Postural coping strategies of the active elderly on shoulder disturbance related to anterior falls

Postural coping strategies of the active elderly on shoulder disturbance related to anterior falls | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Postural coping strategies of the active elderly on shoulder disturbance related to anterior falls Zheng Dong, Ju-won Song, Min-Ju Shin, Du-Bin Im, JiaHao Xu, XuanRu Wang, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4451886/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: Static postural stability in older adults is often subject to external disturbances leading to sudden changes in balance. Understanding the ability of older adults who engage in regular physical activity to adjust and control their posture under static conditions will help to develop and promote strategies to reduce fall risk. This study examined the differential effects of regular physical activity on postural adjustment and control in older adults, focusing on responses to pre-shoulder barriers and visual conditions. Methods: Thirty participants were divided into two groups: 15 younger and 15 physically active older adults. The study assessed their postural responses to controlled anterior shoulder perturbations under different visual conditions. Muscle activation patterns and co-contraction rates were measured using electromyography, joint angle changes were analyzed using imaging techniques, and postural control was assessed using a force platform. Results: The active older participant group demonstrated better balance control and faster postural adjustment, with notable findings including improved use of compensatory postural adjustment strategies and reduced postural sway. Visual conditions significantly affected postural control strategies, with reduced visual input increasing thigh and trunk stiffness. Conclusions: Physically active older adults demonstrate good performance in response to a forward perturbation experiment. This study emphasizes that faster anticipatory postural adjustments in response to forward perturbations, reduced postural amplitude and increased joint stiffness are effective in reducing fall risk. Biological sciences/Neuroscience Biological sciences/Neuroscience/Motor control Biological sciences/Neuroscience/Sensorimotor processing External disturbances Falls Elderly Posture adjustment Posture control Anterior disturbances Figures Figure 1 Figure 2 Figure 3 Figure 4 1 Introduction As the world grapples with an aging population, projections suggest that by 2050, over 16% of the global population will be aged 65 and above (World Health Organization, 2004 ). This trend is particularly pronounced in South Korea, where it is estimated that by 2030, the elderly population (aged 65 and above) will constitute 25.5% of the total population, escalating to 40.1% by 2050 (Korea Ministry of Health & Welfare, Future population estimation 2022). Such a demographic shift heralds a slew of public health challenges, with the issue of falls among the elderly being especially critical. Falls are not just a leading cause of injury-related hospitalization in those over 65, but the resultant increase in medical-economic burden and decline in health-related quality of life due to falls have enduring adverse effects (Boyé, Nicole DA, et al. 2013). 85% of falls occur in a forward or backward direction (Morikawa, Masanori, et al. 2021), and the fall direction is significantly associated with the injuries sustained by the elderly group. Lateral and backward falls are key factors leading to hip fractures in older individuals (Kannus, Pekka, et al. 2006). In contrast, forward falls are responsible for approximately 39% of wrist fractures, a rate substantially higher than that of hip fractures (Nevitt, M. C. et al. 1993). This highlights the significance of researching forward falls. Studies underscore that regular physical activity not only enhances the postural control abilities of the elderly (Lord, S., & Castell, S. 1994 ), preserves muscle mass (Summerhill, E.M., Angov, N., Garber, C. et al. 2007 ), but also reduces the incidence of falls (Sherrington, Catherine, et al. 2017; Papalia, Giuseppe Francesco, et al.2020). Elderly individuals who regularly engage in physical activities (PSA) exhibit markedly better balance control compared to their inactive peers (Perrin, Philippe P., et al.1999). This enhanced balance control is pivotal for the elderly, effectively reducing the risk of falls (Gerards, Marissa HG, et al.2017). In everyday life, external disturbances such as sudden stops while standing on public transport or being bumped by pedestrians increase the complexity of postural control. When the body's center of gravity extends beyond the support boundary, maintaining postural stability becomes a challenge. To adjust the posture and swiftly regain balance, two strategies are employed: Anticipatory Postural Adjustments (APAs) and Compensatory Postural Adjustments (CPAs). APA involves pre-emptive muscle activation in response to a disturbance through feedforward signals (Massion, Jean.1992; Aruin, Alexander S.et al.1995), while CPA entails compensatory postural adjustments post-disturbance through sensory feedback signals (Macpherson, J. M., et al.1989; Park, Sukyung, et al.2004). Effective postural control plays a crucial role in these adjustments. The stability of the human standing posture in the sagittal plane is maintained through a synergy of various postural control strategies, including those involving the ankle and hip joints (Alexandrov, Alexei V., et al.2005; Horak, F. B., & Nashner, L. M. 1986). When external disturbances cause the body's center of gravity to exceed the support surface, simple ankle joint strategies are typically employed to regain balance. However, when the torque at the ankle joint is insufficient for the forces generated by body movement, the hip joint strategy is employed in conjunction. As the speed of disturbance increases, the contribution of the hip joint also escalates (Runge, C. F., et al.1999), and compared to visual and vestibular signals, the hip joint angle becomes crucial for rapidly initiating balance recovery (Fujisawa, N., et al. 2005 ). The width of the Center of Pressure (COP) can be used to assess the balance condition of the elderly (Lafond, Danik, et al.2004; Nakamura, H., Tsuchida, T., & Mano, Y. 2001 ), and the changes in ankle muscles at the Anterior-Posterior direction and hip muscles at the Medial-Lateral direction, which seem to assume a defensive dominance, are closely related to reducing postural sway (Winter, D. A. 1995 ). Therefore, while joint strategies influence postural control, changes in neuromuscular function from a neuromuscular perspective also reinforce postural control. For the elderly, aging-related changes in neuromuscular function, such as enhanced co-contraction characteristics of muscles increasing joint stiffness, reduce the difficulty of balance control (Nagai, Koutatsu, et al.2011; Hortobágyi, Tibor, and Paul DeVita.2000), but also increase muscle stiffness, thereby affecting the efficiency of postural control (Mian, Omar S., et al.2006; Nagai, Koutatsu, et al.2011; Piche, Elodie, et al. 2022). There is a lack of research on postural coping strategies of the elderly in response to anterior shoulder perturbations. Therefore, given the potential negative effects of aging, it is imperative to examine how older adults cope with external perturbations from the perspective of postural adjustment and control. Furthermore, the differences in sagittal postural adjustment and control in response to anterior shoulder perturbations between physically active older adults and younger adults under different visual conditions remain unclear. 2 Methods 2.1 Subjects This research incorporated 15 young (10 male, 5 female) and 15 physically active elderly (9 male, 6 female). The young group had an average age of 25.07 ± 2.52 years, height of 166.27 ± 9.37 cm, and weight of 63.40 ± 12.83 kg. The elderly group's averages were 72.07 ± 2.34 years for age, 161.57 ± 5.21 cm for height, and 63.04 ± 7.89 kg for weight. Young participants were recruited from universities, whereas older participants were recruited from local senior activity centers. The criteria for the physically active elderly group were determined via a survey, indicating participation in physical activity for three consecutive months, at least five days a week, with sessions lasting more than 60 minutes (80%) or between 30 to 60 minutes (20%). Activities comprised fitness (40%), table tennis (33.3%), and brisk walking (26.7%). All participants had normal vision, adequate cognitive abilities, and no neurological or musculoskeletal conditions, with no surgical procedures in the past six months. Each participant signed an informed consent form approved by the institutional review committee of the university (202310-SB-179-01). 2.2 Experimental setup and procedure Before the onset of the anterior disturbance participants were soft upper-body wearable vest to which a rope was attached at a fixed point on the shoulder of the vest. The rope remained slack until the moment of pull, at which point the tension increased until the rope was fully extended horizontally, marking the moment of disturbance (T0). This instant was accurately calculated using an accelerometer. The method involved participants standing barefoot on a force platform with their feet shoulder-width apart. Using tape to mark the position of their feet at the top of the force platform, the experimenter ensured consistency in foot position throughout the experiment to maintain uniformity among all participants. The weight was set (mass = base weight of 2 kg + 5% of the participant's weight). After securing the harness to the ceiling. The pendulum height was adjusted to ensure that the point of disturbance was also parallel to the participant when the pendulum was dropped, and a rope was attached to the subject's shoulder at rest. The pendulum started from a 60° angle in a vertical direction, at a distance of 0.8m from the participant. Facing the external disturbance device, participants were blindfolded and wore earplugs. Upon disturbance, they were instructed to maintain balance and avoid lifting their soles of the force platform as much as possible. Experiments under both predictable and unpredictable conditions were conducted five times each, with a 2-minute interval between each trial, starting with the trials under unpredictable conditions. 2.3 Instrumentation Muscle electrical signals were collected using a wireless electromyography (EMG) device (Cometa Wave Plus, Italy) with a frequency range of 10-500Hz and a sampling rate of 2000Hz. An acceleration sensor (Cometa Wave Plus, Italy) was placed at the point where the rope connected to the flexible vest worn by the participants to record the instant of pulling (T0). According to the recommendations of the SENIAM (2014) EMG guidelines, seven muscles were recorded: Rectus Femoris (RF), Biceps Femoris (BF), Tibialis Anterior (TA), Medial Gastrocnemius (MG), Soleus (SOL), Rectus Abdominis (RA), and Longus Erector Spinae (LE). After cleaning the muscles with alcohol wipes, electrodes were attached to each muscle. A force platform (Kistler 9260AA, Switzerland) was used to record ground reaction forces and torques. The force platform was connected to the Cometa system, and the start times were synchronized. A camera (SONY FDR-AX700, Japan) and software (Dartfish Pro, Switzerland) were used to record and calculate changes in angle data. Markers were placed on each joint segment: Segment one was defined from the acromioclavicular joint to the midpoint of the anterior-posterior (AP) superior iliac spines; segment two from the lateral border of the thigh to the lateral epicondyle of the femur and then to the lateral malleolus; and segment three from the lateral epicondyle of the femur to the lateral malleolus and then to the second metatarsal head. The angular changes between each segment were calculated based on these axes. 2.4 Data processing EMG data were filtered and rectified using a fourth-order, zero-lag Butterworth filter through the device's proprietary processing software. The force platform data were also filtered using the device's software. The moment when the pendulum fell and remained parallel to the participant's torso, with the disturbance rope fully stretched, was identified as the moment of disturbance (T0). This was determined by the first major peak in the acceleration signal, confirmed and recorded by experienced researchers. T0 was set as the common reference point for all signals and aligned accordingly. Data were segmented and processed using Python 3.10 programming, averaging the three trial data for each participant. Following the guidelines for processing and normalizing electromyographic activity integrals for anticipatory and compensatory movements as suggested by Kanekar, N., & Aruin, A. S. (2014), the data were divided into four periods: APA1 (-250ms ~ -100ms), APA2 (-100ms ~ + 50ms), CPA1 (+ 50ms ~ + 200ms), CPA2 (+ 200ms ~ + 350ms). The IEMG for each period was further corrected against the baseline activity from − 600ms to -450ms relative to T0: $${Int}_{EMGi}=\underset{twi}{\overset{ }{\int }}EMG-\underset{-600}{\overset{-450}{\int }}EMG$$ Peak muscle activity for each muscle of each participant was normalized, with all integrals (IEMG NORM) ranging from + 1 to -1. Positive values indicated muscle activation, while negative values indicated activity below the background level (muscle inhibition): $${IEMG}_{NORM} = \frac{{Int}_{{EMG}_{i}}}{{IEMG}_{max}}$$ The force parameters derived from the force platform were calculated using the COP formula by (Donath, Lars, et al. 2012.): $${\text{COP}}_{pathlenght} = {\sum }_{i=2}^{n}\sqrt{{({ax}_{i}-{ax}_{i-1})}^{2}+{({ay}_{i}-{ay}_{i-1})}^{2}}$$ The Co-contraction ratio (CCR) was calculated using the formula proposed by(Hammond et al. 1988 ): $$\text{CCR}\text{=}\frac{sEMG\left(antagonisticmuscle\right)}{sEMG\left(agonisticmuscle\right)+sEMG\left(antagonisticmuscle\right)}$$ Joint angle calculations were performed for each participant by measuring the angle before the disturbance and the maximum angle within one second after the disturbance. The change in angle between segments was calculated by subtracting the pre-disturbance angle from the post-disturbance maximum angle. For segment one, with the hip joint as the axis, the angle changes within 180 degrees, based on this axis as the reference plane. In segment two, with the knee joint as the axis, the angle changes occurred within 180 degrees. For segment three, with the ankle joint as the axis, the angle changes occurred within 90 degrees. 2.5 Statistical analysis Statistical analyses were performed in SPSS26 for Windows 11 (SPSS Inc., Chicago, USA). The IEMG NORM was tested for significant differences for each muscle, differences in COP movement trajectories, CCR indices, and joint angle changes. Data were tested for normal distribution using the Shapiro-Wilk test, with independent t-tests between groups and paired t-tests within groups for data that met normal distribution, and nonparametric Mann-Whitney U tests between groups and Wilcoxon signed rank-sum tests within groups for data that did not meet normal distribution. All tests for statistical significance were set at P < 0.05. 3 Methods 3.1 Integrated electromyographic activity The IEMG NORM data shown in Fig. 1 shows that under unpredictable conditions, statistically significant differences were found between the elderly and younger groups for MG but not for BF, SOL, and LE muscles.MG muscles were found to have higher muscle activation in the elderly group during the CPA1 phase (p < 0.010), and in the CPA2 phase, the elderly group was faster to lower muscle activation, while the younger group had higher MG than the elderly group (p < 0.004). Under predictable conditions, dorsal muscle activity was increased in the elderly group during the APA phase compared to the younger group, with significant differences observed between groups in the APA1 phase SOL (p < 0.004), and between groups in the APA2 phase BF (p < 0.009), MG (p < 0.014), SOL (p < 0.001). In addition, significant differences were observed in MG (p < 0.044), and CPA2 MG (p < 0.045) between groups in the CPA1 phase, and MG muscle activation was more active in the CPA phase in the young group. In the within-group comparisons between the unpredictable and predictable conditions, the elderly group had a higher prevalence of APA1 phase BF (p < 0.016), MG (p < 0.001), SOL (p < 0.011), LE (p < 0. 018), APA2 phase BF (p < 0.000), MG (p < 0.000), SOL (p < 0.000), LE (p < 0.004), CPA1 phase MG (p < 0.001), LE (p < 0.014), CPA2 phase MG (p < 0.001), SOL (p < 0.011) had significant between-group differences between conditions. Compared to the unpredictable group, the elderly group had active muscle activation responses in the dorsal muscles in the APA phase at the predictable time, along with reduced muscle activation in the MG muscles in the CPA1 phase, in addition to increased muscle activation in the LE muscles in the CPA1 phase. 3.2 Co-Contraction Index of muscle Figure 2 's findings reveal no discernible difference in the Co-Contraction Ratio (CCR) between the elderly group and young group participants under unpredictable circumstances. Nevertheless, a significant divergence in trunk muscle co-contraction rates during the APA under predictable conditions was evident between the groups (p < 0.035). In the face of unpredictable conditions, the elderly group demonstrated a notably higher co-contraction index in the thigh and trunk areas during the APA, showing significant differences (APA thigh, p < 0.026; APA trunk, p < 0.051). In contrast, the young group exhibited an elevated co-contraction index in the shank during the APA in predictable settings, compared to unpredictable ones (APA shank, p < 0.033). 3.3 Displacements of center of pressure and A/P and M/L As shown in Fig. 3 , under unpredictable conditions, the center of pressure (COP) motion trajectory was significantly longer in the older group than in the younger group (p < 0.033), and the anterior-posterior (A/P) motion trajectory (p < 0.031) and the medial-lateral (M/L) motion trajectory (p < 0.011) were longer in the older group than in the younger group. In contrast, medial-lateral (M/L) movement trajectories were significantly longer in the older group than in the younger group under predictable conditions (p < 0.007). 3.4 Displacements of Joint Angle As shown in Fig. 4 , in predictable conditions, the elderly group demonstrated less variation in three joint angles compared to the young group, exhibiting significant intergroup differences (Back p < 0.018; Knee p < 0.036; Ankle p < 0.016). Under unpredictable conditions, the elderly group has smaller changes in the ankle joint angle relative to the young group, marking a significant intergroup difference (p < 0.027). 4 Discussion The focus of this study was to examine differences in postural adjustment and control between a group of regularly exercising elderly and a group of young in general across visual conditions. The group of elderly who exercised regularly would perform better in the APA phase compared to younger ones and the elderly group would be less adept at using ankle strategies. Overall, visual feedback is critical, and faster APA activation contributes to postural control in the elderly who rely more on improved postural stability through synergistic control between multiple joints. 4.1 Gains from exercise In scenarios involving predictable postural disturbances, our IEMG analyses showed that the elderly group exhibited faster muscle activation responses during the initial 'anticipatory postural adjustment' (APA) compared to the younger group. During the APA2 phase, The dorsal four muscles in particular showed significant muscle activation. Research by Kanekar, N., & Aruin, A. S. (2014) highlights that aging increases the delay in APA and consequently increases the amplitude of Compensatory Postural Adjustments (CPA) due to the reduced ability of the elderly to make feedforward anticipatory postural adjustments. Despite the age-related effects on APA, the elderly retain an inherent capacity for anticipatory adjustments (Kanekar, N., & Aruin, A. S. 2014). This aspect was particularly pronounced in our subjects during APA2, where muscle activation was observed. Furthermore, regular physical activity was found to increase muscle activation in APA2. Although this increase did not significantly reduce the amplitude of the CPA, it proved to be beneficial for the management of postural control after disturbances. The study by Lelard, T., & Ahmadi, S.2015 highlights the significant benefits of regular physical activity in improving postural balance. The elderly showed significantly greater activation of the biceps femoris (BF) muscle during CPA2 compared to the young group, regardless of visual constraints. This observation is in line with the findings of (Maeda, Yusuke, et al. 2015), who found more vigorous muscle activation in the femoral region in the elderly group. This phenomenon is related to the strategic selection of muscle activations to improve postural stability, such as the integration of hip joint strategies when ankle joint strategies are inadequate (Horak, F. B., & Nashner, L. M. 1986). Crucially, the elderly were able to minimize changes in joint angle through these adjustments in muscle activity. Regardless of the visual intervention, there were no significant changes in ankle angle in the elderly group, especially when compared to the young group. Given the age-related decline in ankle stability (Nakamura, H., Tsuchida, T., & Mano, Y. 2001 ), the elderly are sensitive to plantarflexion movements of the ankle. In contrast, the young group is more likely to use ankle strategies, as the elderly rely more on strategic control due to aging (Manchester, Diane, et al. 1989). 4.2 Effect of Vision For elderly adults, vision has a significant effect on postural stability. Compared to the unpredictable, the IEMG results at the predictable showed that no significant differences were found in the younger group for the within-group comparison between the two visual conditions, but the elderly group had significant differences in the predictable condition for the dorsal muscles BF, MG, SOL and LE in the APA1, APA2, and it is important to note the feedback from vision that the elderly group MG and SOL muscles at the predictable time had decreased muscle activation in the CPA phase reduced muscle activation. Combined with changes in COP displacement longer COP and A/P displacements in elderly group in the absence of visual feedback. A study by (Shelton, Andrew D., et al. 2024) reported that the elderly group has relatively weaker postural stability in the AP direction than younger adults. While the influence of vision is critical for postural stability in the elderly group, the addition of visual feedback in our study decreased displacement in the AP direction and increased displacement in the ML direction. Because the elderly group relies more on postural control through vision (Pyykko, I., Jantti, P., & Aalto, H. ( 1990 ). However, it has also been suggested that the elderly group is better at stabilizing and orienting their bodies relative to support surfaces, relying more on proprioception than visual cues (Wiesmeier, I. K., Dalin, D., & Maurer, C. (2015). On the other hand, A/P directional balance is dominated by dorsiflexion and plantarflexion, and M/L directional balance is derived from hip control (Winter, David A., et al. 1996). In the absence of visual information, the elderly group has an increased reliance on the ankle and thigh muscles to maintain A/P and M/L balance. Therefore, the elderly group must activate the ankle and hip muscles more to minimize postural sway. This is supported by the results of muscle co-contraction rates: muscle co-contraction indices are higher in the thigh and trunk segments in unpredictable compared to the predictable elderly group and serve to compensate for joint stiffness (Lee, P. J., Rogers, E. L., & Granata, K. P. (2006)) (Granata, K. P., et al. 2004). The decrease in visual dependence is accompanied by a shift in dependence to increased muscle contraction (Benjuya, N., Melzer, I., & Kaplanski, J. ( 2004 ). While COP and A/P shifts in young adults are greater when shifts are predictable compared to when they are unpredictable, the increased COP and A/P shifts appear to respond to changes in perturbation in a precisely tuned and controlled manner. They exhibit a reduction in dorsal muscle activation and an increase in muscle co-contraction, along with significant ankle joint angle changes, preferring ankle joint strategies for postural control. Beyond visual factors, fear and anxiety are pivotal in influencing postural control. Research has shown that the elderly group concerned about falling (Maki, B. E., Holliday, P. J., & Topper, A. K., 1991), and those experiencing fear (Davis, Justin R., et al., 2009) and anxiety, demonstrate notable differences in postural control. The fear associated with falling (Nagai, Koutatsu, et al., 2012) correlates with increased co-contraction during standing postural control in the elderly. Although our study did not directly measure fear and anxiety, the heightened muscle co-contraction observed in the elderly under unpredictable disturbances likely reflects their apprehension about falling. Conversely, the young group, seemingly devoid of such fears, showed greater COP, A/P displacements and ankle angle changes in predictable conditions, suggesting a higher confidence in their control capabilities. When considering the impact of fear, a more comprehensive understanding of the elderly's postural adjustments and control strategies emerges, especially when comparing their responses in both predictable and unpredictable scenarios to those of the young group. 5 Conclusion This study confirms that regular physical activity significantly enhances the postural control abilities of elderly individuals when coping with anterior disturbances. The findings indicate that the elderly participants were able to more effectively activate their thigh and trunk muscles during anterior shoulder disturbances, which significantly reduced the angular changes in the ankles and knees, thereby improving postural stability. Moreover, this group appeared quicker response times in anticipatory postural adjustments (APA) utilizing visual feedback, further enhancing their overall postural control capabilities. In addition, the group demonstrated faster reaction times when using visual feedback for anticipatory postural adjustment (APA), further improving their overall postural control. In unpredictable conditions, older adults reduce the risk of falling by increasing the co-contraction of muscle groups and limiting their range of motion. Declarations Ethics approval and consent to participate This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of Chungnam National University Bioethics Committee (No.202310-SB-179-01). Consent for publication Informed consent was obtained from all individual participants included in the study. Availability of data and materials The datasets generated or analyzed during this study are available from the corresponding author on reasonable request. Competing interests All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. Funding This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korean government(MSIT)：2022R1A5A7085156. Authors' contributions Conceptualization: M.Y.J, D.Z; Recruitment of experimenters and full assistance: D.Z, S.M.J, I.D.B, X.J.H; Methodology: M.Y.J, D.Z; Data processing and analysis: D.Z, S.M.J, I.D.B, X.J.H, W.X.R ; Writing: D.Z, M.Y.J; Writing - review and editing: S.J.W. Acknowledgments This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korean government(MSIT)：2022R1A5A7085156. 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Nagai, Koutatsu, et al.2011 ;Piche, Elodie, et al. 2022; Python. Available online: https://www.python.org Pyykko, I., Jantti, P., & Aalto, H. (1990). Postural control in elderly subjects. Age and ageing, 19(3), 215-221. Runge, C. F., et al. (1999) "Ankle and hip postural strategies defined by joint torques." Gait & posture 10.2 (1999): 161-170. Shelton, Andrew D., et al. (2024) "Does the effect of walking balance perturbations generalize across contexts?." Human Movement Science 93 (2024): 103158. Sherrington, Catherine, et al. (2017) "Exercise to prevent falls in elderly group: an updated systematic review and meta-analysis." British journal of sports medicine 51.24 (2017): 1750-1758. Summerhill, E.M., Angov, N., Garber, C. et al. (2007) Respiratory Muscle Strength in the Physically Active Elderly. Lung 185, 315–320 (2007). https://doi.org/10.1007/s00408-007-9027-9 Taylor, Adrian H., et al. (2004) "Physical activity and elderly group: a review of health benefits and the effectiveness of interventions." Journal of sports sciences 22.8 (2004): 703-725. Wiesmeier, I. K., Dalin, D., & Maurer, C. (2015). Elderly use proprioception rather than visual and vestibular cues for postural motor control. Frontiers in aging neuroscience, 7, 97. Winter, D. A. (1995). Human balance and posture control during standing and walking. Gait & posture, 3(4), 193-214.） Winter, David A., et al. (1996) "Unified theory regarding A/P and M/L balance in quiet stance." Journal of neurophysiology 75.6 (1996): 2334-2343. World Health Organization, 2004. http://www.who.int/en Accessed, June 2004. Wuehr, Max, et al. (2014) "Balance control and anti‐gravity muscle activity during the experience of fear at heights." Physiological reports 2.2 (2014): e00232. Additional Declarations No competing interests reported. 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University","correspondingAuthor":false,"prefix":"","firstName":"Ju-won","middleName":"","lastName":"Song","suffix":""},{"id":309626572,"identity":"33082cc4-5647-44ad-a935-e60dab5fff44","order_by":2,"name":"Min-Ju Shin","email":"","orcid":"","institution":"Chungnam National University","correspondingAuthor":false,"prefix":"","firstName":"Min-Ju","middleName":"","lastName":"Shin","suffix":""},{"id":309626573,"identity":"df418f97-04c3-4c65-9e69-f48c9afb1577","order_by":3,"name":"Du-Bin Im","email":"","orcid":"","institution":"Chungnam National University","correspondingAuthor":false,"prefix":"","firstName":"Du-Bin","middleName":"","lastName":"Im","suffix":""},{"id":309626575,"identity":"b13c9ec2-56aa-4f30-9666-e8b88369d684","order_by":4,"name":"JiaHao Xu","email":"","orcid":"","institution":"Chungnam National University","correspondingAuthor":false,"prefix":"","firstName":"JiaHao","middleName":"","lastName":"Xu","suffix":""},{"id":309626576,"identity":"c33d7549-e889-4166-8281-c3b56b0010b6","order_by":5,"name":"XuanRu Wang","email":"","orcid":"","institution":"Chungnam National University","correspondingAuthor":false,"prefix":"","firstName":"XuanRu","middleName":"","lastName":"Wang","suffix":""},{"id":309626577,"identity":"bcf9e619-f921-4e60-adbd-9cf4adb1a040","order_by":6,"name":"Young-Jin Moon","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAsUlEQVRIiWNgGAWjYNACHhsYK4FoLWkka2E4TIIW3fbmY495ZM7Lm0skMH74wZCWT1CL2Zlj6cY8PLcNd85IYJbsYcixbCCo5UaOmTRQS4LBjQQGaQaGCgPCtkC0nANpYf5NipYDIC1sQFtyiNBy5lia5ByeZMMNZx62WfYYpBGh5XjzMYm3PXbyBseTD9/4UZFMWAsIMPH2gCjGBgYG4jQA1f74QaTKUTAKRsEoGJkAACoKNe9LWFZPAAAAAElFTkSuQmCC","orcid":"","institution":"Chungnam National University","correspondingAuthor":true,"prefix":"","firstName":"Young-Jin","middleName":"","lastName":"Moon","suffix":""}],"badges":[],"createdAt":"2024-05-21 03:22:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4451886/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4451886/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":57949706,"identity":"3150c91c-bbbe-41e7-85b6-47d1e73cce11","added_by":"auto","created_at":"2024-06-07 20:52:47","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":522638,"visible":true,"origin":"","legend":"\u003cp\u003eEMG integral activity of four states under unpredictable and predictable conditions\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4451886/v1/cd4803267f30848f05bf6251.jpg"},{"id":57949544,"identity":"d1d3aebd-806d-41cd-b01f-22c7881c51d8","added_by":"auto","created_at":"2024-06-07 20:44:47","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":354130,"visible":true,"origin":"","legend":"\u003cp\u003eMuscle co-contraction rates in the APA and CPA phases under unpredictable and predictable conditions\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4451886/v1/0a108941ab6c471b77deceb9.jpg"},{"id":57948395,"identity":"bd19fd1c-887c-4487-aaf6-35554ac141c2","added_by":"auto","created_at":"2024-06-07 20:36:47","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":198074,"visible":true,"origin":"","legend":"\u003cp\u003eUnpredictable and Predictable Center of Pressure Trajectory\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4451886/v1/74ecd98018e5ad7c90970305.jpg"},{"id":57948397,"identity":"85b12d34-9d3b-4584-bd57-52a1fa361470","added_by":"auto","created_at":"2024-06-07 20:36:47","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":139327,"visible":true,"origin":"","legend":"\u003cp\u003eJoint angle displacements in unpredictable and predictable conditions\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4451886/v1/f42208826bed27599e8c79e5.jpg"},{"id":66740218,"identity":"1571673f-1351-497c-bd04-d20f9cbec383","added_by":"auto","created_at":"2024-10-16 05:38:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1639752,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4451886/v1/62185828-12d7-461f-93da-6c4bc77b15fe.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Postural coping strategies of the active elderly on shoulder disturbance related to anterior falls","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eAs the world grapples with an aging population, projections suggest that by 2050, over 16% of the global population will be aged 65 and above (World Health Organization, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). This trend is particularly pronounced in South Korea, where it is estimated that by 2030, the elderly population (aged 65 and above) will constitute 25.5% of the total population, escalating to 40.1% by 2050 (Korea Ministry of Health \u0026amp; Welfare, Future population estimation 2022). Such a demographic shift heralds a slew of public health challenges, with the issue of falls among the elderly being especially critical. Falls are not just a leading cause of injury-related hospitalization in those over 65, but the resultant increase in medical-economic burden and decline in health-related quality of life due to falls have enduring adverse effects (Boy\u0026eacute;, Nicole DA, et al. 2013). 85% of falls occur in a forward or backward direction (Morikawa, Masanori, et al. 2021), and the fall direction is significantly associated with the injuries sustained by the elderly group. Lateral and backward falls are key factors leading to hip fractures in older individuals (Kannus, Pekka, et al. 2006). In contrast, forward falls are responsible for approximately 39% of wrist fractures, a rate substantially higher than that of hip fractures (Nevitt, M. C. et al. 1993). This highlights the significance of researching forward falls.\u003c/p\u003e \u003cp\u003eStudies underscore that regular physical activity not only enhances the postural control abilities of the elderly (Lord, S., \u0026amp; Castell, S. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1994\u003c/span\u003e), preserves muscle mass (Summerhill, E.M., Angov, N., Garber, C. et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), but also reduces the incidence of falls (Sherrington, Catherine, et al. 2017; Papalia, Giuseppe Francesco, et al.2020). Elderly individuals who regularly engage in physical activities (PSA) exhibit markedly better balance control compared to their inactive peers (Perrin, Philippe P., et al.1999). This enhanced balance control is pivotal for the elderly, effectively reducing the risk of falls (Gerards, Marissa HG, et al.2017).\u003c/p\u003e \u003cp\u003eIn everyday life, external disturbances such as sudden stops while standing on public transport or being bumped by pedestrians increase the complexity of postural control. When the body's center of gravity extends beyond the support boundary, maintaining postural stability becomes a challenge. To adjust the posture and swiftly regain balance, two strategies are employed: Anticipatory Postural Adjustments (APAs) and Compensatory Postural Adjustments (CPAs). APA involves pre-emptive muscle activation in response to a disturbance through feedforward signals (Massion, Jean.1992; Aruin, Alexander S.et al.1995), while CPA entails compensatory postural adjustments post-disturbance through sensory feedback signals (Macpherson, J. M., et al.1989; Park, Sukyung, et al.2004). Effective postural control plays a crucial role in these adjustments.\u003c/p\u003e \u003cp\u003eThe stability of the human standing posture in the sagittal plane is maintained through a synergy of various postural control strategies, including those involving the ankle and hip joints (Alexandrov, Alexei V., et al.2005; Horak, F. B., \u0026amp; Nashner, L. M. 1986). When external disturbances cause the body's center of gravity to exceed the support surface, simple ankle joint strategies are typically employed to regain balance. However, when the torque at the ankle joint is insufficient for the forces generated by body movement, the hip joint strategy is employed in conjunction. As the speed of disturbance increases, the contribution of the hip joint also escalates (Runge, C. F., et al.1999), and compared to visual and vestibular signals, the hip joint angle becomes crucial for rapidly initiating balance recovery (Fujisawa, N., et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The width of the Center of Pressure (COP) can be used to assess the balance condition of the elderly (Lafond, Danik, et al.2004; Nakamura, H., Tsuchida, T., \u0026amp; Mano, Y. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), and the changes in ankle muscles at the Anterior-Posterior direction and hip muscles at the Medial-Lateral direction, which seem to assume a defensive dominance, are closely related to reducing postural sway (Winter, D. A. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). Therefore, while joint strategies influence postural control, changes in neuromuscular function from a neuromuscular perspective also reinforce postural control. For the elderly, aging-related changes in neuromuscular function, such as enhanced co-contraction characteristics of muscles increasing joint stiffness, reduce the difficulty of balance control (Nagai, Koutatsu, et al.2011; Hortob\u0026aacute;gyi, Tibor, and Paul DeVita.2000), but also increase muscle stiffness, thereby affecting the efficiency of postural control (Mian, Omar S., et al.2006; Nagai, Koutatsu, et al.2011; Piche, Elodie, et al. 2022). There is a lack of research on postural coping strategies of the elderly in response to anterior shoulder perturbations. Therefore, given the potential negative effects of aging, it is imperative to examine how older adults cope with external perturbations from the perspective of postural adjustment and control. Furthermore, the differences in sagittal postural adjustment and control in response to anterior shoulder perturbations between physically active older adults and younger adults under different visual conditions remain unclear.\u003c/p\u003e"},{"header":"2 Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Subjects\u003c/h2\u003e \u003cp\u003eThis research incorporated 15 young (10 male, 5 female) and 15 physically active elderly (9 male, 6 female). The young group had an average age of 25.07\u0026thinsp;\u0026plusmn;\u0026thinsp;2.52 years, height of 166.27\u0026thinsp;\u0026plusmn;\u0026thinsp;9.37 cm, and weight of 63.40\u0026thinsp;\u0026plusmn;\u0026thinsp;12.83 kg. The elderly group's averages were 72.07\u0026thinsp;\u0026plusmn;\u0026thinsp;2.34 years for age, 161.57\u0026thinsp;\u0026plusmn;\u0026thinsp;5.21 cm for height, and 63.04\u0026thinsp;\u0026plusmn;\u0026thinsp;7.89 kg for weight. Young participants were recruited from universities, whereas older participants were recruited from local senior activity centers. The criteria for the physically active elderly group were determined via a survey, indicating participation in physical activity for three consecutive months, at least five days a week, with sessions lasting more than 60 minutes (80%) or between 30 to 60 minutes (20%). Activities comprised fitness (40%), table tennis (33.3%), and brisk walking (26.7%). All participants had normal vision, adequate cognitive abilities, and no neurological or musculoskeletal conditions, with no surgical procedures in the past six months. Each participant signed an informed consent form approved by the institutional review committee of the university (202310-SB-179-01).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Experimental setup and procedure\u003c/h2\u003e \u003cp\u003eBefore the onset of the anterior disturbance participants were soft upper-body wearable vest to which a rope was attached at a fixed point on the shoulder of the vest. The rope remained slack until the moment of pull, at which point the tension increased until the rope was fully extended horizontally, marking the moment of disturbance (T0). This instant was accurately calculated using an accelerometer. The method involved participants standing barefoot on a force platform with their feet shoulder-width apart. Using tape to mark the position of their feet at the top of the force platform, the experimenter ensured consistency in foot position throughout the experiment to maintain uniformity among all participants. The weight was set (mass\u0026thinsp;=\u0026thinsp;base weight of 2 kg\u0026thinsp;+\u0026thinsp;5% of the participant's weight). After securing the harness to the ceiling. The pendulum height was adjusted to ensure that the point of disturbance was also parallel to the participant when the pendulum was dropped, and a rope was attached to the subject's shoulder at rest. The pendulum started from a 60\u0026deg; angle in a vertical direction, at a distance of 0.8m from the participant. Facing the external disturbance device, participants were blindfolded and wore earplugs. Upon disturbance, they were instructed to maintain balance and avoid lifting their soles of the force platform as much as possible. Experiments under both predictable and unpredictable conditions were conducted five times each, with a 2-minute interval between each trial, starting with the trials under unpredictable conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Instrumentation\u003c/h2\u003e \u003cp\u003eMuscle electrical signals were collected using a wireless electromyography (EMG) device (Cometa Wave Plus, Italy) with a frequency range of 10-500Hz and a sampling rate of 2000Hz. An acceleration sensor (Cometa Wave Plus, Italy) was placed at the point where the rope connected to the flexible vest worn by the participants to record the instant of pulling (T0). According to the recommendations of the SENIAM (2014) EMG guidelines, seven muscles were recorded: Rectus Femoris (RF), Biceps Femoris (BF), Tibialis Anterior (TA), Medial Gastrocnemius (MG), Soleus (SOL), Rectus Abdominis (RA), and Longus Erector Spinae (LE). After cleaning the muscles with alcohol wipes, electrodes were attached to each muscle.\u003c/p\u003e \u003cp\u003eA force platform (Kistler 9260AA, Switzerland) was used to record ground reaction forces and torques. The force platform was connected to the Cometa system, and the start times were synchronized.\u003c/p\u003e \u003cp\u003eA camera (SONY FDR-AX700, Japan) and software (Dartfish Pro, Switzerland) were used to record and calculate changes in angle data. Markers were placed on each joint segment: Segment one was defined from the acromioclavicular joint to the midpoint of the anterior-posterior (AP) superior iliac spines; segment two from the lateral border of the thigh to the lateral epicondyle of the femur and then to the lateral malleolus; and segment three from the lateral epicondyle of the femur to the lateral malleolus and then to the second metatarsal head. The angular changes between each segment were calculated based on these axes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Data processing\u003c/h2\u003e \u003cp\u003eEMG data were filtered and rectified using a fourth-order, zero-lag Butterworth filter through the device's proprietary processing software. The force platform data were also filtered using the device's software. The moment when the pendulum fell and remained parallel to the participant's torso, with the disturbance rope fully stretched, was identified as the moment of disturbance (T0). This was determined by the first major peak in the acceleration signal, confirmed and recorded by experienced researchers. T0 was set as the common reference point for all signals and aligned accordingly.\u003c/p\u003e \u003cp\u003eData were segmented and processed using Python 3.10 programming, averaging the three trial data for each participant. Following the guidelines for processing and normalizing electromyographic activity integrals for anticipatory and compensatory movements as suggested by Kanekar, N., \u0026amp; Aruin, A. S. (2014), the data were divided into four periods: APA1 (-250ms ~ -100ms), APA2 (-100ms\u0026thinsp;~\u0026thinsp;+\u0026thinsp;50ms), CPA1 (+\u0026thinsp;50ms\u0026thinsp;~\u0026thinsp;+\u0026thinsp;200ms), CPA2 (+\u0026thinsp;200ms\u0026thinsp;~\u0026thinsp;+\u0026thinsp;350ms). The IEMG for each period was further corrected against the baseline activity from \u0026minus;\u0026thinsp;600ms to -450ms relative to T0:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$${Int}_{EMGi}=\\underset{twi}{\\overset{ }{\\int }}EMG-\\underset{-600}{\\overset{-450}{\\int }}EMG$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ePeak muscle activity for each muscle of each participant was normalized, with all integrals (IEMG NORM) ranging from +\u0026thinsp;1 to -1. Positive values indicated muscle activation, while negative values indicated activity below the background level (muscle inhibition):\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$${IEMG}_{NORM} = \\frac{{Int}_{{EMG}_{i}}}{{IEMG}_{max}}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe force parameters derived from the force platform were calculated using the COP formula by (Donath, Lars, et al. 2012.):\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$${\\text{COP}}_{pathlenght} = {\\sum }_{i=2}^{n}\\sqrt{{({ax}_{i}-{ax}_{i-1})}^{2}+{({ay}_{i}-{ay}_{i-1})}^{2}}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe Co-contraction ratio (CCR) was calculated using the formula proposed by(Hammond et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1988\u003c/span\u003e):\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\text{CCR}\\text{=}\\frac{sEMG\\left(antagonisticmuscle\\right)}{sEMG\\left(agonisticmuscle\\right)+sEMG\\left(antagonisticmuscle\\right)}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eJoint angle calculations were performed for each participant by measuring the angle before the disturbance and the maximum angle within one second after the disturbance. The change in angle between segments was calculated by subtracting the pre-disturbance angle from the post-disturbance maximum angle. For segment one, with the hip joint as the axis, the angle changes within 180 degrees, based on this axis as the reference plane. In segment two, with the knee joint as the axis, the angle changes occurred within 180 degrees. For segment three, with the ankle joint as the axis, the angle changes occurred within 90 degrees.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Statistical analysis\u003c/h2\u003e \u003cp\u003eStatistical analyses were performed in SPSS26 for Windows 11 (SPSS Inc., Chicago, USA). The IEMG NORM was tested for significant differences for each muscle, differences in COP movement trajectories, CCR indices, and joint angle changes. Data were tested for normal distribution using the Shapiro-Wilk test, with independent t-tests between groups and paired t-tests within groups for data that met normal distribution, and nonparametric Mann-Whitney U tests between groups and Wilcoxon signed rank-sum tests within groups for data that did not meet normal distribution. All tests for statistical significance were set at P\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Methods","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Integrated electromyographic activity\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe IEMG NORM data shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows that under unpredictable conditions, statistically significant differences were found between the elderly and younger groups for MG but not for BF, SOL, and LE muscles.MG muscles were found to have higher muscle activation in the elderly group during the CPA1 phase (p\u0026thinsp;\u0026lt;\u0026thinsp;0.010), and in the CPA2 phase, the elderly group was faster to lower muscle activation, while the younger group had higher MG than the elderly group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.004).\u003c/p\u003e \u003cp\u003eUnder predictable conditions, dorsal muscle activity was increased in the elderly group during the APA phase compared to the younger group, with significant differences observed between groups in the APA1 phase SOL (p\u0026thinsp;\u0026lt;\u0026thinsp;0.004), and between groups in the APA2 phase BF (p\u0026thinsp;\u0026lt;\u0026thinsp;0.009), MG (p\u0026thinsp;\u0026lt;\u0026thinsp;0.014), SOL (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In addition, significant differences were observed in MG (p\u0026thinsp;\u0026lt;\u0026thinsp;0.044), and CPA2 MG (p\u0026thinsp;\u0026lt;\u0026thinsp;0.045) between groups in the CPA1 phase, and MG muscle activation was more active in the CPA phase in the young group.\u003c/p\u003e \u003cp\u003eIn the within-group comparisons between the unpredictable and predictable conditions, the elderly group had a higher prevalence of APA1 phase BF (p\u0026thinsp;\u0026lt;\u0026thinsp;0.016), MG (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), SOL (p\u0026thinsp;\u0026lt;\u0026thinsp;0.011), LE (p\u0026thinsp;\u0026lt;\u0026thinsp;0. 018), APA2 phase BF (p\u0026thinsp;\u0026lt;\u0026thinsp;0.000), MG (p\u0026thinsp;\u0026lt;\u0026thinsp;0.000), SOL (p\u0026thinsp;\u0026lt;\u0026thinsp;0.000), LE (p\u0026thinsp;\u0026lt;\u0026thinsp;0.004), CPA1 phase MG (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), LE (p\u0026thinsp;\u0026lt;\u0026thinsp;0.014), CPA2 phase MG (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), SOL (p\u0026thinsp;\u0026lt;\u0026thinsp;0.011) had significant between-group differences between conditions. Compared to the unpredictable group, the elderly group had active muscle activation responses in the dorsal muscles in the APA phase at the predictable time, along with reduced muscle activation in the MG muscles in the CPA1 phase, in addition to increased muscle activation in the LE muscles in the CPA1 phase.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Co-Contraction Index of muscle\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e's findings reveal no discernible difference in the Co-Contraction Ratio (CCR) between the elderly group and young group participants under unpredictable circumstances. Nevertheless, a significant divergence in trunk muscle co-contraction rates during the APA under predictable conditions was evident between the groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.035).\u003c/p\u003e \u003cp\u003eIn the face of unpredictable conditions, the elderly group demonstrated a notably higher co-contraction index in the thigh and trunk areas during the APA, showing significant differences (APA thigh, p\u0026thinsp;\u0026lt;\u0026thinsp;0.026; APA trunk, p\u0026thinsp;\u0026lt;\u0026thinsp;0.051). In contrast, the young group exhibited an elevated co-contraction index in the shank during the APA in predictable settings, compared to unpredictable ones (APA shank, p\u0026thinsp;\u0026lt;\u0026thinsp;0.033).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Displacements of center of pressure and A/P and M/L\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, under unpredictable conditions, the center of pressure (COP) motion trajectory was significantly longer in the older group than in the younger group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.033), and the anterior-posterior (A/P) motion trajectory (p\u0026thinsp;\u0026lt;\u0026thinsp;0.031) and the medial-lateral (M/L) motion trajectory (p\u0026thinsp;\u0026lt;\u0026thinsp;0.011) were longer in the older group than in the younger group. In contrast, medial-lateral (M/L) movement trajectories were significantly longer in the older group than in the younger group under predictable conditions (p\u0026thinsp;\u0026lt;\u0026thinsp;0.007).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Displacements of Joint Angle\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, in predictable conditions, the elderly group demonstrated less variation in three joint angles compared to the young group, exhibiting significant intergroup differences (Back p\u0026thinsp;\u0026lt;\u0026thinsp;0.018; Knee p\u0026thinsp;\u0026lt;\u0026thinsp;0.036; Ankle p\u0026thinsp;\u0026lt;\u0026thinsp;0.016). Under unpredictable conditions, the elderly group has smaller changes in the ankle joint angle relative to the young group, marking a significant intergroup difference (p\u0026thinsp;\u0026lt;\u0026thinsp;0.027).\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Discussion","content":"\u003cp\u003eThe focus of this study was to examine differences in postural adjustment and control between a group of regularly exercising elderly and a group of young in general across visual conditions. The group of elderly who exercised regularly would perform better in the APA phase compared to younger ones and the elderly group would be less adept at using ankle strategies. Overall, visual feedback is critical, and faster APA activation contributes to postural control in the elderly who rely more on improved postural stability through synergistic control between multiple joints.\u003c/p\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Gains from exercise\u003c/h2\u003e \u003cp\u003eIn scenarios involving predictable postural disturbances, our IEMG analyses showed that the elderly group exhibited faster muscle activation responses during the initial 'anticipatory postural adjustment' (APA) compared to the younger group. During the APA2 phase, The dorsal four muscles in particular showed significant muscle activation. Research by Kanekar, N., \u0026amp; Aruin, A. S. (2014) highlights that aging increases the delay in APA and consequently increases the amplitude of Compensatory Postural Adjustments (CPA) due to the reduced ability of the elderly to make feedforward anticipatory postural adjustments. Despite the age-related effects on APA, the elderly retain an inherent capacity for anticipatory adjustments (Kanekar, N., \u0026amp; Aruin, A. S. 2014). This aspect was particularly pronounced in our subjects during APA2, where muscle activation was observed. Furthermore, regular physical activity was found to increase muscle activation in APA2. Although this increase did not significantly reduce the amplitude of the CPA, it proved to be beneficial for the management of postural control after disturbances. The study by Lelard, T., \u0026amp; Ahmadi, S.2015 highlights the significant benefits of regular physical activity in improving postural balance. The elderly showed significantly greater activation of the biceps femoris (BF) muscle during CPA2 compared to the young group, regardless of visual constraints. This observation is in line with the findings of (Maeda, Yusuke, et al. 2015), who found more vigorous muscle activation in the femoral region in the elderly group. This phenomenon is related to the strategic selection of muscle activations to improve postural stability, such as the integration of hip joint strategies when ankle joint strategies are inadequate (Horak, F. B., \u0026amp; Nashner, L. M. 1986). Crucially, the elderly were able to minimize changes in joint angle through these adjustments in muscle activity. Regardless of the visual intervention, there were no significant changes in ankle angle in the elderly group, especially when compared to the young group. Given the age-related decline in ankle stability (Nakamura, H., Tsuchida, T., \u0026amp; Mano, Y. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), the elderly are sensitive to plantarflexion movements of the ankle. In contrast, the young group is more likely to use ankle strategies, as the elderly rely more on strategic control due to aging (Manchester, Diane, et al. 1989).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Effect of Vision\u003c/h2\u003e \u003cp\u003eFor elderly adults, vision has a significant effect on postural stability. Compared to the unpredictable, the IEMG results at the predictable showed that no significant differences were found in the younger group for the within-group comparison between the two visual conditions, but the elderly group had significant differences in the predictable condition for the dorsal muscles BF, MG, SOL and LE in the APA1, APA2, and it is important to note the feedback from vision that the elderly group MG and SOL muscles at the predictable time had decreased muscle activation in the CPA phase reduced muscle activation. Combined with changes in COP displacement longer COP and A/P displacements in elderly group in the absence of visual feedback. A study by (Shelton, Andrew D., et al. 2024) reported that the elderly group has relatively weaker postural stability in the AP direction than younger adults. While the influence of vision is critical for postural stability in the elderly group, the addition of visual feedback in our study decreased displacement in the AP direction and increased displacement in the ML direction. Because the elderly group relies more on postural control through vision (Pyykko, I., Jantti, P., \u0026amp; Aalto, H. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). However, it has also been suggested that the elderly group is better at stabilizing and orienting their bodies relative to support surfaces, relying more on proprioception than visual cues (Wiesmeier, I. K., Dalin, D., \u0026amp; Maurer, C. (2015). On the other hand, A/P directional balance is dominated by dorsiflexion and plantarflexion, and M/L directional balance is derived from hip control (Winter, David A., et al. 1996). In the absence of visual information, the elderly group has an increased reliance on the ankle and thigh muscles to maintain A/P and M/L balance. Therefore, the elderly group must activate the ankle and hip muscles more to minimize postural sway. This is supported by the results of muscle co-contraction rates: muscle co-contraction indices are higher in the thigh and trunk segments in unpredictable compared to the predictable elderly group and serve to compensate for joint stiffness (Lee, P. J., Rogers, E. L., \u0026amp; Granata, K. P. (2006)) (Granata, K. P., et al. 2004). The decrease in visual dependence is accompanied by a shift in dependence to increased muscle contraction (Benjuya, N., Melzer, I., \u0026amp; Kaplanski, J. (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). While COP and A/P shifts in young adults are greater when shifts are predictable compared to when they are unpredictable, the increased COP and A/P shifts appear to respond to changes in perturbation in a precisely tuned and controlled manner. They exhibit a reduction in dorsal muscle activation and an increase in muscle co-contraction, along with significant ankle joint angle changes, preferring ankle joint strategies for postural control. Beyond visual factors, fear and anxiety are pivotal in influencing postural control. Research has shown that the elderly group concerned about falling (Maki, B. E., Holliday, P. J., \u0026amp; Topper, A. K., 1991), and those experiencing fear (Davis, Justin R., et al., 2009) and anxiety, demonstrate notable differences in postural control. The fear associated with falling (Nagai, Koutatsu, et al., 2012) correlates with increased co-contraction during standing postural control in the elderly. Although our study did not directly measure fear and anxiety, the heightened muscle co-contraction observed in the elderly under unpredictable disturbances likely reflects their apprehension about falling. Conversely, the young group, seemingly devoid of such fears, showed greater COP, A/P displacements and ankle angle changes in predictable conditions, suggesting a higher confidence in their control capabilities. When considering the impact of fear, a more comprehensive understanding of the elderly's postural adjustments and control strategies emerges, especially when comparing their responses in both predictable and unpredictable scenarios to those of the young group.\u003c/p\u003e \u003c/div\u003e"},{"header":"5 Conclusion","content":"\u003cp\u003eThis study confirms that regular physical activity significantly enhances the postural control abilities of elderly individuals when coping with anterior disturbances. The findings indicate that the elderly participants were able to more effectively activate their thigh and trunk muscles during anterior shoulder disturbances, which significantly reduced the angular changes in the ankles and knees, thereby improving postural stability. Moreover, this group appeared quicker response times in anticipatory postural adjustments (APA) utilizing visual feedback, further enhancing their overall postural control capabilities. In addition, the group demonstrated faster reaction times when using visual feedback for anticipatory postural adjustment (APA), further improving their overall postural control. In unpredictable conditions, older adults reduce the risk of falling by increasing the co-contraction of muscle groups and limiting their range of motion.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch1\u003eEthics approval and consent to participate\u003c/h1\u003e\n\u003cp\u003eThis study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of Chungnam National University Bioethics Committee (No.202310-SB-179-01).\u003c/p\u003e\n\u003ch1\u003eConsent for publication\u003c/h1\u003e\n\u003cp\u003eInformed consent was obtained from all individual participants included in the study.\u003c/p\u003e\n\u003ch1\u003eAvailability of data and materials\u003c/h1\u003e\n\u003cp\u003eThe datasets generated or analyzed during this study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003ch1\u003eCompeting interests\u003c/h1\u003e\n\u003cp\u003eAll authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.\u003c/p\u003e\n\u003ch1\u003e\u0026nbsp;Funding\u003c/h1\u003e\n\u003cp\u003eThis work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korean government(MSIT)：2022R1A5A7085156.\u0026nbsp;\u003c/p\u003e\n\u003ch1\u003eAuthors\u0026apos; contributions\u003c/h1\u003e\n\u003cp\u003eConceptualization: M.Y.J, D.Z; Recruitment of experimenters and full assistance: D.Z, S.M.J, I.D.B, X.J.H; Methodology: M.Y.J, D.Z; Data processing and analysis: D.Z, S.M.J, I.D.B, X.J.H, W.X.R ; Writing: D.Z, M.Y.J; Writing - review and editing: S.J.W.\u003c/p\u003e\n\u003ch1\u003eAcknowledgments\u003c/h1\u003e\n\u003cp\u003eThis work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korean government(MSIT)：2022R1A5A7085156.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAlexandrov, Alexei V., et al.(2005) \u0026quot;Feedback equilibrium control during human standing.\u0026quot; Biological cybernetics 93 (2005): 309-322.\u003c/li\u003e\n\u003cli\u003eAruin, Alexander S., and Mark L. 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(2004) \u0026quot;Physical activity and elderly group: a review of health benefits and the effectiveness of interventions.\u0026quot; Journal of sports sciences 22.8 (2004): 703-725.\u003c/li\u003e\n\u003cli\u003eWiesmeier, I. K., Dalin, D., \u0026amp; Maurer, C. (2015). Elderly use proprioception rather than visual and vestibular cues for postural motor control. Frontiers in aging neuroscience, 7, 97.\u003c/li\u003e\n\u003cli\u003eWinter, D. A. (1995). Human balance and posture control during standing and walking. Gait \u0026amp; posture, 3(4), 193-214.）\u003c/li\u003e\n\u003cli\u003eWinter, David A., et al. (1996) \u0026quot;Unified theory regarding A/P and M/L balance in quiet stance.\u0026quot; Journal of neurophysiology 75.6 (1996): 2334-2343.\u003c/li\u003e\n\u003cli\u003eWorld Health Organization, 2004. http://www.who.int/en Accessed, June 2004.\u003c/li\u003e\n\u003cli\u003eWuehr, Max, et al. (2014) \u0026quot;Balance control and anti‐gravity muscle activity during the experience of fear at heights.\u0026quot; Physiological reports 2.2 (2014): e00232.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"External disturbances, Falls, Elderly, Posture adjustment, Posture control, Anterior disturbances","lastPublishedDoi":"10.21203/rs.3.rs-4451886/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4451886/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cb\u003eBackground:\u003c/b\u003e\u003c/p\u003e \u003cp\u003eStatic postural stability in older adults is often subject to external disturbances leading to sudden changes in balance. Understanding the ability of older adults who engage in regular physical activity to adjust and control their posture under static conditions will help to develop and promote strategies to reduce fall risk. This study examined the differential effects of regular physical activity on postural adjustment and control in older adults, focusing on responses to pre-shoulder barriers and visual conditions.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMethods:\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThirty participants were divided into two groups: 15 younger and 15 physically active older adults. The study assessed their postural responses to controlled anterior shoulder perturbations under different visual conditions. Muscle activation patterns and co-contraction rates were measured using electromyography, joint angle changes were analyzed using imaging techniques, and postural control was assessed using a force platform.\u003c/p\u003e\u003cp\u003e\u003cb\u003eResults:\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe active older participant group demonstrated better balance control and faster postural adjustment, with notable findings including improved use of compensatory postural adjustment strategies and reduced postural sway. Visual conditions significantly affected postural control strategies, with reduced visual input increasing thigh and trunk stiffness.\u003c/p\u003e\u003cp\u003e\u003cb\u003eConclusions:\u003c/b\u003e\u003c/p\u003e \u003cp\u003ePhysically active older adults demonstrate good performance in response to a forward perturbation experiment. This study emphasizes that faster anticipatory postural adjustments in response to forward perturbations, reduced postural amplitude and increased joint stiffness are effective in reducing fall risk.\u003c/p\u003e","manuscriptTitle":"Postural coping strategies of the active elderly on shoulder disturbance related to anterior falls","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-07 20:36:42","doi":"10.21203/rs.3.rs-4451886/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2a14b91e-4ce3-40d8-980c-9c11d6dff8b8","owner":[],"postedDate":"June 7th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":32713917,"name":"Biological sciences/Neuroscience"},{"id":32713918,"name":"Biological sciences/Neuroscience/Motor control"},{"id":32713919,"name":"Biological sciences/Neuroscience/Sensorimotor processing"}],"tags":[],"updatedAt":"2024-10-16T05:38:45+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-07 20:36:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4451886","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4451886","identity":"rs-4451886","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}