Developmental coordination disorder (DCD) affects up to 6% of children aged 5 to 11 years and is characterized by significant delays in development of motor skills that interfere with successful, efficient completion of daily activities.1 Although DCD is commonly used to describe children with motor coordination difficulties,2 little agreement is found regarding its cause or the effectiveness of interventions.3 When compared with their peers, children with DCD have a delayed rate of acquisition of motor learning and functions.4–7
According to the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition, Text Revision), “marked impairments in the development of motor coordination” are present in children with DCD.1 These children use more compensatory strategies such as associated movements and cocontraction than children developing typically.5,7 Associated movements are excessive and unnecessary movements that decrease the effectiveness or fluency of movement.7 Cocontraction occurs when muscles other than the prime mover are activated to “lock out” extra degrees of freedom.5 Children developing typically initially lock out degrees of freedom during motor learning; but when provided with practice, they quickly unlock the degrees of freedom and produce coordinated movement. Children with DCD are not able to unlock their degrees of freedom at the same rate as children developing typically, suggesting that they may not learn motor skills at the same pace.5
The challenges with coordinated movements in children with DCD may be because of the difficulty in learning feedforward control or the poor ability to use past movement experiences to predict movement requirements.5–8 Compared with children developing typically, children with DCD demonstrated similar motor responses during skills requiring feedback control, such as imposed unloading of a limb; however, when examining motor skills requiring feedforward control, such as voluntary, self-unloading of a limb, they demonstrated more variability and decreased coordination.8 When planning simple movements with a single degree of freedom, children with DCD demonstrated larger variability in force production and greater end point errors, rather than a well-matched response to specific force requirements.4 The greater end point variability supports the theory that preplanning the force required for specific movements, or feedforward motor control, is decreased with simple tasks requiring a single degree of freedom and may be amplified with more complex tasks.6 Because daily function requires complex movements, repeated practice requiring control of multiple degrees of freedom, as found in activity-level intervention, may not be effective at decreasing compensatory strategies and improving feedforward control in children with DCD.4,5
During function, children with DCD may benefit from a prolonged period of learning feedforward control. This could reduce the need to use cocontraction for stability and decrease associated movements to counteract passive forces produced by the movements the child cannot yet anticipate. For example, a child who can use feedforward control while riding a bicycle will coordinate braking the bicycle after repeated practice of this skill. The child with feedforward control can match the force on the brake to the decrease in speed required to slow the bicycle. This latter child simultaneously activates hip and trunk extensors while braking to maintain the trunk over the legs and eliminate or minimize a forward shift of the trunk. Control of the trunk allows the child to maintain balance and steer with the upper extremities.
Conversely, a child without feedforward control may not be able to match downward force for braking to the proportion needed for the change in speed, resulting in either too much or too little force for braking. Without feedforward control needed to anticipate the effect of the force of braking on the trunk, the trunk will shift forward and larger feedback contractions will be required in trunk and hip muscles, and potentially, the upper extremities to stop forward progression of the trunk. Use of the upper extremities to stop this forward progression could interfere with the ability to steer the bicycle. Cocontraction at the joints and associated movements may be required to maintain balance, but these result in excessive energy cost and more challenges to stability and control. Without feedforward control, skills like riding a bicycle will become more challenging and a larger number of repetitions will be needed for learning and carryover. With poor success, the child's motivation to continue practice may decrease.
Prolonged experience with isolated, simple joint movements may allow the child with DCD to learn feedforward control and reduce cocontraction and associated movements. Although practicing meaningful functional activities is an effective method for intervention once isolated, simple joint movements are learned,9 children with DCD may initially require practice at a simpler skill level. With prolonged, blocked practice, improved motor learning of isolated, simple joint movements may allow children with DCD to develop and improve strategies at the cognitive stage of motor learning,10 before progressing to more complex functional skills. This type of blocked, isolated, simple joint movement is consistent with a strength training program.
Kaufman and Schilling11 provided the only case report available on effectiveness of practicing isolated, simple joint movements in children with DCD. They documented the results of a 12-week strength training program for a 5-year-old boy with DCD who had previously received more than 1 year of activity-based intervention, with limited improvements. Because of the child's generalized weakness, the authors had decided on a trial of strengthening or repetitive, isolated, simple joint movements.11 Following intervention, the boy demonstrated improved dynametric force production, improved scores on the Bruinicks-Oseretsky Test of Motor Proficiency, Second Edition (BOTMP-2), and improved scores on static and dynamic proprioception in both his upper and lower extremities. His parents and teacher reported improved function in the classroom and home environment as well. Improvements on the BOTMP-2 and proprioceptive testing suggest that the functional improvements may have resulted from improved feedforward control or the ability to plan his movements, rather than muscle hypertrophy and increased force generation. The results of their case report11 and current motor learning theories raise the question of whether repeated, isolated, simple joint movements will improve function in a child who has not benefited from repetition of more complex activity-level skills.
The purpose of this case report was to evaluate the outcomes following a strength training program for a child demonstrating motor signs consistent with DCD. Evidence regarding strength training for children developing typically suggest that observed strength gains are the result of improved neural pathways and motor unit recruitment, as opposed to muscle hypertrophy.12,13 Recommendations for strength training in this population call for a high number of repetitions and low resistance.14 This provides the opportunity for blocked practice of isolated, simple joint movements, controlled force generation, and repeated motor planning, with appropriate stabilization at surrounding joints. Although only 1 case study on effectiveness of strength training in children with DCD was found in the literature,11 the evidence available on mechanisms for strength gains in children14–16 and effective motor learning17 supports the use of strength training as a potentially valuable treatment approach in children with DCD.
G.D., a girl, was aged 6 years 11 months, with a medical diagnoses of apraxia and hypotonia. G.D. was initially referred for physical therapy services at the age of 4 years 3 months, due to her mother's concerns regarding her delayed motor development and how these skills may affect her ability to “fit in” the preschool class she attended. Although G.D. qualified for an Individualized Education Program, she did not have a program in place, due to her parent's decision to have her attend private school. Throughout 3 episodes of care over a 2-year period, G.D. had a history of limited and poorly maintained progress in physical therapy using activity-based interventions. During an episode of care, G.D. received physical therapy services twice a week; whereas during all other episodes of care, services were received once a week. G.D.'s mother reported small improvements in motor function during these episodes of care, with limited success in specific functional areas, particularly the playground, and with declines in function during periods of no service. In addition, it was noted that with repeated practice of a skill, G.D. demonstrated improvement in that specific skill; however, without consistent practice, her ability to perform the skill degraded rapidly. Over her previous episodes of care, G.D.'s Peabody Developmental Motor Scales, Second Edition, and BOTMP-2 scores were found to be 1.5 to 2 standard deviations below the mean, except during the episode of care when she received skilled physical therapy twice a week. During the period when G.D. received physical therapy twice a week, her motor scores improved to 1 standard deviation below the mean, but her scores deteriorated when the frequency of intervention returned to once a week. G.D.'s mother terminated all therapy services 4 months before the start of this episode of care because of funding difficulties.
G.D. was chosen for this case report because of her repeated return to physical therapy with persistent motor delay and difficulties with participation on the playground. At the initiation of this fourth episode of care, G.D. consistently complained about her inability to traverse monkey bars; inability to stand in line or stand for any period of time without wanting to sit down because her legs were “tired”; difficulty coordinating pedaling, steering, and breaking while riding a bike; inability to do a cartwheel; and difficulty running fast. G.D.'s mother reported similar complaints regarding G.D's abilities and also noted that she gives up easily or does not even try if she perceives a task is too difficult. We believe G.D.'s motor difficulties are consistent with a diagnosis of DCD. On the basis of the complaints of activity-based limitations and difficulty performing motor tasks, G.D.'s primary problem was hypothesized to be related to a persistent delay in learning feedforward motor control.
G.D. demonstrated cognition, language, and behavior consistent with her age. However, when presented with tasks she perceived to be challenging, she demonstrated decreased compliance with instructions. She demonstrated appropriate physiological responses to exercise and rest, such as becoming flushed with an increased respiratory rate and deep breathing after exertion, with rapid returns to baseline. Screening of the musculoskeletal and neuromuscular systems revealed positive findings consistent with DCD, such as hypotonia and poorly coordinated movement. No remarkable findings were present during screening of the cardiovascular or pulmonary, integumentary, or endocrine systems.
G.D. presented with complaints of both increased difficulty and/or failure to attempt several age-appropriate motor tasks that she perceived as hard or considered her performance unsuccessful, such as traversing monkey bars, riding a two-wheeled bicycle, performing a cartwheel, running fast, and standing for a “long time” without wanting to sit down. Her history clearly demonstrated a lack of substantial and sustained progress in past episodes of care where activity-based intervention was selected to address the acquisition of gross motor skills. This suggests that practice of the whole task may not have been sufficient to effectively learn new motor skills. After compiling the list of the above-mentioned tasks that G.D. had difficulty with or avoided, the authors noted that a majority of these tasks were complex motor tasks that required strength, endurance, an ability to stabilize and use feedforward control, and an ability to effectively coordinate movement at multiple joints simultaneously. On the basis of her history, effective recruitment and activation of muscles for feedforward control of coordination and motor planning were hypothesized to be possible impairments related to difficulties with acquisition and performance of gross motor tasks.
Tests and Measures
A series of standardized assessments was selected to evaluate G.D.'s current performance in the participation, activity, and body structures or function (impairment) components of the International Classification of Functioning, Disability and Health. The Canadian Occupational Performance Measure (COPM) was selected to provide information on participation and to serve as a self-assessment of G.D.'s current motor function. The COPM uses a Likert scale with anchors at either end, to evaluate the patient's satisfaction and performance of activities of daily living that are important to her. This assessment is based on a detailed, semistructured interview to identify activities that are important to the patient and creates an open dialogue between the therapist and the patient. It provides information regarding the patient's self-assessment of participation and satisfaction with selected tasks that are not measurable by other standardized assessments.18 A change of 2.0 or more points on the COPM is considered clinically significant.19
Activity was assessed by using 3 standard assessments. These assessments are described below.
The Developmental Coordination Disorder Questionnaire–Revised 2007 (DCDQ'07) was selected to measure parent perception of G.D.'s motor skills and coordination difficulties. The DCDQ'07 is a revised version of the Developmental Coordination Disorder Questionnaire, parent questionnaire that includes a 5- to 8-year-old age band. The DCDQ'07 was developed to help rule in and rule out a suspected diagnosis of DCD and meets criterion B of the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition, Text Revision). In the 5- to 8-year-old age band, a score of 15 to 46 is considered suspected DCD, while a score of 47 to 75 is considered probably not DCD.20 While the DCDQ'07 has been shown to meet the standards of a screening instrument in terms of internal consistency, concurrence, and construct validity, the 5- to 8-year-old age band shows moderate sensistivity and specificity and requires an additional assessment tool for confirmation of a DCD diagnosis.20,21 This questionnaire was selected as an assessment to determine whether G.D's motor presentation was consistent with a diagnosis of DCD.
The Test of Gross Motor Development–Second Edition (TGMD-2) was selected as a standardized measure to assess the sequencing and quality of locomotor and object control skills common to children aged 3 to 10 years.22 The TGMD-2 is a norm- and criterion-referenced standardized assessment22,23 and has been found to be a reliable and valid measure for children with mild disabilities.24,25 A change of 3 or more points on the subtest scores or 15 or more points on the total score suggests a change of 1 standard deviation.22 The TGMD-2 was administered and scored as described in the manual.22
The BOTMP-2 is a norm-referenced,26 reliable, and valid26,27 standardized assessment selected to identify motor proficiency in various specific areas, including bilateral coordination, strength, and balance.26,27 The BOTMP-2 is considered the reference standard in evaluating motor skills of a child with DCD27 and was scored as outlined in the manual.26 A total motor composite score of −1.5 standard deviations less than the mean is consistent with a diagnosis of DCD and an increase of 1 standard deviation is considered a clinically significant improvement.26 The 4- to 7-year-old age band demonstrates high reliability on subtests. Since there is a slight practice effect in this age band when the test is readministered within 35 days, all testing for G.D. was completed with more than 35 days between tests.26
On the basis of the tasks G.D. identified as difficult, traversing monkey bars was selected as an additional activity-based measure that was not included in standardized assessments. The ability to traverse monkey bars was measured by counting the number of rungs G.D. was able to move forward. The presentation and scoring of the monkey bars was kept consistent in an attempt to standardize this measure.
Impairment component information on muscular strength, endurance, and coordination was obtained through the use of the strength subtest of the BOTMP-2 and functional strength measures (Table 1). These measures were selected over manual muscle testing because of G.D.'s difficulty following directions during tasks she perceived as difficult, her inability to demonstrate consistent isolated motor control, and the lack of reliability reported in the literature on manual muscle testing for children with neurological impairments.28
The selected measures of participation, activity, and impairment demonstrated results consistent with several of the areas of concern expressed by G.D. and her mother before testing. Using the COPM, G.D. identified her 5 most important performance concerns, which included hitting a pinata, kicking a ball, standing for a long time, jumping rope, and swimming. Her average performance rating on these tasks was a 4.2 of 10, with a score of 10 indicating the ability to do the task extremely well. G.D.'s average satisfaction rating was 9.2 of 10, with a 10 indicating she was highly satisfied with her performance. Limitations in participation resulted in self-assessment of low performance, but did not result in low satisfaction ratings.
Consistent with the limitations demonstrated in participation, scores on the standardized assessments demonstrated motor delays at the activity level. G.D.'s mother rated her ability to perform motor activities on the DCDQ'07 within the range for suspected DCD. A total raw score of 17 (control during movement: 6; fine motor/handwriting: 6; general coordination: 5) suggested discoordination in all areas of fine and gross motor skill. On the TGMD-2, G.D. demonstrated a standard score of 7 on the locomotion subtest and a standard score of 8 on the object control subtest, suggesting a decreased quality of movement. The BOTMP-2 subtests revealed balance subtest score −1.4 standard deviations below the mean (scale score, 8), bilateral coordination score −1.6 standard deviations below the mean (scale score, 7), and running speed and agility score −1.2 standard deviations below the mean (scale score, 9). In addition, the composite scores showed body coordination −1.7 standard deviations below the mean and strength and agility −1.6 standard deviations below the mean. On the monkey bars, G.D. hung limply from the first rung, without activating the muscles from her shoulder girdle to her hips, and relied solely on her grip strength to attempt to move to the second rung. Without the assistance of her core musculature, her grip strength was insufficient, causing her to drop to the ground after the first rung. These measures highlight G.D.'s difficulty with various age-appropriate activity-based skills that are consistent with DCD and delayed motor learning.
Examination of impairments focused on motor control by looking at repetitive muscle activation, maintenance of muscle contraction, and ability to produce power. Limitations at the impairment level were observed on the BOTMP-2, with the strength subtest score −1.8 standard deviations below the mean (scale score, 4). Strength deficits, defined as decreased ability to repetitively activate and/or maintain a muscle contraction against gravity, were observed during heel raises, posterior pelvic tilt, bridging, plank, trunk extension, and hanging from a bar. During these measures, G.D. demonstrated increased cocontractions and associated movements, as well as decreased ability to coordinate muscle groups, stabilize, and activate isolated muscle activity likely resulting in her presentation of decreased muscle strength and endurance (Table 2).
On the basis of the BOTMP-2 scores, G.D. presented with gross motor skills that are labeled “well below average” in the BOTMP-2 manual and in a range consistent with a diagnosis of DCD.26 Additional evidence of a diagnosis consistent with DCD was her difficulty with the quality and coordination of complex movements1,3,5,7 included in her standardized and functional measures, such as traversing monkey bars, hitting a ball (which could relate to hitting a pinata), and jumping (which could relate to jumping rope). Despite her past practice of these tasks in physical therapy, she continued to demonstrate poor control and use compensatory strategies like cocontraction to lock out degrees of freedom while performing complex movements. When considering G.D.'s examination results and her response to prior activity-level interventions, an intervention using a strength training program was designed to provide blocked practice of isolated, simple joint movements and to decrease cocontraction at joints and associated movements during motor skills. The aim of the 24 strength training sessions were to facilitate G.D. to complete a high number of movement repetitions and to enhance learning feedforward control of simple motor skills. After completing the strength training program, it is theorized that G.D. will demonstrate improved performance of complex motor skills as a result of decreased reliance on compensatory strategies such as cocontraction and associated movements, which will translate to improved success and quality of motion on standardized measures.
A strength training program using a Universal Exercise Unit (UEU) was initiated. The UEU provided resistance through a pulley weight system. This strength training program was initially planned to occur twice a week for a period of 12 weeks, consistent with the literature available on strength training to produce functional gains in children.11 Because of cancelled sessions that are typical in any pediatric therapy setting, the protocol was shifted to simply completing all 24 sessions.
Since strength gains in children have been attributed to improved motor unit recruitment within the nervous system rather than the hypertrophy of muscle tissue, resistance training was completed using a high number of repetitions and a moderate load, as defined in the literature, to facilitate motor learning.14,15,17,29 A moderate load for G.D. was determined by having her initially complete all exercises prescribed for 30 repetitions without any resistance. Once G.D. successfully completed 3 sets of 30 repetitions of isolated movement, without cocontraction and/or associated movements, 0.5 kg weight was added, which was the minimal increment of change on the UEU. Weight was increased by 0.5 kg until G.D. was not able to successfully complete 3 sets of 30 repetitions of isolated movement without compensation.
Research examining the effectiveness of motor learning strategies suggests that blocked repetitions are a more effective form of practice during acquisition or the cognitive stage of motor learning.17 On the basis of literature suggesting strength gains are the result of improved motor unit recruitment12,13 and the effectiveness of blocked practice for early learning,17 the exercise prescription of 3 sets of 30 repetitions, with rest as needed, was selected.
Specific joint motions were chosen to address strength deficits found during G.D.'s examination (Table 2). These findings may be partly due to the actual strength deficits consistent with hypotonia, but may also be magnified as a result of her motor control difficulties presenting as increased cocontractions and associated movements and decreased stabilization, coordination, and isolated muscle activity. These motor control difficulties were noted in several muscle groups, including scapular stabilizers, back extensors, hip extensors, hip abductors, hip adductors, abdominals, knee flexors, knee extensors, and plantar flexors. Strength exercises using the UEU were selected to produce isolated, simple joint motions during blocked practice. The high frequency of repetitions allowed G.D. to practice coordinated movement within and between limbs while providing an opportunity to learn to release the degrees of freedom5 and decrease associated movements7 (Table 3). Because of the time required for G.D. to complete each exercise, it was not possible to complete all chosen exercises during each 60-minute treatment session. Because of this, exercises were rotated so that all exercises were completed an equal number of times.
At the completion of 24 strength training sessions, G.D. reported improvements in participation by self-assessment on the COPM, as well as demonstrated performance improvement on both activity and impairment measures postintervention. When self-assessing participation by using the COPM, G.D. reported an average score of 8.2 of 10 on both her performance rating and her satisfaction rating of her 5 most important skills (Figure 1).
The improvement of 4 mean points for satisfaction is a clinically significant improvement, with the decrease of 1 mean point for performance representing a nonclinically significant change.
Activity-level measures support an improvement in functional skills. On the DCDQ'07, G.D.'s mother reported an increase in her ability to perform motor activities to the point that she no longer fell within the suspected DCD range. Her total raw score increased from 17 during the initial examination to 51 postintervention (control during movement: 18; fine motor/handwriting: 18; general coordination: 15) (Figure 2). On the TGMD-2, G.D. demonstrated nonclinically significant changes with an increase of her standard score from 7 to 8 on the locomotor subsection and a decrease of her standard score from 8 to 7 on the object control subsection (Figure 3). The BOTMP-2 showed clinically significant improvement in the balance and bilateral coordination subtests, with a 1.2 and 1 standard deviation increase, respectively, and a nonclinically significant decrease in the running speed and agility subtest, −0.2 standard deviations (Figure 4). Her body coordination composite score showed a clinically significant increase of 1.1 standard deviations, while her strength and agility composite score showed a nonclinically significant decrease of 0.1 standard deviations. Lastly, at the activity level, G.D. demonstrated an improvement from the pretest of 0 bars to traversing 10 monkey bars postintervention, resulting in an increase of 10 monkey bars.
Postintervention impairment measures demonstrated improvements on the BOTMP-2 and functional strength measures. Despite an increase in the strength subtest scale score from 4 to 6 on the BOTMP-2, this change was less than 1 standard deviation and therefore nonclinically significant (Figure 4). Decreased cocontraction and associated movements, as well as increased ability to coordinate muscle groups, stabilize, and activate isolated muscle activity was observed during intervention testing, possibly contributing to her improvements during heel raises, posterior pelvic tilt, bridging, plank, trunk extension, and hanging from a bar (Table 4).
As hypothesized, the use of blocked practice of isolated, simple joint movements through strength training did result in clinically significant improvements in G.D.'s motor skills. Gains in G.D.'s participation and activity-level function may have been due to her ability to more effectively and efficiently use feedforward control and isolate simple joint movements without compensations. In addition, this intervention positively affected both G.D.'s and her mother's perception of her motor skills, noted by clinically significant improvements on the DCDQ'07 and the COPM. Despite G.D.'s clinically significant performance score increase on the COPM, she had a nonclinically significant change in her satisfaction score.
G.D.'s largest gains were seen in the areas of balance and coordination, as opposed to strength and locomotion. On the basis of scores on the BOTMP-2 manual coordination composite and observations of bridging, trunk extension and plank, we hypothesized that increased ability to hold the position for a longer period of time on functional strength occurred as a result of improved stabilization during movement without cocontractions or associated movements. The selected intervention positively affected motor learning and may have allowed G.D. to more effectively coordinate her available degrees of freedom.
Variability in G.D.'s performance contributed to a nonclinically significant improvement on the TGMD-2 from pre- to postintervention. During TGMD-2 pretest, G.D. used her dominant hand on top of the nondominant hand when swinging the bat for “striking a stationary ball.” Following intervention, G.D. did not receive these same points on the test item “striking a stationary ball” when she placed her nondominant hand on top of her dominant. Had G.D. performed this task on the posttest the same way she performed it at pretest, her object control standard score could have increased from an 8 at pretest to an 11 at posttest, resulting in a clinically significant improvement of 1 standard deviation on the TGMD-2. Although using her dominant hand could have led to a different outcome and conclusion on the TGMD-2, this variability in performance and potentially weak-hand dominance is frequently observed in children with DCD.3,4,30,31
Whereas our repetitive, blocked practice demonstrated the potential for increased stability and coordinated movement in G.D, it did not result in changes on subtests for skills requiring control of locomotion and movement through the environment. The BOTMP-2 speed and agility, and strength subtests, as well as the locomotor subtest on the TGMD-2, demonstrated no clinically significant change. Locomotion and movement through the environment require efficient use of momentum, which was not addressed during the strength training program. While strength training may be an initial step to improve stability, now that G.D. is demonstrating better stability and coordination, she would most likely benefit from additional treatment addressing locomotor practice.
The strong positive improvements documented in G.D. need to be examined cautiously. First, G.D. was not medically diagnosed with DCD; however, at the initiation of therapy, on the basis of our examination and the input from her mother, G.D. did meet the diagnostic criteria as listed in the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition, Text Revision).1 One reason she may not have been medically diagnosed with DCD is her age. Most children who are diagnosed with DCD are 6 years or older.32 Since G.D. was aged 6 years at the start of this study, she was at the younger end of the age range when children are typically identified as having DCD. In addition, G.D.'s participation in the intervention was interrupted over the 12 weeks and the therapists adjusted their intervention to 24 sessions versus 12 weeks. Therefore, functional motor gains could have potentially been stronger if G.D. had been able to consistently attend intervention twice a week. In addition, a follow-up test several weeks later could provide valuable information on retention of skills to determine whether motor learning was maintained. These limitations, overall, should not detract from the improvements G.D. made during this strength training program.
This case report supports the need to complete a randomized, controlled trial of strength training intervention, possibly followed by a functional intervention, compared with an intervention focused solely on strength training. While the assessments selected in this study demonstrated an ability to measure clinically significant changes, future research may use other outcome measures that demonstrate the potential to show change such as the Movement ABC, dynamometry or the School Function Assessment. Functional motor improvements in other children with DCD may occur in a similar fashion as demonstrated in this study; however, a larger, experimentally designed study will be needed before making this conclusion. Clinically, the trend in physical therapy has been to focus on activity-based intervention, but in some cases, a focus on high-frequency repetitive, isolated, simple joint movements may result in improved ability to combine movement over many joints and promote functional improvements in gross motor skills.
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