Introduction
The knee is a large, functional joint that is often injured. A pressure equal to 3 to 4 times the bodyweight had applied to the knees during walking and running [1]. Among the various injuries to the body, the knee had injured in many activities, especially in activities that involve heavy physical impact or when an extra load had applied to the legs. These injuries are due to the knee’s position in the lower limb and its simple hinged structure [3]. Common injury assessment and rehabilitation procedures in athletes with lower limb injuries are usually performed by the balance test of standing on one leg (healthy leg) [5].
As a functional ability, balance is essential for performing more daily activities. Impaired gait and balance increase the risk of falls, which can cause a variety of injuries [6]; Therefore, it is necessary to pay attention to strengthening the balance in people and athletes, so increasing the amount of balance in these people can improve balance performance and posture [7]. Water training also allows the patient to perform training and physical activity with no pain. The buoyancy, hydrostatic pressure, and viscosity of water, due to their properties, reduce the weight borne by the individual and thus reduce the compressive forces on the joint surfaces and subsequently prevent the progression of destructive damage. In addition, it provides a suitable environment for easy and comfortable movement of this group of people [8].
Due to the contradictory research in water therapy training on the knee and the unclarity of the exact effect of shallow water training on balance, further research in this area is necessary. This study aimed to evaluate the effect of 8 weeks of shallow water training on the static balance of soldiers with knee injuries.
Materials and Methods
The method of the present study is quasi-experimental in experimental and control groups as pre-test and post-test. A total of 46 members of NEZAJA, North Khorasan Province, who had knee injuries in 1400, were randomly selected and voluntarily participated in this study. Subjects had randomly divided into experimental and control groups of 23 people. Subjects entered the research after completing the consent form and obtaining information about the nature and manner of cooperation.
The knee limb injury collection form had used to assess lower limb injuries, and the stork balance test had used to assess static balance. To analyze the data, Spss software v. 22 had used at a significance level of 0.05. Descriptive statistics (Mean±SD) and inferential statistics (Shapiro-Wilk test had used to measure the normality of the data and dependent t-test had used to analyze the data within the group, and an independent t-test had used to analyze the intergroup data) had used to analyze the results.
Results
The dependent t-test and independent t-test results in Table 1 show that the balance in the experimental group was significantly different between pre-test and post-test (P=0.001).


However, there was no significant difference between pre-test and post-test in the control group’s static balance (P=0.393). Also, the results were significantly different between the experimental and control groups (P=0.001).
Discussion
This study’s results had concluded shallow water exercising is significant on the static balance of soldiers with knee injuries. This may indicate that shallow water training is more effective, so water training can be recommended to improve static balance in people with knee injuries.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles were 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; Moreover, They were allowed to leave the study whenever they wish, and if desired, the results of the research 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 contributed equally in preparing all parts of the research.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The cooperation of the Brigade Command, the Brigade Command and the dear personnel who participated in this research and provided the necessary assistance in achieving this research is appreciated.