1.    Introduction
Postural stability is compromised with increasing age (4). As a result, assessment of postural sway allows healthcare professionals to evaluate neuromuscular condition and safety. Strengthening the muscles of the central region of the body improves the functional ability of the body (10), leading to better performance of daily activities and greater psychological independence for the elderly (11). The discussion about the symmetry of postural sway is interesting because the body's organs must have complete coordination to achieve balanced and smooth movement (12). On the other hand, in many cases, asymmetry is considered a factor in walking pathology, and studies that assume walking symmetry may encounter challenges in interpreting their results (11). Therefore, accepting the symmetry or asymmetry of postural sway in healthy individuals is important for physicians and for studies evaluating walking, designing orthoses and prostheses, and designing rehabilitation protocols for pathological walking (12). The present research aims to compare the symmetry of postural sway while maintaining static balance in elderly women with and without poor central stability. Given that the elderly, particularly elderly women, are prone to osteoporosis, balance and symmetry of postural sway are important for maintaining physical stability. Additionally, maintaining proper posture is necessary for most daily activities, especially walking. Conducting this research can increase awareness about the importance of correct posture, particularly in the elderly, and help prevent or ameliorate the risks associated with poor central stability.
2.    Methods
The method of this study is an applied and developmental, and comparative causal type. The statistical sample of the study was made up of 16 elderly women over 55 years of age, who were selected using available and targeted sampling. The FMS test (13) was used to place individuals into two groups with and without central stability. In this study, the stability of the central region of the body was chosen as an independent variable, and the symmetry of postural sway (in the mediolateral (ML), anterior-posterior (AP), and total directions) on both sides of the body was selected as the dependent variables of this study. Subjects were placed on the force plate to perform balance analysis, and their postural sway was evaluated in ML, AP, and overall directions according to the protocol described in the balance evaluation process section (14). The balance status of the individuals was processed, and the balance index was obtained using MATLAB software. Independent t-tests were used to compare groups using SPSS version 26 statistical software (P < 0.05).
3.    Results
The investigations showed that the postural sway of the left supporting leg in the ML direction (to the medial side) and the right supporting leg in the AP direction (to the posterior side) were relatively higher in the group of elderly women with instability in the central region. Additionally, the average index of imbalance in the left and right limbs in both ML and AP directions in two groups of elderly women with and without central stability showed the greatest difference in the ML direction of the right leg (0.77 cm). Comparing the balance asymmetry index percentage in the group of elderly women with and without central instability also showed the greatest asymmetry in the ML direction (32.65%).

4.    Conclusion
From the results of this research, it can be stated that there is a significant difference between elderly women with and without central stability weakness in the symmetry of postural fluctuations while maintaining static balance. The results of the regression test in the study of Ramesh et al. (2020) showed that the measurement of sway, which has a high correlation with the reaction time of people, can help in identifying the elderly who are at risk of falling (15), and these findings are in line with the present study. They stated that height sway in the ML direction has a lot to do with the risk of falling. The increase in sway in this direction can be caused by the decrease in the tone of hip abductor and adductor muscles in the elderly (16). It is clear that with increasing age, muscle strength decreases, not only in the radial muscles but also in the axial muscles of the trunk, such as the muscles of the central region, and it increases body fluctuations and may cause disturbances that lead to body balance. As a result, the elderly without poor central stability have stronger central muscles, and their balance and posture control are also better. Therefore, it is possible to improve people's central stability by performing proper physical exercises (17,18). In addition, anatomically, the central area of the body is the area where the center of gravity is located and movements originate from there (19). Therefore, it seems that considering that there is a significant difference in the symmetry of postural sway while maintaining static balance between elderly women with and without poor central stability, the neuromuscular system of the elderly without poor central stability is more efficient and the displacement of the center of gravity is outside the surface and their level of reliance and sway is less. According to the results of the present research, it can be said that poor central stability has an effect on the symmetry of the postural sway while maintaining the static balance of the elderly, and considering that the asymmetry in the postural sway has a direct relationship with the loss of balance and the increase in the rate of falls, daily exercises of the elderly should include exercises that lead to an increase in central stability and, as a result, improve their physical condition. They can benefit from these exercises along with other programs aimed at preparing, rehabilitating, and improving the performance of the elderly. However, more research is needed in this area.

Ethical Considerations
Compliance with ethical guidelines
There were no ethical considerations to be considered in this research.
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 article.
Conflicts of interest
The authors declared no conflict of interest.