1. Introduction
ntellectual Disability (ID) is a complex disorder that is difficult to define precisely. This disorder significantly impairs the functioning of affected people in all areas of their lives and affects their minds and spirit. This disorder disrupts both the “self-concept” and “interpersonal relationships” approaches and significantly reduces the quality of coexistence of these individuals in society [1]. Researchers study the human development process from different aspects, which has led to creating different areas for further research. One of the most important fields of study created in this area includes body postural control [3].
The ability to control different body positions in space is due to the complex interaction of the nervous, sensory, and musculoskeletal systems, which is generally defined as the postural control system. Movement limitations and problems with balance and gait are high in people with intellectual disabilities [2]. On the other hand, for most functional tasks, the body’s vertical orientation must be maintained; therefore, several sensory systems are used in this process. The vestibular system is used to control the force of gravity. The proprioceptive system is used to control the base of support, and the visual system is used to control the relationship between the body and objects in the environment [5]. Therefore, this study aimed to compare postural control between different age groups in girls with intellectual disabilities.
2. Materials and Methods
The present study was a causal-comparative study whose data were quantitatively measured. Measurements were performed in exceptional schools of students with mental disabilities in Gilan Province. It should be noted that all measurements were performed equally. The statistical population of this study included all female students with intellectual disabilities in Gilan Province. Due to the limitations in selecting subjects, this study’s statistical sample included 60 female students with intellectual disabilities in the age groups of 7-9, 10-12, and 16-18 years who were randomly and purposively selected and evaluated. Then, to evaluate the subjects’ ability to control their standing position, a postural control test was performed on them in four different sensory positions.
The four sensory positions in this test were as follows: the first position, standing on one foot on a stable surface with open eyes; the second position, standing on one foot on an unstable surface with open eyes and head hyperextension; the third position, standing on one foot on a stable surface with eyes closed and head hyperextension; the fourth position, standing on one foot on an unstable surface with eyes closed. Each stage of the test was performed in 20 seconds, and the number of errors made was recorded as the subject’s score in that stage. In this study, the Shapiro-Wilk test was used to evaluate the data’s normality, and descriptive statistics indices (Mean±SD) were used to describe the data. Inferential statistical indices (such as one-way ANOVA and Bonferroni post hoc test) were used to analyze the data by SPSS software, V. 21 at the level of P<0.05.
3. Results
To analyze postural control data in the study groups, the Bonferroni post hoc test was used. This test confirmed no sensory interference in the first position, and all three sensory systems of the subject (visual, vestibular, and proprioceptive systems) were available.
The results of the three groups’ significant differences in postural control scores were P=0.043, P=0.005, P=0.003, P=0.000. Based on the results, there was a significant difference between the first, second, and third positions between the first and third groups and between the second and third groups (P<0.05).
4. Discussion and Conclusion
According to the results of this study, in children with intellectual disabilities, sensory systems in terms of organization and integration continue to develop and mature until the age of 16-18, and the central nervous system, by receiving information from the proprioceptive system, provides better postural control. This study revealed a significant difference between the first and third groups in the first position, where no sensory manipulation was performed, and all three systems were available to the individual. Observation of postural control scores in Table 1 confirmed that the development and maturity of the proprioceptive and visual systems were insignificant in the first and second groups, but in the third group, there was significant development and maturity. 


However, the vestibular system’s rate of development and maturity was noticeable among all three age groups. Since postural control scores were not the same in all four positions in the three age groups, the results obtained in this section were consistent with different results. The results of this study and other similar studies confirm that each of the visual, somatosensory, and vestibular systems that play an essential role in postural control in people with intellectual disabilities are constantly developing and maturing (up to the age of 16-18) in terms of organization and integration with other postural control systems. On the other hand, in all three age groups studied, the central nervous system provided better postural control based on somatosensory information.

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 and were free to leave the study whenever they wished, and if desired, the research results would be available to them.

Funding
The paper was extracted from the MA. thesis of the first author, Department of Sport Sciences, Faculty of Physical Education, University of Guilan, Rasht.Also, This study was conducted in collaboration with the Exceptional Education Department of Gilan Province. 

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

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgement
All author would like to thank all the participants and the principles of exceptional schools in Gilan province for their collaboration.


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