Introduction
Osteoarthritis is one of the most common joint diseases and the main cause of disability in the elderly, which increases with aging [1]. The prevalence of osteoarthritis in Iran is 11.8%, and 69.4% of those suffering from it have this disease in their knee joints [2]. Due to bearing high pressures during daily activities, the knee is the most prone joint to this osteoarthritis [3]. The prevalence of this disease in the medial part of the knee is more common than the lateral part [4]. Knee osteoarthritis causes physical, psychological, social and economic pressure and stress and can cause a significant inability to perform daily activities [5].
Exercise therapy can be used as an effective method to reduce complications and improve the functional activities of patients with knee osteoarthritis [15, 16, 17]. This method can lead to the prevention of muscle atrophy and increase in muscle strength, range of motion of joints, and balance [15, 18]. Exercise therapy reduces joint pain and stiffness and increases the patient’s ability to move and be more active; as a result, the ability to perform functional activities and the quality of life increase [19]. Despite the report of positive cases related to the effect of exercise therapy in dry land on reducing the complications of knee osteoarthritis, it is sometimes accompanied by pain and leads to the unwillingness of the elderly to this type of exercise. Therefore, hydrotherapy has been recommended as one of the most important exercises for managing this disease. It has many benefits for the elderly; it can lead to the improvement of their physical performance and mental conditions [21]. A study showed that exercise in water improved the results of 6-min walk test and 30-second chair stand test in patients with knee osteoarthritis [24].
Methods
This study was conducted in Isfahan, Iran in 2018. Participants were 54 women with knee osteoarthritis aged 60-69 years (height=159.96±5.53, weight=76.93±9.50) who were selected using a purposive sampling method and based on the inclusion criteria, and were randomly divided into two groups of hydrotherapy and land-based exercise. In the pre-test phase, the height, weight and characteristics of each subject were recorded. After providing explanations, they were asked to perform functional tests (Timed up and go test, 30-second chair stand test, 40-m fast-paced walk test, stair climb test, and 6-min walk test). The exercises in land and water were performed for 8 weeks, 3 sessions per week, each for 60 minutes based on the protocol proposed by National Academy of Sports Medicine which includes four stages of inhibition, lengthening, activation, and integration. Repeated mesures ANOVA was used for assessing differences based on measurement time (pre-test and post-test) and type of exercise (group). It evaluates the effects of time and group and their interaction effect. Data were analyzed in SPSS v. 26 and the significance level was set at 0.05.
Results
The results of the repeated measures ANOVA for functional 5 tests showed that the effect of time was significant (P≤0.05), but the effect of group and the interaction of time and group was not significant (P≥0.05). Figure 1 illustrates the changes in timed up and go (TUG) test scores in two groups. As can be seen, in both groups, the time of performing test decreased after exercise which indicates that patients were faster in performing this test and their functional activities including standing up, walking, turning back and sitting were improved. There was no significant difference between the results of the two groups in the post-test phase (P≥0.05).
The changes in the scores of other four tests were all similar to those of TUG test (Figure 2). It can be said that after participating in hydrotherapy and land-based exercise, the improvements occurred in both groups in the scores of 30-second chair stand test (CST-30), 40-m fast-paced walk test (FPWT-40), stair climb test (SCT), and 6-min walk test (6WT) (P≤0.05). There was no significant difference in the results of CST-30, FPWT-40, SCT, and 6WT between the two groups in the post-test phase (P≥0.05).
Discussion
The results of this study showed that hydrotherapy and land-based exercise led to significant changes in the scores of TUG, CST-30, FPWT-40, SCT, and 6WT in older women with knee osteoarthritis. There was no significant difference between the results of the two methods. This indicates that functional performance of women increased after exercise therapy both in land and water. Considering the spread of the coronavirus and the closure of pools for hydrotherapy of these patients, the use of land-based exercises can be of great help to the older women suffering from knee osteoarthritis. It is recommended that this study be conducted on older men with knee osteoarthritis and the results be compared with the findings of the present study.
Both hydrotherapy and land-based exercise can improve the functional performance oof older women with knee osteoarthritis in timed up and go test, 30-second chair stand test, 40-m fast-paced walk test, stair climb test, and 6-min walk test. These methods can be used to improve physical performance and various abilities of older women with knee osteoarthritis in performing functional activities.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles are considered in this article. The participants were informed of 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
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-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.
 

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