,
19]. Physical activity intervention is a suggested method to improve one’s timing ability [
20]; however, research on the effectiveness of school-based intervention that aims to improve the timing ability for children with DCD is insufficient.
Exercise interventions for children are important because poor health-related physical fitness can have potentially serious health consequences later in life [
11]. Children with DCD are less physically active and have lower levels of participation in play because they have motor functional limitations [
9,
21]. Previous research has suggested that an exercise program for children with DCD can have positive effects on health-related physical fitness [
22]. However, differences can occur in the results of intervention depending on a child’s age and the type and periods of interventions. In fact, a clear conclusion on whether exercise intervention can improve a child’s health-related physical fitness in early childhood has been difficult to reach.
Delayed motor development persists into adolescence or even adulthood in over half of the children with DCD; therefore, appropriate early interventions should be provided [
9,
23]. According to previous studies, school-based interventions to improve fundamental motor skills (FMS) have shown positive effects on the proficiency of FMS, participation in physical activity, and self-perceived competence in children with DCD [
24]. Although previous studies have reported improvements in the functional ability of children with DCD who received training in FMS, only a limited number of studies have been conducted that investigated the change in motor performance, including the timing ability and health-related physical fitness, of children with DCD [
4,
24,
25]. An Interactive Metronome (IM) is designed to activate the central nervous system and evaluate children with nerve disorders that are associated with reduced cognitive and motor functions. To the best of our knowledge, no intervention study in children with DCD that utilizes training in FMS and measures timing ability with an IM has been reported.
This study assessed the changes of motor performance, timing ability, and health-related physical fitness in children with DCD following a 12-week exercise program that targeted FMS. We hypothesized that the motor performance and health-related physical fitness of children with DCD would improve after participation in the intervention.
4. Discussion
We examined whether training in FMS improves the motor performance (motor coordination ability, FMS, and timing ability) and health-related physical fitness of children with DCD. We found that children with DCD showed significant improvements in motor performance and health-related physical fitness, but not in body composition, after participation in a 12-week intervention program designed to promote FMS.
We found that the MABC-2 score, which evaluates the motor coordination ability of children with DCD, improved after the children participated in the 12-week training (
Table 3). These results are in agreement with those of previous studies that reported an improvement in coordination ability after an exercise intervention [
31,
32,
33]. Most notably, nine out of 27 children with DCD in our study (MABC-2 score ≤ 15%) showed a reduction of symptoms to the point that the children were no longer considered to be at risk for DCD (MABC-2 score >15%). We are unable to conclude that symptoms can fully resolve within 12 weeks of an exercise intervention because our DCD group included only three child with severe indicator symptoms (MABC-2 score ≤ 5%); however, this possibility cannot be ignored. The MABC-2 score of the bottom 5% of children improved from 52.5 to 72. Additionally, no significant change was observed in the manual dexterity score because the intervention program focused only on the improvement of FMS and did not include fine motor skill exercises.
Previous studies reported that training in FMS had positive effects on motor skills and activity in children [
25,
34,
35]. Our results show that locomotor and object control skills improved significantly in the intervention group (
Table 3). This finding suggests that the intervention program was effective at improving the FMS of children with DCD and is in agreement with previous research that showed training in FMS supported by error-reduced learning was effective in a sample of children with DCD [
25]. Notably, our observed improvement of FMS is higher than previously reported results [
25,
35]. Our results showed that around 51% of FMS improved and reached the normal standard range for TGMD-2. Therefore, we have demonstrated that intervention has the ability to improve the FMS of children with DCD to normal levels.
This investigation is the first to evaluate the effect of training in FMS on the timing ability of children with DCD using the IM. Our findings reveal that the intervention group showed interactive effects on timing abilities. The different components of the timing ability in children with DCD showed significant effects for all assessments: hands 23% (pre-post, 139.43 milliseconds-107.38 milliseconds), feet 25.9% (pre-post, 192.31 milliseconds-142.52 milliseconds), and bilateral 25.8% (pre-post, 210.24 milliseconds-156.04 milliseconds). Significant changes were also observed within the control group (hands 5.6%, feet 8.5%, and bilateral performance 5%), although these changes were small compared to the results of the intervention group and were most likely due to a repetition of the active metronome evaluation. This trend is consistent with the findings of previous studies that reported intervention effects in the timing ability of children with DCD [
20,
36].
An analysis of the IM-based test data shows that children with DCD had poor reaction times in hand, foot, and bilateral performance. The most pronounced difference was in task 11 (bilateral performance), which is consistent with the findings of Rosenblum and Regev (2013) [
17]. These results demonstrate that children with DCD have difficulty reacting to auditory signals and simultaneously carrying out designated movements, and this difficulty is more pronounced for tasks involving symmetrical movement because a higher coordination ability is required. Our findings are in agreement with previous observations that suggested children with DCD have slower motor reaction to auditory stimulus [
37,
38]. Whitall et al., attributed the cause of this phenomenon to a deficit in auditory processing associated with DCD [
38].
Children’s health-related physical fitness has important implications in relation to development [
7]. Health-related physical fitness has been considered an important factor for the healthy development of children with DCD (Li et al., 2011). Both longitudinal and cross-sectional studies have indicated that children with DCD have poorer health-related physical fitness than children with typical development [
39,
40]. As previously reported, children with DCD have poor indicators of health-related physical fitness, which is consistent with our findings [
39,
40]. However, these indicators improved after participation in the 12-week exercise program focused on training in FMS; this improvement was most likely due to increased participation in physical activities, which would be expected to positively influence cardiorespiratory fitness, muscle strength, muscular endurance, and flexibility. However, the percentage of body fat increased significantly in the children from both the intervention group (DCD-int) and the control group (DCD-con); this increase is likely related to the fact that diet was not restricted during the study period, and the participants were going through a major developmental growth phase.
The positive results in the timing ability of children with DCD could be related to the content of the intervention program and the method of teaching. Children with DCD use their hands, feet, and body to improve their FMS, such as catching, hitting, throwing, and kicking, through trial and error of timing and spatial awareness. Such trial and error enable the successful planning and subsequent execution of movement-related timing abilities. This process is similar to the changes of timing ability within the internal models [
41]. The reasons behind the success of our intervention program can be found in the principles of the provision of education environments for children with DCD and the task-oriented class method [
42]. Specifically, our program included physical activities tailored for children with DCD that were integrated into their regular education environment, and our program limited the number of children in each session so that each child had sufficient interaction with the teacher. Furthermore, although the nature and difficulty of the tasks were decided beforehand, the supervising teacher could modify these parameters based on the individual response of each child. By observing their own success in various tasks, children with DCD gained confidence in their motor skills, and this confidence motivated them to continue training and effectively helped them improve their motor performances [
25,
31].
Scientific results from both our study and previous studies indicate that children with DCD can improve their motor abilities and health-related physical fitness with appropriate interventions. For young children who especially need to develop their FMS, participation in physical activities involving play and sports can promote motor coordination and health-related physical fitness. We utilized a 12-week intervention program with a focus on FMS in a school setting. However, whether the motor deficit noted in children with DCD is innate or represents a lack of appropriate educational activities is unclear. Further research is needed to investigate the mechanisms of change in both motor behavior and the physiological, neurological, and cognitive aspects of motor skill development.
This study had several limitations. First, we recruited children from only two schools in Incheon City; therefore, our findings should be interpreted with caution. Second, we excluded participants with medical diagnoses other than DCD, which could result in a potential bias since the DSM-5 considers that DCD co-occurs with other conditions. However, in our case, we only excluded one child with intellectual disabilities whose school performance was difficult to evaluate by teachers. Third, this study may not sufficiently reflect the characteristics of DCD because of the small sample size (27-28 children with DCD in each group) and use of a MABC-2 cut-off standard below 15% for DCD screening. Fourth, the low teacher-student ratio in the intervention group may have had a positive effect on the results. Hence, future studies should be conducted to examine these various limitations.