Among the musculoskeletal diseases of middle-aged females, problems such as arthritis, disc, and osteoporosis are emerging, and among these, pain and diseases occurring in the knees and lower back in particular account for the highest proportion. The main causes of musculoskeletal diseases in middle-aged females are lack of exercise and weight gain, and in middle-aged females, weakened muscle strength increases the incidence of exercise-induced injuries and adult diseases [1]. In particular, weakening of the lower extremity muscles causes instability in the joints, which leads to knee diseases [2].
Severe knee pain or disease is recognized as a major cause of lowering the quality of life by limiting physical activities such as walking, running, and climbing stairs, which leads to mental problems such as depression, anxiety, chronic fatigue, and decreased efficacy. This phenomenon is not limited to an individual’s problem, but can also lead to a decline in the quality of life of the family [3].
Treatment methods for improving musculoskeletal diseases and pain are divided into drug and non-drug treatments, and surgical treatments. Drug treatment is effective in alleviating symptoms and reducing pain, but it does not stop the progression of the disease [4]. Surgical treatment has the disadvantages of high cost and the possibility of complications such as secondary infection. Non-pharmacological treatment through exercise has the advantage of reducing side effects and complications of drugs, allowing patients to manage their disease and pain on their own, and can be applied regardless of the level of disease and pain and functional status [5].
Regular exercise has been shown to lower the risk of chronic diseases, improve health [6], and have a positive effect on mental health, such as increasing opportunities for social contact and self-efficacy [7].
Despite the proven positive effects of exercise on musculoskeletal disorders and pain, older adults may believe that increased physical activity may worsen their disease. I also reduced my physical activity because I thought exercise wasn’t very effective [8]. In fact, for patients with knee disease, exercise in a normal environment can cause pain due to the weight load placed on the knee joint.
Exercising in an aquatic environment can result in less knee pain than exercising on land due to the properties of water such as buoyancy, temperature, and hydrostatic pressure, allowing you to perform movements that you would not be able to perform on land [9]. In particular, the buoyancy of water in an aquatic environment reduces the weight load on the joints, so the risk of injury during exercise is relatively lower than when exercising on land. Exercises such as walking, running, and jumping on land can cause knee pain due to weight load [10], but this is complemented by the advantage of being able to perform exercises in water.
A previous study on the effects of aquatic exercise showed that elderly females who performed aquatic exercise for 12 weeks showed improvements in muscle strength and positive changes in body composition [11], and it was reported that females in their 60s and 70s diagnosed with degenerative arthritis in the knee showed significant increases in the range of joint motion and isometric knee strength after performing aqua aerobics for 12 weeks [12]. In this way, aquatic exercise is known to be effective in improving muscle strength and increasing joint range of motion (ROM).
However, a study that qualitatively analyzed the effects of aquatic exercise reported that aquatic exercise was positive in improving walking disorders and relieving pain in lumbago, arthritis, and rheumatic diseases, but could not provide clear evidence for long-term effects. Therefore, this study applied hot spring water exercise to middle-aged females with knee osteoarthritis for 8 weeks and observed changes in body composition, isokinetic muscle function, joint ROM, and Korean Western Ontario and McMaster Universities (K-WOMAC).
| Ethics statement: The research plan was reviewed by the Dankook University Hospital Research Ethics Committee (DKUH 2022-05-008) before recruitment, and only those who voluntarily signed the consent form were informed of the significance and procedures of participating in the study, inconveniences, etc. and participated. |
The number of subjects in this study was analyzed using the G*power program with a power of 0.9 and an effect size of 0.7, and the required number of subjects was 24 or more. The study participants were females aged 40 to 60 living in Chungcheongnam-do who were diagnosed with knee osteoarthritis. Exclusion criteria included those with cardiovascular disease or metabolic disease or symptoms, those taking medications that could affect back pain, and those with pain that prevented them from performing physical activities.
Those who agreed to participate in the study were randomly assigned to a 10-person hot-spring aquatic exercise group (EG) and a 16-person control group (CG). The characteristics of the research subjects are as shown in Table 1.
Table 1 . Characteristics of the research subjects
| Aquatic exercise group | Control group | t | ||
|---|---|---|---|---|
| Age (yr) | 52.19 ± 8.50 | 60.30 ± 4.55 | .598 | .948 |
| Height (cm) | 158.44 ± 5.73 | 158.60 ± 6.79 | .066 | .011 |
| Weight (kg) | 58.36 ± 8.60 | 59.53 ± 9.08 | .331 | .743 |
Values are presented as mean ± standard deviation.
The subjects selected as research participants visited the Dankook University laboratory 2 weeks before the start of the program for a pre-evaluation, and body composition, knee isokinetic muscle function, joint ROM were evaluated, and the K-WOMAC questionnaire was administered. Afterwards, the treatment group performed an aquatic exercise program twice a week for 8 weeks at P hot springs in Asan city, and the CG was instructed to refrain from moderate-intensity or higher physical activity more than twice a week. After the end of the 8-week hot spring aquatic exercise program, a post-evaluation of the same items as the pre-evaluation was conducted on all subjects within 2 weeks, and then the experiment was terminated.
The aquatic exercise program was conducted at A spa facility in city Asan. Aquatic exercise was conducted for a total of 8 weeks, twice a week, for 60 minutes each time. The exercise intensity was set differently in two stages for weeks 1 to 4 and weeks 5 to 8 by examining the rate of perceived exertion (RPE scale) each time. It was conducted in three sessions: warm-up, main exercise, and cool-down. Two exercises were performed each in the warm-up and cool-down, and six exercises were performed in the main exercise. The detailed aquatic exercise program control factors are listed in Table 2, and the aquatic exercise program exercise items are listed in Table 3.
Table 2 . Aquatic exercise factor
| Period (wk) | Frequency (day/wk) | Intensity (RPE scale) | Repitition | Set |
|---|---|---|---|---|
| 1-4 | 2 | 12-13 | 10-15 | 2 |
| 5-8 | 2 | 14-17 | 15-25 | 2 |
RPE, rate of perceived exertion.
Table 3 . Aquatic exercise program
| Warm-up (5 min) | Main exercise (50 min) | Cool-down (5 min) |
|---|---|---|
| ➀ Stretching ➁ Gait exercise | ➀ One leg standing ➁ Hip flexion/extension ➂ Hip abduction/adduction ➃ Leg curl/extension ➄ Squat or lunge ➅ Squat jump or lunge jump | ➀ Stretching ➁ Gait exercise |
Body composition was measured using a bioelectrical impedance analyzer (Inbody 570; Biospace), and body weight, muscle mass, body fat mass, body fat percentage, and body mass index (BMI) were compared before and after.
Flexion and extension of the knee joint were measured using Biodex system 4 (Biodex). The subject’s lateral epicondyle was aligned with the axis of the dynamometer for measurement, and one belt was fixed to the thigh that was not being measured, two to the torso, and one to the waist to fix the subject’s body and backrest to the measuring device. Five times at 60° and 15 times at 180° were performed. A 60-seconds rest period was provided between measurements, and the examiner gave a command during the measurement to induce the subject’s maximum force.
The range of joint motion was measured as the active ROM of knee flexion, and was measured using a goniometer in the prone position. The measurement method and order are as shown in Table 4.
Table 4 . Range of motion measurement procedure
| Procedure | Explanation |
|---|---|
| 1 | Have the subject lie face down in the prone position with their stomach and chest facing downward |
| 2 | The center of the goniometer is aligned with the lateral epicondyle of the femur and the fixed arm is aligned parallel to the lateral midline of the femur |
| 3 | Goniometer parallel to the fibular head and lateral malleolus |
| 4 | Bend the subject’s knee joint |
| 5 | Measure the angle between the femur and tibia |
The Korean version of the World Outcomes of Daily Living Questionnaire (WOMAC) was used to check for changes in pain.
All data collected in this study were statistically analyzed using the IBM SPSS statistics (ver. 22.0; IBM Corp.) program. Mixed design two-way ANOVA was performed on all variables to analyze differences between groups and periods. If there was an interaction effect or a significant difference between groups and periods, a post-hoc test was performed using the Bonferroni method. The statistical significance level was α = .05.
The results of the mixed design two-way ANOVA and post-test comparison of 60°/sec peak torque (PQ) according to 8 weeks of aquatic exercise are shown in Table 5. The changes in body fat percentage are as shown in Fig. 1.
Table 5 . Mixed design two-way ANOVA of body composition
| n | Group | Pre | Post | F | |||
|---|---|---|---|---|---|---|---|
| Weight (kg) | 16 | CG | 58.36 ± 8.60 | 57.48 ± 7.00 | G | .131 | .721 |
| 10 | EG | 59.53 ± 9.08 | 58.67 ± 8.89 | T | 1.163 | .214 | |
| GXT | .000 | .988 | |||||
| Muscle mass (kg) | 16 | CG | 21.02 ± 2.37 | 22.83 ± 0.66 | G | .140 | .711 |
| 10 | EG | 21.32 ± 3.06 | 21.38 ± 2.97 | T | .593 | .449 | |
| GXT | .519 | .478 | |||||
| Body fat mass (kg) | 16 | CG | 19.64 ± 5.80 | 8.95 ± 5.46 | G | .01 | .920 |
| 10 | EG | 20.04 ± 5.71 | 19.01 ± 6.31 | T | 3.642 | .068 | |
| GXT | .145 | .707 | |||||
| Percent body fat (%) | 16 | CG | 32.59 ± 5.88 | 32.09 ± 5.93 | G | .005 | .946 |
| 10 | EG | 33.20 ± 6.25 | 31.82 ± 7.59 | T | 5.277 | .031 | |
| GXT | 1.156 | .293 | |||||
| BMI (score) | 16 | CG | 23.12 ± 2.64 | 22.77 ± 2.08 | G | .203 | .657 |
| 10 | EG | 23.57 ± 2.55 | 23.19 ± 2.67 | T | 2.688 | .114 | |
| GXT | .005 | .947 |
Values are presented as mean ± standard deviation.
CG, control group; EG, exercise group; G, group; T, time; GXT, graded exercise test; BMI, body mass index.
Figure 1. Difference of percent of fat. CG, control group; EG, exercise group.
There was no difference between the groups in the 60°/sec PQ comparison of the extensor muscles. There was a significant difference between the periods, and the post-test comparison showed that the treatment group statistically significantly increased from the pretest to the posttest (
There was no difference between the groups in the 60°/sec PQ comparison of the flexor muscles. There was a significant difference between the periods, and the treatment group statistically significantly increased from the pretest to the posttest (
The results of the mixed design two-way ANOVA and post-test comparison of 60°/sec PQ according to 8 weeks of aquatic exercise are shown in Table 6. The change in 60°/sec PQ of the knee extensor is as shown in A of Fig. 2. And the change in 60°/sec PQ of the knee flexor is as shown in B of Fig. 2.
Table 6 . Mixed design two-way ANOVA of 60°/sec peak torque (N/m)
| n | Group | Pre | Post | F | |||
|---|---|---|---|---|---|---|---|
| Extensor | 16 | CG | 68.06 ± 22.04 | 71.88 ± 24.78 | G | .426 | .520 |
| 10 | EG | 52.33 ± 30.67 | 76.36 ± 17.01** | T | 10.836 | .003 | |
| GXT | 5.708 | .025 | |||||
| Flexor | 16 | CG | 35.81 ± 16.42 | 37.48 ± 15.91 | G | .022 | .883 |
| 10 | EG | 28.34 ± 17.84 | 43.19 ± 11.45** | T | 14.113 | .001 | |
| GXT | 8.971 | .006 |
Values are presented as mean ± standard deviation.
PQ, peak torque; CG, control group; EG, exercise group; G, group; T, time; GXT, graded exercise test.
**
Figure 2. (A) Difference of extensor 60°/sec PQ. (B) Difference of flexor 60°/sec PQ. PQ, peak torque; CG, control group; EG, exercise group.
There was no difference between the groups in the 60°/sec PQ comparison of the extensor muscles. There was a significant difference between the periods, and the post-test comparison showed that the treatment group statistically significantly increased from the pretest to the posttest (
There was no difference between the groups in the 60°/sec PQ comparison of the flexor muscles. There was a significant difference between the periods, and the treatment group statistically significantly increased from the pretest to the posttest (
The results of the mixed design two-way ANOVA and post-test comparison of 60°/sec average power according to 8 weeks of aquatic exercise are shown in Table 7. The change in 60°/sec average power of the knee extensor is as shown in A of Fig. 3. And the change in 60°/sec average power of the knee flexor is as shown in B of Fig. 3.
Table 7 . Mixed design two-way ANOVA of 60°/sec average power (watts)
| n | Group | Pre | Post | F | |||
|---|---|---|---|---|---|---|---|
| Extensor | 16 | CG | 42.39 ± 19.74 | 43.31 ± 16.62 | G | .629 | .435 |
| 10 | EG | 28.95 ± 19.09 | 46.78 ± 12.44** | T | 8.697 | .007 | |
| GXT | 7.076 | .041 | |||||
| Flexor | 16 | CG | 23.74 ± 14.94 | 22.93 ± 12.75 | G | .407 | .530 |
| 10 | EG | 15.84 ± 13.39 | 24.44 ± 12.43 | T | 3.203 | .086 | |
| GXT | 4.679 | .041 |
Values are presented as mean ± standard deviation.
CG, control group; EG, exercise group; G, group; T, time; GXT, graded exercise test.
**
Figure 3. (A) Difference of extensor 60°/sec average power. (B) Difference of flexor 60°/sec average power. CG, control group; EG, exercise group.
There was no difference between groups in the 60°/sec average power comparison of the extensor muscles. There was a significant difference between periods, and the post-test comparison showed that the treatment group increased statistically significantly from the pretest to the posttest (
There was no difference between groups in the 60°/sec average power comparison of the flexor muscles. There was also no difference between periods. There was an interaction effect between groups and periods (
The results of the mixed design two-way ANOVA and post-test comparison of 180°/sec total work (TW) according to the 8-week aquatic exercise are shown in Table 8. The change in 180°/sec TW of the knee extensor is as shown in A of Fig. 4. And the change in 180°/sec TW of the knee flexor is as shown in B of Fig. 4.
Table 8 . Mixed design two-way ANOVA of 180°/sec total work (J)
| n | Group | Pre | Post | F | |||
|---|---|---|---|---|---|---|---|
| Extensor | 16 | CG | 743.23 ± 257.28 | 807.79 ± 278.84 | G | .109 | .744 |
| 10 | EG | 591.91 ± 321.52 | 896.21 ± 232.76* | T | 11.122 | .003 | |
| GXT | 4.698 | .04 | |||||
| Flexor | 16 | CG | 481.36 ± 296.99 | 481.64 ± 266.62 | G | .086 | .772 |
| 10 | EG | 347.93 ± 296.79 | 554.10 ± 181.17** | T | 11.351 | .003 | |
| GXT | 11.289 | .003 |
Values are presented as mean ± standard deviation.
TW, total work; CG, control group; EG, exercise group; G, group; T, time; GXT, graded exercise test.
*
Figure 4. (A) Difference of extensor 180°/sec TW. (B) Difference of flexor 180°/sec TW. TW, total work; CG, control group; EG, exercise group.
There was no difference between the groups in the 180°/sec TW comparison of the extensor muscles. There was a significant difference between the periods, and the post-test comparison showed that the treatment group increased statistically significantly from the pretest to the posttest (
There was no difference between the groups in the 180°/sec TW comparison of the flexor muscles. There was a significant difference between the periods, and the treatment group increased statistically significantly from the pretest to the posttest (
The results of the mixed design two-way ANOVA and post-test comparison of the range of joint motion after 8 weeks of aquatic exercise are shown in Table 9. The changes in ROM are as shown in Fig. 5.
Table 9 . Mixed design two-way ANOVA of range of motion (°)
| n | Group | Pre | Post | F | ||
|---|---|---|---|---|---|---|
| 16 | CG | 113.31 ± 12.76 | 112.81 ± 14.04 | G | 3.997 | .057 |
| 10 | EG | 118.20 ± 10.45 | 126.10 ± 7.09* | T | 5.513 | .027 |
| GXT | 7.104 | .014 |
Values are presented as mean ± standard deviation.
CG, control group; EG, exercise group; G, group; T, time; GXT, graded exercise test.
*
Figure 5. Difference of range of motion (ROM). CG, control group; EG, exercise group.
There was no difference between the groups in the results of the comparison of the range of joint motion. There was a significant difference between the periods, and the results of the post-test comparison showed that the treatment group increased statistically significantly from the pretest to the posttest (
The results of the mixed design two-way ANOVA and post-test comparison of K-WOMAC after 8 weeks of aquatic exercise are shown in Table 10. The changes in K-WOMAC are as shown in Fig. 6.
Table 10 . Mixed design two-way ANOVA of K-WOMAC (score)
| n | Group | Pre | Post | F | ||
|---|---|---|---|---|---|---|
| 16 | CG | 57.13 ± 4.60 | 57.44 ± 4.46 | G | 2.848 | .104 |
| 10 | EG | 60.50 ± 16.95 | 43.90 ± 15.69* | T | 7.152 | .013 |
| GXT | 7.712 | .010 |
Values are presented as mean ± standard deviation.
K-WOMAC, Korean Western Ontario and McMaster Universities; CG, control group; EG, exercise group; G, group; T, time; GXT, graded exercise test.
*
Figure 6. Difference of activities of daily living (K-WOMAC). K-WOMAC, Korean Western Ontario and McMaster Universities; CG, control group; EG, exercise group.
There was no difference between the groups in the K-WOMAC comparison results. There was a significant difference between the periods, and the post-test comparison results showed that the treatment group’s post-test was statistically significantly higher than the pretest (
Knee osteoarthritis is a chronic degenerative disease that occurs as articular cartilage is gradually lost. Its prevalence has been continuously increasing due to the aging population, and this phenomenon is also a burden in terms of socioeconomic costs due to increased medical expenses. Knee osteoarthritis occurs in the knee joint due to weight load and causes deterioration of the function of the knee joint due to deformation [13]. In particular, as people age, they have more difficulty walking due to pain and joint function problems, and it affects not only mobility but also daily life activities [14].
It is known that lukewarm hot springs (approximately 36°C-39°C) have healing effects such as sedative effects, analgesic effects, and relaxation of muscles, ligaments, and joint capsules, and aquatic exercise performed using the physical characteristics of the aquatic environment is effective in improving muscle strength and joint ROM, and reducing pain [15], without putting a great strain on the body. Therefore, this study aimed to investigate physical changes by conducting 8 weeks of hot spring aquatic exercise on middle-aged females with knee osteoarthritis.
Among the body compositions, the body fat percentage showed a significant difference in CG and decreased after the pre-test compared to the post-test. The main effects of physical activity, weight and body fat reduction, are already well known, and the effect of improving body composition in middle-aged females through aquatic exercise has been proven through previous studies [16].
Aquatic exercise consists of repetitive movements of large muscle groups of the body, and the density of water is about 800 times that of air, which consumes more energy than moving on land [17]. In addition, hot spring water induces sweating to dissipate body heat due to its hot spring effect, and the heat of evaporation generated when sweat dries on the skin promotes calorie consumption, contributing to body fat reduction [18]. It has been reported that about 0.58 kg of calories are consumed per 1 ml of sweat when it evaporates from the skin [19]. In addition, hot spring water can promote calorie consumption because it improves blood circulation through hydrostatic pressure, which is a characteristic of water, and increases metabolism.
On the other hand, although there were changes in the average values of body weight and lean body mass, they did not show a specific trend or reach a significant level. Looking at the exercise programs of studies in which body composition significantly changed through exercise, the exercise period was at least 12 weeks and was performed at a frequency of more than 3 times per week [20]. On the other hand, the hot spring water exercise program implemented in this study was implemented twice per week for 8 weeks. Therefore, it is thought that the exercise program implemented in this study was because the exercise period and frequency were too short for body weight, muscle mass, body fat mass, and BMI to change.
Isokinetic muscle strength test, which is considered the standard for evaluating muscle function by joint, can evaluate PQ, which is an indicator of maximum force generated during movement [21], TW which represents the maximum capacity of the muscle to generate force and the ability to maintain it over the entire repetition and joint ROM [22], and average power, which is an indicator that reflects muscle efficiency by indicating work speed by calculating the amount of work per unit time [23], and has been reported to be a reliable scale for evaluating muscle function of the lower back [24].
In this study, EG that performed 8 weeks of hot spring water exercise showed statistically significant increases in PQ of knee flexion and extension movements and average power of TW flexion movement. The average power of extension movement also showed an increasing trend although there was no significant difference. Kim et al. [25] study that reported that performed water exercise on middle-aged females for 8 weeks and observed isokinetic muscle strength of the knee joint and reported that both extension and flexion muscle strength of the knee increased. There was also a report that lower body muscle strength increased after performing an water exercise program twice a week for 18 weeks on 43 arthritis patients [26]. The subjects of this study participated in the study with weakened muscle strength due to inactivity for more than a year. For beginners in exercise, muscle strength or endurance can increase even with low intensity exercise, and since exercise performed in water increases the load due to viscosity that increases as the speed of movement increases, it is similar to a form of resistance exercise, so it is thought that the muscle strength-related variables in this study improved.
The WOMAC is a questionnaire to evaluate the function and health status of patients with osteoarthritis. The K-WOMAC, which has been revised and supplemented for use by Koreans, is a questionnaire on subjective functional limitations in daily life related to knee joint pain, consisting of a total of 24 items (5 pain, 2 stiffness, and 17 physical function). The score is calculated by adding up the three items, with 0 indicating no problem and 4 indicating very severe problem, from 0 to 20 for pain, 0 to 8 for stiffness, and 0 to 68 for physical function. A higher sum of the scores indicates more severe pain and joint dysfunction [27].
A previous study that reported that strengthening the hip abductor muscles had a positive effect on improving the WOMAC scores of patients undergoing total knee arthroplasty. In addition, a previous study reported that subjects with functional abnormalities in the knee joint significantly improved their knee joint function when they participated in a muscle strengthening and resistance exercise program for 8 weeks [28], and a previous study that investigated the changes in the WOMAC scores measured before and after surgery in patients who underwent total knee arthroplasty showed that all items improved by more than 40 points 1 year after the surgery [29]. In this study, the K-WOMAC index of EG statistically significantly decreased from 60.50 ± 16.95 to 43.90 ± 15.69 after 8 weeks of hot spring water exercise. These results are thought to be due to the environmental characteristics of lukewarm hot springs that provide calming and analgesic effects and the physical characteristics of water due to buoyancy [30].
However, this study has the following three limitations. First, it did not recruit diverse subjects in terms of age, sex, and disease severity. Second, it did not compare with non-pharmacological methods such as exercise in a terrestrial environment or other aquatic treatment methods. Third, K-WOMAC is a method that evaluates an individual’s subjective judgment.
In conclusion, This study aimed to analyze the effects of an 8-week aquatic exercise program in a hot spring environment for middle-aged females with knee osteoarthritis. The body composition, isokinetic muscle function of the lower back, knee joint ROM, and arthritis symptom evaluation index were evaluated before and after the program, and the following results were obtained.
Among the body composition, the body fat percentage significantly decreased after EG compared to before. Among the isokinetic muscle function, the PQ and TW of EG’s flexion and extension movements and the average power of the flexion movement significantly increased, while the average power of the extension movement did not change. The range of joint motion significantly increased after EG compared to before. The WOMAC significantly decreased after EG compared to before.
In summary, the 8-week aquatic exercise using hot spring water is effective in increasing the strength of the knee joint and improving daily life activities, so it can be used as an interventional therapy for low back pain in elderly people and obese people who have difficulty exercising on land. In addition, it is thought that future research on the long-term effects of hot spring water exercise is necessary.
None.
None.
Conceptualization: KHK. Data curation: BKK. Formal analysis: JHS. Funding acquisition: HJJ. Investigation: JSP. Methodology: SHL. Project administration: BKK. Software: JSP. Validation: HJJ. Visualization: JHS. Writing–original draft: BKK. Writing–review & editing: all authors.
No potential conflict of interest relevant to this article was reported.
This study was conducted with the support of the ‘Hot Spring Industry Activation Project’ funded by the Ministry of the Interior and Safety and Asan City in 2021.
Contact the corresponding author for data availability.
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Author ORCID Information Ki Hong Kim Byung Kwan Kim Jae Heon Son Jun Sik Park Sang Hyun Lee Hwan Jong Jeong
Funding Information Ministry of the Interior and Safety Asan City |
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