Improvement of Gender Balance Based on the Real-Time Visual Feedback System of the Pressure Center of Smart Wearable Devices: A Case Control Study

Background: The body maintains stability by integrating inputs from the central nervous system of vision, hearing, proprioception, and multiple senses. With the development of smart wearable devices, smart wearable devices can provide real-time center of pressure (COP) position-assisted balance control, which is benecial to maintain physical balance. Methods: Forty healthy college students (20 male-20 female) participated in this study, and the posture balance actions of left-leg stance non-visual feedback, left -leg stance visual feedback, right-leg stance non-visual feedback, and right-leg stance visual feedback are performed. Visual feedback provides smart insoles matching Podoon APP on a tablet computer with the COP position displayed by a dot as real-time visual feedback. A mixed-design two-way ANOVA was performed and included the study. Results: The experimental results show that the displacement, velocity, radius, and area of the COP decreased signicantly in the left-leg stance visual feedback/right-leg stance visual feedback, the test compared with the parameters in the eft-leg stance non-visual feedback/right-leg stance non-visual feedback (P < 0.05). Providing visual feedback through intelligent insoles can reduce the movement of the center of mass (COM) and maintain physical stability for healthy young people of different genders. In the one leg visual/non-visual in standing, the COP maximum anteroposterior displacement, COP anteroposterior velocity, COP radius, and COP area of women are signicantly decreased than men (P < 0.05). Women have better real-time balance control ability than men with smart insoles. Conclusion: The simple intelligent wearable assisted devices can immediately increase the control ability in static stance men women, and women have better control ability than men.


Background
The body maintains its stability through its perception of space (i.e., balance ability) [1], and balance control is one of the important physical tness in humans [2]. To maintain such a static balance, the body typically uses "hip strategy" or "ankle strategy" to project the center of mass (COM) in the base of support [3]. The COM sway and its spatial relationship with the base of support are the basis for balance control and performance [4]. Therefore, in the study of biomechanics, the change in the center of pressure (COP) in balance of systems is often considered as the main analysis parameter. The smaller the plantar COP displacement, the higher is the body's ability in maintaining a static balance [5]. In other words, a good control of the change in planar COP while maintaining a static balance will be bene cial to the performance of balance ability. Maintenance or improvement of balance is important for athletes, the elderly, those with ankle or knee injury history, and patients with sarcopenia.
Through the integration of vision, hearing, proprioception, and multiple sensory inputs from the central nervous system, organisms understand the relative movements of various parts of the body, the relationship between the body and the environment, and achieve the goal of stable standing by continuously adjusting muscle activity [6]. With regard to the distance between a space and an object, the prediction, direction, reaction time, time point, stability, and balance re ected by the brain are mainly provided by vision, and these factors signi cantly affect players' performances in competitions [7]. Therefore, the visual system is crucial for balance control. When moving, human beings often use the information provided by the visual system as a reference [8]. Real-time visual feedback (VF) can effectively reduce COP sway and accelerate posture control during standing posture balance [9]. Past studies used the Wii balance board real-time feedback function to improve postural control and balance in people with multiple disabilities [10]. VF can strengthen the body's control of COP displacement and reduce the movement of the body's COM, and nally achieve the rehabilitation effect of improving the body's balance [11]. Therefore, assisting proprioception through the balance board or VF system may improve body posture and stability during movement or balance control. The body balance system is affected by many different factors, including age, height, BMI, and gender [12]. Gender differences exist in human postural stability. Past studies comparing boys and girls of the same age indicated that girls often demonstrated less postural sway [13], indicating gender differences in maintaining body balance. Furthermore, the study of gender differences in children's postural stability revealed that girls can integrate sensory input more effectively and rely more on somatosensory feedback than boys [14]. In addition, men are more likely to sway and cause physical instability than women because of their greater COP displacement during postural control [15]. Static and dynamic exercises show that women are excellent in maintaining static balance, affording posture stabilization and body balance maintenance [16]. Previous studies have shown that men have greater COP displacements after open-eyes/closed-eyes balance training, indicating that men are more unstable than women [17].
Therefore, the use of smart wearable devices to assist women or men with body posture control feedback will improve balance ability and women may perform better than men after VF.
In summary, COP change is an important index of balance control; it is an effective auxiliary method to provide real-time VF information. Smart wearable devices have been vigorously used in daily life. In the test of muscle fatigue in young healthy people, the vibration of insoles can compensate for the postural instability caused by fatigue and maintain the body balance [18]. Therefore, using real-time VF on the position of the COP provided by smart wearable devices effectively to maintain body balance can yield the bene ts of technology-assisted homeostasis in maintaining body balance and help maintain body balance and physical rehabilitation. This study hypothesizes the following: 1) The balance posture ability of young people to maintain standing balance in VF is higher than non-visual feedback (NF). 2) When using smart insoles to provide VF, it is suitable for healthy people of different genders to improve physical stability. The aim of this study is to investigate the immediate effects of real-time VF information provided by smart insoles on the balance control ability of static balance movement. This study provides insights into the effects of real-time VF systems of the COP provided by smart wearable devices on the body's balance ability.

Materials And Methods
Participants Forty healthy participants [20 males (age, 19.63±0.73; height, 1.67. ± 0.04; weight, 58 kg ± 6; mean ± SD) and 20 females (age, 20.74±0.98; height, 1.78. ± 0.05; weight, 71 kg ± 6; mean ± SD)] with no known balance pathology were included in the study. In addition, the inclusion criteria were normal visual acuity and contrast sensitivity. As required by the Helsinki Declaration, participants will be informed of the content, process, and precautions of the study group. They must understand and be willing to cooperate fully with the experimenter to sign the consent form. The study was approved by the Research Ethics balance included the support leg standing upright, and the nonsupport leg was exed at the knee of the support leg with the toes drooping naturally, the arms on the chest, and the palms on the shoulders. The iPad Pro used (iPad Pro, including the smart insoles APP) should be located at an eye-level height and 1.0 m apart from the participants. The NF group did not use the iPad VF.

Equipment
A force plate (BTS P6000, BTS Bioengineering, Italy) was used to collect the COP kinematics data: the COP maximum mediolateral displacement (COP ML maximum displacement), COP maximum anteroposterior displacement (COP AP maximum displacement), the COP mediolateral velocity (COP ML velocity), COP anteroposterior velocity (COP AP velocity), COP radius, and COP area. Force plate signals were collected at a sampling frequency of 600 Hz. Each data point of the pretest and post-test was calculated from the average of three COPs.

Statistical analysis
Statistical analyses were performed using MATLAB (R2014a, The MathWorks, USA). A mixed-design twoway ANOVA was performed and included the following: two vision conditions (NF and VF) × gender (woman and man) were used to compare the COP ML /COP AP maximum displacement, COP ML /COP AP velocity COP radius, and COP area. The statistical signi cance level was set at α = .05. Intraclass correlation coe cients (ICC) were calculated for the COP parameters in the NF and VF, as poor (ICC < 0.40), moderate (0.40 ≤ ICC < 0.60), good (0.60 ≤ ICC < 0.80), and excellent (ICC ≥ 0.80) [19]. The ICC ranged from 0.64 to 0.96.  62% and ▽6.82%). Therefore, the COP ML velocity or COP AP velocity of men/women decreased signi cantly decreased in the VF group compared with the NF group, and the COP AP velocity of women was signi cantly lower than that of men in each balance condition. This shows that women have better balance control ability than men.  93% and ▽14.21%). Therefore, the COP radius or COP area of men/women decreased signi cantly in the VF group compared with the NF group, and the COP radius and COP area of women decreased signi cantly decreased compared with that of men in each balance condition.

Discussion
The purpose of this study is to investigate the auxiliary effect of VF provided by smart insoles on realtime static balance control in healthy young people of different genders. The results showed that the displacement, velocity, radius, and area of COP decreased signi cantly, whereas those of men or women in OLS-VF, and the COP AP displacement, COP AP velocity, COP radius, and COP area of women decreased signi cantly 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 realtime balance control ability of women was higher than that of men.
After VF was provided, the COP AP maximum displacement, COP AP variance, COP ML maximum displacement, and COP ML 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 COP ML 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, COP AP velocity, and COP ML 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 COP AP 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 COP AP velocity controlled by the "ankle strategy" and the COP ML 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 COP AP velocity and COP ML 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 COP AP 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 COP AP 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 bene cial 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 di cult 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 bene ts 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.

Conclusions
Intelligent auxiliary equipment increases the participants' visual information, and the increase in VF may promote the integration of the central nervous system to increase the body's real-time postural stability. When a smart auxiliary equipment is applied to VF to increase visual information, it can increase the autonomous control ability of young people. It is bene cial for the central nervous system to control the balance mechanism to perform autonomous adjustments to maintain physical stability, and it would be better for women to control the sensory information around them autonomously. In this study, a simple smart auxiliary equipment was used to provide VF information of the COM to maintain the real-time balance ability of healthy people of different genders for static standing. Women demonstrated higher real-time balance ability in VF than men. Moreover, the use of smart insoles to provide VF yielded intuitive, simple, and real-time feedback with strong operability. In the future, this technology can be further extended to various rehabilitation purposes or improve the balance of the human body.

Declarations Ethical approval
The study was approved by the Research Ethics Committee of Hualien Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation (IRB109-053-B).

Consent for publication
Not applicable.

Availability of data and materials
The datasets during and/or analyzed during this study are available from the corresponding author on reasonable request.

Competing interests
There were no con icts of interest with other authors or institutions for this study.

Funding
This research received grant from the Lo-Hsu Medical Foundation, Inc., Lotung Poh-Ai Hospital (Number: E157).
Authors' contributions SJX, YL, JQL, and RH prepared the manuscript. ILW and YMC contributed to the experimental design and balance training exercise program. ILW, SJX, YL, and RH analyzed the data to describe the effects of body movement on VF training. SJX and YL analyzed the effects of training under the COP parameters between the pretest and post-test. ILW reviewed and edited the manuscript. All authors have read and approved the nal manuscript.