## 4 Discussion
[49] further analyzed the effects of WT induced instability during the bench press, showing increased activation of the oblique and erector spinae muscles. Nevertheless, previous research has suggested that the primary contribution of instability training may be the improvement of core stability rather than limb strength. Furthermore, the initial goal of instability training may not necessarily be significant strength gains but rather an enhancement of balance, stability, and proprioceptive capabilities [30]. Water inertia-based unstable exercises also have beneficial effects on postural stability, inducing greater medial-lateral movement. [PERSON] et al. [49] further noted that the introduction of the WT significantly affected the mediolateral direction, with the impact being more pronounced in the range of the center of pressure (CoP) than in its sway velocity. This effect is attributed to the shape and size of the WT, which continuously alters the weight distribution as the water flows along its main axis. The Aqua Vest introduces an innovative approach to unstable load training by incorporating partially filled water tubes that generate dynamic weight distribution shifts. Furthermore, [PERSON] et al. [29] suggested that the fluidity of the water in a water bag could introduce greater asymmetrical disturbances during exercises, especially in the final phases of movement. These findings suggest that tools utilizing water inertia may offer advantages in sports that demand enhanced somatosensory or proprioceptive contributions to balance control. The inertia of the water responds dynamically to body movements, continuously altering the load distribution and creating an inherently unstable resistance. This instability enhances neuromuscular control, postural adjustments, and core muscle activation. [PERSON] and [PERSON] [50] demonstrated that adjusting water volume in such devices modulated inertial perturbation, offering a scalable challenge for users. The dynamic variability induced by water inertia aligns with principles of dynamic systems theory and ecological movement approaches, fostering adaptability in movement patterns [36]. A key advantage of the Aqua Vest over other unstable load devices is its ability to leave the arms and hands free, allowing for greater movement flexibility and coordination during training. Unlike traditional unstable load tools, which may limit upper limb mobility, the Aqua Vest facilitates whole-body dynamic balance. Despite its potential, the effects of unstable training using wearable water-filled devices on postural stability and gait function remain underexplored. This study addresses this gap by investigating the influence of Aqua Vest on gait and postural stability in middle-aged women with DKA. This highlights the novelty of the present study and the need for further investigations to explore its full rehabilitative potential. Meanwhile, the portability of Aqua Vest presents a practical option for home-based rehabilitation, an area that has not been widely studied in previous research. This study has several limitations. Firstly, this study focused on lower extremity kinematics and postural stability but did not assess joint kinetics, muscle activation, or load distribution. The findings confirm that water inertia-based training improves functional performance and reduces pain in individuals with degenerative knee arthritis (DKA), laying the groundwork for future research on its effects on joint moments and ground reaction forces (GRF). Notably, it did not compare different phases of the gait cycle, limiting the analysis of movement changes. The small changes in knee and hip abduction-abduction range of motion (ROM) suggest that the exercise protocol may need adjustments to improve frontal plane stability. Future studies should explore modifications to training methods that enhance muscle engagement in this plane for better results. Secondly, the lack of electromyography (EMG) analysis limits insight into muscle contributions to postural stability.