Background and Purpose
In the elderly with knee osteoarthritis, postural fluctuations and the risk of falling increase significantly (1). Elderly individuals suffering from knee osteoarthritis often experience pronounced postural instability and an elevated risk of falls. [Therefore, improving balance and reducing pain in these individuals is an effective strategy to mitigate fall risk (2).] Consequently, interventions aimed at enhancing balance and alleviating pain are critical methods for fall prevention. Many exercises have been proposed to improve balance and thus reduce fall incidence. Various forms of exercise are recognized to bolster balance and diminish fall-related risks.
However, arthritis pain frequently hinders patients’ ability to pursue and benefit from exercising (2). Nonetheless, pain associated with arthritis often undermines exercise adherence and effectiveness. Exercising in water is more suitable for individuals with musculoskeletal problems than land-based exercise. Aquatic exercise offers an advantageous alternative, providing a supportive environment particularly beneficial for those with musculoskeletal limitations. This is because as water depth increases, joint load and pain sensation decrease (3). Increasing immersion depth reduces joint loading and pain perception.
However, as water depth increases, if the foot loses contact with the pool floor, proprioceptive input diminishes, weakening balance-related sensory feedback. Yet, in deeper water, lack of foot-ground contact diminishes proprioceptive cues essential for postural control and fall prevention. This proprioceptive perception is vital for maintaining balance and decreasing fall risk. The integrity of proprioception is paramount in sustaining postural stability.
Hence, the fundamental question arises: which water depth maximizes improvements in balance, fall risk reduction, and pain alleviation? Therefore, identifying the optimal pool depth for maximizing therapeutic benefits on balance, fall risk, and pain is crucial. Water depth influences training efficacy through variables such as gravity, hydrostatic pressure, and exercise chain configurations (open or closed) (4). Training parameters, including gravitational forces, hydrostatic pressure, and kinetic chain characteristics, vary with water depth and impact outcomes.
Accordingly, the purpose of this research was to investigate the effects of training in two water depths—shallow water, where the feet maintain contact with the pool floor, and deep water, where feet do not touch the bottom—on dynamic balance, fall risk, and pain in elderly women with knee osteoarthritis. This study compares shallow and deep water exercise effects on dynamic balance, fall risk, and pain among elderly women afflicted with knee osteoarthritis.
 
Methods
This semi-experimental, pretest-posttest study involved 43 elderly women aged 55 and older with chronic knee osteoarthritis of at least eight months duration. A semi-experimental design with pretest and posttest measurements was used on 43 elderly female participants (age ≥ 55) diagnosed with chronic knee osteoarthritis of minimum eight months.  The intervention lasted 12 weeks with three training sessions per week in two aquatic environments: shallow and deep water. Participants underwent 12 weeks of aquatic training, thrice weekly, in either shallow or deep water settings.
After preliminary assessments and informed consent, participants were divided into three groups: two shallow water exercise groups (14 each), one deep water exercise group (14), and one control group. Following baseline evaluation and consent, subjects were assigned to three groups: two shallow water exercise groups (each n=14), one deep water exercise group (n=14), and a control group.
Dynamic balance, fall risk, and pain were measured using the Star test (5), Berg Balance Scale (6), and KOOS questionnaire (7), respectively. Outcome measures included the Star Excursion Balance Test for dynamic balance, the Berg Balance Scale for fall risk assessment, and the KOOS (Knee Injury and Osteoarthritis Outcome Score) for pain evaluation.
Data analysis employed a 2 (time: pretest/posttest) × 3 (group: shallow water/deep water/control) repeated-measures ANOVA with LSD post hoc tests at a significance level of p < 0.05. Statistical analyses were conducted via repeated-measures ANOVA (2 × 3 design) with LSD post hoc tests, maintaining an alpha of 0.05.
[SPSS version 26 was used for all statistical analyses. All analyses utilized SPSS version 26.
 
Results
Table 1 presents the demographic characteristics of participants across groups.
 
 Table 1. Descriptive statistics related to the individual characteristics of the subjects by groups





Groups


Variables




Control
(n=14)


Deep-water
(n=14)


Shallow-water (n=14)




63.41 ± 5.16


63.11 ± 5.37


62.41 ± 5.16


Age (year)




154.85 ± 3.99


155.22 ± 4.03


154.92 ± 4.63


Height (cm)




60.13 ± 10.86


61.03 ± 11.20


59.84 ± 10.45


Weight (kg)




25.83 ± 4.21


26.11 ± 4.09


25.71 ± 3.96


Body mass index (kg/m²)




31.17 ± 7.55


31.83 ± 6.88


30.69 ± 7.24


fat percentage (%)





Table 2 depicts the result of two factor repeated measure ANOVAs of main effects (within groups: aquatic exercise and between groups: depth of water) on dynamic balance, falling risk and pain were statistically significant.
Table 2. The result of main effects on dynamic balance, falling risk, quality of life, and pain





Variables


Source


df1


df2


F


p


²η




Dynamic Balance


Aquatic exercise


1


40


3.06


0.01^*


0.08




Depth (shallow/ deep/ control)


2


40


3.15


0.01^*


0.08




Aquatic exercise× Depth


2


40


4.90


0.007^**


0.13




Falling risk


Aquatic exercise


1


40


8.72


0.001^***


0.20




Depth (shallow/ deep/ control)


2


40


9.39


0.001^***


0.23




Aquatic exercise× Depth


2


40


12.40


0.001^***


0.35




Pain


Aquatic exercise


1


40


9.04


0.001^***


0.21




Depth (shallow/ deep/ control)


2


40


9.67


0.001^***


0.24




Aquatic exercise× Depth


2


40


12.97


0.001^***


0.35





* Significance at p≤0.05, **significance at p≤0.01, ***significance at p≤0.001
Due to the significance of the main effect of water depth, the LSD test was used to perform multiple comparisons. Results are shown in table 3.
Table 3. The results of LSD test for between groups comparison of dynamic balance, falling risk and pain.





Variables


Groups


 


Mean difference


Standard error


P




Dynamic Balance


Shallow water


Deep water


3.58


0.89


0.001^***




Control


5.58


0.83


0.001^***




Deep water


Control


2.00


0.90


0.02^*




Falling risk


Shallow water


Deep water


6.69


0.96


0.001^***




Control


16.01


0.74


0.001^***




Deep water


Control


9.32


1.08


0.001^***




Pain


Shallow water


Deep water


7.53


0.78


0.001^***




Control


17.07


0.54


0.001^***




Deep water


Control


9.54


0.69


0.001^***





*Significance at p≤0.05, *** significance at p≤0.001
 
descriptive statistics (Table 1) report participant demographics by group.
Results demonstrated that 12 weeks of aquatic exercise in both shallow and deep water significantly improved dynamic balance and reduced fall risk and pain. Both shallow and deep water exercise groups exhibited significant post-intervention improvements in dynamic balance and reductions in fall risk and pain.
Improvements were more pronounced in the shallow water group compared to the deep water group. Notably, enhancements were significantly greater for the shallow water group. This suggests that foot contact with the pool floor facilitates more effective proprioceptive feedback, stimulating balance mechanisms more robustly than skin receptor stimulation via hydrostatic pressure alone (3). The presence of foot-floor contact in shallow water likely provides superior proprioceptive stimulation compared to deep water’s reliance on hydrostatic pressure and cutaneous receptors.
Shallow water training also yielded greater reductions in fall risk and pain, likely due to more considerable balance improvements. These superior outcomes in fall risk and pain may be mediated by enhanced balance function observed in the shallow water cohort. Improved balance corrects motor patterns and establishes effective muscle coordination, crucial for postural stability, thereby reducing pain and fall risk (8). Enhanced postural stability involves coordinated muscular control, mitigating pain and decreasing susceptibility to falls.
Overall, these findings support the therapeutic efficacy of aquatic exercise, particularly in shallow water, for elderly individuals with knee osteoarthritis. The results corroborate prior evidence endorsing water-based therapy and emphasize shallow water exercise’s superiority for this population.
 
 
Article Message
Elderly individuals with chronic knee osteoarthritis can benefit significantly from water-based exercise to improve balance, reduce pain, and lower fall risk. Aquatic exercise provides substantial benefits for elderly patients with chronic knee osteoarthritis in terms of balance, pain relief, and fall prevention. Adjusting water depth to chest level, where feet maintain contact with the pool floor, is more effective than exercising in deep water. Optimizing water depth to allow foot-floor contact enhances therapeutic outcomes more than training in non-weight-bearing deep water.
Authors’ Contributions
Conceptualization: Faezeh Zamanian, Mahdi Armandnia
Data Collection: Faezeh Zamanian, Mahdie Gharehlar
Data Analysis: Mahdi Armandnia, Majid Vesalinaseh
Manuscript Writing: Faezeh Zamanian, Mahdi Armandnia, Mahdie Gharehlar, Majid Vesalinaseh
Review and Editing: Mahdi Armandnia
Responsible for funding: No financial support was received for this study.
Literature Review: Faezeh Zamanian و Mahdi Armandnia, Mahdie Gharehlar, Majid Vesalinaseh
Project Manager: Mahdi Armandnia, Faezeh Zamanian
Ethical Considerations
The ethical code is UMIN000058649. This study was approved under ethical code UMIN000058649.
Conflict of Interest
The authors have no conflict of interest. The authors declare no conflicts of interest.
 
Acknowledgments
We are grateful to all individuals and participants who provided significant help during our research. The authors express sincere gratitude to all participants and collaborators who contributed to this study.