Models of Postural Control: Shared Variance in Joint and COM Motions

Influence of Impaired Upper Extremity Motor Function on Static Balance in People with Chronic Stroke

BACKGROUND

Stroke is a leading cause of disability, especially due to an increased fall risk and postural instability. The objective of this study was to analyze the impact of motor impairment in the hemiparetic UE on static balance in standing, in subject with chronic stroke.

METHODS

Seventy adults with chronic stroke, capable of independent standing and walking, participated in this cross-sectional study. The exclusion criteria included vestibular, cerebellar, or posterior cord lesions. The participants were classified based on their UE impairment using the Fugl-Meyer Assessment of Motor Recovery after Stroke (FMA-UE). A posturographic evaluation (mCTSIB) was performed in the standing position to analyze the center of pressure (COP) displacement in the mediolateral (ML) and anteroposterior (AP) axes and its mean speed with eyes open (OE) and closed (EC) on stable and unstable surfaces.

RESULTS

A strong and significant correlation (r = -0.53; p < 0.001) was observed between the mediolateral (ML) center of pressure (COP) oscillation and the FMA-UE, which was particularly strong with eyes closed [r(EO) = 0.5; r(EC) = 0.54]. The results of the multiple linear regression analysis indicated that the ML oscillation is influenced significantly by the FMA-Motor, and specifically by the sections on UE, wrist, coordination/speed, and sensation.

CONCLUSIONS

The hemiparetic UE motor capacity is strongly related to the ML COP oscillation during standing in individuals with chronic stroke, with a lower motor capacity associated with a greater instability. Understanding these relationships underpins the interventions to improve balance and reduce falls in people who have had a stroke.

Effects of arm movement strategies on emotional state and balance control during height-induced postural threat in young adults

BACKGROUND

It is firmly established that postural threat seems to lead to an increased. reliance on an ankle control ('stiffening') strategy. However, little is known about how. postural threat affects performance in challenging tasks that require the use of upper. body postural control strategies for stability. It is logical to assume that in such. conditions, being able to utilise an upper body strategy may reduce the reliance on. such ankle stiffening strategy. Research question The objective of this study was to determine how arm movement. influences balance control during a challenging balance task performed under. conditions of postural threat.

METHODS

Thirty young adults (mean ± SD age; 22.0 ± 4.0 years) balanced in tandem. stance whilst standing at both ground-level (no threat) and 0.8 m above ground. (threat). In both conditions, participants performed the task under two different arm.

POSITIONS

restricted arm movements and free arm movements. Postural sway. amplitude and frequency were calculated to infer postural stiffening response. Selfreported. emotional responses were quantified by assessing balance confidence, fear. of falling, perceived stability, and conscious balance processing.

RESULTS

Independent of arm movements, postural threat evoked an increase in fear of. falling and conscious balance processing, and reductions in balance confidence and. perceived stability. These threat-related changes in emotional state were further. amplified when arm movements were restricted. Whilst significant increases in sway. frequency during threat were observed in both arm conditions, reductions in sway. amplitude were only observed during the restricted arm movement condition.

SIGNIFICANCE

We propose that these responses likely reflect a fear-related cautious. strategy intended to reduce the postural destabilisation associated with individuals. being unable to use their arms to counter any destabilisation, as would normally be the. case in daily life.

Optimal controllers resembling postural sway during upright stance

The human postural control system can maintain our balance in an upright stance. A simplified control model that can mimic the mechanisms of this complex system and adapt to the changes due to aging and injuries is a significant problem that can be used in clinical applications. While the Intermittent Proportional Derivative (IPD) is commonly used as a postural sway model in the upright stance, it does not consider the predictability and adaptability behavior of the human postural control system and the physical limitations of the human musculoskeletal system. In this article, we studied the methods based on optimization algorithms that can mimic the performance of the postural sway controller in the upright stance. First, we compared three optimal methods (Model Predictive Control (MPC), COP-Based Controller (COP-BC) and Momentum-Based Controller (MBC)) in simulation by considering a feedback structure of the dynamic of the skeletal body as a double link inverted pendulum while taking into account sensory noise and neurological time delay. Second, we evaluated the validity of these methods by the postural sway data of ten subjects in quiet stance trials. The results revealed that the optimal methods could mimic the postural sway with higher accuracy and less energy consumption in the joints compared to the IPD method. Among optimal approaches, COP-BC and MPC show promising results to mimic the human postural sway. The choice of controller weights and parameters is a trade-off between the consumption of energy in the joints and the prediction accuracy. Therefore, the capability and (dis)advantage of each method reviewed in this article can navigate the usage of each controller in different applications of postural sway, from clinical assessments to robotic applications.

Task Specific and General Patterns of Joint Motion Variability in Upright- and Hand-Standing Postures

The preservation of static balance in both upright- and hand-stance is maintained by the projection of center of mass (CM) motion within the region of stability at the respective base of support. This study investigated, from a degrees of freedom (DF) perspective, whether the stability of the CM in both upright- and hand-stances was predicted by the respective dispersion and time-dependent regularity of joint (upright stance—ankle, knee, hip, shoulder, neck; hand stance—wrist, elbow, shoulder, neck) angle and position. Full body three-dimensional (3D) kinematic data were collected on 10 advanced level junior female gymnasts during 30 s floor upright- and hand-stands. For both stances the amount of the dispersion of joint angle and sway motion was higher than that of the CM and center of pressure (CP) with an inverse relation to time-dependent irregularity (SampEn). In upright-standing the variability of neck motion in the anterior–posterior direction was significantly greater than that of most joints consistent with the role of vision in the control of quiet upright posture. The findings support the proposition that there are both task specific and general properties to the global CM control strategy in the balance of upright- and hand-standing induced by the different active skeletal-muscular organization and the degeneracy revealed in the multiple distributional variability patterns of the joint angle and position in 3D.

Influence of Controlled Stomatognathic Motor Activity on Sway, Control and Stability of the Center of Mass During Dynamic Steady-State Balance—An Uncontrolled Manifold Analysis

Multiple sensory signals from visual, somatosensory and vestibular systems are used for human postural control. To maintain postural stability, the central nervous system keeps the center of mass (CoM) within the base of support. The influence of the stomatognathic motor system on postural control has been established under static conditions, but it has not yet been investigated during dynamic steady-state balance. The purpose of the study was to investigate the effects of controlled stomatognathic motor activity on the control and stability of the CoM during dynamic steady-state balance. A total of 48 physically active and healthy adults were assigned to three groups with different stomatognathic motor conditions: jaw clenching, tongue pressing and habitual stomatognathic behavior. Dynamic steady-state balance was assessed using an oscillating platform and the kinematic data were collected with a 3D motion capturing system. The path length (PL) of the 3D CoM trajectory was used for quantifying CoM sway. Temporal dynamics of the CoM movement was assessed with a detrended fluctuation analysis (DFA). An uncontrolled manifold (UCM) analysis was applied to assess the stability and control of the CoM with a subject-specific anthropometric 3D model. The statistical analysis revealed that the groups did not differ significantly in PL, DFA scaling exponents or UCM parameters. The results indicated that deliberate jaw clenching or tongue pressing did not seem to affect the sway, control or stability of the CoM on an oscillating platform significantly. Because of the task-specificity of balance, further research investigating the effects of stomatognathic motor activities on dynamic steady-state balance with different movement tasks are needed. Additionally, further analysis by use of muscle synergies or co-contractions may reveal effects on the level of muscles, which were not visible on the level of kinematics. This study can contribute to the understanding of postural control mechanisms, particularly in relation to stomatognathic motor activities and under dynamic conditions.

Specific Posture-Stabilising Effects of Vision and Touch Are Revealed by Distinct Changes of Body Oscillation Frequencies

We addressed postural instability during stance with eyes closed (EC) on a compliant surface in healthy young people. Spectral analysis of the centre of foot pressure oscillations was used to identify the effects of haptic information (light-touch, EC-LT), or vision (eyes open, EO), or both (EO-LT). Spectral median frequency was strongly reduced by EO and EO-LT, while spectral amplitude was reduced by all "stabilising" sensory conditions. Reduction in spectrum level by EO mainly appeared in the high-frequency range. Reduction by LT was much larger than that induced by the vision in the low-frequency range, less so in the high-frequency range. Touch and vision together produced a fall in spectral amplitude across all windows, more so in anteroposterior (AP) direction. Lowermost frequencies contributed poorly to geometric measures (sway path and area) for all sensory conditions. The same subjects participated in control experiments on a solid base of support. Median frequency and amplitude of the spectrum and geometric measures were largely smaller when standing on solid than on foam base but poorly affected by the sensory conditions. Frequency analysis but not geometric measures allowed to disclose unique tuning of the postural control mode by haptic and visual information. During standing on foam, the vision did not reduce low-frequency oscillations, while touch diminished the entire spectrum, except for the medium-high frequencies, as if sway reduction by touch would rely on rapid balance corrections. The combination of frequency analysis with sensory conditions is a promising approach to explore altered postural mechanisms and prospective interventions in subjects with central or peripheral nervous system disorders.

The Relationship between Postural Control and Muscle Quality in Older Adults

This study aimed to determine relationships between muscle quality, the ratio of muscle strength to muscle mass, and postural control and compare postural control of older adults with higher and lower muscle quality. Twenty-five older adults had leg muscle quality and postural control with eyes open and closed measured. Linear and non-linear postural control variables were calculated from center of pressure movements. There was a significant canonical correlation between muscle quality and sway complexity, but no relationship between muscle quality and sway magnitude. Higher muscle quality older adults had greater medio-lateral sway complexity than lower muscle quality older adults. These findings suggest that higher muscle quality relates to greater sway complexity in older adults, suggesting maintenance of muscle quality should be considered important to attenuate postural control declines.

The trunk's contribution to postural control under challenging balance conditions

BACKGROUND

The double inverted pendulum model is imprecise when applied to studies of postural control. Although multijoint analyses have improved our understanding of how balance is maintained, the exact role of the trunk remains unclear.

RESEARCH QUESTIONS

What is the trunk's contribution in postural control with respect to the other joints and how do trunk muscles control trunk kinematics?

METHODS

Thirty-six healthy athletes (handball, karate, long jump) performed a highly challenging balance task while the ground support was dynamically tilted in the sagittal plane. The center of force (CoF) as well as lower limb joint angles and the trunk-pelvis angle were respectively measured with a force platform and inertial measurement units. The amplitude, sway path and standard deviation of the CoF and the joint angles were then calculated. Electromyography was used to record the activity of the rectus abdominis, external obliquus, and erector spinae muscles. Multiple linear regressions were computed to determine the joints' and muscles' contributions (β-coefficients) in predicting CoF variables and trunk kinematics, respectively.

RESULTS

The linear combination of joint kinematic variables accounted for between 33 % and 75 % of the variance in the CoF. The ankle had the highestβ and was a significant predictor of all CoF variables. The trunk yielded the second highest β-coefficient and was a significant predictor of the CoF sway path. Electromyography variables accounted for no more than 35 % of the variance in the trunk kinematics, and erector spinae activity was the only significant predictor.

SIGNIFICANCE

The trunk appears to be the second most important element during this specific postural task, in the magnitude of body sway in particular. But neuromuscular control of these trunk processes is difficult to characterize with surface electromyography only. The trunk should be taken into account when seeking to improve overall postural control (e.g. during training, rehabilitation).

Collective Variables and Task Constraints in Movement Coordination, Control and Skill

In this paper we review studies that have identified collective variables (order parameters) in movement coordination, control and skill with emphasis on whole-body multiple joint degree of freedom (DF) tasks. Collective variables of a dynamical system have been proposed formally and informally from a diverse set of perceptual-motor tasks, from which we emphasize: bimanual coordination, locomotion (pedalo, walking, running, bicycle riding), roller ball task, static (quiet standing) and dynamic (moving on a ski-simulator) balance, grasping, and juggling. Several types of candidate collective variables have been identified, including: relative phase, frequency ratio, number of hands active in grasping, synchrony, learning rate and relative timing. There is a strong influence of the task goal in determining the collective variable that can be body or environment relative. The emergence of the task relevant collective variable is typically in the early stage of skill learning where subjects through practice adapt movement organization to realize a never previously produced movement coordination pattern. Throughout, the paper elaborates on open theoretical, experimental and analysis issues for collective variables in the context of task constraints and Bernstein's (1967) view of skill acquisition as learning to master redundant DF.

Multiple roles of active stiffness in upright balance and multidirectional sway

Both passive and active mechanisms are necessary to explain small amplitude forward-backward (FB) voluntary swaying. Parallel and symmetric leg inverted pendulum models with stiffness control are a simple way to replicate FB swaying during quiet stance. However, it has been more difficult to model lateral left-right (LR) voluntary swaying involving the dual mechanisms of hip loading-unloading and ankle pressure distribution. To assess these factors, we had subjects perform small amplitude FB and LR sways and circular rotation. We experimentally identified three parameters that characterized their two-dimensional stiffnesses: AP stiffness (K_S^AP), and lateral stiffness (K_S^ML), at the ankles and a parameter we refer to as the engagement-disengagement rate (K_ED) of the legs. We performed simulations with our engaged leg model (Bakshi A, DiZio P, Lackner JR. J Neurophysiol 121: 2042-2060, 2019; Bakshi A, DiZio P, Lackner JR. J Neurophysiol 121: 2028-2041, 2019) to test its predictions about the limits of balance stability during sway in the three test conditions. Comparing the model's predictions with the experimental data, we found that K_S^AP has a task-dependent dual role in upright balance and is crucial to prevent falling; K_S^ML helps overcome viscous drags but is not instrumental to stability; K_ED has a key role in stability and is dependent on the biomechanical geometry of the body, which is invariant across balance tasks. These findings provide new insights into balance control that have important clinical implications for falling, especially for patients who are unable to use a hip strategy during balance control.NEW & NOTEWORTHY Our previously published Engaged Leg Model here shows how stiffness plays complex multicausal roles in balance. In one role, it is crucial to stability, with task contingent influences over balance. In another, it overcomes viscous drag. Task-dependent stiffness alone does not explain stable balance; geometrical, invariant aspects of body biomechanics also matter. Our model is fully applicable to clinical balance pathologies involving asymmetries in movement and balance control.

A case control study to investigate differences in motor control between individuals with and without non-specific low back pain during standing

Recent literature has indicated altered motor control in individuals with non-specific low back pain (NSLBP). These individuals present variations in back muscular activity and center of mass (CoM) oscillations. The aim of this study is to explore the possibility of quantitatively measuring these differences using standard parameters with electronic devices. Twenty individuals with NSLBP and 20 healthy controls, matched by sex and age, performed a total of three trials under three different conditions for 90 seconds each. These conditions were standing on firm ground with eyes open, with eyes closed and standing on unstable foam with eyes open. Balance data was acquired via a Kistler force platform and muscular activity was measured by electromyography derived bilaterally from the erector spinae. Afterwards, participants were asked to complete a questionnaire on their current mood, pain rating, well-being, disability and physical activity. Descriptive data from the questionnaire showed an average acute pain score of 2.6 and an average pain score of 5.1 for the prior six weeks in the NSLBP group, while the control group reported an acute pain of 0.1 and an average pain of 0.5. For wellbeing, differences were found only for the physical scale. Average disability was low for the NSLBP group. No differences in physical activity were found among groups. A repeated measures ANOVA did not show significant differences between groups for any parameter. There was also no main effect for the standing conditions and no interaction between group and condition. Simultaneously measuring biomechanical and neuromuscular parameters, allowed for a fine grain approach to understanding motor control in individuals with NSLBP. This study did not find differences as described in the literature, and suggests further examination of factors involved in pain and control processes to better understand implications of NSLBP and possible avenues for support.

A Proposed Postural Control Theory Synthesizing Optimal Feedback Control Theory, Postural Motor Learning, and Cerebellar Supervision Learning

Multiple theories regarding motor learning and postural control development aim to explain how the central nervous system (CNS) acquires, adjusts, and learns postural behaviors. However, few theories of postural motor development and learning propose possible neurophysiologic correlates to support their assumptions. Evidence from behavioral and computational models support the cerebellum's role in supervising motor learning through the production of forward internal models, corrected by sensory prediction errors. Optimal Feedback Control Theory (OFCT) states that the CNS learns new behaviors by minimizing the cost of multi-joint movements that attain a task goal. By synthesizing principles of the OFCT, postural sway characteristics, and cerebellar anatomy and its internal models, we propose an integrated learning model in which cerebellar supervision of postural control is governed by movement cost functions.

Joint Angle Coordination Strategies During Whole Body Rotations on a Single Lower-Limb Support: An Investigation Through Ballet Pirouettes

Despite the prevalence of turning maneuvers in everyday life, relatively little research has been conducted on joint angle kinematic coordination during whole-body rotations around a vertical axis. Ballet pirouettes provide an opportunity to study dynamically balanced, whole-body rotations on a single support and the potential to scale results to smaller angular displacements executed by general populations. The purpose of this study was to determine the supporting limb's ankle, knee, hip, and pelvis-trunk joint angle excursions and kinematic coordination strategies utilized during the pirouette's turn phase. Advanced dancers (n = 6) performed pirouettes while whole-body 3-dimensional kinematics were recorded. Group mean ankle ab/adduction excursion was significantly greater than all other excursions (P < .05). Principal components analysis was applied to joint angle time-series data (4 joints × 3 degrees of freedom = 12 variables). The first 4 principal components explained 92% (2%) of variance, confirming redundancy in joint angle data. Evolution of the data along the first principal component in successful pirouettes oscillated at the pirouette's rotational frequency. Principal component eigenvector coefficients provided evidence of ankle-hip coordination, although specific coordination patterns varied between individuals and across trials. These results indicate that successful pirouettes are executed with continuous, oscillatory joint angle coordination patterns.

Can arm movements improve postural stability during challenging standing balance tasks?

BACKGROUND

There is growing evidence that arm movements make a substantial and functionally relevant contribution to dynamic balance. Additional insight of the important role of arm movements may be gained by quantifying the effects of arm restriction on the performance of commonly recommended static balance tasks of increasing difficulty.

RESEARCH QUESTION

The purpose of the present study was to determine whether restricting/permitting arm movements influences postural sway during tasks of various levels of difficulty.

METHODS

A total of 20 healthy and physically active adults (females; n = 10; age, 20.7 ± 1.3 years) randomly completed (a) quiet standing postural control tasks of increasing difficulty (bipedal, tandem, unipedal) on a fixed and foam surface, and (b) a dynamic postural control task (Y balance test), under two different verbally conveyed instructions of arm position; (1) restricted arm movement and (2) free arm movement. Centre of pressure outcomes measured during quiet standing served as a measure of static balance performance.

RESULTS

The results showed that restricting movements of the arms elicited large magnitude (Cohen's d = 0.97 - 1.28) increases in mediolateral postural sway (P < 0.05) but not anteroposterior (P > 0.05) sway. These effects were only observed during challenging (tandem and unipedal) standing balance tasks. Restricting arm movements elicited a marked reduction in the Y Balance reach distance (all directions, P < 0.001, d = -0.53 to -1.15).

SIGNIFICANCE

The findings from the present study suggest that the contribution of the arms only become relevant when frontal plane balance is challenged. Moreover, the data indicate that arm movements are vital for the control of mediolateral postural sway.

Impaired Motor Function in the Affected Arm Predicts Impaired Postural Balance After Stroke: A Cross Sectional Study

Background: Impaired postural balance is a common symptom after stroke and a common cause of falling. Most common daily tasks use arm and hand movements. Impairment in an upper extremity is a common stroke symptom, affecting 50–80% in the acute phase after stroke, and 40–50% in the sub-acute phase. The impact of leg function on postural balance has been investigated in several studies, but few have stressed the importance of arm function on postural balance.

Objective: To explore whether there is any association between arm function and postural balance after stroke.

Method: A cross sectional study where 121 adults (mean age: 70 ± 12.3 years, 72 men) from two different data sources, Gothenburg Very Early Supported Discharge (GOTVED), and a study by Carvalho et al. were merged. Time for assessments ranged from 1 to 13 years when the patients were in the chronic phase. The dependent variables were Berg Balance scale (BBS) and Time Up and Go (TUG) both dichotomized to “impaired postural balance” and “not impaired postural balance.” As independent variables, the Fugl-Meyer Assessment-Upper Extremity (FMA-UE) scale was used. The FMA-UE was presented with the total score.

Results: The motor function in the arm affected after stroke onset correlated with postural balance both measured with the BBS (0.321, p < 0.001) and the TUG (−0.315, p = 0.001). Having impaired motor function in the arm was significantly associated with impaired postural balance assessed with the BBS with OR = 0.879 (CI 0.826–0.934, p < 0.001). Regression analysis with the TUG showed the same result, OR = 0.868 (CI 0.813–0.927, p < 0.001) for FM-UE.

Conclusion: The motor function of the affected arm was significantly associated with impaired postural balance post stroke, as assessed by BBS or TUG. It could be of clinical importance to be aware of the fact that not only lower extremity impairment, but also arm function can have an impact on postural balance in a late stage after stroke.

Trial Registration: VGFOUGSB-669501.

PManalyzer: A Software Facilitating the Study of Sensorimotor Control of Whole-Body Movements

Motion analysis is used to study the functionality or dysfunctionality of the neuromuscular system, as human movements are the direct outcome of neuromuscular control. However, motion analysis often relies on measures that quantify simplified aspects of a motion, such as specific joint angles, despite the well-known complexity of segment interactions. In contrast, analyzing whole-body movement patterns may offer a new understanding of movement coordination and movement performance. Clinical research and sports technique evaluations suggest that principal component analysis (PCA) provides novel and valuable insights into control aspects of the neuromuscular system and how they relate to coordinative patterns. However, the implementation of PCA computations are time consuming, and require mathematical knowledge and programming skills, drastically limiting its application in current research. Therefore, the aim of this study is to present the Matlab software tool "PManalyzer" to facilitate and encourage the application of state-of-the-art PCA concepts in human movement science. The generalized PCA concepts implemented in the PManalyzer allow users to apply a variety of marker set independent PCA-variables on any kinematic data and to visualize the results with customizable plots. In addition, the extracted movement patterns can be explored with video options that may help testing hypotheses related to the interplay of segments. Furthermore, the software can be easily modified and adapted to any specific application.

Non-specific Low Back Pain and Postural Control During Quiet Standing-A Systematic Review

Background: There is a great number of people who require treatment for non-specific low back pain (LBP) yet the causes are still unclear. One proposed cause for LBP is impaired motor control and more specific an impaired postural control.

Objective: The purpose of this review is to provide an overview of postural control parameter differences in persons with and without non-specific LBP during quite standing.

Methods: A literature search in five databases from January 2000 until January 2018 was performed and was followed by a hand search. Twenty-one articles comparing healthy adults and adults with non-specific LBP in neuromuscular and/or biomechanical parameters during bipedal stance without external perturbation in lab studies were examined. Data extraction and quality assessment were independently performed by two persons. Factors such as study population, outcome measures, and results were extracted from the articles and included in this analysis.

Results: The results show that persons with and without non-specific LBP differed in several parameters of postural control such as the center of pressure displacement, postural control strategy, and muscle activation patterns.

Conclusion: While the results show that none of the parameters alone lead to significant effects, the combination of neuromuscular and biomechanical parameters was associated with the impairment of postural control in individuals with LBP during standing. Since the studies included in this analysis used different methodological procedures a replication of these studies with standardized procedures is imperative for the acquisition of more conclusive evidence on the differences in postural control during standing.

Dynamic Postural Control in Children: Do the Arms Lend the Legs a Helping Hand?

There is growing empirical evidence lending support to the existence of an "upper body strategy" to extend the ankle and hip strategies in maintaining upright postural stability among adults. Both postural stability and arm movement functions are still developing in children. Therefore, enquiry concerning arm contribution to postural stability among children is needed. This proof of concept study seeks to determine whether the arms play a functionally relevant role in dynamic postural control among children. Twenty-nine children (girls, n = 15; age, 10.6 ± 0.5 years; height, 1.48 ± 0.08 m; mass, 42.8 ± 11.4 kg; BMI, 19.2 ± 3.7 kg/m²) completed three dynamic balance tests; (1) Y Balance test^®, (2) timed balance beam walking test, (3) transition from dynamic to static balance using the dynamic postural stability index (DPSI). Each test was performed with free and restricted arm movement. Restricting arm movements elicited a marked degradation in the Y Balance reach distance (all directions, P ≤ 0.001, d = -0.85 to -1.13) and timed balance beam walking test (P ≤ 0.001, d = 1.01), while the DPSI was the only metric that was not different between free and restricted arm movements (P = 0.335, d = -0.08). This study provides direct evidence that the arms play a functionally relevant role in dynamic balance performance among children. These findings may provide the impetus to develop training interventions to improve the use of the arms in activities of daily living.

Postural Stability Variables for Dynamic Equilibrium

Experiments on the maintenance of postural stability on flat stationary support surfaces (quiet standing) that show only limited modes of the potential configurations of balance stability have dominated investigations of balance in quiet upright standing. Recent studies have revealed coordination properties of the whole body in maintaining dynamic postural stability with the application of moving platform paradigms. This paper examines properties of candidate collective variables for postural control within the dynamic systems framework. Evidence is discussed in this paper for: (i) self-organization properties of dynamic postural balance; (ii) enhanced variability and entropy prior to a phase transition between center of mass and center of pressure coupling; (iii) co-existence of intermittent postural control strategies that oscillate between periodic to chaotic transitions to maintain upright postural balance. These collective findings indicate postural attractor dynamic states progressively emerge to the changing task constraints of a moving platform revealing insights into the deterministic and stochastic properties of the multiple time scales of human postural behavior.

Targeted Athletic Training Improves the Neuromuscular Performance in Terms of Body Posture From Adolescence to Adulthood - Long-Term Study Over 6 Years

Poor posture in childhood and adolescence is held responsible for the occurrence of associated disorders in adult age. This study aimed to verify whether body posture in adolescence can be enhanced through the improvement of neuromuscular performance, attained by means of targeted strength, stretch, and body perception training, and whether any such improvement might also transition into adulthood. From a total of 84 volunteers, the posture development of 67 adolescents was checked annually between the age of 14 and 20 based on index values in three posture situations. 28 adolescents exercised twice a week for about 2 h up to the age of 18, 24 adolescents exercised continually up to the age of 20. Both groups practiced other additional sports for about 1.8 h/week. Fifteen persons served as a non-exercising control group, practicing optional sports of about 1.8 h/week until the age of 18, after that for 0.9 h/week. Group allocation was not random, but depended on the participants’ choice. A linear mixed model was used to analyze the development of posture indexes among the groups and over time and the possible influence of anthropometric parameters (weight, size), of optional athletic activity and of sedentary behavior. The post hoc pairwise comparison was performed applying the Scheffé test. The significance level was set at 0.05. The group that exercised continually (TR20) exhibited a significant posture parameter improvement in all posture situations from the 2nd year of exercising on. The group that terminated their training when reaching adulthood (TR18) retained some improvements, such as conscious straightening of the body posture. In other posture situations (habitual, closed eyes), their posture results declined again from age 18. The effect sizes determined were between η² = 0.12 and η² = 0.19 and represent moderate to strong effects. The control group did not exhibit any differences. Anthropometric parameters, additional athletic activities and sedentary behavior did not influence the posture parameters significantly. An additional athletic training of 2 h per week including elements for improved body perception seems to have the potential to improve body posture in symptom free male adolescents and young adults.

Adaptation of kinematic synergy and postural control to mechanical ankle constraint on an unsteady stance surface

Joint constraint interferes with the coordinative structure in joint movements used to optimize postural stability. This study aimed to investigate changes in postural synergy when the ankle joints were bilaterally braced during a stabilometer stance. Twenty-four young adults stood on a stabilometer plate while wearing a pair of ankle-foot orthoses, which were either unlocked or locked to restrict ankle motion (the ankle constraint (AC) and non-constraint (NC) conditions). Although ankle constraint did not significantly affect the dynamics of the stabilometer movements, the size and regularity of the first principal component (PC1), which explained more than 80% of the variance of joint movements in the lower limb, were increased. In addition, PC1 exhibited higher communalities with angular movements of the knee and hip joints in the AC condition than in the NC condition. Those subjects who exhibited a constraint-induced increase in postural sway (the I group) showed greater increases in the size and regularity of PC1 than did those who exhibited reduced postural sway during ankle constraint (the D group). Constraint-induced changes in postural synergy were group-dependent. Only the I group exhibited an increase of communality of PC1 with the hip angular movement following bilateral ankle constraint. In summary, bilateral ankle constraint altered the coordination solution, with increasing reliance on compensatory knee movement to maintain a balanced posture on the stabilometer. However, accessory hip movement due to ankle constraint was not economical and was disadvantageous to stance stability.

The Contribution of Upper Body Movements to Dynamic Balance Regulation during Challenged Locomotion

Recent studies suggest that in addition to movements between ankle and hip joints, movements of the upper body, in particular of the arms, also significantly contribute to postural control. In line with these suggestions, we analyzed regulatory movements of upper and lower body joints supporting dynamic balance regulation during challenged locomotion. The participants walked over three beams of varying width and under three different verbally conveyed restrictions of arm posture, to control the potential influence of arm movements on the performance: The participants walked (1) with their arms stretched out perpendicularly in the frontal plane, (2) spontaneously, i.e., without restrictions to the arm movements, and (3) with their hands on their thighs. After applying an inverse-dynamics analysis to the measured joint kinematics, we investigated the contribution of upper and lower body joints to balance regulation in terms of torque amplitude and variation. On the condition with the hands on the thighs, the contribution of the upper body remains significantly lower than the contribution of the lower body irrespective of beam widths. For spontaneous arm movements and for outstretched arms we find that the upper body (including the arms) contributes to the balancing to a similar extent as the lower body. Moreover, when the task becomes more difficult, i.e., for narrower beam widths, the contribution of the upper body increases, while the contribution of the lower body remains nearly constant. These findings lend further support to the hypothetical existence of an "upper body strategy" complementing the ankle and hip strategies especially during challenging dynamic balance tasks.

How does cryotherapy effect ankle proprioception in healthy individuals?

Objectives To investigate how a 15-min cryotherapy intervention effects proprioception by measuring joint positional sense (JPS) and static single legged balance. Design Repeated measures design. Setting Laboratory. Participants Eighteen healthy university sports team students (11 males, 7 females) aged between 20 and 21 years old. Main outcome measures Participants were treated with 15 min of Aircast Cryo-cuff. The subject's skin temperature was measured before and immediately after 15 min of cryotherapy treatment. Ankle active joint positional sense (A-JPS) and passive joint positional sense (P-JPS) were measured at pre-test, immediately post-test, and 5 min post-test. Static balance was measured by centre of pressure (CoP) mean path length, medial-lateral (ML) CoP mean deviation, and anterior-posterior (AP) CoP mean deviation and mean time-to-boundary (TtB) minima for AP and ML directions. Results No significant differences were found for the variables of JPS and static single balance testing after 15 min of cryotherapy treatment. However, mean differences for CoP mean path length and ML mean deviation were shown to improve following cryotherapy treatment, results not previously found in the literature. Conclusion Results suggest that 15 min of Cryo-cuff treatment does not significantly affect proprioception. Although the effect of cryotherapy on proprioception depends on cooling modality used, time frame applied, and joint applied to.

Bayesian inference of physiologically meaningful parameters from body sway measurements

The control of the human body sway by the central nervous system, muscles, and conscious brain is of interest since body sway carries information about the physiological status of a person. Several models have been proposed to describe body sway in an upright standing position, however, due to the statistical intractability of the more realistic models, no formal parameter inference has previously been conducted and the expressive power of such models for real human subjects remains unknown. Using the latest advances in Bayesian statistical inference for intractable models, we fitted a nonlinear control model to posturographic measurements, and we showed that it can accurately predict the sway characteristics of both simulated and real subjects. Our method provides a full statistical characterization of the uncertainty related to all model parameters as quantified by posterior probability density functions, which is useful for comparisons across subjects and test settings. The ability to infer intractable control models from sensor data opens new possibilities for monitoring and predicting body status in health applications.

The validity of forceplate data as a measure of rapid and targeted volitional movements of the centre of mass in transtibial prosthesis users

PURPOSE

To validate outcome variables from the limits of stability protocol that are derived from the center of pressure with those same variables derived from the center of mass during rapid, volitional responses in transtibial prosthesis users.

METHOD

Prosthesis users (n = 21) and matched controls (n = 21) executed movements while force and motion data were collected. Correlation coefficients were used to investigate relationships between center of pressure and center of mass for: x/y coordinates positions, limits of stability outcome variables and muscular reaction times.

RESULTS

Significant differences were seen in correlation between x/y coordinate positions toward the intact limb (mean effect size of differences: r = .38). Limits of stability variables were positively correlated (reaction time and maximum excursion range r_s: .585-.846; directional control and mean velocity range r_s: .307-.472). Muscular reaction times correlated weakly with those from center of pressure (mean r_s prosthesis users: .186 and controls: .101).

CONCLUSIONS

Forceplate measures are valid in describing rapid, volitional movements in unilateral transtibial prosthesis users. Limits of stability outcomes extracted from center of pressure and center of mass are highly correlated, but can be sensitive to direction. Muscular reaction time correlates very little with reaction times extracted from the other variables. Implications for rehabilitation Rehabilitation programs utilizing limits of stability are valid measures of postural control in transtibial prosthesis users. Clinicians interpreting the outcomes from limits of stability need to be aware of their varying validity. Muscular reaction times correlate weakly with other measures of reaction time, highlighting the complexity of rapidly coordinating volitional movements in prosthesis users.

Real-time visual feedback of COM and COP motion properties differentially modifies postural control structures

The experiment was setup to investigate the control of human quiet standing through the manipulation of augmented visual information feedback of selective properties of the motion of two primary variables in postural control: center of pressure (COP) and center of mass (COM). Five properties of feedback information were contrasted to a no feedback dual-task (watching a movie) control condition to determine the impact of visual real-time feedback on the coordination of the joint motions in postural control in both static and dynamic one-leg standing postures. The feedback information included 2D COP or COM position and macro variables derived from the COP and COM motions, namely virtual time-to-contact (VTC) and the COP-COM coupling. The findings in the static condition showed that the VTC and COP-COM coupling feedback conditions decreased postural motion more than the 2D COP or COM positional information. These variables also induced larger sway amplitudes in the dynamic condition showing a more progressive search strategy in exploring the stability limits. Canonical correlation analysis (CCA) found that COP-COM coupling contributed less than the other feedback variables to the redundancy of the system reflected in the common variance between joint motions and properties of sway motion. The COP-COM coupling had the lowest weighting of the motion properties to redundancy under the feedback conditions but overall the qualitative pattern of the joint motion structures was preserved within the respective static and dynamic balance conditions.

Changes in Habitual and Active Sagittal Posture in Children and Adolescents with and without Visual Input - Implications for Diagnostic Analysis of Posture

INTRODUCTION

Poor posture in children and adolescents has a prevalence of 22-65% and is suggested to be responsible for back pain. To assess posture, photometric imaging of sagittal posture is widely used, but usually only habitual posture positions (resting position with minimal muscle activity) are analysed.

AIM

The objective of this study was 1) to investigate possible changes in posture-describing parameters in the sagittal plane, when the subjects changed from a habitual passive posture to an actively corrected posture, and 2) to investigate the changes in posture parameters when an actively corrected posture was to be maintained with closed eyes.

MATERIALS AND METHODS

In a group of 216 male children and adolescents (average 12.4 ± 2.5 years, range 7.0 - 17.6 years), six sagittal posture parameters (body tilt BT, trunk incline TI, posture index PI, horizontal distances between ear, shoulder and hip and the perpendicular to the ankle joint) were determined by means of photometric imaging in an habitual passive posture position, in an actively erect posture with eyes open, and in active stance with eyes closed. The change in these parameters during the transition between the posture positions was analysed statistically (dependent t-Test or Wilcoxon-Test) after Bonferroni correction (p<0.004).

RESULTS

When moving from a habitual passive to an active posture BT, TI, PI, dEar, dShoulder, and dHip decreased significantly(p< 0.004). When the eyes were closed, only the perpendicular distances (dEar, dShoulder, and dHip) increased significantly. The parameters that describe the alignment of the trunk sections in relation to each other (BT, TI, PI), remained unchanged in both actively regulated posture positions.

CONCLUSION

Changes in sagittal posture parameters that occur when a habitual passive posture switches into an active posture or when an active posture is to be maintained while the eyes are closed can be used for diagnostic purposes regarding poor posture and posture regulation.

Human upright posture control models based on multisensory inputs; in fast and slow dynamics

Posture control to maintain an upright stance is one of the most important and basic requirements in the daily life of humans. The sensory inputs involved in posture control include visual and vestibular inputs, as well as proprioceptive and tactile somatosensory inputs. These multisensory inputs are integrated to represent the body state (body schema); this is then utilized in the brain to generate the motion. Changes in the multisensory inputs result in postural alterations (fast dynamics), as well as long-term alterations in multisensory integration and posture control itself (slow dynamics). In this review, we discuss the fast and slow dynamics, with a focus on multisensory integration including an introduction of our study to investigate "internal force control" with multisensory integration-evoked posture alteration. We found that the study of the slow dynamics is lagging compared to that of fast dynamics, such that our understanding of long-term alterations is insufficient to reveal the underlying mechanisms and to propose suitable models. Additional studies investigating slow dynamics are required to expand our knowledge of this area, which would support the physical training and rehabilitation of elderly and impaired persons.

Techniques and Methods for Testing the Postural Function in Healthy and Pathological Subjects

The different techniques and methods employed as well as the different quantitative and qualitative variables measured in order to objectify postural control are often chosen without taking into account the population studied, the objective of the postural test, and the environmental conditions. For these reasons, the aim of this review was to present and justify the different testing techniques and methods with their different quantitative and qualitative variables to make it possible to precisely evaluate each sensory, central, and motor component of the postural function according to the experiment protocol under consideration. The main practical and technological methods and techniques used in evaluating postural control were explained and justified according to the experimental protocol defined. The main postural conditions (postural stance, visual condition, balance condition, and test duration) were also analyzed. Moreover, the mechanistic exploration of the postural function often requires implementing disturbing postural conditions by using motor disturbance (mechanical disturbance), sensory stimulation (sensory manipulation), and/or cognitive disturbance (cognitive task associated with maintaining postural balance) protocols. Each type of disturbance was tackled in order to facilitate understanding of subtle postural control mechanisms and the means to explore them.