Introduction
taxic cerebral palsy, which accounts for 5%-10% of the patients with cerebral palsy [1], is caused by damage to the cerebellum and is characterized by balance and coordination problems. Involuntary tremor, clumsiness, and poor instability in the proximal joints are other signs of this disease [2]. Therefore, teaching balance skills is an integral part of the rehabilitation program for these patients. So far, various interventions have been employed in postural control and balance abilities for children with ataxic cerebral palsy. The most widely-used interventions are neurodevelopmental treatment, reactive balance training, treadmill training, and visual feedback training [3]. Rehabilitation of children with cerebral palsy is often challenging for therapists due to their insufficient motivation to receive rehabilitation interventions and lack of careful progress monitoring. Therefore, the tool of choice for the rehabilitation of these children should be fun and increase their motivation to receive rehabilitation. 
The use of Virtual Reality (VR) is more fun for children than conventional exercises, and their motivation to participate in a VR-based rehabilitation program is far greater than in a conventional training program [4]. The Wii Balance Board (WBB) is a portable and accessible tool for VR-based balance training. The studies on the effectiveness of WBB in balance training of children with cerebral palsy have shown that the use of this device has a much greater impact on increasing the balance of these children compared to conventional balance training due to the presence of visual feedback, more motivation and recording the amount of change quantitatively [5]. This device can also make intervention easier for occupational therapists and reduce physical pressure [6, 7]. Various studies have proved the effectiveness of WBB on balance indicators in people with different physical problems, such as acquired brain injury, developmental coordination disorder, Down syndrome, and spastic and dyskinetic cerebral palsy [8, 9, 10, 11, 12]. WBB can improve static and dynamic balance [5, 13 ,14 ,15] and independence in performing activities of daily living in children with spastic and dyskinetic cerebral palsy [5]. However, there is very little and or unreliable scientific evidence on the effects of WBB in people with ataxic cerebral palsy. The study of the long-term effects of WBB requires further research [8]. Therefore, this study aims to assess the effectiveness of WBB and the persistence of its impact in children with ataxic cerebral palsy.
Materials and Methods
This research is a preliminary study (single-case study) with a pre-test, post-test and follow-up design conducted from April to December 2019 on 3 children with ataxic cerebral palsy Mean±SD age= 10.56±1.09 years) who were selected using a purposive sampling method. The inclusion criteria included the diagnosis of ataxic cerebral palsy, being at level 1 or 2 of motor function based on the Gross Motor Function Classification System (GMFCS), no history of fractures, and lower extremity surgery during the past six months, according to the family report, adequate cognitive ability to participate in WBB-based activities (ability to attend school or score above 70 in the Sparkle test). After explaining the research process and intervention method to the parents of children, their written informed consent was obtained. All three children received routine occupational therapy three sessions per week throughout the study. The duration of sessions in the baseline and follow-up phases was 45 minutes. In the intervention phase, the duration of sessions was 25 minutes, followed by balance training by the WBB for 12 weeks, three times a week, each session for 20 minutes (12 hours).
WBB is a device connected to a far-enough monitor. The results of displacement of the Center of Pressure (CoP) on the WBB were displaced in the monitor. During the intervention process, the child tried to control the CoP displacement by using visual feedback information. The child performs dynamic balance exercises by changing the center of gravity in different directions and static balance exercises by maintaining the center of gravity at a fixed point. The therapist also monitored the intervention process and provided progressive balance training by giving verbal feedback when needed and coordinating the difficulty of each exercise with each participant’s balance abilities.
The outcome of the intervention was measured by Pediatric Balance Scale (PBS) and Timed Up and Go (TUG) test three times in the baseline phase (before the intervention), three times in the intervention phase (at the end of 12th, 24th, and 36th sessions) and two times in follow-up phase (one and two months after the intervention). It should be noted that all assessments were performed by an occupational therapist unaware of the study process.
Results
Results of PBS and TUG test in the baseline, intervention, and follow-up phases are presented in Table 1.


Findings from visual analysis of graphs for all three subjects (Figures 1 and 2) showed that balance training by WBB in the intervention and follow-up phases improved their functional balance compared to the baseline. The Percentage of Nonoverlapping Data (PND) in both tests was 100% for all children. The Hedeges’ g value for all children was above 0.8, indicating a significant difference between the baseline and follow-up results (Table 2).


According to the 2SD (2 standard deviations) method, the results of PBS in the intervention and follow-up phases were greater than the sum of the mean and twice the standard deviation of its results in the baseline, indicating a significant improvement in PBS score in all three children. The results of the TUG test in the intervention and follow-up phases were less than twice the standard deviation of the test result in the baseline, indicating a significant reduction in the duration of the TUG test in all three children (Table 3).


Discussion and Conclusion
The purpose of this pilot study was to investigate the effect of balance training with WBB on the functional balance of 3 children with ataxic cerebral palsy and also to evaluate the stability of the effect one and two months after the intervention. The functional balance variable was measured by PBS and the TUG test. The results showed significant changes in the functional balance of children during the intervention period and the persistence of these effects up to two months after the intervention. These results are consistent with studies on the impact of WBB on balance indicators in different types of cerebral palsy [8]. For example, the results of Tarakcy et al. [5, 14] and Gatica et al. [13] on the effectiveness of using WBB in teaching balance to children with cerebral palsy suggested an efficient method for teaching balance to children with spastic and dyskinetic cerebral palsy. Another study by Silva et al. on a child with ataxic cerebral palsy showed that using WBB in combination with kinesiotherapy interventions improved balance in this child [16]. Therefore, balance training by WBB can effectively improve balance in different types of cerebral palsy.
A study conducted by Gatica et al. on four children with spastic cerebral palsy showed that six weeks of WBB-based balance training intervention consisted of three 25-min sessions per week (7.5 hours) significantly improved children’s functional balance based on the TUG test results, but it did not affect the static balance of children based on One-Leg Stance Test (OLST) results [17]. Another study by Tarakcy et al. on 12 children with spastic cerebral palsy and three children with dyskinetic cerebral palsy found that 12 weeks of balance training by the WBB, 2 sessions of 40 minutes per week (16 hours) significantly improved the static balance of participants according to the OLST test [14]. The discrepancy in the results of two different studies can be attributed to the different duration of balance training interventions. Since the base of support of a person in the OLST test is smaller than in functional balance tests such as the TUG test, its implementation requires higher levels of balance indicators [14]. Therefore, more time is needed to improve a person’s performance in the OLST test. Hence, we suggested that in future studies, the effects of intervention by WBB on the static balance of children with ataxic cerebral palsy be investigated at appropriate durations.
The results of PBS in our study showed that child No. 2 with GMFCS level 2 showed no progress in the last four weeks of the intervention phase. We even witnessed the reduction of PBS score in this child between the first and second months of follow-up. However, children No. 1 and No. 3, both with GMFCS level 1, not only progressed throughout the intervention phase but also maintained their progress for up to two months after the intervention. Therefore, the effect of balance training by WBB on children with ataxic cerebral palsy and GMFCS level 1 may be more significant and more lasting than its effect on children with ataxic cerebral palsy and GMFCS level 2. It should be noted that these differences were not observed in the results of the TUG test. Further documented studies in this field can provide more information.
Based on the observations during the research process, the motivation of the children to receive interventions in the initial sessions was much higher and gradually decreased during the implementation process. This finding indicates the limited number and visual aspects of the exercises. Although exercises by WBB are more motivating and fun for children than conventional occupational therapy exercises, for longer use of such tools, it is better to consider the greater variety and more attractive graphics for them. According to the parents of children, the WBB-based balance training also improved their ability and independence in some of their daily activities, including games that require gross motor function and bathing tasks. Tarakci et al. also found that balance training by the WBB can increase the independence of children with cerebral palsy in their daily activities [5]. Therefore, it is recommended that the effect of WBB-based interventions on the ability to perform daily living activities in children with ataxic cerebral palsy be examined more comprehensively in future studies. Some of the limitations and disadvantages of the present study were the preliminary nature of the study, the impossibility of generalizing the results to all children with ataxic cerebral palsy, the relatively high cost of the device, the impossibility of providing the device for all rehabilitation centers, and the small number of samples.
Balance training by the WBB can effectively improve the functional balance of children with ataxic cerebral palsy. These results can be used as a basis for conducting clinical trial studies with an appropriate sample size to evaluate the effects of this technique on children with ataxic cerebral palsy.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles are considered in this article. The participants were informed about the purpose of the research and its implementation stages. They were also assured about the confidentiality of their information. They were free to leave the study whenever they wished, and if desired, the research results would be available to them.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 

Authors' contributions
All authors equally contributed to preparing this article.

Conflict of interest
The authors declared no conflict of interest.

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