Postural Feedback Research Articles

Serious Gaming to Support Exercise Therapy for Patients with Chronic Nonspecific Low Back Pain: A Feasibility Study

To investigate the feasibility of a functional exercise program supported by serious gaming for patients with chronic nonspecific low back pain (LBP). Ten patients with chronic nonspecific LBP and an underlying motor control impairment were recruited. Subjects performed a partially supervised exercise program (36 sessions, 18 weeks) that included 30 minutes of general conditioning and 90 minutes of individually tailored functional motor control exercises (MCEs). Serious games (SGs) were used to (1) improve thoracolumbar dissociation and (2) to provide postural feedback during functional MCEs. The SGs were also available at home. Treatment satisfaction and the scores on the credibility/expectancy questionnaire were good and did not change throughout the intervention. Patients remained motivated throughout the rehabilitation program and no serious adverse events were reported. Overall, participants indicated that the SGs helped them to perform the home exercises more correctly, and as a consequence, they felt more confident doing them. However, the time needed to set up the games was a barrier for home use and participants would have found it useful to receive postural feedback during daily life activities. It is feasible to support a functional exercise program with SGs for patients with chronic nonspecific LBP, both in a supervised and a home environment. Time-efficiency and the integration of SGs in daily life activities are challenges that need to be addressed in the future.

Postural compensation strategy depends on the severity of vestibular damage.

The purpose of this study was to investigate the effects of various levels of vestibular function on balance in two, free-standing rhesus monkeys. We hypothesized that postural control strategy depended on the severity of vestibular damage. More specifically, that increased muscle stiffness (via short-latency mechanisms) was adequate to compensate for mild damage, but long-latency mechanisms must be utilized for more severe vestibular damage.One animal was studied for pre-ablated and mild vestibular dysfunction states, while a second animal was studied in a pre-ablated and severe vestibular dysfunction state. The vestibulo-ocular reflex (VOR), an eye movement reflex directly linked to vestibular function, was used to quantify the level of vestibular damage. A postural feedback controller model, previously only used for human studies, was modified to interpret non-human primate postural responses (differences observed in the measured trunk roll) for these three levels of vestibular function. By implementing a feedback controller model, we were able to further interpret our empirical findings and model results were consistent with our above hypothesis. This study establishes a baseline for future studies of non-human primate posture.

Effectiveness of a lumbopelvic monitor and feedback device to change postural behaviour: a protocol for the ELF cluster randomised controlled trial

IntroductionLow back pain (LBP) is the most common, costly and disabling musculoskeletal disorder worldwide, and is prevalent in healthcare workers. Posture is a modifiable risk factor for LBP shown to...

Evaluation of Novel EMG Biofeedback for Postural Correction During Computer Use.

Postural correction is an effective rehabilitation technique used to treat chronic neck and shoulder pain, and is aimed toward reducing the load on the surrounding muscles by adopting a neutral posture. The objective of this investigation was to evaluate the effectiveness of real-time high-density surface EMG (HDsEMG) biofeedback for postural correction during typing. Twenty healthy participants performed a typing task with two forms of postural feedback: (1) verbal postural coaching and (2) verbal postural coaching plus HDsEMG biofeedback. The interface used activity from two HDsEMG arrays placed over the trapezius designed to shift trapezius muscle activity inferiorly. The center of gravity across both arrays was used to quantify the spatial distribution of trapezius activity. Planar angles taken from upper extremity reflective markers quantified cervicoscapular posture. During the biofeedback condition, trapezius muscle activity was located 12.74±3.73mm more inferior, the scapula was 2.58±1.18° more adducted and 0.23±0.24° more depressed in comparison to verbal postural coaching alone. The results demonstrate the short-term effectiveness of a real-time HDsEMG biofeedback intervention to achieve postural correction, and may be more effective at creating an inferior shift in trapezius muscle activity in comparison to verbal postural coaching alone.

The effectiveness of a lumbopelvic monitor and feedback device to change postural behavior: a feasibility randomized controlled trial.

Feasibility randomized controlled trial. To assess the feasibility of a trial to investigate the effectiveness of a lumbopelvic monitor as a feedback device for modifying postural behavior during daily work-related activities. Frequent or sustained flexed postures play a role in the development or maintenance of nonspecific low back pain. The provision of postural feedback could help individuals with or at risk of nonspecific low back pain improve their postural awareness and avoid hazardous or pain-provoking postures. Sixty-two participants employed in a health care organization were randomly allocated into 1 of 3 groups: a control group, an intermittent feedback group, and a constant feedback group. Adherence and follow-up rates were assessed. Differences in postural pattern between baseline and follow-up measurements were used to assess the effectiveness of the lumbopelvic monitor as a postural feedback device. Adherence was approximately 75%. With the exception of 1 center, the follow-up overall rates exceeded the a priori desired threshold of 80%. Within-group comparisons revealed no significant differences in postural pattern for the control group and intermittent feedback group. The constant feedback group showed a significant reduction in flexed posture at the follow-up period compared with the baseline period. Differences between groups did not reach statistical significance; however, the constant feedback group, compared with the control group, demonstrated an effect size (d) of 0.60. The provision of constant postural feedback seems promising for promoting changes in postural behavior. This feasibility trial identified adherence and follow-up rates and sample-size estimates important to the conduct of a fully powered efficacy trial. Level of Evidence Therapy, level 2b-.

Joint role exploration in sagittal balance by optimizing feedback gains

SUMMARYThis paper investigates the contributions of each joint in perturbed balance by employing multiple balance strategies and exploring gain scheduling. Hybrid controllers are developed for sagittal standing in response to constant pushes, and a hypothesis is then investigated that postural feedback gains in standing balance should change with perturbation size via an optimization approach. Related research indicates the roles of each joint: the ankles apply torque to the ground, the hips and/or arms generate horizontal ground forces, and the knees and hips squat. To investigate it from an optimization point of view, this paper uses a horizontal push of a given size, direction, and location as a perturbation, and optimizes controllers for different push sizes, directions, and locations. It applies to the ankle, hip, squat, and arm swinging strategies in standing balance. By comparing the capability of handling disturbances and investigating the feedback gains of each strategy, this paper quantitatively analyzes the contributions of each joint to perturbed balance. We believe this work is also instructive to study the progressive behavioral changes as the model gets more and more complex.

She Stoops to Conquer? How Posture Interacts With Self-Objectification and Status to Impact Women’s Affect and Performance

Research suggests that posture exerts powerful affective and cognitive influences, although recent studies have indicated that these embodiment effects are moderated by gender. We examined two sociocultural factors that may contribute to the effects of postural feedback in women: self-objectification and power. Across a 2 × 2 × 2 between-subjects design, 80 female undergraduates completed various cognitive tasks and self-report measures after having been in an upright or slouched posture, seated in either a (powerful) throne or child’s chair, and wearing either a formfitting (objectifying) tank top or loose sweatshirt. The results showed that posture had the predicted influence on mood, with those seated upright reporting more positive mood than those seated in a slouched position. For the cognitive tasks, our findings were more complex and, due to low power, are best considered preliminary. Participants who were seated upright in a child’s chair while wearing a sweatshirt attempted the highest number of math items compared to those in the other conditions, supporting our prediction that postural benefits would be greatest in a context where power cues were gender-appropriate and self-objectification effects were attenuated. On a measure of satisfaction with performance, our findings suggest that self-objectification outweighed the power manipulation, leading to poorer outcomes when a seated position emphasized sexualized features of the body. Taken together, our results suggest that embodiment effects appear to be impacted by contextual cues, perhaps particularly for women.

Postural leaning direction challenges the manifestation of tendon vibration responses at the ankle joint

In this study, we examined the interaction between central and peripheral proprioceptive afferent pathways by applying ankle tendon vibration during postural leaning in different directions. Twenty young participants stood for 60s over the midline of two adjacent force platforms in (a) neutral stance distributing Body Weight (BW) equally between the platforms, (b) forward leaning transferring 80% of BW to the front platform and (c) backward leaning transferring 80% of BW to the rear platform. Participants controlled the degree of leaning by receiving on-line visual feedback of BW distribution matched to a target line. Vibration (80Hz, 1.5–1.8mm) was applied over the Achilles or tibialis anterior tendon during the middle 20s of standing. This induced a postural shift towards the vibration side and an increase in the variability of the BW distribution that was greater in backward compared to forward leaning. EMG responses to tendon vibration were independent of the leaning direction. Antagonistic activity also increased in response to vibration, the amplitude of this increase however was direction dependent. These results favor the hypothesis about the central co-modulation of the vibration evoked proprioceptive inflow based on postural and visual feedback rather than muscle tension constraints.

Experimental System for Investigation of Visual Sensory Input in Postural Feedback Control

The human postural control system represents a biological feedback system responsible for maintenance of upright stance. Vestibular, proprioceptive and visual sensory inputs provide the most important information into the control system, which controls body centre of mass (COM) in order to stabilize the human body resembling an inverted pendulum. The COM can be measured indirectly by means of a force plate as the centre of pressure (COP). Clinically used measurement method is referred to as posturography. In this paper, the conventional static posturography is extended by visual stimulation, which provides insight into a role of visual information in balance control. Visual stimuli have been designed to induce body sway in four specific directions – forward, backward, left and right. Stabilograms were measured using proposed single-PC based system and processed to calculate velocity waveforms and posturographic parameters. The parameters extracted from pre-stimulus and on-stimulus periods exhibit statistically significant differences.

Influences of visual feedback indicator scales on human upright postural control

Human upright postural control is highly related to visual information. In order to explore the influence of visual feedback on static upright postural control, postural sway of eight healthy young adults was investigated under visual feedback circumstances. In the investigation, postural feedback information was visualized by an indicator composed of a movable spot and a stationary circle, and in addition to Shannon entropy analysis, time domain and frequency domain analyses were employed to inspect postural control adjustment. The experiment results indicate that even though indicator scale changes do not induce significant postural differences in time domain and random characteristics, reduction of the visual feedback indicator scale inspires a postural power shift to higher frequencies. In addition, this reduction also induces a fall-after-rise pattern of postural energy distribution in the frequency range of 0.5–1 Hz.

Arm training in standing also improves postural control in participants with chronic stroke

PurposeTo prove the concept that postural control will improve without specific balance control training during arm training in standing with individuals with chronic stroke. MethodsNine participants (mean age 64±7) received training involving hand orthotic assisted grasp, reach and release in standing 1h, 3×’s/week for 6weeks. Training focused on task completion with no explicit instructions provided for postural alignment, weight shift or balance strategy. Testing consisted of quantified measures using NeuroCom™ Balance Master, Berg Balance Scale (BBS) and Activities-specific Balance Confidence Scale (ABC). ResultsPost training participants demonstrate increased (p<.05) composite stability scores for sensory organization testing (mean 71.55±12.7–75.55±11). Velocity and directional control of COP weight shift improved for all 9 subjects with 6/9 achieving 100% target acquisition. Directional control improved (p<.05) for medial/lateral movements for all speeds and composite score. Anterior/posterior rhythmic weight shifting increased significantly in COP velocity control at moderate and fast velocities and composite score. Increases in mean BBS (p<.01) from 41.33±10.1–46.88±8.03 exceeded the clinically important cutoff for the scale. Balance confidence improved with ABC mean scores 70.22±14.5–79.55±12.86 (p<.05). Seven participants demonstrated changes above the minimally important difference for this scale. ConclusionsPostural control improved following task oriented arm training in standing without explicit postural control goals, instruction or feedback challenging current training paradigms of isolated postural control training with conscious attention directed to center of pressure location and movement.

Perturbation-dependent selection of postural feedback gain and its scaling

In this study we examined whether the selection of postural feedback gain and its scaling is dependent on perturbation type. We compare forward pushes applied to the back of a standing subject to previous work on responses to support translation. As was done in the previous work, we quantified the subject's response in terms of perturbation-dependent feedback gains. Seven healthy young subjects (25±3yr) experienced five different magnitudes of forward push applied by a 1.25m-long pendulum falling from the height of 1.4m toward the center of mass of the subject's torso. The loads on the pendulum ranged from 2 to 10kg. Impulsive force, ground reaction forces and joint kinematics were measured, and joint torques were calculated from inverse dynamics. A full-state feedback control model was used to quantify the empirical data, and the feedback gains that minimized the fitting error between the data and model simulation were identified. As in previously published feedback gains for support translation trials, gradual gain scaling with push perturbation magnitude was consistently observed, but a different feedback gain set was obtained. The results imply that the nervous system may be aware of body dynamics being subjected to various perturbation types and may select perturbation-dependent postural feedback gains that satisfy postural stability and feasible joint torque constraints.

Virtual Reality–Enhanced Partial Body Weight–Supported Treadmill Training Poststroke: Feasibility and Effectiveness in 6 Subjects

Walker ML, Ringleb SI, Maihafer GC, Walker R, Crouch JR, Van Lunen B, Morrison S. Virtual reality–enhanced partial body weight–supported treadmill training poststroke: feasibility and effectiveness in 6 subjects. Objective To determine whether the use of a low-cost virtual reality (VR) system used in conjunction with partial body weight–supported treadmill training (BWSTT) was feasible and effective in improving the walking and balance abilities of patients poststroke. Design A before-after comparison of a single group with BWSTT intervention. Setting University research laboratory. Participants A convenience sample of 7 adults who were within 1 year poststroke and who had completed traditional rehabilitation but still exhibited gait deficits. Six participants completed the study. Intervention Twelve treatment sessions of BWSTT with VR. The VR system generated a virtual environment that showed on a television screen in front of the treadmill to give participants the sensation of walking down a city street. A head-mounted position sensor provided postural feedback. Main Outcome Measures Functional Gait Assessment (FGA) score, Berg Balance Scale (BBS) score, and overground walking speed. Results One subject dropped out of the study. All other participants made significant improvements in their ability to walk. FGA scores increased from mean of 13.8 to 18. BBS scores increased from mean of 43.8 to 48.8, although a ceiling effect was seen for this test. Overground walking speed increased from mean of .49m/s to .68m/s. Conclusions A low-cost VR system combined with BWSTT is feasible for improved gait and balance of patients poststroke.

Postural Feedback Scaling Deficits in Parkinson's Disease

Many differences in postural responses have been associated with age and Parkinson's disease (PD), but until now there has been no quantitative model to explain these differences. We developed a feedback control model of body dynamics that could reproduce the postural responses of young subjects, elderly subjects, and subjects with PD, and we investigated whether the postural impairments of subjects with PD can be described as an abnormal scaling of postural feedback gain. Feedback gains quantify how the nervous system generates compensatory joint torques based on kinematic responses. Seven subjects in each group experienced forward postural perturbations to seven different backward support surface translations ranging from 3- to 15-cm amplitudes and with a constant duration of 275 ms. Ground reaction forces and joint kinematics were measured to obtain joint torques from inverse dynamics. A full-state feedback controller with a two-segment body dynamic model was used to simulate joint kinematics and kinetics in response to perturbations. Results showed that all three subject groups gradually scaled postural feedback gains as a function of perturbation amplitudes, and the scaling started even before the maximum allowable ankle torque was reached. This result implies that the nervous system takes body dynamics into account and adjusts postural feedback gains to accommodate biomechanical constraints. PD subjects showed significantly smaller than normal ankle feedback gain with low scaling and larger hip feedback gain, which led to an early violation of the flat-foot constraint and unusually small (bradykinetic) postural responses. Our postural feedback control model quantitatively described the postural abnormality of the patients with PD as abnormal feedback gains and reduced ability to modify postural feedback gain with changes in postural challenge.

Metabolic profile of the perivertebral muscles in small therian mammals: implications for the evolution of the mammalian trunk musculature

In order to gain a better understanding of the ancestral properties of the perivertebral muscles of mammals, this study investigated the fiber type composition of these muscles in six small, extant therians (two metatherians and four eutherians) similar in body shape to early mammals. Despite a few species-specific differences, the investigated species were very similar in their overall distribution of fiber types indicating similar functional demands on the back muscles in mammals of this body size and shape. Deep and short, mono- or multisegmental muscles (i.e., mm. interspinales, intermammillares, rotatores et intertransversarii) consistently showed the highest percentage of slow, oxidative fibers implying a function as local stabilizers of the vertebral column. Superficial and large, polysegmental muscles (i.e., mm. multifidus, sacrospinalis, iliopsoas et psoas minor) were predominantly composed of fast, glycolytic fibers suggesting they function to both globally stabilize and mobilize the spine during rapid non-locomotor and locomotor activities. Some muscles contained striking accumulations of oxidative fibers in specific regions (mm. longissimus et quadratus lumborum). These regions are hypothesized to function independently from the rest of the muscle belly and may be comparable in their functionality to regionalized limb muscles. The deep, central oxidative region in the m. longissimus lumborum appears to be a general feature of mammals and likely serves a proprioceptive function to control the postural equilibrium of the pelvic girdle and lumbar spine. The potential functions of the m. quadratus lumborum during ventilation and ventral stabilization of the vertebral column are discussed. Because representatives of the stem lineage of mammals were comparable in their body proportions and probably also locomotor parameters to the species investigated here, I suggest that the described fiber type distribution is representative of the ancestral condition in mammals. The origin of mammals was associated with a substantial enlargement of the epaxial muscles and the addition of subvertebral muscle mass. Because this novel muscle mass is mainly composed of fast, glycolytic fibers in extant species, it is plausible that these changes were associated with the evolution of increased sagittal mobility in the posterior trunk region in the therapsid ancestors of mammals. The caudally increasing role of sagittal bending in body propulsion is consistent with the overall increase in the percentage of glycolytic fibers in the cranio-caudal direction. The evolution of mammals was also associated with a loss of ribs in the posterior region of the trunk. This loss of ribs is thought to have decreased the stability of the posterior trunk, which may explain the observed greater oxidative capacity of the caudal local stabilizers. The increased need for postural feedback in the more mobile lumbar region may also explain the evolution of the proprioceptive system in the m. longissimus lumborum. Furthermore, the anatomical subdivision of the transversospinal muscle into several smaller muscle entities is suggested to facilitate their functional specialization.

Motor Control Learning in Chronic Low Back Pain

A randomized prospective cohort study of participants with chronic low back pain, seeking physical therapy, with follow-up at weeks 6 and 28. Effects of conventional physiotherapy and physiotherapy with the addition of postural biofeedback were compared. To evaluate the benefits of postural biofeedback in chronic low back pain participants. Biofeedback using electromyographic signals has been used in chronic low back pain with mixed results. Postural feedback had not been previously used. Demographic and psychological baseline data along with range of motion were analyzed from a sample of 47 chronic participants with low back pain randomized into conventional physiotherapy with or without the addition of postural biofeedback. After 6 months, there were 21 dropouts. The participants with biofeedback had markedly improved status in visual analog pain scales, short form-36, and range of motion. The study strongly suggests that postural feedback is a useful adjunct to conventional physiotherapy of chronic low back pain participants.

Human Postural Feedback Response Described by Eigenvector

Human postural responses appeared to have stereotyped modality, such as ankle mode, knee mode, and hip mode in response to various levels of postural challenges. We examined whether human postural control gain of full-state feedback could be decoupled along with the eigenvectors. To verify the model, postural responses subjected to fast backward perturbation were used. Upright posture was modeled as 3-segment inverted pendulum incorporated with linear feedback control, and joint torques were calculated using inverse dynamics. Postural modalities, such as ankle, knee and hip mode, were obtained from eigenvectors of biomechanics model. As oppose to the full-state feedback control, independent modal control assumes that modal control input is determined by the linear combinations of corresponding modality. We used linear regression to obtain and compare the feedback gains for both eigenvector control gain and full-state feedback. As a result, we found that both feedback gains of two control models that fit the joint torque data are reasonably closed each other especially at the joint angle feedback gains. This implies that the simple parameterization using eigenvectors may be used to correlate the feedback gains of full-state feedback control.

Effect of Initial Lean on Scaling of Postural Feedback Responses

We examined how the central nervous system adjusts postural responses to an increased postural challenge due to an initial lean. Postural feedback responses scale to accommodate biomechanical constraints, such as an allowable ankle joint torque. Initial forward leaning, which is observed among the elderly who are inactive or afraid of falling, brings subjects near to the limit of stability and makes the biomechanical constraints more difficult to obey. We hypothesized that the central nervous system is aware of body dynamics and restrains postural responses when subjects initially lean forward. To test this hypothesis, fast backwards perturbations of various magnitudes were applied to 12 healthy young subjects (3 male, 9 female) aged 20 to 32 years. The subjects were instructed to stand quietly on a hydraulic servo-controlled force platform with their arms crossed over their chests, then to recover from a perturbation by returning to their upright position, without stepping or lifting their heels off the ground, if possible. Initially, the subjects were either standing upright or leaning forward. The force platform was movable in the translational direction and programmed to move backward with various ramp displacements ranging from 1.2 to 15 cm, all with the duration of 275 msec. For each trial, the kinematics and ground reaction force data were recorded, then used to compute the net joint torques, employing a least squares inverse dynamics method. Optimization methods were used to identify a set of equivalent feedback control gains for each trial so that the biomechanical model incorporating this feedback control would reproduce the empirical response. The results showed that the kinematics, joint torque, and feedback gains gradually scaled as a function of the perturbation magnitude before they reached the biomechanical constraint, and the scaling became more severe with an initial forward lean. For example, the model suggested that the magnitude of the ankle joint angle feedback to ankle torque was smaller in the leaning trials than in the initially upright trials, as if the subjects experienced a larger postural perturbation in the leaning trials. These results imply that the central nervous system restrained the postural responses to accommodate the additional biomechanical constraint imposed by the forward posture, thereby suggesting that the central nervous system is aware of body dynamics and biomechanical constraints. The scaling of the postural feedback gains with the perturbation magnitude and initial lean indicates that the postural control can be interpreted as a feedback scheme with scalable gains.

An Optimal Estimator Model of Multi-Sensory Processing in Human Postural Control

We hypothesized that multi-sensory processing at the central nervous system (CNS) in human postural control can be described using an optimal estimator model. The estimates on body dynamics from multi-sensory signals contain sensory noise, transmission delays, and process disturbances. The state estimates approximate actual body movement. Erroneous estimates degrade the performance of feedback control and could cause a loss of balance if distorted severely. To test the hypothesis, we examined the frequency response of a visually-induced postural sway with stimulus frequency ranging from 0.075 to 1Hz and established an optimal estimator model. Two healthy young (33yrs ± 1) subjects stood on a force platform located 1.25m behind a projection screen with their arms crossed over their chests. They were asked to maintain an upright posture against the sinusoidal visual field stimuli. Each sinusoidal visual stimulus was generated by a projector for 200secs in pitch direction with a maximum pitch angle of 20o. Kinematics data was recorded to calculate the frequency response function of the center of mass (COM). There were three components in the modeling procedure: a biomechanical model of body and sensor dynamics, a linear feedback control model to stabilize the biomechanical model, and a state estimator to estimate body dynamic states based on multi-sensory outputs. We modeled the sensor dynamics of the semicircular canal, otolth, vision, and muscle spindles at the ankle and hip joint. We used the Kalman filter and linear quadratic regulator to determine feedback gains. Results showed that the frequency response function of a visually-induced postural sway decreased as stimulus frequency increased, and this low-pass filtering characteristic with an approximate cutoff frequency of 0.2Hz was also simulated by the postural feedback control model with optimal estimator. Low-pass filtering characteristics of the frequency response are mainly due to body and sensor dynamics, which show reduced responses for high frequency stimulus. The Kalman filter represents that the CNS utilizes redundant sensory information in a way that minimizes discrepancies between actual body dynamics and estimated body dynamics based on sensory output and an internal model. The results suggest that the CNS may make use of an internal representation of body dynamics, and can integrate sensory information in an optimal way to best estimate human postural responses.

Postural feedback responses scale with biomechanical constraints in human standing.

We tested whether human postural responses can be described in terms of feedback control gains, and whether these gains are scaled by the central nervous system to accommodate biomechanical constraints. A feedback control model can describe postural responses for a wide range of perturbations, but biomechanical constraints-such as on the torque that can be exerted on the ground-make a single set of feedback gains inappropriate for all perturbations. To observe how postural responses change with perturbation magnitude, we applied fast, backward perturbations of magnitudes 3-15 cm to 13 healthy young volunteers (4 men, 9 women, aged 20-32 years). We used a 3-segment, sagittal-plane biomechanical model and a linear state feedback controller to reproduce the observed postural responses. Optimization was used to identify the best-fit feedback control gains for each trial. Results showed that trajectories of joint angles and joint torques were scaled with perturbation magnitude. This scaling occurred gradually, rather than abruptly changing at magnitudes where biomechanical constraints became active. Feedback gains were found to fit reasonably well with data ( R(2)=0.92) and to be multivariate and heterogenic in character, meaning that the torque produced at any joint is generally a function of motions not only at the same joint, but other joints as well. Hip gains increased and ankle gains decreased nearly linearly with perturbation magnitude, in accordance with biomechanical limitations on ground reaction torque. These results indicate that postural adjustments can be described as a single feedback control scheme, with scalable heterogenic gains that are adjusted according to biomechanical constraints.