Background: Aquatic exercise utilizing hot springs helps individuals with nonspecific knee pain by reducing joint stress and providing a safe environment for movement. It can improve muscle strength and balance, enhancing overall functional mobility. Objects: This study aims to examine the muscle strength of knee flexion, knee extension, dorsiflexion, and plantar flexion, as well as to investigate static and dynamic balance in middleaged females after performing hot spring aquatic exercise for 4 weeks. Methods: Twenty-two middle-aged females participated in the study. The participants performed hot spring aquatic exercise for 4 weeks. The hot spring aquatic exercise consisted of aquatic walking, aquatic stretching, aquatic side step, aquatic forward reach, aquatic squat, leg lift, and aquatic arm and leg rotation. Muscle strength was measured using microFET2, while static balance was assessed through the one-leg stance test, and dynamic balance was evaluated using the Y-balance test. This study utilized the paired t-test for statistical analysis, with a significance level set at 0.05. Results: The muscle strength of bilateral knee flexion showed a significant increase in the pre- and post-comparison (p < 0.05), and the muscle strength of bilateral knee extension also improved significantly (p < 0.05). In addition, a significant increase was observed in the muscle strength of bilateral dorsiflexion (p < 0.05). The one-leg stance test performed while supporting on the right leg showed a significant increase in the pre- and post-comparison (p < 0.05). Furthermore, the dynamic balance measurements performed while supporting on both the right and left legs demonstrated significant improvements in both legs when compared before and after the intervention (p < 0.05). Conclusion: In individuals with nonspecific knee pain, a 4-week hot spring aquatic exercise program can contribute to the improvement of lower extremity strength, as well as static and dynamic balance ability.

INTRODUCTION
MATERIALS AND METHODS
    1. Subjects
    2. Measurement Tools
    3. Experimental Procedure
    4. Hot Spring Aquatic Exercise
    5. Statistical Analyses
RESULTS
    1. Strength
    2. Static Balance
    3. Dynamic Balance
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTION
ORCID
REFERENCES

• Ki-Song Kim(Department of Physical Therapy, College of Life and Health Sciences, Hoseo University, Research Institute for Basic Sciences, Hoseo University, Smart Healthcare Convergence Research Center, Hoseo University)
• In-Cheol Jeon(Department of Physical Therapy, College of Life and Health Sciences, Hoseo University, Research Institute for Basic Sciences, Hoseo University, Smart Healthcare Convergence Research Center, Hoseo University) Corresponding author
• Tae-Hyeong Kim(Department of Physical Therapy, Graduate School, Hoseo University)
• Jong-Min Woo(Test and Evaluation Team, Healthcare & Spa Industry Promotion Agency, Asan, Korea)
• Sunhee Lee(Test and Evaluation Team, Healthcare & Spa Industry Promotion Agency, Asan, Korea)
• Hana Yu(Test and Evaluation Team, Healthcare & Spa Industry Promotion Agency, Asan, Korea)