1. Introduction
he health sector is the largest employment sector in most countries, with the majority of the workforce being women. One of the characteristics of working in a hospital is that all tasks are performed manually, which causes early onset of musculoskeletal disorders among its staff. Today, the prevention of musculoskeletal disorders has become a national necessity and priority in most countries [1]. 
Many studies have shown the importance of core muscle stability in human movements [2]. Core muscle strength and endurance seem to be one of the important prerequisites for most daily activities [3]. It is also believed that the weak core area causes changes in energy transfer and, as a result, reduces performance and increases the risk of injury to weak muscle groups [4]. Recently, core area exercises have been used by trainers as an intervention to prevent and treat injuries, as well as to correct the posture and spine [5].
The ability of individuals to maintain balance is essential for almost all daily activities [6]. Movement assessment allows health professionals to observe motor defects, asymmetry, and muscle balance [7]. Limb asymmetry increases the risk of injury; hence, it seems that before participation in any training programs there is a need for performance assessment [8]. Functional Movement Screen (FMS) method is a way to initially evaluate motor performance and help identify asymmetry, muscle imbalance, and other injury risk factors, and can easily measure the state of neuromuscular coordination [9, 10, 11]. FMS is a fast, non-invasive and inexpensive test that is easy to use and emphasizes the quality of the movement pattern [1, 12]. Although the FMS test is more commonly used to screen athletes, it may also be used on non-athletes to assess their weaknesses in movement. The present study aims to evaluate the effect of core stability exercises on functional performance and balance of female staff in hospitals.
2. Methods
The study population included all female employees of Imam Khomeini Hospital aged 30-50 years. Based on the inclusion criteria, 60 were selected using a convenience sampling method and randomly divided into two groups of exercise and control. For 12 weeks, the exercise group entered performed core stability exercises while the control group engaged in their daily activities. Subjects underwent FMS, performance screening, and balance tests before and after the exercise period. For this purpose, first the height and weight of the subjects were measured in centimeters and kilograms. Then, Y-balance test for dynamic balance, Agility T-Test for agility, seated forward bend for flexibility, Vertical Jump Test for body power, 20-m running test for Speed, and FMS for movement performance were carried out. Good Intra-rater and inter-rater reliability have been reported for FMS [13]. The total score of FMS is 21; a score less than 14 indicates that a person is prone to injury [14]. The core stability exercise protocol was according to Jeffreys [15]. After the end of exercise, the above mentioned tests were carried out again. It should be noted that the number of samples studied was reduced from 60 to 34 due to lack of cooperation. To analyze the collected data, first the paired test was used to show whether the post-test scores of each group were different from their pre-test scores. Then, in order to investigate the between-group difference, the effect of the independent variable (core stability exercise) on the dependent variables was examined using the analysis of covariance (ANCOVA) to determine whether the intervention, without interacting with the confounding factor (pre-test score), could have a significant effect on the dependent variables or not.
3. Results
The results of paired test showed that after 12 weeks of core stability exercise, there was a significant difference in the scores of test between the pre-test and post-test phases in the exercise group, such that the scores earned in the post-test phase were significantly higher than the pre-test scores for all variables (p<0.05). In the control group, there was no significant difference (p>0.05). In order to investigate the effect of central stability exercises on dependent variables, ANCOVA was used to for assessing between-group differences. It requires that the assumptions of homogeneity of variances, linearity, and homogeneity of regression slopes be observed in the study variables. The results showed that the assumption of homogeneity of variances, homogeneity of regression slopes (p>0.05), as well as the assumption of linearity of the correlation between the covariate and the independent variable (p<0.05) were confirmed in all study variables. The results of ANCOVA related to post-test scores showed that the significance level was less than 0.05; hence, the mean difference between the groups in the post-test phase was significant after controlling the possible effect of the pre-test score (Table 1). 


Therefore, as can be seen, core stability exercises had a significant effect on all study variables (p<0.05).
4. Discussion and conclusion
The purpose of the present study was to investigate the effect of a core stability exercise program on functional performance and balance in women aged 30-50 years working in a Hospital. The results revealed that 12 weeks of core stability exercise improved their functional performance, dynamic balance and other fitness factors such as speed, power, agility and flexibility in women. Regarding the effect of core stability exercises on the improvement of functional performance, our findings are consistent with the findings of many previous studies. Goss et al. showed that during a six-week functional training program, a significant increase in FMS score was observed [16]. Kiesel et al. also concluded that a period of training program increased FMS scores in 51.6% of football players [17]. Shirey et al. stated that voluntary activation of the core muscles had positive effects in reducing the risk of limb injuries [18].
Because balance in the motor chain relies on movement and feedback strategies, facilitating simultaneous contraction of the muscles around the lumbar vertebrae, such as oblique muscle, transverse abdominis, and erector spinae muscles, may increase the stability of vertebrae [19, 20]. The results of the present study are consistent with the results of Johnson et al. and Carpes et al. regarding the significant effect of trunk muscle strengthening exercises on improving dynamic balance [21, 22] as well as the findings of Imai et al., Carr and Shepherd, Samson, and Abdi and Sadeghi who reported the effect of core stability training program on dynamic balance [23, 24, 25, 26].
It can be concluded that the core stability exercise program used in this study is a proper method with no complications and can improve the efficiency of the neuromuscular system. This causes optimal movement of the spinal, pelvic, and hip joints along the motor-function chain; proper muscle balance, enhanced proximal stability and functional strength, and ultimately reduces the risk of injury.

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 study was extracted from a research project approved by Tehran University of Medical Sciences. 

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

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors would like to thank the participants and the personnel of Imam Khomeini Hospital in Tehran for their cooperation


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