This study hypothesized that a 12-week DNS training program using the inertial load of water would improve COP and FMS scores in middle-aged women. The following results were obtained: DNS training showed significant interaction effects (p < 0.001) in all variables of COP Distance, as well as in the variable of COP RMS distance (p < 0.05). Furthermore, significant interaction effects were observed in the FMS variables of Deep Squat (p < 0.01), Inline Lunge (p < 0.01), Leg Raise (p < 0.05), and Total score (p < 0.001). Furthermore, the DNS training demonstrated significant interaction effects in all variables of COP aiming to maintain a stable posture [15]. In this study, we assessed balance ability using COP variables commonly used in previous research on postural sway. These variables included anterior–posterior and medial–lateral displacement distance, total distance, RMS distance, and sway area (the sum of the areas traversed by the center of mass) [22].
Body balance is achieved through the perception of limb and body movements, as well as head movements, and is influenced by proprioception [23]. Muscle spindles, Golgi tendon organs, and joint receptors are responsible for maintaining balance and providing stability by eliciting responses in the muscle tissue to external perturbations. These proprioceptive receptors respond to external movements and contribute to the preservation of balance and the provision of safety [24].
Based on the FMS measurement results, which assess balance, symmetry, and core stability along with various joint movements, the DNS training demonstrated significant interaction effects in the Deep Squat, Inline Lunge, Leg Raise, and Total Score. Although no significant differences were observed between the two groups in terms of Rotary Stability, a trend towards improvement was noted in those who underwent DNS training compared to those who did not. This too can be considered a very important aspect. This indicates that the 12-week DNS training employed here, improved the body's stability through reduced COP distance, COP area and RMS. The observed changes in FMS are expected to lead to improvements in upright posture and gait ability.
Utilizing unstable surfaces, core and balance exercises that employ the BOSU, Swiss balls and wobble balance boards are commonly used [25]. However, according to a study by Brumagne, Janssens [26], it was found that stimulation of the ankle muscles was actually lower on unstable surfaces compared to rigid and stable surfaces. As well, the effect on COP position changes was minimal. This suggests that during upright posture training on an unstable surface, the ankle angle may not provide accurate information related to the overall body orientation with respect to the surface [27]. To eliminate this concern, we implemented DNS training on a stable surface.
This study found significant interaction effects in the comparison of COP displacement, RMS, and sway area, pre—and post -training. This supports results reported by Adlerton, Moritz [28], where a decrease in COP variables indicated an increase in postural stability. Additionally, it is consistent with the findings of Palmieri, Ingersoll [29], who reported that reduced movement of the center of pressure is associated with the maintenance of postural stability. In particular, by demonstrating that DNS training reduces COP variables and improves balance ability in middle-aged women, this study provides an approach to combat the reported decline in balance capacity and in particular, lateral balance in middle age [3].
Bloomquist, Langberg [30] reported that the Deep Squat and Hurdle Step movements in the FMS assessment can evaluate the coordination between the hip, ankle, and shoulder, since these movements involve vertical gravitational loading on the joints [31] and are related to dynamic stabilization during activities such as upright posture and gait. The mechanics of the Inline Lunge movement are related to lateral balance [32]. Therefore, an increase in the Inline Lunge movement score is interpreted as an improvement in lateral balance ability.
DNS training is a rehabilitation approach developed by Kolar, aimed at developing ideal posture, functional joint centration, optimal breathing, and movement similar to that observed in newborn infants. Park et al. [33] have demonstrated its effectiveness in baseball pitchers with scapular dyskinesis. Additionally, other studies have shown its effectiveness in improving forward head posture and respiration [34] as well as the thickness of neck flexor muscles [35].
Kolar particularly emphasizes the importance of IAP, which is an effective factor in joint centration and efficient muscle activation. Therefore, in this study, a training program was designed to promote spinal alignment, stability, and increased mobility through training in IAP. To generate external perturbations, the exercise involved using the inertial load of water while performing breathing patterns and IAP formation training. The exercise progressed from the tripod position, focusing on proper foot and hand support, to the high kneeling position, which is effective for developing proper weight-bearing ability based on hip joint centration. Horak and Nashner [36] reported that there are changes in postural control strategies and differences in muscle activation patterns based on the location of the center of mass relative to the hip, knee, and ankle joints during external perturbations. In the human body, joints require a fixed point from an ergonomic standpoint for proper mobility, and the core plays an intermediary role in connecting the limbs. Therefore, the function of IAP is considered to be the formation of abdominal stability, enabling the limbs to move freely.
In this study, the Aqua Bag was utilized to incorporate the DNS training and use of inertial water to promote joint centration and prevent joint compression. DNS training using the inertial load of water can enhance core stability and improve overall fitness [12]. Behm, Anderson [37] reported that DNS training increases the number of repetitions capable of being performed during exercise and improves coordination between agonist, antagonist, and stabilizer muscles. This can be considered evidence for improvements in lower limb joint function such as hip joint function, related to maintaining an upright posture, as evaluated in the FMS assessment conducted in this study. DNS training using inertial water load is considered a valid method to activate the inherent potential function of the human body in the process of self-stabilization from external perturbations. Further research related to DNS training using inertial water loads is warranted to explore its potential benefits.
There have been several previous studies that have assessed dynamic stability, but there is limited research that specifically measures COP during the RUS task. The RUS task involves reaching forward with the arm while standing on one leg, and it can be considered a challenging task that requires a high level of coordination. In the human gait cycle, the double-support phase, where both feet are in contact with the ground, only accounts for approximately 10% of the cycle, while the rest consists of the single-support and swing phases [38]. Therefore, in unstable situations, the ability to maintain stability during these phases becomes crucial. When performing purposeful actions, our bodies employ reflexive strategies and compensatory movements to control postural sway and maintain stability [39, 40].
Cresswell, Oddsson [8] emphasized the importance of spinal alignment and stability in the performance of elite athletes in their study. They reported that an increase in IAP contributes to spinal neutrality and stability and highlighted the significant role of co-contraction of muscles such as the transverse abdominal. In this study, the exercise group underwent training to increase IAP and were guided to be conscious of their breathing during movement. The participants in the exercise group maintained their understanding and training of breathing patterns throughout the experimental period. However, the duration of the effects of this training on joint centration was not determined, indicating the need for further research in this area. Additionally, the study focused on measuring balance ability through variables such as COP and FMS. It is suggested that future research should involve measuring electromyography, which directly reflects muscle responses.
