Effect of Annoying Sounds on Postural Control.

Objectives: This study aimed to explore the impact of irritating sounds on the postural control of healthy adults, considering both linear and nonlinear parameters, subjective assessments, and gender differences. Methods: Thirty-four young participants (17 females, 17 males) completed three 30 s bipedal standing stability tests on a balance platform: one with visual control (EO), another without visual control (EC), and a third without visual control but accompanied by irritating sounds (ECS). Additionally, participants filled out a questionnaire evaluating their sound sensitivity. Linear and nonlinear parameters from each balance test were considered for statistical analysis. Results: The findings reveal significant gender-based variations in sensitivity to sound, with women exhibiting higher sensitivity. No statistically significant differences in postural control were observed between males and females, except for a notable increase in irregularity (SampEn values) in the anterior-posterior direction for females in the ECS trial. Correlation analyses revealed a moderate and statistically significant correlation between SampEn values in the AP direction and SE scores. Conclusions: This study highlights the intricate relationship between sensory stimuli, attention, and the body's ability to maintain balance. The presence of irritating sounds led to increased irregularity in postural control, particularly in the absence of visual control.

Non-Linear Measures of Postural Control in Response to Painful and Non-Painful Visual Stimuli.

Over the past decade, researchers have focused on studying the functional context of perceiving painful stimuli, particularly concerning the posturographic correlates of emotional processing. The aim of this study was to investigate the differential modulation of non-linear measures characterizing postural control in the context of perceiving painful stimuli. The study involved 36 healthy young participants who, while standing, viewed images depicting feet and hands in painful or non-painful situations, both actively (by imagining themselves affected by the situation) and passively. For Center of Pressure (COP) displacement, three non-linear measures (Sample Entropy, Fractal Dimension, and Lyapunov exponent) were calculated. The results suggest lower values of FD and LyE in response to active stimulation compared to those recorded for passive stimulation. Above all, our results pledge for the usefulness of the Lyapunov exponent for assessing postural modulation dynamics in response to painful stimuli perception. The feasibility of this calculation could provide an interesting insight in the collection of biomarkers related to postural correlates of emotional processes and their modulation in neurological disease where socio-affective functions can be often impaired before cognitive ones.

Dynamical Analyses Show That Professional Archers Exhibit Tighter, Finer and More Fluid Dynamical Control Than Neophytes.

Quantifying the dynamical features of discrete tasks is essential to understanding athletic performance for many sports that are not repetitive or cyclical. We compared three dynamical features of the (i) bow hand, (ii) drawing hand, and (iii) center of mass during a single bow-draw movement between professional and neophyte archers: dispersion (convex hull volume of their phase portraits), persistence (tendency to continue a trend as per Hurst exponents), and regularity (sample entropy). Although differences in the two groups are expected due to their differences in skill, our results demonstrate we can quantify these differences. The center of mass of professional athletes exhibits tighter movements compared to neophyte archers (6.3 < 11.2 convex hull volume), which are nevertheless less persistent (0.82 < 0.86 Hurst exponent) and less regular (0.035 > 0.025 sample entropy). In particular, the movements of the bow hand and center of mass differed more between groups in Hurst exponent analysis, and the drawing hand and center of mass were more different in sample entropy analysis. This suggests tighter neuromuscular control over the more fluid dynamics of the movement that exhibits more active corrections that are more individualized. Our work, therefore, provides proof of principle of how well-established dynamical analysis techniques can be used to quantify the nature and features of neuromuscular expertise for discrete movements in elite athletes.

Symmetry of the Neck Muscles' Activity in the Electromyography Signal during Basic Motion Patterns.

The activity of muscles during motion in one direction should be symmetrical when compared to the activity of the contralateral muscles during motion in the opposite direction, while symmetrical movements should result in symmetrical muscle activation. The literature lacks data on the symmetry of neck muscle activation. Therefore, this study aimed to analyse the activity of the upper trapezius (UT) and sternocleidomastoid (SCM) muscles at rest and during basic motions of the neck and to determine the symmetry of the muscle activation. Surface electromyography (sEMG) was collected from UT and SCM bilaterally during rest, maximum voluntary contraction (MVC) and six functional movements from 18 participants. The muscle activity was related to the MVC, and the Symmetry Index was calculated. The muscle activity at rest was 23.74% and 27.88% higher on the left side than on the right side for the UT and SCM, respectively. The highest asymmetries during motion were for the SCM for the right arc movement (116%) and for the UT in the lower arc movement (55%). The lowest asymmetry was recorded for extension-flexion movement for both muscles. It was concluded that this movement can be useful for assessing the symmetry of neck muscles' activation. Further studies are required to verify the above-presented results, determine muscle activation patterns and compare healthy people to patients with neck pain.

"Fine synergies" describe motor adaptation in people with drop foot in a way that supplements traditional "coarse synergies".

Synergy analysis via dimensionality reduction is a standard approach in biomechanics to capture the dominant features of limb kinematics or muscle activation signals, which can be called "coarse synergies." Here we demonstrate that the less dominant features of these signals, which are often explicitly disregarded or considered noise, can nevertheless exhibit "fine synergies" that reveal subtle, yet functionally important, adaptations. To find the coarse synergies, we applied non-negative matrix factorization (NMF) to unilateral EMG data from eight muscles of the involved leg in ten people with drop-foot (DF), and of the right leg of 16 unimpaired (control) participants. We then extracted the fine synergies for each group by removing the coarse synergies (i.e., first two factors explaining ≥ 85% of variance) from the data and applying Principal Component Analysis (PCA) to those residuals. Surprisingly, the time histories and structure of the coarse EMG synergies showed few differences between DF and controls-even though the kinematics of drop-foot gait is evidently different from unimpaired gait. In contrast, the structure of the fine EMG synergies (as per their PCA loadings) showed significant differences between groups. In particular, loadings for Tibialis Anterior, Peroneus Longus, Gastrocnemius Lateralis, Biceps and Rectus Femoris, Vastus Medialis and Lateralis muscles differed between groups ( p < 0.05 ). We conclude that the multiple differences found in the structure of the fine synergies extracted from EMG in people with drop-foot vs. unimpaired controls-not visible in the coarse synergies-likely reflect differences in their motor strategies. Coarse synergies, in contrast, seem to mostly reflect the gross features of EMG in bipedal gait that must be met by all participants-and thus show few differences between groups. However, drawing insights into the clinical origin of these differences requires well-controlled clinical trials. We propose that fine synergies should not be disregarded in biomechanical analysis, as they may be more informative of the disruption and adaptation of muscle coordination strategies in participants due to drop-foot, age and/or other gait impairments.

Methods for Spatiotemporal Analysis of Human Gait Based on Data from Depth Sensors.

Gait analysis may serve various purposes related to health care, such as the estimation of elderly people's risk of falling. This paper is devoted to gait analysis based on data from depth sensors which are suitable for use both at healthcare facilities and in monitoring systems dedicated to household environments. This paper is focused on the comparison of three methods for spatiotemporal gait analysis based on data from depth sensors, involving the analysis of the movement trajectories of the knees, feet, and centre of mass. The accuracy of the results obtained using those methods was assessed for different depth sensors' viewing angles and different types of subject clothing. Data were collected using a Kinect v2 device. Five people took part in the experiments. Data from a Zebris FDM platform were used as a reference. The obtained results indicate that the viewing angle and the subject's clothing affect the uncertainty of the estimates of spatiotemporal gait parameters, and that the method based on the trajectories of the feet yields the most information, while the method based on the trajectory of the centre of mass is the most robust.

Effect of wearing high-heeled shoes on postural control and foot loading symmetry.

Purpose: This study aimed to evaluate the effects of high-heeled shoes (HHS) and experience with such footwear on foot loading and standing balance using linear and nonlinear methods. Methods: Sixteen young female experts in wearing high-heeled shoes (HHE) and sixteen young females who occasionally wore high-heeled shoes (HHO) completed a Fall Risk Test (FRT) on the Biodex Balance System platform. They also underwent a both-leg standing test on the Zebris pressure mapping platform, both barefoot and while wearing 11 cm HHS. The study analyzed several parameters, including the FRT index, foot loading parameters, linear measures of postural stability (Center of Pressure (CoP) path length and velocity), and nonlinear postural control measures (sample entropy - SampEn, fractal dimension - FD, and the largest Lyapunov exponent - LyE). Results: HHS caused a significant increase the fall risk of more than 44%, but only in the HHE group. The presence of HHS caused a significant increase in CoP path length and CoP velocity by almost 78%. The values of these parameters increased by more than 67% in the HHO group and by more than 92% in the HHE group. HHS caused a significant increase in the values of nonlinear measures (FD and LyE) in the mediolateral direction. Higher FD and LyE values suggest the ability to react faster to destabilizing stimuli and better balance control related to plasticity and adaptability to new conditions. HHS also led to up to 70% loading on the supporting limb. Conclusions: High heels in the population of young women significantly worsen static balance.

The Effect of the Weight and Type of Equipment on Shoulder and Back Muscle Activity in Surface Electromyography during the Overhead Press-Preliminary Report.

The overhead press is a multi-joint exercise that has the potential to use a high external load due to the cooperation of many muscle groups. The purpose of this study was to compare the activity of shoulder and back muscles during the overhead press with a kettlebell and a dumbbell. Surface electromyography (EMG) for the anterior and posterior deltoid, upper and lower trapezius, serratus anterior, and spinal erectors was analysed for 20 subjects. Participants performed the four trials of pressing kettlebell and dumbbell, weighted at 6 kg, and 70% of one maximum repetition (1RM) in the sitting position. Statistical analysis was performed using a non-parametric Friedman test and a post-hoc test of Dunn Bonferroni. No significant differences were found in the activation of assessed muscles when comparing dumbbell to kettlebell press trials with the same load (6 kg and 70% of 1RM). However, muscle activity of all muscles except the upper trapezius was always higher for kettlebell pressing. Different center of gravity locations in the kettlebell versus the dumbbell can increase shoulder muscle activity during the overhead press. However, more studies are required to confirm these results.

Effectiveness of Warm-Up Exercises with Tissue Flossing in Increasing Muscle Strength.

Tissue flossing is an increasingly popular method in physiotherapy and sports. There is a belief that tissue flossing can improve range of motion and muscle strength, shorten muscle recovery time, and reduce the risk of injury. The aim of this study was to analyse the effectiveness of tissue flossing for immediately improving muscle strength in recreational athletes when it is performed during warm-up. All participants were randomly assigned to either an experimental group (n = 36) or a control group (n = 34) using a random number generator. The experimental group (n = 36) performed an intervention comprising exercises with muscle tissue flossing and exercises without flossing. The control group (n = 30) performed the same protocol without a floss band. Muscle strength was measured for knee flexion end extension at three speeds (60, 120, and 180 °/s) 3 times. Analysed parameters include peak torque, work, and power related to body weight, flexors−extensors ratio, and time to peak torque. There were no significant changes in the muscle strength parameters from before to after the warm-up in either group (p > 0.05). Significantly lower values of peak torque, work, and power were observed in the experimental group during the warm-up with the floss band applied to muscles (p < 0.05). No clinically significant changes in time to peak torque or flexors−extensors ratio were observed. A single application of flossing does not improve muscle strength or power and can even reduce individuals' maximum muscle strength capabilities.

Effectiveness of Early Rehabilitation with Exergaming in Virtual Reality on Gait in Patients after Total Knee Replacement.

Total knee replacement (TKR) is the treatment of choice for advanced stages of osteoarthritis but it requires good postoperative rehabilitation. This study aimed to assess the effectiveness of exercises using virtual reality to improve gait parameters in patients after TKR. Fifty-nine patients 7−14 days after TKR surgery were divided into a study group (VRG, n = 38) and a control group (CG, n = 21). Both groups underwent the same 4-week rehabilitation protocol. The VRG group had 12 additional nonimmersive virtual reality game sessions on the Virtual Balance Clinic prototype system at 30 min each, focusing on gait and balance improvement. Spatiotemporal, force and foot plantar pressure parameters were collected on an instrumented treadmill during a 30 s walk. The most significant improvement was in the symmetry indices of forefoot force, maximum forefoot force, loading response time, and preswing time (p < 0.05) in both groups. Gait speed increased by 31.25% and 44% in the VRG and CG groups, respectively (p < 0.005). However, the extra exergaming sessions did not significantly improve rehabilitation outcomes. Therefore, additional VR training does not improve gait better than standard rehabilitation alone, but the improvement of gait, especially its symmetry, is significant within the first six weeks after surgery.

Evaluation of Geometric Attractor Structure and Recurrence Analysis in Professional Dancers.

BACKGROUND: Human motor systems contain nonlinear features. The purpose of this study was to evaluate the geometric structure of attractors and analyze recurrence in two different pirouettes (jazz and classic) performed by 15 professional dancers. METHODS: The kinematics of the body's center of mass (CoM) and knee of the supporting leg (LKNE) during the pirouette were measured using the Vicon system. A time series of selected points were resampled, normalized, and randomly reordered. Then, every second time series was flipped to be combined with other time series and make a long time series out of the repetitions of a single task. The attractors were reconstructed, and the convex hull volumes (CHV) were counted for the CoM and LKNE for each pirouette in each direction. Recurrence quantification analysis (RQA) was used to extract additional information. RESULTS: The CHVs calculated for the LKNE were significantly lower for the jazz pirouette. All RQA measures had the highest values for LKNE along the mediolateral axis for the jazz pirouette. This result underscores the high determinism, high motion recurrence, and complexity of this maneuver. CONCLUSIONS: The findings offer new insight into the evaluation of the approximation of homogeneity in motion control. A high determinism indicates a highly stable and predictive motion trajectory.

Nonlinear and Linear Measures in the Differentiation of Postural Control in Patients after Total Hip or Knee Replacement and Healthy Controls.

Primary osteoarthritis treatments such as a total hip (THR) or knee (TKR) replacement lead to postural control changes reinforced by age. Balance tests such as standing with eyes open (EO) or closed (EC) give a possibility to calculate both linear and nonlinear indicators. This study aimed to find the group of linear and/or nonlinear measures that can differentiate healthy people and patients with TKR or THR from each other. This study enrolled 49 THR patients, 53 TKR patients, and 16 healthy controls. The center of pressure (CoP) path length, sample entropy (SampEn), fractal dimension (FD), and the largest Lyapunov exponent (LyE) were calculated separately for AP and ML directions from standing with EO/EC. Cluster analysis did not result in correct allocation to the groups according to all variables. The discriminant model included LyE (ML-EO, ML-EC, AP-EC), FD (AP-EO, ML-EC, AP-EC), CoP-path AP-EC, and SampEn AP-EC. Regression analysis showed that all nonlinear variables depend on the group. The CoP path length is different only in THR patients. It was concluded that standing with EC is a better way to assess the amount of regularity of CoP movement and attention paid to maintain balance. Nonlinear measures better differentiate TKR and THR patients from healthy controls.

Influence of the base of support widths on postural control and feet loading symmetry during squat - preliminary study.

PURPOSE: The symmetry of feet loading and adequate postural control are crucial aspects of proper squat performance. The study aimed to evaluate the effect of various stance widths during squat on postural control and symmetry of feet loading. METHODS: Thirty healthy individuals participated in this study. Each participant performed one type of squat with a narrow stance (NS), hip stance (HS) and wide stance (WS). RESULTS: A significantly higher value of CoP path length, the velocity of sways and Area95 were obtained for the WS squat compared to NS and HS. In addition, the wide feet setting significantly affected not only the feet loading symmetry but also the strategy (high LyE), the amount of irregularities (high SampEn) and the CoP time-series roughness complexity (high FD). It has been shown that as the base of support grew, the asymmetry index grew. CONCLUSIONS: The wide squat is less stable, requiring more complex postural control behavior and more flexibility. Performing this squat significantly shifts the pressure to the dominant limb.

Using nonlinear measures to evaluate postural control in healthy adults during bipedal standing on an unstable surface.

PURPOSE: This study examined the use of nonlinear measures - sample entropy (SampEn), fractal dimension (FD), and the Lyapunov exponent (LyE) - to evaluate postural control in adults during standing on an unstable surface, with and without visual feedback. METHODS: 14 healthy young adults (24.07 ± 7.32 years) completed bipedal standing trials on an unstable-plate Biodex Balance System (BBS) connected to a Vicon system, with eyes open and closed. Each trial lasted 20 sec. Analysis was performed based on the center of mass (CoM), for which the three nonlinear measures were calculated. RESULTS: Excluding visual feedback was found to cause a significant increase in linear and nonlinear parameters. Moreover, SampEn and FD values were found to be significantly higher in the PD direction, compared to AP or ML, whereas LyE values in this direction were minimal. CONCLUSIONS: Results show that the three nonlinear measures provide a useful way of evaluating postural control in healthy adults. Moreover, it seems that introducing an unstable surface meant that the projection of the CoM was not perpendicular to the surface, but rather set at a certain continually changing angle, forcing the whole system to adapt to chaotic and unpredictable conditions. Such refined changes in conditions can be evaluated in a precise way only by using nonlinear measures.

Joint loads and muscle force distribution during classical and jazz pirouettes.

PURPOSE: The objective of this study was to analyze the muscle force distribution and lower limb joint loading during two types of pirouettes and check which muscle in which pirouette generates the highest force and which joint is the most loaded. METHODS: Skilled dancers (n = 16) performed single-turn pirouettes in jazz and classic styles. Kinematic and kinetic data were collected using the Vicon system and Kistler plates. The joint reaction forces and muscle forces were calculated using a musculoskeletal model in the AnyBody Modeling System. RESULTS: No statistically significant differences were found for the duration of the turn in both pirouettes. The range of motion in all joints of supporting leg in sagittal plane and in hip joint in frontal plane for non-supporting leg were significantly higher in classic pirouette. The ankle joint was the most loaded joint in both pirouettes and its maximal value was significantly higher in classic pirouette. The force generated by ankle plantar flexors muscles was significantly greater in the jazz pirouette in turn phase. For the nonsupport limb, external hip rotators generated significantly greater force when performing the classic pirouette. CONCLUSIONS: It seems that early stage dancers may start their lessons with jazz pirouettes, where necessary joint mobility is lesser. They also are supposed to increase muscle strength and body awareness with such proceedings. A better awareness of the mechanical loads on the musculoskeletal system which a dancer performing pirouettes faces should have an impact on the way dance classes are conducted and choreographic elements are sequenced.

Muscle Force Patterns in Lower Extremity Muscles for Elite Discus Throwers, Javelin Throwers and Shot-Putters - A Case Study.

Optimal release variables, as well as the kinematics and kinetics of athletes, are crucial for the maximization of throwing distance in athletics. Mathematical models and simulations allow throwing techniques to be studied. However, muscle force patterns and the contribution of specific muscle groups in athletics throwing events are not well understood and require detailed research. In this study, important variables of the muscle force generated during the javelin, discus and shot put events were determined using OpenSim software. Musculoskeletal simulations were carried out based on kinematic and kinetic data collected using the Vicon system and Kistler plates with the help of nine top Polish athletes (three in each event). OpenSim software was used to calculate muscle forces and joint velocities. For each discipline, it was found that the main muscle groups involved in the throwing movement were better at distinguishing throwers than joint velocities. The contribution of right ankle plantar flexors at the beginning of the final acceleration phase as well as left hip extensors at the end of the final acceleration phase was given special attention. This work provides a better understanding of the techniques used in athletics throws. Musculoskeletal simulations of throwing styles might help coaches analyze the techniques of individual athletes, resulting in better adjustment of training programmes and injury prevention protocols.

The Impact of Visual Input and Support Area Manipulation on Postural Control in Subjects after Osteoporotic Vertebral Fracture.

Osteoporosis is a prevalent health concern among older adults and is associated with an increased risk of falls that may result in fracture, injury, or even death. Identifying the risk factors for falls and assessing the complexity of postural control within this population is essential for developing effective regimes for fall prevention. The aim of this study was to assess postural control in individuals recovering from osteoporotic vertebral fractures while performing various stability tasks. Seventeen individuals with type II osteoporosis and 17 healthy subjects participated in this study. The study involved maintaining balance while standing barefoot on both feet for 20 s on an Advanced Mechanical Technology Inc. (AMTI) plate, with eyes open, eyes closed, and eyes closed in conjunction with a dual-task. Another three trials lasting 10 s each were undertaken during a single-leg stance under the same conditions. Fall risk was assessed using the Biodex Balance platform. Nonlinear measures were used to assess center of pressure (CoP) dynamics in all trials. Reducing the support area or elimination of the visual control led to increased sample entropy and fractal dimension. Results of the nonlinear measurements indicate that individuals recovering from osteoporotic vertebral fractures are characterized by decreased irregularity, mainly in the medio-lateral direction and reduced complexity.

Assessment of the Effectiveness of Rehabilitation after Total Knee Replacement Surgery Using Sample Entropy and Classical Measures of Body Balance.

Exercises in virtual reality (VR) have recently become a popular form of rehabilitation and are reported to be more effective than a standard rehabilitation protocol alone. The aim of this study was to assess the efficacy of adjunct VR training in improving postural control in patients after total knee replacement surgery (TKR). Forty-two patients within 7-14 days of TKR were enrolled and divided into a VR group and a control group (C). The C group underwent standard postoperative rehabilitation. The VR group additionally attended twelve 30-min exercise sessions using the Virtual Balance Clinic prototype system. Balance was assessed on the AMTI plate in bipedal standing with and without visual feedback before and after the four-week rehabilitation. Linear measures and sample entropy of CoP data were analyzed. After four weeks of rehabilitation, a significant reduction in parameters in the sagittal plane and ellipse area was noted while the eyes remained open. Regression analysis showed that sample entropy depended on sex, body weight, visual feedback and age. Based on the sample entropy results, it was concluded that the complexity of the body reaction had not improved. The standing-with-eyes-closed test activates automatic balance mechanisms and offers better possibilities as a diagnostic tool.

Nonlinear Measures to Evaluate Upright Postural Stability: A Systematic Review.

Conventional biomechanical analyses of human movement have been generally derived from linear mathematics. While these methods can be useful in many situations, they fail to describe the behavior of the human body systems that are predominately nonlinear. For this reason, nonlinear analyses have become more prevalent in recent literature. These analytical techniques are typically investigated using concepts related to variability, stability, complexity, and adaptability. This review aims to investigate the application of nonlinear metrics to assess postural stability. A systematic review was conducted of papers published from 2009 to 2019. Databases searched were PubMed, Google Scholar, Science-Direct and EBSCO. The main inclusion consisted of: Sample entropy, fractal dimension, Lyapunov exponent used as nonlinear measures, and assessment of the variability of the center of pressure during standing using force plate. Following screening, 43 articles out of the initial 1100 were reviewed including 33 articles on sample entropy, 10 articles on fractal dimension, and 4 papers on the Lyapunov exponent. This systematic study shows the reductions in postural regularity related to aging and the disease or injures in the adaptive capabilities of the movement system and how the predictability changes with different task constraints.

Nonlinear measures in posturography compared to linear measures based on yoga poses performance.

PURPOSE: Yoga is known as a type of exercise that combines physical, mental and spiritual aspects. There has not been much research on the postural control in various yoga poses. The aim of this study was to examine CoP regularity in both yoga instructors and novices during the performance of four yoga poses, and to verify the sensitivity of linear and nonlinear methods for assessing postural stability. METHODS: The dynamic characteristics of CoP fluctuations were examined using linear and nonlinear methods on a group of 22 yoga instructors (Y) and 18 age-matched non-practitioners of yoga (NY). The study involved maintaining a balance for 20 seconds while performing four yoga poses. RESULTS: Conventional analysis of CoP trajectories showed that NY and Y exhibited similar control of postural sway, as indicated by similar CoP path-length and area values observed in both groups. These results suggest that the special balance yoga training received by Y may not have an impact on less challenging balance conditions, such as the poses used in this experiment. Interestingly, nonlinear dynamical analysis of CoP showed that Y exhibited less CoP regularity and more complex signal than NY, as evidenced by higher values of sample entropy and fractal dimension. CONCLUSIONS: The results shed light on the surplus values of CoP trajectories in the nonlinear dynamical analysis to gain further insight into the mechanisms involved in posture control.