INTRODUCTION

Down syndrome (DS) is a chromosome abnormality and is one of the most common genetic causes of the developmental disabilities. Individuals with DS have three number 21 chromosomes instead of two in some or all cells. They have unique physical, neurological, musculoskeletal, sensorimotor, and learning and communication characteristics that can impact each other as well as the individuals’ ability to develop age appropriate skills. Individuals with DS tend to exhibit joint laxity, excessive hip abduction and external rotation, shoulder girdle instability, asymmetrical or excessive range of motion and difficulty initiating movement. They tend to avoid weight bearing, weight shifts and trunk rotation and have difficulty with equilibrium, balance, protective response and graded muscle movement. All of these factors contribute to the use of wide base of support in sitting and standing and delay in locomotion. Most children with DS walk independently between the ages of 2 and 3 years¹. Their developmental progress is variable as a consequence of a number of complicating medical factors. The relative rate of children’s progress is highly correlated with hypotonicity and the severity of cardiac defects^2,3.

Motor development in children with DS is similar to those normal developing children, but occurs at a much slower rate. Ligamentous laxity, decreased strength and hypotonia are thought to contribute to delays in motor development^3-5. Postural control problems in young children with DS have also been identified⁶. Slow postural responses to loss of balance lead to inefficiencies in maintaining stability. Such balance problems may result from higher-level postural control mechanisms. Children with DS also have lower scores on balance and agility tasks as well as on running speed, strength, and visual-motor control than do children with other mental impairments^7-10. Such problems may be related to delayed cerebellar maturation and a relatively small cerebellum and brainstem.

Weight-bearing exercises include any activity in which the feet and legs carry body weight. Walking, running, jumping, jumping rope, dancing, climbing stairs, jogging, aerobic dancing, hiking, inline skating/ice skating, racquet sports such as tennis or racquetball and team sports such as soccer, basketball, field hockey, volleyball and softball or baseball are some examples of weight-bearing exercises¹¹.

The purpose of this study was to examine the effect a program of weight-bearing exercises on static and dynamic balance in children with DS. The research hypothesis was that weight-bearing exercises could improve both static and dynamic balance in children with DS.

SUBJECTS AND METHODS

Subjects:

Twenty six children with DS were divided into two equal groups (study and control). The inclusion criteria were: 1. Children with medical diagnosis of DS with mild to moderate mental retardation (IQ from 36:67 according to Stanford Binet intelligence scale), 2. Age ranging from 2 to 5 years and 3. Children who were able to stand and walk. Exclusion criteria were: 1. Uncontrolled cardiovascular disease and 2. Orthopedic limitation to exercise such as hip, knee, foot or spinal deformities. All children were selected from Down syndrome Charitable Association (DSCA) in Riyadh, Kingdom of Saudi Arabia. Ethical approval was obtained from DSCA authority. Children’s parents were informed of all aspects of the study and were given their consents. The subjects' distribution is shown in table (1).

Table 1. Subjects distribution and places of their collection.

^*This association is located in Riyadh, Kingdom of Saudi Arabia.

Materials:

There were both evaluative and intervention materials. The evaluative materials were the balance subtest of the Bruininks-Oseretsky Test of Motor Proficiency (BOTMP).  The following materials were used to assess balance in the BOTMP: a. balance beam (25 cm height, 2.5 m long and 10 cm top surface taper to 15 cm wide base), b. stopwatch to measure the time, c. adhesive tape past on floor to make a straight line, d. stick and e. piece of texture to close eyes. In addition, a small ball was used to determine the preferred leg. The intervention materials were balance beam, stairs, spongy surfaces, foot ball, a basket, tilting board and an inclined surface¹².

The BOTMP has been widely used to assess motor proficiency for children with mental retardation^9,13. Based on several studies in motor development using factor analysis, the BOTMP was also reported as being technically dependable and as presenting favorable construct validity¹⁴.

Procedures:

The participated children underwent IQ examination before participating in the study. Each child was asked to kick a ball twice to determine the preferred leg. For assessing balance, each child was asked to do the following tests: 1. Standing on the preferred foot on a line drawn on the floor while looking at a target on the wall. 2. Standing on the preferred foot on a balance beam while looking at a target on the wall. 3. Standing as in item 2, except with eyes closed. In the previous items, both hands were on the hips and the free leg was flexed at the knee, the trial was stopped after 10 seconds and the time was then recorded. The trial was stopped before 10 seconds if the child touched the free leg to the floor, hooked the free leg behind the supporting leg or shifted the supporting leg out of place. 4. Walking forward on a line on the floor using a normal stride. 5. Walking forward on a balance beam using a normal stride. In items 4 and 5, both hands were on the hips. They were scored with a maximum of six steps. If the child placed one foot or both feet completely off the line or beam prior to six steps, the test was stopped and the number of the successful steps was recorded. 6. Walking forward on a line on the floor with a heel-to-toe gait. 7. Walking forward on a balance beam with a heel-to-toe gait. In items 6 and 7, both hands were on the hips. They were scored with a maximum of six correct steps. A step was incorrect if one foot or both feet were placed completely off the line or beam, the heel of the front foot failed to touch the toe of the rear foot, or the toe of the rear foot was moved forward to touch the heel of the front foot. 8. Stepping over response speed stick on balance beam: The child walked on a balance beam using a normal stride. Both hands were on the hips. The child stepped over a wand held by the examiner above the beam, at a height just below the knee. The trial was recorded as a failure if the child touched the stick firmly, swung the leg around the stick, or stepped off the beam.

All subjects were tested individually. As recommended in the BOTMP handbook, subjects wore either sneakers or crepe-soled shoes without regard to the height of the shoe. All directions were explained to each child via total communication, which involves speech, sign language, body language, facial expression and demonstration. To ensure that the instructions were understood, each child was permitted to practice trial for each item. The test was administered before and after 6 weeks of treatment for each child. According to the BOTMP, the first three items measure static balance with a total point score of 17 while the last five items measure dynamic balance with a total point score of 15.

Each child in the control group received the traditional physical therapy program that was applied by the physical therapists in the DSCA for one hour as follows: Approximation and strengthening exercises for 30 minutes followed by rest for 5 minutes. In addition, walking on an even surface in the treatment room and climbing stairs were provided for another 30 minutes (10 minutes each with 10 minutes rest in-between). Each child in the study group received approximation and strengthening exercises for 30 minutes followed by rest for 5 minutes. Instead of the second part of the traditional physical therapy program that was given to the control group, a weight-bearing exercises program was created for six weeks in which each week had distinct program that was applied for 30 minutes as follows. 1. Walking on an even surface in the treatment room in the 1^st week. 2. Walking on an uneven surface in the garden and climbing up and down stairs in the 2^nd week. 3. Climbing up and down stairs and walking on inclined surfaces in the 3^rd week. 4. Playing football then kicking a ball alternatively by each leg in the 4^th week. 5. Holding a ball, jogging 4 meters distance to put the ball into a basket then jumping forward from a circle to another circle in the 5^th week. 6. Walking on the tilting board then throwing a ball to the target while standing on the board in the 6^th week. This was followed by a home program that included climbing stairs and walking on uneven surfaces twice daily for 10 minutes each with 5 minutes rest in-between for both groups.

Data Analysis:

Static balance was determined by the number of seconds, up to a maximum of 10 seconds, the subject could perform in each of the three items. Dynamic balance was determined in items 4 through 7 by counting the number of steps, up to a maximum of six steps, taken during each item. Item 8 was rated as pass or fail. Raw scores were converted to point scores as described in the BOTMP manual. The total point score of static balance for each child was the summation of the point score of the first three tested items of the balance subtest. The total point score of dynamic balance for each child was the summation of the point score of the last five tested items.

The collected data were statistically analyzed to show the means and standard deviations of the scores in the static, dynamic and total balance for each group before and after 6 weeks of intervention. Then, a comparative study was conducted between the mean differences of the pre-intervention measures and post-intervention measures for static, dynamic as well as total balance for each group by using the Wilcoxon test to show the statistical difference at 0.05 level. Last, a comparative study was conducted between the mean differences in the two tested groups for each tested item and for the total balance score by using the Mann-Whitney test to show the statistical difference at 0.05 level before as well as after 6 weeks of intervention.

RESULTS

When comparing the pre-intervention mean values of static, dynamic as well as total balance for the study group with that for the control group by using Wilcoxon test, the results revealed non-significant difference (p=0.088, 0.999 and 0.554 respectively). On the other hand, when comparing the post-intervention mean values of static, dynamic as well as total balance for the study group with that for the control group by using Wilcoxon test, the results revealed significant difference (p=0.006, 0.002 and 0.002 respectively) (Table 2 and Fig. 1).

Mann-Whitney test  showed a non-significant difference of static balance when comparing pre-intervention mean values with that of the post-intervention for the study group as well as for the control group (p=0.129 and 0.125 respectively). On the other hand, when comparing the pre-intervention mean values with that of the post-intervention for both the dynamic balance and total balance for both the study and control groups separately, the results revealed a high significant difference (p=0.000 and 0.000 respectively) for the study group and a significant difference (p=0.007 and 0.002 respectively) for the control group (Tables 3 and 4).

Table 2. Comparison between study and control groups in balance measures.

SD: Standard deviation.                              Min.: Minimum.                                           Max.: Maximum.

* Significant                                               Pre: pre-intervention.                                    Post: post-intervention.

Table 3. Comparison between pre and post intervention in study group.

SD: Standard deviation.                              Min.: Minimum.                                           Max.: Maximum.

^*Significant.                                                Pre: pre-intervention.                                    Post: post-intervention.

Table 4. Comparison between pre and post intervention in control group.

SD: Standard deviation.                              Min.: Minimum.                                           Max.: Maximum.

^* Significant.                                               Pre: pre-intervention.                                    Post: post-intervention.

Figure 1. Balance measures before and after six weeks of intervention for both study and control groups.

DISCUSSION

The results of  the present study revealed non-significant difference between the pre-intervention mean values of static, dynamic as well as total balance for  both study and control groups  (P=0.088, 0.999 and 0.554 respectively). On the other hand, when comparing the post-intervention mean values of static, dynamic as well as total balance for the study group with that for the control group, the results revealed significant difference (P=0.006, 0.002 and 0.002 respectively). When comparing between pre-intervention mean values with that of the post-intervention for the study group as well as for the control group, the results showed  non-significant difference of static balance (P=0.129 and 0.125 respectively). Regarding dynamic and total balance, when comparing the pre-intervention mean values with that of the post-intervention for both study and control groups separately, the results revealed a high significant difference (P=0.000 and 0.000 respectively) for the study group and a significant difference (P=0.007 and 0.002 respectively) for  the control group.

The results are consistent with previous reports of balance problems in other studies of children with DS. The neuropathology associated with children with DS included delayed cerebellar maturation and a relatively small cerebellum and brain stem. The problems noted in balance, running speed (as related to motor planning) and coordination (as measured by reaction times) in the children with DS may be related to neuropathological causes¹⁵.

The results of this study revealed that children with DS are able to significantly improve their walking behavior on the balance beam following active task-specific practice. They modified their use of dynamic resources to achieve levels of stiffness and impulse similar to their peers without DS. Functionally, balance may be a problem for the older child with DS who must be able to perform in situations in which his or her center of gravity is routinely perturbed (e.g., crowded school hallways, shopping malls, city streets, playgrounds, and other recreational areas). The results of the present study concurred with others who suggested that techniques that involve proprioceptive, vestibular, and visual input might be beneficial to children with DS¹¹.

Wang and Ju¹⁶ reported significant improvement on scores for floor walk, beam walk and horizontal and vertical jumping by subjects with DS. LeBlanc et al.⁷ found that children with DS whose mean age was 12 years had difficulty with static balance when they were compared with children matched for chronological age and IQ. Shea⁵ assessed a group of 11- to 14-year-old children with DS using the Peabody Developmental Motor Scales and found that static balance was the area in the test of greatest difficulty in gross motor skills.

Shumway-Cook and Woollacott⁶ found that postural responses to loss of balance were slow in young children (1-6 years of age) with DS, and they concluded that these responses were inefficient for maintaining stability. They also stated that the presence of the monosynaptic reflex during platform perturbations suggested that balance problems in children with DS do not result from hypotonia, but rather from defects within higher-level postural control mechanisms.

Henderson et al.⁸ has reported that children with DS have more difficulty with balance tasks than children with mental retardation but without DS. Their findings supported the findings of the present study because there were significant differences in balance scores between the two groups.

The rate of balance change in this study seems notable. Previous studies have reported that improvement in gross motor skills occurred at a slower rate in children with DS over the age of 3 years¹⁷. Yet in this study, significant improvement in postural stability was found within short period for less complex skills and within six weeks of intervention with weight-bearing exercises for more challenging skills.

One of the outcomes of an 8-week muscle-training program on the muscular fitness and gait characteristics in children with DS was increasing postural stability with smaller medio-lateral sway of the body center of mass and less toe-out during the gait cycle¹⁸. Stability enables the child to develop coordinated mobility throughout his body and to use his arms and hands for object exploration and manipulation. Stability in these areas, as well as in the head and neck, facilitates oral-motor, feeding, expressive communication skills. The program of intervention could include the following: Balance, equilibrium, and protective reactions, vestibular functioning (i.e., the ability to orient our self when you move your head or body; to maintain a stable position),  muscle tone and strength, joint and postural stability, weight bearing, weight shifts, trunk rotation, sensory awareness and processing, sensorimotor integration, awareness of the body in space, bilateral integration, positioning and position transitions, locomotion, abdominal strength (these muscles are the central control area for postural stability, respiration, and breath support of speech). It is important to work closely with a pediatric physical therapist and/or occupational therapist to facilitate normal skills, to improve the quality of these skills, and to decrease abnormal skills¹.

Weight-bearing exercises provide improved and more consistent proprioceptive feed-back that in turns improves control of movement. Functional weight-bearing exercise programs have been shown to have effects on balance, gait, and lower-limb strength among subjects with moderate or no cognitive and physical impairments. On other hand weight-bearing exercises allow for reactivation of the proprioceptors, whose role is to sense the amount, speed and timing of joint positioning¹⁹. In a closed chain environment, proprioceptors respond to such extrinsic factors as change in terrain, footwear, ground reaction forces, speed and direction of activity. The patient needs to be placed in an environment that is biomechanically and clinically safe to induce proprioceptive enhancement via closed kinetic chain exercises²⁰.

Jumping activity might be added to the program of treatment to effectively evoke the automatic and dynamic postural control. Moreover, the floor-walk and beam walk performances might be improved due to the transferred effects via the practice of dynamic jumping activity²¹. In addition aerobic conditioning and strength training for a child with DS displayed not only gains in cardiovascular variables and strength measures but also demonstrated improved balance, coordination and power in gross motor tasks²².

The areas in which the children with DS performed poorly—running speed, balance, strength, and visual motor skill control—suggested that the child with DS may continue to have neurological problems far beyond the preschool period and into adolescence. The present study has shown that differences in the balance parameters existed between the study and the control groups. Therefore, the child with DS may need weight-bearing exercises to improve balance in addition to traditional physical therapy as a part of his special education programming to address his particular motor skill needs.

Conclusion

Results of the current study showed that improvement in postural stability of children with DS, aged 2 to 5 years, is possible through relatively short-term use of weight-bearing exercises. These results suggest that clinicians should consider the use of weight-bearing exercises for preschool-age children with DS as a way of improving their overall functional mobility.

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