The purpose of this study is to investigate the auxiliary effect of VF provided by smart insoles on real-time static balance control in healthy young people of different genders. The results showed that the displacement, velocity, radius, and area of COP decreased significantly, whereas those of men or women in OLS-VF, and the COPAP displacement, COPAP velocity, COP radius, and COP area of women decreased significantly decreased. Furthermore, the COP parameter decreased as the body stability strengthened [5]. The VF real-time static balance ability provided by smart insoles was higher than that of NF, and the real-time balance control ability of women was higher than that of men.
After VF was provided, the COPAP maximum displacement, COPAP variance, COPML maximum displacement, and COPML variance reduced, indicating the effectiveness of VF as a posture control strategy [9]. The direction of the COP track shows different control strategies for postural sway during standing. The postural sway in the mediolateral (ML) direction is related to hip joint stability, whereas the postural sway in the anteroposterior (AP) direction is related to ankle joint stability [20]. In the AP direction, body sway and posture changes are closely related to the ankle neuromuscular function. The “ankle strategy” can increase the stability of the ankle joint and reduce the COP displacement to improve the balance ability [21]. In this study, the decrease in COP displacement in the AP direction may be due to the effect of VF on the stability of the ankle joint. Static balance can be maintained through an active torque regulation/control of sensory motor integration for muscle contraction during ankle position modulation [7]. Therefore, the intervention of VF enables the COP to be displayed on the screen, and the body actively controls the COP according to the change in the COP to maintain physical stability. The central nervous system is fully involved in regulating the movement of the ankle muscles to maintain the stability of the COM. In this study, the COPML maximum displacement decreased after VF intervention. Previous studies revealed that the COP displacement improved in both the and AP directions during the exercise of stable static balance [22]. When controlling the ML displacement, the “hip strategy” accompanied by VF control balance results in autonomous adduction and abduction [23]. Moreover, the displacement in the ML direction can improve balance ability through this autonomous adduction and abduction change. Therefore, static balance standing after VF may cause the joint activity of “ankle strategy” and “hip strategy” to maintain stability, thereby reducing the degree of body sway and displacement variation after VF.
The COP mean velocity, COPAP velocity, and COPML velocity decreased after VF intervention. Previous studies regarding the balance of soccer players revealed that the decrease in COP velocity was due to the more effective prediction of body position changes by the visual system of soccer players [7]. The difference in parameters before and after the experiment in this study may be caused by the VF information obtained after VF intervention to predict body position changes. The decrease in the COPAP velocity may be due to the body’s assessment of body status through VF to achieve better stability [7]. When standing, the body feeds back position and sensory information to the central nervous system to control the muscle activity of the ankle joint mechanism and facilitate the body in maintaining balance. In the OLS, the COPAP velocity controlled by the “ankle strategy” and the COPML velocity controlled by the “hip strategy” decreased, thereby increasing the stability of posture control [24].The maintenance of static balance in the human body is typically completed by the activities of the trunk and lower limb muscles, such as the “hip strategy” or “ankle strategy” [3]. Therefore, the decrease in the COPAP velocity and COPML velocity may be the result of the mediation of joint motion between the ankle and hip after VF, which can enhance the stability of the lower extremities.
The COP area and COP radius under VF decreased, indicating that the stability of the participants may increase after VF intervention. Previous studies revealed that using VF and virtual reality balance tests can reduce the COP radius and area [25]. Therefore, the enhancement of VF will strengthen the participants’ ability in controlling balance. Balance control is a dynamic adaptation process of active (autonomous control) and passive (accidental, external disturbance) balance control actions [26]. When visual information increases, the body’s autonomous control ability is strengthened [27]. Moreover, the enhancement in autonomous control ability reduces the displacement area and COP radius to strengthen the physical stability [8]. The decrease in COP area and COP radius in this study may be due to the increase in the autonomous control ability of VF for enhancing physical stability. In addition, previous studies revealed that healthy adults under VF maintained body balance more effectively [28]. Therefore, visual information strengthens the sensory system of young people and increases the ability of autonomous control under the regulation of the central nervous system to enhance physical stability.
Previous studies revealed that the COP displacement of men was greater than that of women [17], which is consistent with the results of this study, i.e., the COPAP displacement of men is greater than that of women. The sway lengths of men and women were longer in the AP direction than in the ML direction, and the displacement range of men was larger; women indicated a stronger ability to perceive surrounding information and effectively integrated perceptual information [29]. In addition, the difference in height and weight between men and women caused the displacement range of men to be greater than that of women [17]. Therefore, in this study, women used the surrounding sensory system to integrate movement and promote greater stability. The COPAP velocity of men in this study was greater than that of women, which may be due to the higher upper body weight of men, resulting in a higher relative vertical position of the COM [17]. This will affect the projection of the COM and reduce the physical stability. In the absence of sensory aids, the posture control ability of men was worse [30]. Therefore, the lower COM of women with the participation of intelligent auxiliary equipment is beneficial for controlling the stability of the body. The COP radius and COP area of both women and men decreased after VF intervention, whereby those of women decreased more than those of men. Compared with men, women have less motor function, are more sensitive to surrounding information, and exhibit higher autonomous ability in balance control [30]. Therefore, smart insoles can increase VF and maintain physical stability. During balance control, women use the surrounding sensory information to increase autonomous control under the regulation of the central nervous system, thereby improving the stability of static standing. The limitations of this study were that the EMG and kinematic images of participants were not collected; moreover, it was difficult to detect the balance regulation of joint muscle vision conditions and joint angle. Therefore, the application of smart wearables in several weeks of balance training to assist the body to improve balance should be applied to individuals with unstable postures in future studies to investigate the benefits of VF on balance improvement.
Study limitations
The limitation of this study is that there is no comparison of age balance performance differences. Maturational processes also affecting the development of balance performance in youth differ in onset and velocity inter individually, consequently complicating comparisons based on chronological age only. future studies on children and adolescents of different ages should be compared in terms of their physiological age balance to explore their athletic performance.