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Assessment of physical fitness and exercise tolerance in children with developmental coordination disorder
Research in Developmental Disabilities 45–46 (2015) 210–219
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Research in Developmental Disabilities
Assessment of physical fitness and exercise tolerance in children with developmental coordination disorder Faic¸al Farhat a,*, Ines Hsairi a, Hamza Baiti b, John Cairney c, Radhouane Mchirgui d, Kaouthar Masmoudi e, Johnny Padulo f, Chahinez Triki a, Wassim Moalla b a
Neuropediatry UR.0805, Hedi Chaker Hoˆpital, Faculty of Medicine, Sfax, Tunisia UR EM2S: Education, Motricite´, Sport et Sante´, ISSEP, Sfax, Tunisia Departments of Family Medicine and Kinesiology, The Infant Child Health (INCH) Research Lab, and The CanChild Centre for Studies in Childhood Disability, McMaster University, Hamilton, ON, Canada d Service de Pseudo Psychiatrie, Hoˆpital Hedi Chaker, Faculte´ de Me´dicine, Sfax, Tunisia e Service d’Explorations Fonctionnelles, Unite´ d’Effort Cardio-pulmonaire, Hoˆpital Habib Bourguiba, Sfax, Tunisia f Research Laboratory ‘‘Sports Performance Optimisation’’ National Center of Medicine and Science in Sports (CNMSS), Tunis, Tunisia b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 January 2015 Received in revised form 11 July 2015 Accepted 22 July 2015 Available online
Children with developmental coordination disorder (DCD) have been shown to be less physically fit when compared to their typically developing peers. The purpose of the present study was to examine the relationships among body composition, physical fitness and exercise tolerance in children with and without DCD. Thirty-seven children between the ages of 7 and 9 years participated in this study. Participants were classified according to results obtained on the Movement Assessment Battery for Children (MABC) and were divided in 2 groups: 19 children with DCD and 18 children without DCD. All children performed the following physical fitness tests: The five-jump test (5JT), the triple-hop distance (THD) and the modified agility test (MAT). Walking distance was assessed using the 6-min walking test (6MWT). Children with DCD showed higher scores than children without DCD in all MABC subscale scores, as well as in the total score (p < 0.001). Participants with DCD were found to perform significantly worse on the MAT (p < 0.001), the THD (p < 0.001) and 5JT (p < 0.05). Moreover, children with DCD had poorer performance on the 6MWT than children without DCD (p < 0.01). Our results found significant correlations among body mass index (BMI), THD (r = 0.553, p < 0.05), 5JT (r = 0.480, p < 0.05) and 6MWT (r = 0.544, p < 0.05) only in DCD group. A significant correlation between MAT and 5JT (r = 0.493, p < 0.05) was found. Similarly, THD and 5JT (r = 0.611, p < 0.01) was found to be correlated in children with DCD. We also found relationships among 6MWT and MAT (r = 0.522, p < 0.05) and the 6MWT and 5JT (r = 0.472, p < 0.05) in DCD group. In addition, we found gender specific patterns in the relationship between exercise tolerance, explosive strength, power, DCD, and BMI. In conclusion, the present study revealed that BMI was indicative of poorer explosive strength, power and exercise tolerance in children with DCD compared to children without DCD probably due to a limited coordination on motor control. ß 2015 Published by Elsevier Ltd.
Keywords: Children Developmental coordination disorder BMI Physical fitness Exercise tolerance
* Corresponding author at: Research Unit EM2S: Education, Motricite´, Sport et Sante´, ISSEP, Sfax, Tunisia. E-mail address: [email protected] (F. Farhat). http://dx.doi.org/10.1016/j.ridd.2015.07.023 0891-4222/ß 2015 Published by Elsevier Ltd.
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1. Introduction Children with developmental coordination disorder (DCD) are often described as having considerable difficulties coordinating and controlling their body movements, involving both fine and gross motor skills (Visser, 2003). Poor coordination and difficulty performing motor based activities leads to decreased motivation to participate in physical activity (Haga, 2009). Bouffard, Watkinson, Thompson, Dunn, and Romanow (1996) described the phenomenon of withdraw from physical activity as an ‘activity deficit’. The links between motor coordination deficits and physical activity have been well documented in the extant literature. Moreover, the physical fitness of children with and without DCD has been explored in several research studies (Rivilis et al., 2011). In the last decade, findings suggest that children with lower motor competence demonstrated significantly poorer performance on important components of physical fitness, such as aerobic and anaerobic endurance and muscular strength, when compared against developing typically peers (Ferguson, Aertssen, Rameckers, Jelsma, & Smits-Engelsman, 2014). Raynor (2001) found that children with DCD showed difficulties in tasks using explosive power due to poor motor coordination and ineffective motor patterns. Van der Hoek et al. (2012) identified several factors that may contribute to poorer fitness in children with DCD such as, muscular strength, inability to exert maximal force, and variability in rate of power and timing in performing work. As such, the difficulties children with DCD have performing fundamental motor skills (Hands & Larkin, 2006) may be associated with both strength and power deficits. Withdrawal from physical activity and poor physical fitness in these children is an important concern for later health outcomes (Hands & Larkin, 2006). Additional research is needed to identify how physical fitness in children with movement difficulties differs from other groups. Numerous standardized fitness tests, such as the EUROFIT (Adam, Klissouras, Ravazollo, Renson, & Tuxworth, 1998), the TPF (Fjørtoft, Pedersen, Sigmundsson, & Vereijken, 2003) and the functional strength measure (Smits-Engelsman & Verhoef-Aertssen, 2012), are available for assessment of pediatric physical fitness in both general and special populations. Most of these tests consist of activities that are part of children’s everyday activities such as jumping, throwing, running and climbing. Descriptive studies using such tests may provide a more thorough understanding of the physical fitness profiles of children with poor motor coordination. Moreover, sub-maximal exercise testing provides a safe, practical means of evaluating functional status, monitoring treatment effectiveness and establishing prognosis in children with DCD. Indeed, several studies have examined physical fitness (cardiorespiratory fitness) in children with DCD using field-based running tests such as the 20 m shuttle run test (Rivilis et al., 2011). Moreover, the development of field tests, such as the 6-min walking test (6MWT), can be used to measure the functional exercise capacities of healthy or unfit subjects. The 6MWT has emerged as a common sub-maximal test in clinical settings, and the provision of recent normative data for the test has extended its application in other settings (Li et al., 2005). The 6MWT has shown good validity and reliability in pediatric clinical populations, and is considered to be a clinically relevant test because it closely resembles common physical activities of daily living (walking), in healthy children and in children with various diseases (Solway, Brooks, Lacasse, & Thomas, 2001). The 6MWT may be a particularly useful sub-maximal test for children with DCD. For example, the 6MWT requires minimal coordination skills, especially when compared to submaximal tests such as the shuttle run, where aspects of the test such as line contact pivots, may prove very difficult for children with DCD. Compared to these other tasks, walking may be easier for children with motor coordination difficulties. Likewise, because children with DCD have been found to be less likely to participate in physical activities, it has been hypothesized that this condition may be a risk factor for obesity and overweight (Cairney et al., 2010). Only a few studies have examined the associations among motor coordination problems, physical fitness and overweight or obesity in children. Several studies however have explored the relationship between weight status and gross motor skills, with some studies indicating that overweight and obese children showed poorer locomotor skills such as jumping and poor performance on the shuttle run and 30-m sprint when compared to their normal-weight peers (Graf et al., 2004; Okely, Booth, & Chey, 2004). According to the results of field tests, such as 6MWT, researchers have found that children with DCD were poor in exercise tolerance (Farhat et al., 2014). However, no empirical study has investigated the relationships among body composition, exercise tolerance and physical ability such as anaerobic power, explosive strength and agility. Therefore, the purpose of the present study was to examine, through a cross-sectional study, body composition, exercise tolerance and physical fitness in children with and without DCD (DCD). 2. Methods 2.1. Participants The study has been approved by the Ethical local Committee of the University Hospital of Sfax. Prior to testing, the protocol was explained in detail to the participants and their parents. After this, all participants signed a written informed consent in accordance with the principals outlined in the Declaration of Helsinki in 1975. A total of fifty-one children were recruited from three primary schools from a middle-class region in Tunisia; all children were administered the movement assessment battery for children (MABC) to assess motor coordination. Five children (three boys and two girls) were excluded because they had intellectual impairment. In addition, nine children (six boys and three girls) did not attend the assessment session. In total, nineteen children with DCD and eighteen children without DCD aged
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between seven and ten years who completed all tests were included. The participants were examined by a physician to ensure their health was sufficient to participate in testing and to rule out the presence of chronic diseases. Children were assigned to the DCD group if they had difficulties with daily living skills as assessed using parent interviews. Inclusion criteria included no intellectual impairment; no diagnosed emotional, neurological, or motor disorder (cerebral palsy and muscular dystrophy), and no intervention during the past 3 months that would affect leisure participation patterns. Children with a score above the 15th percentile on the MABC were identified as children with typical development. They were recruited from the same three primary schools. They were subject to the same inclusion and exclusion criteria set for the DCD group, except that they did not have any history of DCD. Excluded from control group were children with a medical, neurological and mental disorder or IQ < 70. Children were also excluded if a history of learning difficulties or any behavioral or orthopedics problems were reported by parents. 2.2. Procedure Participants and parents were given written information about the nature of the study. Written informed consent was obtained from the parents of all children. Demographic and anthropometric data were collected on all participants prior to testing. Children were assigned a specific number in order to maintain confidentiality. Children were first assessed for DCD, and to rule out other neurological conditions, by a pediatric neurologist. Participants were then tested by an occupational therapist and a physical education teacher on the MABC (Henderson & Sugden, 1992), a standardized test for children aged between 4 and 12 years that has been validated in typically developing children and in children with DCD (Wright & Sugden, 1996). Children with a score at or below the 15th percentile on the MABC were identified as having DCD (Poulsen, Ziviani, Cuskelly, & Smith, 2007). A psychologist administered the differential scales of intellectual efficiency test–revised (EDEI-A; Ben Rejeb, 2001) to each child, to assess general intelligence level. Physical fitness tests took place during regular physical education instruction at each school in the school sports hall. The participants wore suitable shoes and light clothing (t-shirts and shorts). Children were tested individually by the same research assistants (five physical education teachers) each of whom had been trained in administration of all the test protocols. Each test item was explained and demonstrated before the test was scored. Each test item was performed twice. We always report the best performance score obtained on both of the two tests. If the results of the second test were significantly different from the first, we completed a third administration assuming the outlier score to be due to measurement error. Participants were given standard verbal encouragement and support throughout the testing procedure. When a child made a procedural error, instructions and demonstrations were repeated, and the child was allowed to make another attempt. All children completed the measurements adequately. Finally, all subjects completed the 6MWT test. 2.3. Demographic questionnaire This questionnaire was designed by the authors and included data on family socio-demographic status, child’s health status, medications, treatments and para-medical therapies received. 2.4. Anthropometry Height and weight were measured in the laboratory with the child dressed in light clothing and without shoes. Height was measured to the nearest 0.5 cm using a fixed stadiometer (Seca, Hultafors, Sweden) and body mass (weight) was measured to the nearest 0.5 kg with an electronic device (Avery Berkel model HL 120; Avery Weigh-Tronix Inc., Fairmont, MN, USA). BMI was calculated as body mass in kilograms divided by height in meters squared (kg m 2). 2.5. The movement assessment battery for children In this study, the MABC test was used to identify children with motor coordination problems. Compared to the MABC-2, the original MABC has been translated into several major European languages, such as French (Missiuna, Rivard, & Bartlett, 2006). As such, we felt this version to be more appropriate for use in this study than the second edition, as this would allow us to make comparisons of our data to other studies conducted both in our country and in other French-speaking nations. The MABC is the most commonly used tool to identify DCD in school aged children from 4 to 12 years (Geuze, Jongmans, Schoemaker, & Smits-Engelsman, 2001), and the first edition of the MABC has excellent reliability and concurrent validity (Henderson & Sugden, 2007). In the absence of Tunisian norms for the MABC test used in this study, French norms were used. While it is acknowledged that French norms may not be valid for this population, the intention was to compare groups and not to compare performance of children to population norms. The MABC is an extended version of the test of motor impairment (Stott, Moyes, & Henderson 1985), designed to identify children with movement difficulties. We used the MABC (Henderson & Sugden, 1992) as the criterion test of motor competence, assessing both gross and fine motor coordination in children aged between 4 and 12 years. It is a formal standardized test that provides both a quantitative and a qualitative evaluation of the child’s motor competence in daily life. The psychometric research performed on the MABC reported that is a reliable and useful assessment to use with young children (Crawford, Wilson, & Dewey, 2001).
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Furthermore, it has been found to more accurately identify children with motor difficulties when compared to other motor tests and appears to identify more readily those children who have additional learning or attention problems (Crawford et al., 2001). The MABC gives an estimate of motor ability in terms of speed and/or accuracy (outcome of movement). The eight items used to assess children ages 7–8 years include placing pegs in a peg board, threading a lace and drawing a line following a trail (manual dexterity (MD)); bouncing and catching a ball with one hand and throwing a bean bag into a box (ball skills); standing on one leg (static balance), jumping in squares, and heel-to-toe walking on a line (dynamic balance). The total impairment score (TIS), ranging from 0 to 40, is the sum of converted raw scores on the eight items that each child attempts during a formal assessment. Total impairment score can be converted into a percentile ranks: scores at or below the 5th percentile indicate a definite motor problem while a score at or below the 15th percentile indicates a clinical risk range that should be monitored (Henderson & Sugden, 1992). Test–retest (r = 0.75) and inter-rater reliability (0.70) have been shown to be good in this age range (Henderson & Sugden, 1992). Studies of criterion validity have shown 80% agreement between the MABC and the Bruininks-Oseresky test of motor performance (Crawford et al., 2001). 2.6. The differential scales of intellectual efficiency (EDEI-A; Ben Rejeb, 2001) These scales were used in order to exclude participants which IQ < 70. They made it possible to distinguish between the verbal developmental age (VDA) and the non-verbal developmental age (NVDA). The VDA was calculated by means of scores on five scales: picture identification vocabulary, word definition vocabulary, knowledge, social understanding and conceptualization. The NVDA was calculated by means of scores on four scales: classification of pairs of pictures, classification of three pictures, categorical analysis and practical adaptation. These scales’ applicability to participants with intellectual disabilities has previously been demonstrated (Tourrette, 2006). 2.7. Physical fitness test Several tests of physical fitness were included in the protocol and described below. 2.7.1. The modified agility test (MAT) The MAT was developed from the standard t-test to evaluate lower extremity. The agility test, pro shuttle, and long shuttle activities are used in field settings to determine timed performance on tasks related to activities and tasks that require quick starts, dynamic changes in direction, and efficient movement (Haj-Sassi et al., 2011). The MAT described by Haj-Sassi et al. (2011) consisted of sprints involving four changes of direction with three displacement modes: forward, lateral (left/right in randomized order), and backward. The participant began with both feet behind a starting line (position A). At his own discretion, for the first sprint, subject sprinted forward to a cone (B) and touched the base of it with the right hand. Facing forward and without crossing feet, they shuffled to the left to another cone (C) and touched its’ base with the left hand. Subjects then repeated this task with a different cone (D), before shuffling back to the left to cone B once again where again the base of the cone was touched. Finally, children ran backward as quickly as possible and returned to line A. Participants who crossed one foot in front of the other, failed to touch the base of the cone or failed to face forward throughout the task were required to repeat the test. The MAT performances were recorded using an electronic timing system (photo cells Globus, MicrogateTM), with accuracy recorded to 0.01 s. One pair of the electronic timing system sensors mounted on tripods were set approximately 0.75 m above the floor and positioned 3 meters apart facing each other on either side of the starting line. 2.7.2. The triple-hop distance (THD) The THD is a useful clinical test to predict an athlete’s lower extremity strength and power. A standard tape measure was fixed to the ground, perpendicular to a starting line to measure the THD. Participants stood on the designated testing leg, with the big toe on the starting line. They performed three consecutive maximal hops forward on the same (dominant) limb. Arm swing was allowed. The investigator measured the distance hopped from the starting line to the point where the heel struck the ground upon completing the third hop (Bolgla & Keskula, 1997). All participants were allowed one to three practice trials (self-selected) on each leg and then completed three test trials. The practice trials were provided to allow athletes to familiarize themselves with the test protocol. Practice trials were limited to 3 on each leg to avoid fatigue. 2.7.3. The 5 jump-test (5JT) The 5JT is currently used in field conditions to assess lower limb explosive power (Chamari et al., 2008) and to measure horizontal stretch shortening cycle capabilities in the distance traveled using lower limb actions. The 5JT is very easy to perform and does not require any sophisticated equipment. The 5JT, as described by Chamari et al. (2008), consist of 5 consecutive strides with joined feet position at the start and end of the jumps. From the starting position, the participant had to directly jump to the front with one leg and after the first 4 strides, i.e. alternating left and right feet for 2 times each, perform the last stride and end the test with both feet together. The best performance (as indicated by the distance) was recorded. All tests were separated by 2 min of recovery.
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2.8. 6-Min walking test (6MWT) The 6MWT was conducted at the school on a flat surface in a 30-m-long covered corridor marked every 2 m. The test was conducted according to the recommendations of the American Thoracic Society (American Thoracic Society, 2002). To allow for acclimatization to the task, each participant completed the 6MWT test twice (with an hour of test allowed between tests). We recorded the longer distance of the two tests. Participants were instructed to walk the longest distance possible at their own pace during the allotted time. Children were allowed to stop and rest during the test, but were instructed to resume walking as soon as they felt capable of doing so. Standardized encouragements (for example, ‘keep going’, ‘you are doing well’) and announcement of time remaining were given to all children. Before beginning the test, the participants sat on a chair located near the starting position for at least 10 min to determine the rest heart rate (HR) values and oxy-hemoglobin saturation (finger pulse oxymeter; Nonin Medical, Inc., Minneapolis, MN, USA). These parameters were also recorded every minute during and 5 min after the test. Dyspnea scores were measured on a Borg scale at the end of the test (Borg, 1982). The participant indicated the number corresponding to the perception of his effort and his feeling of breathlessness. 2.9. Statistical procedure All statistical analyses were conducted using the statistical package for the social sciences software (SPSS, version 17.0, SPSS Inc., Chicago, IL, USA). All variables were examined to determine whether distributions were normal or skewed. For categorical measures, 2 2 tables were created and used to estimate Odds Ratios to demonstrate the strength of the association, and the 95% confidence interval (CI) to measure precision. Data are presented as means (M) standard deviations (SD). Independent t-test was utilized to assess differences between the DCD and the control groups. Pearson’s correlations were conducted to assess the relationships among, body composition, motor competences, sub-maximal and physical capacity. Multinomial logistic regression analyses were used to investigate the relationship between 6MWT, BMI and physical ability. Four models were estimated: (1) Model 1 included the main effects for 6MWT and THD; (2) Model 2 consisted of the same variables as Model 1, with the addition of BMI; (3) Model 3 included an all variables in Model 1, with the addition of 5JT. Finally, in Model 4, 6MWT, BMI and 5JT were included. The significance level was set at (p < 0.05), and corrected using an appropriate Bonferroni adjustment to maintain an overall type one error at 5% (i.e., alpha = 0.01 for comparisons of the three outcomes among groups).
3. Results 3.1. Participants Anthropometric data and intellectual characteristics of DCD and control groups are shown in Table 1. In total, there were 19 children with DCD, and 18 typically developing peers (n = 37). Significant differences between groups were found for body mass index (p < 0.05). There were no significant group differences for age, weight, height, and IQ (p > 0.05). Differences in sub-scales on the MABC between groups are shown in Table 2. 3.2. Motor ability The results revealed significant group differences in motor abilities (Table 2.). Total score and subscales scores were significantly lower in children with DCD than in children without DCD. 3.3. Physical ability A significant difference in muscle power was found between children with DCD and the control group (Table 2). On the 5TJ test, the DCD group showed a reduction of 12% (p < 0.05) on final distance compared to controls. DCD children also showed a decreased performance during the MAT when compared to controls (9.09 0.51 vs. 10.62 0.94 sec with p < 0.001; Table 2). Children with DCD showed a significantly lower performance on the THD (2.96 0.23 vs. 3.75 0.4 m with p < 0.001; Table 2).
Table 1 Comparison of demographic data between children with and without DCD.
Age (years) Height (cm) Weight (kg) Body mass index (kg m IQ
2
)
DCD children (n = 19)
Typical children (n = 18)
8.60 1.00 137.20 7.50 32.40 6.40 17.10 1.20 101.6 12.60
8.50 0.96 134.20 4.80 28.90 3.40 16 1.20 106.30 12.40
Values are means SD; IQ, intellectual quotient; NS, no significant.
t
p 0.330 1.44 2.093 2.81 1.13
0.730NS 0.159NS <0.05 <0.01 0.26NS
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Table 2 Comparison of MABC test, physical ability and 6MWD between children with and without DCD.
Manual Dexterity Ball Skills Balance MABC score Modified agility test (s) Triple hop distance (M) 5 jump-test (m) 6MWD (m) Dyspnea Heart rate before Heart rate after Oxygen saturation (%) before Oxygen saturation (%) after
DCD children (n = 19)
Typical children (n = 18)
t
p
8.10 3.30 2.90 2.90 4.50 1.80 15.50 3.04 10.80 1.10 3.05 0.30 5.80 0.40 556.30 71.90 5.50 1.30 83.90 9.20 123.60 17.30 99.40 0.70 96.90 0.80
2.87 2.05 0.30 0.80 0.30 0.40 3.50 1.20 9.10 0.50 3.60 0.40 6.40 0.90 652.60 48.20 4.20 0.90 86.80 16.80 139.80 14.20 99.20 0.70 97.70 1.20
5.83 3.72 8.63 14.37 6.10 4.80 3.10 4.80 3.51 0.64 3.11 0.88 2.47
<0.001 <0.01 <0.001 <0.001 <0.001 <0.001 <0.01 <0.001 <0.01 0.52NS <0.01 0.38NS <0.05
6MWD, 6-min walking distance; MABC, Movement Assessment Battery for Children; NS, no significant.
3.4. 6MWT The 6MWT was completed by all participants without premature end or breaks; no symptoms or clinical complications occurred (arrhythmia, cyanosis, etc.) during testing. The mean distance walked during 6MWT was significantly longer in typically developing children when compared to children in the DCD group (663.43 m 43.50 vs. 564.85 m 73.7 m; see Table 2). The distance walked increased from a baseline of 105.30 m (10.12 m) reaching a plateau of 111 m (7.45 m) after 1–3 min, for children without DCD. Children with DCD started out fast and then slowed reaching total distances of between 93.14 m (12.13 m) and 98.13 m (14.45 m) over the duration of the 6MWT (Fig. 1). The dyspnea at the peak of 6MWT was significantly higher in children with DCD than children without DCD. No significant differences between groups were found in heart rate at baseline, maximum heart rate, the oxygen saturation at baseline or minimum oxygen saturation. 3.5. Correlation between body composition, motor competences, sub-maximal and physical capacity A significant correlation between BMI and balance (r = 0.512, p < 0.05) was found for DCD children. BMI and physical ability such as THD (r = 0.553, p < 0.05) and 5JT (r = 0.508, p < 0.05) was also observed. A significant positive correlation among 6MWT and BMI (r = 0.544, p < 0.05) was found for children with DCD (Table 3). No significant correlations was found among body composition, motor competences, sub-maximal and physical capacity for children without DCD. In the next part of the analysis, the relationships between MAT, THD and 5JT were analyzed. A negative correlation between MAT and 5JT (r = 0.493, p < 0.05) was observed. THD and 5JT (r = 0.611, p < 0.01) was found to be correlated in DCD children. A significant correlation among 6MWT, MAT (r = 0.522, p < 0.05) and THD (r = 0.472, p < 0.05) was also found in children with DCD (Table 3). In children without DCD, the only significant correlation observed was between MAT and THD (r = 0.545, p < 0.05; Table 3).
[(Fig._1)TD$IG] 120
Distance (m)
110 100 90 80 70 60
1
2
3
4
5
Minute Fig. 1. 6MWD in children with and without DCD. –~–, children with DCD; –&–, children without DCD.
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Table 3 Correlation between Body Composition, motor competences, exercise tolerance and physical capacity between children with and without DCD. BMI (kg m
2
)
MABC
MAT (s)
THD (m)
5JT (m)
Children with DCD MAT (s) THD (m) 5JT (m) 6MWD (m)
0.356NS 0.553* 0.480* 0.544*
0.449NS 0.076NS 0.075NS 0.232NS
0.384NS 0.493* 0.522*
0.611** 0.375NS
0.472*
Children without DCD MAT (s) THD (m) 5JT (m) 6MWD (m)
0.069NS 0.165NS 0.086NS 0.353NS
0.043NS 0.006NS 0.212NS 0.310NS
0.545* 0.048NS 0.424NS
0.145NS 0.420NS
0.170NS
BMI, body mass index; 6MWD, 6-min walking distance; MAT, modified agility test; THD, triple hop distance; 5JT,five-jump test; MABC, Movement Assessment Battery for Children; NS, no significant. * Significant difference between groups (p < 0.05). ** Significant difference between groups (p < 0.01).
3.6. Multinomial logistic regression analysis of coordination (dependent variable) and relationships between 6MWT, BMI and physical ability in children with and without DCD Table 4 shows the results of the regression analysis where MABC scores were regressed onto 6MWT, THD, 5JT, and BMI in children with and without DCD. Four models were tested. In Model 1, both 6MWT and THD were significant. Model 2 consisted of the same variables as Model 1, with the addition of BMI. After entering BMI into the Model, the main effect for 6MWT and THD remained significant with a parameter estimate of 0.05 (p < 0.05) and 8.95 (p < 0.05) respectively. This indicates that BMI is both a significant independent predictor of motor coordination, but that also some of the effect of 6MWT on MABC scores can be explained by the effect of relative body weight. Model 3 shows the results of the regression analysis of MABC scores onto 6MWT and explosive strength (5JT) in children. After adjustment both 6MWT, there is a significant negative effect of explosive strength on motor coordination with a parameter estimate of 0.044 (p < 0.05) and 1.61 (p < 0.05) respectively. In Model 4, the main effect for 6MWD and 5JT remained significant with a parameter estimate of 0.045 (p < 0.05) and 1.86 (p < 0.05) respectively, after adjustment for BMI. 4. Discussion The purpose of the present study was to determine whether differences exist in various measures of body composition, muscle fitness and exercise tolerance parameters in children with and without DCD. A secondary objective was to analyze correlations among these measures, between children with and without DCD aged 7–10 years. Children with DCD demonstrated significantly lower performance in health-related fitness measures such as strength and power. Children with DCD also showed significantly impaired performance on anaerobic power than children without DCD. Compared to the healthy controls, DCD children had significantly less walking distance during 6MWT. Our results found significant correlations among BMI, MD and balance for DCD children. These outcomes were in accordance with one of the recent studies by Zhu et al. (2014) in which they found that correlations between anthropometric characteristics (weight, BMI and waist circumference) and MABC scores were higher in the DCD with balance problems group compared with typically developing children and DCD children without balance problems groups. Our results were also in accord with other studies that focused on physical fitness in children with motor difficulties (Hands & Larkin, 2002). Schott, Alof, Hultsch, and Meermann (2007) found that children with DCD had significantly lower performance on different fitness components compared with control group. However, reduced physical fitness was found in
Table 4 Regression analysis of coordination (dependent variable) between 6MWD, BMI and physical ability in children with and without DCD. Model 1
Intercept 6MWD (m) THD (m) 5JT (m) BMI (kg m 2)
Model 2
Model 3
Model 4
Estimate
p
Estimate
p
Estimate
p
Estimate
p
35.66 (14.14) 0.34 (0.016) 4.57 (2.30) – –
<0.05 <0.05 <0.05 – –
31.79 (20.51) 0.049 (0.024) 8.95 (4.25) – 1.59 (0.70)
0.113 <0.05 < 0.05 – <0.05
37.17 (13.96) 0.044 (0.018) – 1.61 (0.75) –
<0.01 <0.05 – < 0.05 –
23.18 (17.15) 0.045 (0.020) – 1.86 (0.90) 0.94 (0.45)
0.177 <0.05 – <0.05 <0.05
Values are parameter estimates with standard error in parentheses. BMI, body mass index; 6MWD, 6-min walking distance; THD, triple hop distance; 5JT, five-jump test.
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terms of reduced muscular strength, endurance and speed or agility (Haga, 2008) in children with DCD compared with their peers. In our study, performance on the THD and 5JT was considerably lower for DCD group. It is well established in the literature that the horizontal jump test, THD and 5JT are a strong predictors of lower limb muscular strength and power (Barber, Noyes, Mangine, McCloskey, & Hartman, 1990; Chamari et al., 2008). This result is in line with previous research studies that indicate a significantly lower performance in the explosive power tasks (standing-long-jump) on the functional strength measure (Ferguson et al., 2014) in children with DCD. On the other hand, our results showed a significantly lower performance in the MAT in DCD group, compared with the typically developing group. Studies suggest that children with DCD perform poorly in muscle power sprint test (Ferguson et al., 2014; Cantell, Crawford, & Tish Doyle-Baker, 2008). Hands and Larkin (2006) found that children with motor learning difficulties were significantly slower, and demonstrated less speed as measured by the 50-m run and the shuttle run, than the control group. Furthermore, the exercise intolerance was also reported by Wu, Lin, and Li (2010) who reported that DCD children perform worse on 800 m run test compared to the typical group. Our findings support conclusions from other studies reporting weak correlations among BMI, fine and gross motor skill performance (Zhu, Wu, & Cairney, 2011). Interestingly, the present study demonstrated a significant relationship among BMI, physical ability (THD and 5JT) and 6MWD only in DCD group. Higher BMI has been shown to be associated with poorer performance on physical fitness tasks such as in standing-long jump (D’Hondt et al., 2013) and runs for distance (Schott et al., 2007). The results of the present study revealed that BMI was associated with poorer explosive strength, power and exercise tolerance in children with DCD, but not in children without DCD. Motor coordination was the measure that proved to be an independent predictor of deficits in health-related fitness such as submaximal and anaerobic performance between the DCD and comparison groups (Ferguson et al., 2014). Exercise tolerance, explosive strength, power and BMI were all found to be significant predictors of motor coordination. The results clearly show how body composition (BMI) is related to impaired performance in tests requiring exercise tolerance (6MWT), explosive strength of lower extremities (5JT) and power (THD). This is an important finding given that children with DCD tend to show elevated body mass and BMI relative to typically developing children (Chirico et al., 2011; Cairney, Hay, Veldhuizen, & Faught, 2011; Cantell et al., 2008). Nevertheless, the present study, using comparative analysis with correction of BMI levels, still revealed disparities in the execution of tests in which moving the whole body was required. Overall, these findings reinforce the importance of motor skill level in fitness testing. Our finding showed significant correlations between MAT and 5JT as well as a significant correlation between THD and 5JT in DCD children. The decreased muscular strength and power of children with DCD found in this study may be at least partially attributable to the muscular organization. Previous research has shown that, children with DCD have been found to have planning, programming and muscle activation problems (Raynor, 1989). In the absence of muscle hypertrophy, improved motor coordination has been one of the neural factors associated with increased muscle strength in children (Ramsay et al., 1990). The typical child’s performance in the agility test, could be, in part, explained by either better motor recruitment or neural adaptations. Neural adaptations usually occur when athletes respond or react as a result of improved coordination between the central nervous system signal and proprioceptive feedback (Craig, 2004). Decreased power in children with DCD may also be attributed to age-related increases in anaerobic substrates such as creatine phosphate and glycogen (Coyle, Costill, & Lesmes, 1979), and to reduce of motor unit recruitment and muscle activities of agonists and antagonists (Raynor, 1989). The largest difference in 6MWT between children with and without DCD could be explained, in part, by differences in muscle strength and exercise tolerance (Frontera, Meredith, O’Reilly, Knuttgen, & Evans, 1988). DCD children walk with an irregular pace (see Figure 1), which highlights the sensation of dyspnea due to a diminished ventilator reserve and, probably, lack of motivation to sustain a moderately heavy load for a prolonged time (Bogaard et al., 1993). Moreover, poor performance in submaximal tasks could be attributed to the relative increase in co-contraction or less well-predicted movement outcomes. From this perspective, future research should examine the fatigue profile and the ability to tolerate high-intensity exercise. The determination of neuromuscular fatigue manifestations in muscle strength and electromyography (EMG) signals following a high-intensity exercise may be important for clinical purposes. 4.1. Limitations A number of limitations should be noted in relation to this study. For example, we did not measure habitual physical activity. It is possible that relationships between motor skills, physical activity, physical ability and submaximal exercise might have been stronger if these subcategories of movement skills were assessed. The relationships among motor competence, physical fitness and self perception were also not assessed in this study. 5. Conclusion Overall, the present study showed consistent deficits across a range of health-related fitness tests between children with and without DCD. Our results also revealed that BMI was associated with poorer explosive strength, power and exercise tolerance in children with DCD compared to children without DCD. From this perspective, interventions in children with DCD should target training on motor proficiency and weight control. Moreover, longitudinal studies are strongly
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recommended in order to explore whether children with DCD possess physiological markers that differ from their peers without disabilities. Conflict of interest We have no conflict of interest to disclose[1_TD$IF]. Acknowledgements We thank Mr Haithem Rbai, the Department of Child Neurology, He´di Chaker Hospital (Sfax, Tunisia), Service d’Explorations Fonctionnelles, Unite´ d’Effort Cardio-pulmonaire, Hoˆpital Habib Bourguiba (Sfax, Tunisia), Service de pseudo psychiatry, Hoˆpital Habib Bourguiba (Sfax, Tunisia) El Rahma school (Sfax, Tunisia), El Kamel school (Sfax, Tunisia) and the participating children and their parents, for their contributions. References Adam, C., Klissouras, V., Ravazollo, M., Renson, R., & Tuxworth, W. (1998). EUROFIT: European test of physical fitness. In Handbook. Rome: Council of Europe, Committee for the Development of Sport. American Thoracic Society (ATS) (2002). ATS statement: Guidelines for the six-minute walk test. 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Contents lists available at ScienceDirect
Research in Developmental Disabilities
Assessment of physical fitness and exercise tolerance in children with developmental coordination disorder Faic¸al Farhat a,*, Ines Hsairi a, Hamza Baiti b, John Cairney c, Radhouane Mchirgui d, Kaouthar Masmoudi e, Johnny Padulo f, Chahinez Triki a, Wassim Moalla b a
Neuropediatry UR.0805, Hedi Chaker Hoˆpital, Faculty of Medicine, Sfax, Tunisia UR EM2S: Education, Motricite´, Sport et Sante´, ISSEP, Sfax, Tunisia Departments of Family Medicine and Kinesiology, The Infant Child Health (INCH) Research Lab, and The CanChild Centre for Studies in Childhood Disability, McMaster University, Hamilton, ON, Canada d Service de Pseudo Psychiatrie, Hoˆpital Hedi Chaker, Faculte´ de Me´dicine, Sfax, Tunisia e Service d’Explorations Fonctionnelles, Unite´ d’Effort Cardio-pulmonaire, Hoˆpital Habib Bourguiba, Sfax, Tunisia f Research Laboratory ‘‘Sports Performance Optimisation’’ National Center of Medicine and Science in Sports (CNMSS), Tunis, Tunisia b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 January 2015 Received in revised form 11 July 2015 Accepted 22 July 2015 Available online
Children with developmental coordination disorder (DCD) have been shown to be less physically fit when compared to their typically developing peers. The purpose of the present study was to examine the relationships among body composition, physical fitness and exercise tolerance in children with and without DCD. Thirty-seven children between the ages of 7 and 9 years participated in this study. Participants were classified according to results obtained on the Movement Assessment Battery for Children (MABC) and were divided in 2 groups: 19 children with DCD and 18 children without DCD. All children performed the following physical fitness tests: The five-jump test (5JT), the triple-hop distance (THD) and the modified agility test (MAT). Walking distance was assessed using the 6-min walking test (6MWT). Children with DCD showed higher scores than children without DCD in all MABC subscale scores, as well as in the total score (p < 0.001). Participants with DCD were found to perform significantly worse on the MAT (p < 0.001), the THD (p < 0.001) and 5JT (p < 0.05). Moreover, children with DCD had poorer performance on the 6MWT than children without DCD (p < 0.01). Our results found significant correlations among body mass index (BMI), THD (r = 0.553, p < 0.05), 5JT (r = 0.480, p < 0.05) and 6MWT (r = 0.544, p < 0.05) only in DCD group. A significant correlation between MAT and 5JT (r = 0.493, p < 0.05) was found. Similarly, THD and 5JT (r = 0.611, p < 0.01) was found to be correlated in children with DCD. We also found relationships among 6MWT and MAT (r = 0.522, p < 0.05) and the 6MWT and 5JT (r = 0.472, p < 0.05) in DCD group. In addition, we found gender specific patterns in the relationship between exercise tolerance, explosive strength, power, DCD, and BMI. In conclusion, the present study revealed that BMI was indicative of poorer explosive strength, power and exercise tolerance in children with DCD compared to children without DCD probably due to a limited coordination on motor control. ß 2015 Published by Elsevier Ltd.
Keywords: Children Developmental coordination disorder BMI Physical fitness Exercise tolerance
* Corresponding author at: Research Unit EM2S: Education, Motricite´, Sport et Sante´, ISSEP, Sfax, Tunisia. E-mail address: [email protected] (F. Farhat). http://dx.doi.org/10.1016/j.ridd.2015.07.023 0891-4222/ß 2015 Published by Elsevier Ltd.
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1. Introduction Children with developmental coordination disorder (DCD) are often described as having considerable difficulties coordinating and controlling their body movements, involving both fine and gross motor skills (Visser, 2003). Poor coordination and difficulty performing motor based activities leads to decreased motivation to participate in physical activity (Haga, 2009). Bouffard, Watkinson, Thompson, Dunn, and Romanow (1996) described the phenomenon of withdraw from physical activity as an ‘activity deficit’. The links between motor coordination deficits and physical activity have been well documented in the extant literature. Moreover, the physical fitness of children with and without DCD has been explored in several research studies (Rivilis et al., 2011). In the last decade, findings suggest that children with lower motor competence demonstrated significantly poorer performance on important components of physical fitness, such as aerobic and anaerobic endurance and muscular strength, when compared against developing typically peers (Ferguson, Aertssen, Rameckers, Jelsma, & Smits-Engelsman, 2014). Raynor (2001) found that children with DCD showed difficulties in tasks using explosive power due to poor motor coordination and ineffective motor patterns. Van der Hoek et al. (2012) identified several factors that may contribute to poorer fitness in children with DCD such as, muscular strength, inability to exert maximal force, and variability in rate of power and timing in performing work. As such, the difficulties children with DCD have performing fundamental motor skills (Hands & Larkin, 2006) may be associated with both strength and power deficits. Withdrawal from physical activity and poor physical fitness in these children is an important concern for later health outcomes (Hands & Larkin, 2006). Additional research is needed to identify how physical fitness in children with movement difficulties differs from other groups. Numerous standardized fitness tests, such as the EUROFIT (Adam, Klissouras, Ravazollo, Renson, & Tuxworth, 1998), the TPF (Fjørtoft, Pedersen, Sigmundsson, & Vereijken, 2003) and the functional strength measure (Smits-Engelsman & Verhoef-Aertssen, 2012), are available for assessment of pediatric physical fitness in both general and special populations. Most of these tests consist of activities that are part of children’s everyday activities such as jumping, throwing, running and climbing. Descriptive studies using such tests may provide a more thorough understanding of the physical fitness profiles of children with poor motor coordination. Moreover, sub-maximal exercise testing provides a safe, practical means of evaluating functional status, monitoring treatment effectiveness and establishing prognosis in children with DCD. Indeed, several studies have examined physical fitness (cardiorespiratory fitness) in children with DCD using field-based running tests such as the 20 m shuttle run test (Rivilis et al., 2011). Moreover, the development of field tests, such as the 6-min walking test (6MWT), can be used to measure the functional exercise capacities of healthy or unfit subjects. The 6MWT has emerged as a common sub-maximal test in clinical settings, and the provision of recent normative data for the test has extended its application in other settings (Li et al., 2005). The 6MWT has shown good validity and reliability in pediatric clinical populations, and is considered to be a clinically relevant test because it closely resembles common physical activities of daily living (walking), in healthy children and in children with various diseases (Solway, Brooks, Lacasse, & Thomas, 2001). The 6MWT may be a particularly useful sub-maximal test for children with DCD. For example, the 6MWT requires minimal coordination skills, especially when compared to submaximal tests such as the shuttle run, where aspects of the test such as line contact pivots, may prove very difficult for children with DCD. Compared to these other tasks, walking may be easier for children with motor coordination difficulties. Likewise, because children with DCD have been found to be less likely to participate in physical activities, it has been hypothesized that this condition may be a risk factor for obesity and overweight (Cairney et al., 2010). Only a few studies have examined the associations among motor coordination problems, physical fitness and overweight or obesity in children. Several studies however have explored the relationship between weight status and gross motor skills, with some studies indicating that overweight and obese children showed poorer locomotor skills such as jumping and poor performance on the shuttle run and 30-m sprint when compared to their normal-weight peers (Graf et al., 2004; Okely, Booth, & Chey, 2004). According to the results of field tests, such as 6MWT, researchers have found that children with DCD were poor in exercise tolerance (Farhat et al., 2014). However, no empirical study has investigated the relationships among body composition, exercise tolerance and physical ability such as anaerobic power, explosive strength and agility. Therefore, the purpose of the present study was to examine, through a cross-sectional study, body composition, exercise tolerance and physical fitness in children with and without DCD (DCD). 2. Methods 2.1. Participants The study has been approved by the Ethical local Committee of the University Hospital of Sfax. Prior to testing, the protocol was explained in detail to the participants and their parents. After this, all participants signed a written informed consent in accordance with the principals outlined in the Declaration of Helsinki in 1975. A total of fifty-one children were recruited from three primary schools from a middle-class region in Tunisia; all children were administered the movement assessment battery for children (MABC) to assess motor coordination. Five children (three boys and two girls) were excluded because they had intellectual impairment. In addition, nine children (six boys and three girls) did not attend the assessment session. In total, nineteen children with DCD and eighteen children without DCD aged
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between seven and ten years who completed all tests were included. The participants were examined by a physician to ensure their health was sufficient to participate in testing and to rule out the presence of chronic diseases. Children were assigned to the DCD group if they had difficulties with daily living skills as assessed using parent interviews. Inclusion criteria included no intellectual impairment; no diagnosed emotional, neurological, or motor disorder (cerebral palsy and muscular dystrophy), and no intervention during the past 3 months that would affect leisure participation patterns. Children with a score above the 15th percentile on the MABC were identified as children with typical development. They were recruited from the same three primary schools. They were subject to the same inclusion and exclusion criteria set for the DCD group, except that they did not have any history of DCD. Excluded from control group were children with a medical, neurological and mental disorder or IQ < 70. Children were also excluded if a history of learning difficulties or any behavioral or orthopedics problems were reported by parents. 2.2. Procedure Participants and parents were given written information about the nature of the study. Written informed consent was obtained from the parents of all children. Demographic and anthropometric data were collected on all participants prior to testing. Children were assigned a specific number in order to maintain confidentiality. Children were first assessed for DCD, and to rule out other neurological conditions, by a pediatric neurologist. Participants were then tested by an occupational therapist and a physical education teacher on the MABC (Henderson & Sugden, 1992), a standardized test for children aged between 4 and 12 years that has been validated in typically developing children and in children with DCD (Wright & Sugden, 1996). Children with a score at or below the 15th percentile on the MABC were identified as having DCD (Poulsen, Ziviani, Cuskelly, & Smith, 2007). A psychologist administered the differential scales of intellectual efficiency test–revised (EDEI-A; Ben Rejeb, 2001) to each child, to assess general intelligence level. Physical fitness tests took place during regular physical education instruction at each school in the school sports hall. The participants wore suitable shoes and light clothing (t-shirts and shorts). Children were tested individually by the same research assistants (five physical education teachers) each of whom had been trained in administration of all the test protocols. Each test item was explained and demonstrated before the test was scored. Each test item was performed twice. We always report the best performance score obtained on both of the two tests. If the results of the second test were significantly different from the first, we completed a third administration assuming the outlier score to be due to measurement error. Participants were given standard verbal encouragement and support throughout the testing procedure. When a child made a procedural error, instructions and demonstrations were repeated, and the child was allowed to make another attempt. All children completed the measurements adequately. Finally, all subjects completed the 6MWT test. 2.3. Demographic questionnaire This questionnaire was designed by the authors and included data on family socio-demographic status, child’s health status, medications, treatments and para-medical therapies received. 2.4. Anthropometry Height and weight were measured in the laboratory with the child dressed in light clothing and without shoes. Height was measured to the nearest 0.5 cm using a fixed stadiometer (Seca, Hultafors, Sweden) and body mass (weight) was measured to the nearest 0.5 kg with an electronic device (Avery Berkel model HL 120; Avery Weigh-Tronix Inc., Fairmont, MN, USA). BMI was calculated as body mass in kilograms divided by height in meters squared (kg m 2). 2.5. The movement assessment battery for children In this study, the MABC test was used to identify children with motor coordination problems. Compared to the MABC-2, the original MABC has been translated into several major European languages, such as French (Missiuna, Rivard, & Bartlett, 2006). As such, we felt this version to be more appropriate for use in this study than the second edition, as this would allow us to make comparisons of our data to other studies conducted both in our country and in other French-speaking nations. The MABC is the most commonly used tool to identify DCD in school aged children from 4 to 12 years (Geuze, Jongmans, Schoemaker, & Smits-Engelsman, 2001), and the first edition of the MABC has excellent reliability and concurrent validity (Henderson & Sugden, 2007). In the absence of Tunisian norms for the MABC test used in this study, French norms were used. While it is acknowledged that French norms may not be valid for this population, the intention was to compare groups and not to compare performance of children to population norms. The MABC is an extended version of the test of motor impairment (Stott, Moyes, & Henderson 1985), designed to identify children with movement difficulties. We used the MABC (Henderson & Sugden, 1992) as the criterion test of motor competence, assessing both gross and fine motor coordination in children aged between 4 and 12 years. It is a formal standardized test that provides both a quantitative and a qualitative evaluation of the child’s motor competence in daily life. The psychometric research performed on the MABC reported that is a reliable and useful assessment to use with young children (Crawford, Wilson, & Dewey, 2001).
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Furthermore, it has been found to more accurately identify children with motor difficulties when compared to other motor tests and appears to identify more readily those children who have additional learning or attention problems (Crawford et al., 2001). The MABC gives an estimate of motor ability in terms of speed and/or accuracy (outcome of movement). The eight items used to assess children ages 7–8 years include placing pegs in a peg board, threading a lace and drawing a line following a trail (manual dexterity (MD)); bouncing and catching a ball with one hand and throwing a bean bag into a box (ball skills); standing on one leg (static balance), jumping in squares, and heel-to-toe walking on a line (dynamic balance). The total impairment score (TIS), ranging from 0 to 40, is the sum of converted raw scores on the eight items that each child attempts during a formal assessment. Total impairment score can be converted into a percentile ranks: scores at or below the 5th percentile indicate a definite motor problem while a score at or below the 15th percentile indicates a clinical risk range that should be monitored (Henderson & Sugden, 1992). Test–retest (r = 0.75) and inter-rater reliability (0.70) have been shown to be good in this age range (Henderson & Sugden, 1992). Studies of criterion validity have shown 80% agreement between the MABC and the Bruininks-Oseresky test of motor performance (Crawford et al., 2001). 2.6. The differential scales of intellectual efficiency (EDEI-A; Ben Rejeb, 2001) These scales were used in order to exclude participants which IQ < 70. They made it possible to distinguish between the verbal developmental age (VDA) and the non-verbal developmental age (NVDA). The VDA was calculated by means of scores on five scales: picture identification vocabulary, word definition vocabulary, knowledge, social understanding and conceptualization. The NVDA was calculated by means of scores on four scales: classification of pairs of pictures, classification of three pictures, categorical analysis and practical adaptation. These scales’ applicability to participants with intellectual disabilities has previously been demonstrated (Tourrette, 2006). 2.7. Physical fitness test Several tests of physical fitness were included in the protocol and described below. 2.7.1. The modified agility test (MAT) The MAT was developed from the standard t-test to evaluate lower extremity. The agility test, pro shuttle, and long shuttle activities are used in field settings to determine timed performance on tasks related to activities and tasks that require quick starts, dynamic changes in direction, and efficient movement (Haj-Sassi et al., 2011). The MAT described by Haj-Sassi et al. (2011) consisted of sprints involving four changes of direction with three displacement modes: forward, lateral (left/right in randomized order), and backward. The participant began with both feet behind a starting line (position A). At his own discretion, for the first sprint, subject sprinted forward to a cone (B) and touched the base of it with the right hand. Facing forward and without crossing feet, they shuffled to the left to another cone (C) and touched its’ base with the left hand. Subjects then repeated this task with a different cone (D), before shuffling back to the left to cone B once again where again the base of the cone was touched. Finally, children ran backward as quickly as possible and returned to line A. Participants who crossed one foot in front of the other, failed to touch the base of the cone or failed to face forward throughout the task were required to repeat the test. The MAT performances were recorded using an electronic timing system (photo cells Globus, MicrogateTM), with accuracy recorded to 0.01 s. One pair of the electronic timing system sensors mounted on tripods were set approximately 0.75 m above the floor and positioned 3 meters apart facing each other on either side of the starting line. 2.7.2. The triple-hop distance (THD) The THD is a useful clinical test to predict an athlete’s lower extremity strength and power. A standard tape measure was fixed to the ground, perpendicular to a starting line to measure the THD. Participants stood on the designated testing leg, with the big toe on the starting line. They performed three consecutive maximal hops forward on the same (dominant) limb. Arm swing was allowed. The investigator measured the distance hopped from the starting line to the point where the heel struck the ground upon completing the third hop (Bolgla & Keskula, 1997). All participants were allowed one to three practice trials (self-selected) on each leg and then completed three test trials. The practice trials were provided to allow athletes to familiarize themselves with the test protocol. Practice trials were limited to 3 on each leg to avoid fatigue. 2.7.3. The 5 jump-test (5JT) The 5JT is currently used in field conditions to assess lower limb explosive power (Chamari et al., 2008) and to measure horizontal stretch shortening cycle capabilities in the distance traveled using lower limb actions. The 5JT is very easy to perform and does not require any sophisticated equipment. The 5JT, as described by Chamari et al. (2008), consist of 5 consecutive strides with joined feet position at the start and end of the jumps. From the starting position, the participant had to directly jump to the front with one leg and after the first 4 strides, i.e. alternating left and right feet for 2 times each, perform the last stride and end the test with both feet together. The best performance (as indicated by the distance) was recorded. All tests were separated by 2 min of recovery.
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2.8. 6-Min walking test (6MWT) The 6MWT was conducted at the school on a flat surface in a 30-m-long covered corridor marked every 2 m. The test was conducted according to the recommendations of the American Thoracic Society (American Thoracic Society, 2002). To allow for acclimatization to the task, each participant completed the 6MWT test twice (with an hour of test allowed between tests). We recorded the longer distance of the two tests. Participants were instructed to walk the longest distance possible at their own pace during the allotted time. Children were allowed to stop and rest during the test, but were instructed to resume walking as soon as they felt capable of doing so. Standardized encouragements (for example, ‘keep going’, ‘you are doing well’) and announcement of time remaining were given to all children. Before beginning the test, the participants sat on a chair located near the starting position for at least 10 min to determine the rest heart rate (HR) values and oxy-hemoglobin saturation (finger pulse oxymeter; Nonin Medical, Inc., Minneapolis, MN, USA). These parameters were also recorded every minute during and 5 min after the test. Dyspnea scores were measured on a Borg scale at the end of the test (Borg, 1982). The participant indicated the number corresponding to the perception of his effort and his feeling of breathlessness. 2.9. Statistical procedure All statistical analyses were conducted using the statistical package for the social sciences software (SPSS, version 17.0, SPSS Inc., Chicago, IL, USA). All variables were examined to determine whether distributions were normal or skewed. For categorical measures, 2 2 tables were created and used to estimate Odds Ratios to demonstrate the strength of the association, and the 95% confidence interval (CI) to measure precision. Data are presented as means (M) standard deviations (SD). Independent t-test was utilized to assess differences between the DCD and the control groups. Pearson’s correlations were conducted to assess the relationships among, body composition, motor competences, sub-maximal and physical capacity. Multinomial logistic regression analyses were used to investigate the relationship between 6MWT, BMI and physical ability. Four models were estimated: (1) Model 1 included the main effects for 6MWT and THD; (2) Model 2 consisted of the same variables as Model 1, with the addition of BMI; (3) Model 3 included an all variables in Model 1, with the addition of 5JT. Finally, in Model 4, 6MWT, BMI and 5JT were included. The significance level was set at (p < 0.05), and corrected using an appropriate Bonferroni adjustment to maintain an overall type one error at 5% (i.e., alpha = 0.01 for comparisons of the three outcomes among groups).
3. Results 3.1. Participants Anthropometric data and intellectual characteristics of DCD and control groups are shown in Table 1. In total, there were 19 children with DCD, and 18 typically developing peers (n = 37). Significant differences between groups were found for body mass index (p < 0.05). There were no significant group differences for age, weight, height, and IQ (p > 0.05). Differences in sub-scales on the MABC between groups are shown in Table 2. 3.2. Motor ability The results revealed significant group differences in motor abilities (Table 2.). Total score and subscales scores were significantly lower in children with DCD than in children without DCD. 3.3. Physical ability A significant difference in muscle power was found between children with DCD and the control group (Table 2). On the 5TJ test, the DCD group showed a reduction of 12% (p < 0.05) on final distance compared to controls. DCD children also showed a decreased performance during the MAT when compared to controls (9.09 0.51 vs. 10.62 0.94 sec with p < 0.001; Table 2). Children with DCD showed a significantly lower performance on the THD (2.96 0.23 vs. 3.75 0.4 m with p < 0.001; Table 2).
Table 1 Comparison of demographic data between children with and without DCD.
Age (years) Height (cm) Weight (kg) Body mass index (kg m IQ
2
)
DCD children (n = 19)
Typical children (n = 18)
8.60 1.00 137.20 7.50 32.40 6.40 17.10 1.20 101.6 12.60
8.50 0.96 134.20 4.80 28.90 3.40 16 1.20 106.30 12.40
Values are means SD; IQ, intellectual quotient; NS, no significant.
t
p 0.330 1.44 2.093 2.81 1.13
0.730NS 0.159NS <0.05 <0.01 0.26NS
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Table 2 Comparison of MABC test, physical ability and 6MWD between children with and without DCD.
Manual Dexterity Ball Skills Balance MABC score Modified agility test (s) Triple hop distance (M) 5 jump-test (m) 6MWD (m) Dyspnea Heart rate before Heart rate after Oxygen saturation (%) before Oxygen saturation (%) after
DCD children (n = 19)
Typical children (n = 18)
t
p
8.10 3.30 2.90 2.90 4.50 1.80 15.50 3.04 10.80 1.10 3.05 0.30 5.80 0.40 556.30 71.90 5.50 1.30 83.90 9.20 123.60 17.30 99.40 0.70 96.90 0.80
2.87 2.05 0.30 0.80 0.30 0.40 3.50 1.20 9.10 0.50 3.60 0.40 6.40 0.90 652.60 48.20 4.20 0.90 86.80 16.80 139.80 14.20 99.20 0.70 97.70 1.20
5.83 3.72 8.63 14.37 6.10 4.80 3.10 4.80 3.51 0.64 3.11 0.88 2.47
<0.001 <0.01 <0.001 <0.001 <0.001 <0.001 <0.01 <0.001 <0.01 0.52NS <0.01 0.38NS <0.05
6MWD, 6-min walking distance; MABC, Movement Assessment Battery for Children; NS, no significant.
3.4. 6MWT The 6MWT was completed by all participants without premature end or breaks; no symptoms or clinical complications occurred (arrhythmia, cyanosis, etc.) during testing. The mean distance walked during 6MWT was significantly longer in typically developing children when compared to children in the DCD group (663.43 m 43.50 vs. 564.85 m 73.7 m; see Table 2). The distance walked increased from a baseline of 105.30 m (10.12 m) reaching a plateau of 111 m (7.45 m) after 1–3 min, for children without DCD. Children with DCD started out fast and then slowed reaching total distances of between 93.14 m (12.13 m) and 98.13 m (14.45 m) over the duration of the 6MWT (Fig. 1). The dyspnea at the peak of 6MWT was significantly higher in children with DCD than children without DCD. No significant differences between groups were found in heart rate at baseline, maximum heart rate, the oxygen saturation at baseline or minimum oxygen saturation. 3.5. Correlation between body composition, motor competences, sub-maximal and physical capacity A significant correlation between BMI and balance (r = 0.512, p < 0.05) was found for DCD children. BMI and physical ability such as THD (r = 0.553, p < 0.05) and 5JT (r = 0.508, p < 0.05) was also observed. A significant positive correlation among 6MWT and BMI (r = 0.544, p < 0.05) was found for children with DCD (Table 3). No significant correlations was found among body composition, motor competences, sub-maximal and physical capacity for children without DCD. In the next part of the analysis, the relationships between MAT, THD and 5JT were analyzed. A negative correlation between MAT and 5JT (r = 0.493, p < 0.05) was observed. THD and 5JT (r = 0.611, p < 0.01) was found to be correlated in DCD children. A significant correlation among 6MWT, MAT (r = 0.522, p < 0.05) and THD (r = 0.472, p < 0.05) was also found in children with DCD (Table 3). In children without DCD, the only significant correlation observed was between MAT and THD (r = 0.545, p < 0.05; Table 3).
[(Fig._1)TD$IG] 120
Distance (m)
110 100 90 80 70 60
1
2
3
4
5
Minute Fig. 1. 6MWD in children with and without DCD. –~–, children with DCD; –&–, children without DCD.
6
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Table 3 Correlation between Body Composition, motor competences, exercise tolerance and physical capacity between children with and without DCD. BMI (kg m
2
)
MABC
MAT (s)
THD (m)
5JT (m)
Children with DCD MAT (s) THD (m) 5JT (m) 6MWD (m)
0.356NS 0.553* 0.480* 0.544*
0.449NS 0.076NS 0.075NS 0.232NS
0.384NS 0.493* 0.522*
0.611** 0.375NS
0.472*
Children without DCD MAT (s) THD (m) 5JT (m) 6MWD (m)
0.069NS 0.165NS 0.086NS 0.353NS
0.043NS 0.006NS 0.212NS 0.310NS
0.545* 0.048NS 0.424NS
0.145NS 0.420NS
0.170NS
BMI, body mass index; 6MWD, 6-min walking distance; MAT, modified agility test; THD, triple hop distance; 5JT,five-jump test; MABC, Movement Assessment Battery for Children; NS, no significant. * Significant difference between groups (p < 0.05). ** Significant difference between groups (p < 0.01).
3.6. Multinomial logistic regression analysis of coordination (dependent variable) and relationships between 6MWT, BMI and physical ability in children with and without DCD Table 4 shows the results of the regression analysis where MABC scores were regressed onto 6MWT, THD, 5JT, and BMI in children with and without DCD. Four models were tested. In Model 1, both 6MWT and THD were significant. Model 2 consisted of the same variables as Model 1, with the addition of BMI. After entering BMI into the Model, the main effect for 6MWT and THD remained significant with a parameter estimate of 0.05 (p < 0.05) and 8.95 (p < 0.05) respectively. This indicates that BMI is both a significant independent predictor of motor coordination, but that also some of the effect of 6MWT on MABC scores can be explained by the effect of relative body weight. Model 3 shows the results of the regression analysis of MABC scores onto 6MWT and explosive strength (5JT) in children. After adjustment both 6MWT, there is a significant negative effect of explosive strength on motor coordination with a parameter estimate of 0.044 (p < 0.05) and 1.61 (p < 0.05) respectively. In Model 4, the main effect for 6MWD and 5JT remained significant with a parameter estimate of 0.045 (p < 0.05) and 1.86 (p < 0.05) respectively, after adjustment for BMI. 4. Discussion The purpose of the present study was to determine whether differences exist in various measures of body composition, muscle fitness and exercise tolerance parameters in children with and without DCD. A secondary objective was to analyze correlations among these measures, between children with and without DCD aged 7–10 years. Children with DCD demonstrated significantly lower performance in health-related fitness measures such as strength and power. Children with DCD also showed significantly impaired performance on anaerobic power than children without DCD. Compared to the healthy controls, DCD children had significantly less walking distance during 6MWT. Our results found significant correlations among BMI, MD and balance for DCD children. These outcomes were in accordance with one of the recent studies by Zhu et al. (2014) in which they found that correlations between anthropometric characteristics (weight, BMI and waist circumference) and MABC scores were higher in the DCD with balance problems group compared with typically developing children and DCD children without balance problems groups. Our results were also in accord with other studies that focused on physical fitness in children with motor difficulties (Hands & Larkin, 2002). Schott, Alof, Hultsch, and Meermann (2007) found that children with DCD had significantly lower performance on different fitness components compared with control group. However, reduced physical fitness was found in
Table 4 Regression analysis of coordination (dependent variable) between 6MWD, BMI and physical ability in children with and without DCD. Model 1
Intercept 6MWD (m) THD (m) 5JT (m) BMI (kg m 2)
Model 2
Model 3
Model 4
Estimate
p
Estimate
p
Estimate
p
Estimate
p
35.66 (14.14) 0.34 (0.016) 4.57 (2.30) – –
<0.05 <0.05 <0.05 – –
31.79 (20.51) 0.049 (0.024) 8.95 (4.25) – 1.59 (0.70)
0.113 <0.05 < 0.05 – <0.05
37.17 (13.96) 0.044 (0.018) – 1.61 (0.75) –
<0.01 <0.05 – < 0.05 –
23.18 (17.15) 0.045 (0.020) – 1.86 (0.90) 0.94 (0.45)
0.177 <0.05 – <0.05 <0.05
Values are parameter estimates with standard error in parentheses. BMI, body mass index; 6MWD, 6-min walking distance; THD, triple hop distance; 5JT, five-jump test.
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terms of reduced muscular strength, endurance and speed or agility (Haga, 2008) in children with DCD compared with their peers. In our study, performance on the THD and 5JT was considerably lower for DCD group. It is well established in the literature that the horizontal jump test, THD and 5JT are a strong predictors of lower limb muscular strength and power (Barber, Noyes, Mangine, McCloskey, & Hartman, 1990; Chamari et al., 2008). This result is in line with previous research studies that indicate a significantly lower performance in the explosive power tasks (standing-long-jump) on the functional strength measure (Ferguson et al., 2014) in children with DCD. On the other hand, our results showed a significantly lower performance in the MAT in DCD group, compared with the typically developing group. Studies suggest that children with DCD perform poorly in muscle power sprint test (Ferguson et al., 2014; Cantell, Crawford, & Tish Doyle-Baker, 2008). Hands and Larkin (2006) found that children with motor learning difficulties were significantly slower, and demonstrated less speed as measured by the 50-m run and the shuttle run, than the control group. Furthermore, the exercise intolerance was also reported by Wu, Lin, and Li (2010) who reported that DCD children perform worse on 800 m run test compared to the typical group. Our findings support conclusions from other studies reporting weak correlations among BMI, fine and gross motor skill performance (Zhu, Wu, & Cairney, 2011). Interestingly, the present study demonstrated a significant relationship among BMI, physical ability (THD and 5JT) and 6MWD only in DCD group. Higher BMI has been shown to be associated with poorer performance on physical fitness tasks such as in standing-long jump (D’Hondt et al., 2013) and runs for distance (Schott et al., 2007). The results of the present study revealed that BMI was associated with poorer explosive strength, power and exercise tolerance in children with DCD, but not in children without DCD. Motor coordination was the measure that proved to be an independent predictor of deficits in health-related fitness such as submaximal and anaerobic performance between the DCD and comparison groups (Ferguson et al., 2014). Exercise tolerance, explosive strength, power and BMI were all found to be significant predictors of motor coordination. The results clearly show how body composition (BMI) is related to impaired performance in tests requiring exercise tolerance (6MWT), explosive strength of lower extremities (5JT) and power (THD). This is an important finding given that children with DCD tend to show elevated body mass and BMI relative to typically developing children (Chirico et al., 2011; Cairney, Hay, Veldhuizen, & Faught, 2011; Cantell et al., 2008). Nevertheless, the present study, using comparative analysis with correction of BMI levels, still revealed disparities in the execution of tests in which moving the whole body was required. Overall, these findings reinforce the importance of motor skill level in fitness testing. Our finding showed significant correlations between MAT and 5JT as well as a significant correlation between THD and 5JT in DCD children. The decreased muscular strength and power of children with DCD found in this study may be at least partially attributable to the muscular organization. Previous research has shown that, children with DCD have been found to have planning, programming and muscle activation problems (Raynor, 1989). In the absence of muscle hypertrophy, improved motor coordination has been one of the neural factors associated with increased muscle strength in children (Ramsay et al., 1990). The typical child’s performance in the agility test, could be, in part, explained by either better motor recruitment or neural adaptations. Neural adaptations usually occur when athletes respond or react as a result of improved coordination between the central nervous system signal and proprioceptive feedback (Craig, 2004). Decreased power in children with DCD may also be attributed to age-related increases in anaerobic substrates such as creatine phosphate and glycogen (Coyle, Costill, & Lesmes, 1979), and to reduce of motor unit recruitment and muscle activities of agonists and antagonists (Raynor, 1989). The largest difference in 6MWT between children with and without DCD could be explained, in part, by differences in muscle strength and exercise tolerance (Frontera, Meredith, O’Reilly, Knuttgen, & Evans, 1988). DCD children walk with an irregular pace (see Figure 1), which highlights the sensation of dyspnea due to a diminished ventilator reserve and, probably, lack of motivation to sustain a moderately heavy load for a prolonged time (Bogaard et al., 1993). Moreover, poor performance in submaximal tasks could be attributed to the relative increase in co-contraction or less well-predicted movement outcomes. From this perspective, future research should examine the fatigue profile and the ability to tolerate high-intensity exercise. The determination of neuromuscular fatigue manifestations in muscle strength and electromyography (EMG) signals following a high-intensity exercise may be important for clinical purposes. 4.1. Limitations A number of limitations should be noted in relation to this study. For example, we did not measure habitual physical activity. It is possible that relationships between motor skills, physical activity, physical ability and submaximal exercise might have been stronger if these subcategories of movement skills were assessed. The relationships among motor competence, physical fitness and self perception were also not assessed in this study. 5. Conclusion Overall, the present study showed consistent deficits across a range of health-related fitness tests between children with and without DCD. Our results also revealed that BMI was associated with poorer explosive strength, power and exercise tolerance in children with DCD compared to children without DCD. From this perspective, interventions in children with DCD should target training on motor proficiency and weight control. Moreover, longitudinal studies are strongly
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recommended in order to explore whether children with DCD possess physiological markers that differ from their peers without disabilities. Conflict of interest We have no conflict of interest to disclose[1_TD$IF]. Acknowledgements We thank Mr Haithem Rbai, the Department of Child Neurology, He´di Chaker Hospital (Sfax, Tunisia), Service d’Explorations Fonctionnelles, Unite´ d’Effort Cardio-pulmonaire, Hoˆpital Habib Bourguiba (Sfax, Tunisia), Service de pseudo psychiatry, Hoˆpital Habib Bourguiba (Sfax, Tunisia) El Rahma school (Sfax, Tunisia), El Kamel school (Sfax, Tunisia) and the participating children and their parents, for their contributions. References Adam, C., Klissouras, V., Ravazollo, M., Renson, R., & Tuxworth, W. (1998). EUROFIT: European test of physical fitness. In Handbook. Rome: Council of Europe, Committee for the Development of Sport. American Thoracic Society (ATS) (2002). ATS statement: Guidelines for the six-minute walk test. 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