SEARCH · PubMed Health

Results for “human stance”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed1997

Control model of human stance using fuzzy logic.

A control model of human stance is proposed based on knowledge from behavioral experiments and physiological systems. The proposed model is based on the control of global variables specific to body orientation and alignment, rather than on the control of the body's center of mass within the base of support. Furthermore, the proposed control model is not based on purely inverted pendulum body mechanics where only motion at one joint is controlled, as for instance the ankle. In the proposed model, the degrees of freedom are controlled by using reciprocal and synergistic muscle actions at multiple joints. The control model is based on three sets of different global variables which act in parallel: (1) limb length and its derivative, (2) limb orientation and its derivative, and (3) trunk attitude and its derivative. An important feature of the control model is the use of fuzzy logic, which enables us to model experimental findings and physiological knowledge in a meaningful and explicit way using fuzzy if-then rules. In the control model, 36 fuzzy if-then rules are implemented and applied using a four-linked segment model consisting of a trunk, thigh, shank and foot. Uni- and biarticular limb muscles and trunk muscles are represented as torque actuators at each individual joint. In the model, three sets of global variables act in parallel and make corrective and coordinated responses to internal, self-induced perturbations. The data show that the use of global variables and fuzzy logic successfully enables us to model human standing with sway about a point of equilibrium. Small changes in, for example, total body sway are comparable to those seen during natural sway in human stance. The selected controllers--limb length, limb orientation and trunk attitude--seem to be appropriate for human stance control.

Fuzzy Logic↗

PubMed2001

An adaptive model of sensory integration in a dynamic environment applied to human stance control.

An adaptive estimator model of human spatial orientation is presented. The adaptive model dynamically weights sensory error signals. More specific, the model weights the difference between expected and actual sensory signals as a function of environmental conditions. The model does not require any changes in model parameters. Differences with existing models of spatial orientation are that: (1) environmental conditions are not specified but estimated, (2) the sensor noise characteristics are the only parameters supplied by the model designer, (3) history-dependent effects and mental resources can be modelled, and (4) vestibular thresholds are not included in the model; instead vestibular-related threshold effects are predicted by the model. The model was applied to human stance control and evaluated with results of a visually induced sway experiment. From these experiments it is known that the amplitude of visually induced sway reaches a saturation level as the stimulus level increases. This saturation level is higher when the support base is sway referenced. For subjects experiencing vestibular loss, these saturation effects do not occur. Unknown sensory noise characteristics were found by matching model predictions with these experimental results. Using only five model parameters, far more than five data points were successfully predicted. Model predictions showed that both the saturation levels are vestibular related since removal of the vestibular organs in the model removed the saturation effects, as was also shown in the e xperiments. It seems that the nature of these vestibular-related threshold effects is not physical, since in the model no threshold is included. The model results suggest that vestibular-related thresholds are the result of the processing of noisy sensory and motor output signals. Model analysis suggests that, especially for slow and small movements, the environment postural orientation can not be estimated optimally, which causes sensory illusions. The model also confirms the experimental finding that postural orientation is history dependent and can be shaped by instruction or mental knowledge. In addition the model predicts that: (1) vestibular-loss patients cannot handle sensory conflicting situations and will fall down, (2) during sinusoidal support-base translations vestibular function is needed to prevent falling, (3) loss of somatosensory information from the feet results in larger postural sway for sinusoidal support-base translations, and (4) loss of vestibular function results in falling for large support-base rotations with the eyes closed. These predictions are in agreement with experimental results.

Adaptation, Physiological↗

PubMed1999

A multisensory integration model of human stance control.

A model is presented to study and quantify the contribution of all available sensory information to human standing based on optimal estimation theory. In the model, delayed sensory information is integrated in such a way that a best estimate of body orientation is obtained. The model approach agrees with the present theory of the goal of human balance control. The model is not based on purely inverted pendulum body dynamics, but rather on a three-link segment model of a standing human on a movable support base. In addition, the model is non-linear and explicitly addresses the problem of multisensory integration and neural time delays. A predictive element is included in the controller to compensate for time delays, necessary to maintain erect body orientation. Model results of sensory perturbations on total body sway closely resemble experimental results. Despite internal and external perturbations, the controller is able to stabilise the model of an inherently unstable standing human with neural time delays of 100 ms. It is concluded, that the model is capable of studying and quantifying multisensory integration in human stance control. We aim to apply the model in (1) the design and development of prostheses and orthoses and (2) the diagnosis of neurological balance disorders.

Afferent Pathways↗

PubMed1993

Visual control of human stance on a narrow and soft support surface.

The influence of additional visual feedback (VF) on stance control was studied under conditions of changed afferent information from the foot sole and ankle joint due to different support surfaces. The changes of body sway amplitudes were analyzed and their frequency spectrum was established. The effect of visual feedback on the amplitude and frequency characteristics of human stance was manifested as: a) a decrease of the mean amplitude of body sway during visual feedback, corresponding to the decrease of power spectrum density (PSD) of stabilograms in the frequency range below 0.05 Hz, b) an increase of mean velocity of body sway corresponding to the increase of PSD of stabilograms in the frequency range of 0.4-1.5 Hz. The results showed that the improvement of the upright stance by additional visual feedback is mainly mediated through activation of postural muscles at the ankle level, or ankle strategy. The stabilization effect of VF on stance control is slight or negligible if the performance part in ankle joint (narrow support) was reduced.

Adult↗

PubMed2004

Bifurcation and stability analysis in musculoskeletal systems: a study in human stance.

Reflexes are important in the control of such daily activities as standing and walking. The goal of this study is to establish how reflexive feedback of muscle length, velocity, and force can lead to stable equilibria (i.e., posture) and limit cycles (e.g., ankle clonus and gait). The influence of stretch reflexes on the behavior and stability of musculoskeletal systems was examined using a model of human stance. We computed branches of fold and Hopf bifurcations by numerical bifurcation analysis of the model. These fold and Hopf branches divide the parameter space, constructed by the reflexive feedback gains, into regions of different behavior: unstable posture, stable posture, and stable limit cycles. These limit cycles correspond to a neural deficiency, termed ankle clonus. We also linked bifurcation analysis to known biomechanical concepts by linearizing the model: the fold branch corresponds to zero ankle stiffness and defines the minimal muscle length feedback necessary for stable posture; the Hopf branch is related to unstable reflex loops. Crossing the Hopf branch can lead to the above-mentioned stable limit cycles. The Hopf branch reduces with increasing time delays, making the subject's posture more susceptible to unstable reflex loops. This might be one of the reasons why elderly people, or those with injuries to the central nervous system, often have trouble with standing and other posture tasks. The influence of cocontraction and force feedback on the behavior of the posture model was also investigated. An increase in cocontraction leads to an increase in ankle stiffness (i.e., intrinsic muscle stiffness) and a decrease in the effective reflex loop gain. On the one hand, positive force feedback increases the ankle stiffness (i.e., intrinsic and reflexive muscle stiffness); on the other hand it makes the posture more susceptible to unstable reflex loops. For negative force feedback, the opposite is true. Finally, we calculated areas of reflex gains for perturbed stance and quiet stance in healthy subjects by fitting the model to data from the literature. The overlap of these areas of reflex gains could indicate that stretch reflexes are the major control mechanisms in both quiet and perturbed stance. In conclusion, this study has successfully combined bifurcation analysis with the more common biomechanical concepts and tools to determine the influence of reflexes on the stability and quality of stance. In the future, we will develop this line of research to look at rhythmic tasks, such as walking.

Ankle↗

PubMed1985

Lateral orientation and stabilization of human stance: static versus dynamic visual cues.

The differential contributions of static versus dynamic visual cues to postural control were studied in human subjects. Lateral body oscillations were measured with accelerometers located at head, hips and ankle levels, while subjects righted their balance under various mechanical conditions: on either a soft (foam rubber) support or a hard one, and in either the classical or the sharpened Romberg stance. The visual pattern (horizontal or vertical rectangular grating) was illuminated with either a stroboscopic bulb or a normal one, and control measurements were also taken in darkness for each mechanical condition. Acceleration signals were processed into their frequency power spectra, the mean area and shape of which were taken to characterize the postural skills involved and the effects of either the visual suppressions or the mechanical destabilizations. Although dynamic visual cues have already been found to play a major role in the control of lateral body sway (Amblard and Crémieux 1976), we demonstrate here that static visual cues, the only ones available under stroboscopic illumination, also make a clear though minor contribution. Hence we suggest the existence of two modes of visual control of lateral balance in man, which are well separated in terms of the frequency range of body sway: the first mechanism, which operates below 2 Hz and is strobe-resistant, seems to control the orientation of the upper part of the body; the second mechanism, which operates above 4 Hz, centers on about 7 Hz and is strobe-vulnerable, seems to immobilize the body working upwards from the feet. Thus static visual cues may slowly control re-orientation or displacement, whereas dynamic visual cues may contribute to fast stabilization of the body. In between the frequency ranges at which these two visuomotor mechanisms come into play, at about 3 Hz, there is what we call a "blind frequency", a visually neutral sway frequency which may arise from the incompatibility of visual reorientation with visual stabilization, and where vision appears unable to reduce postural sway to any marked extent. Transmission of the destabilization produced by suppression of visual cues or by mechanical methods from one anatomical level to another is also briefly discussed in terms of bio-mechanical constraints, and the correlations between various pairs of levels are considered.

Adult↗

PubMed1994

Binaural monopolar galvanic vestibular stimulation reduces body sway during human stance.

The influence of monopolar binaural galvanic stimulation of the vestibular system was studied on body sway. Subjects, with eyes closed, were standing on a hard support or on foam rubber. Their body sway was registered on a force platform at intervals of 50 s. Both polarities of direct current with intensity 1 mA were used as a galvanic stimulus during the whole recording interval. Changes of body sway amplitude and velocity were analyzed in situations with and without galvanic stimulation on two different support surfaces. In stance on the hard support, the cathodal polarization of labyrinths (in most subjects) reduced body sway velocity and decreased body sway slightly in the anteroposterior direction. Anodal polarization of labyrinths during 50 s did not affect the body sway parameters. The results on the foam rubber platform exhibited a significant reduction of body sway velocity induced by both anodal and cathodal polarization of the labyrinths. The decrease of body sway in the anteroposterior direction was also observed during cathodal polarization. The stabilizing effect of vestibular binaural monopolar stimulation on the upright stance was mainly observed in the postural control situation where the leg proprioceptive input was changed (stance on soft surface) and the role of vestibular input was more important.

Adolescent↗

PubMed1995

Vestibular stimulation perturbs human stance also at higher frequencies.

The effect of primary vestibular disturbance on postural control was investigated in 11 normal subjects exposed to perturbation by bi-polar binaural galvanic stimulation of the vestibular nerve. The stimulus consisted of 30 s of sinusoidal galvanic stimulation at frequencies of 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 3.0 and 4.0 Hz, with a current of +/- 1 mA, the subject standing with open or closed eyes and the response evoked being recorded with a force platform. As compared with resting values, i.e. no stimuli, variance of lateral body sway was significantly greater at all frequencies tested in the closed eyes condition and at frequencies of 0.2, 0.5, 1.0, 3.0 and 4.0 Hz in the open eyes condition; using a high pass filter with a cut-off frequency of 0.1 Hz, variance of lateral body sway was significantly greater at frequencies 0.2, 0.3, 0.5, 1.0 and 2.0 Hz in the closed eyes condition and at frequencies 0.5 and 2.0 Hz in the open eyes condition. These findings suggest that in the lateral plane vestibular input affects and probably contributes to human postural control over a wider frequency range than suggested by findings in previous studies. Moreover, the visual contribution appears to enable the subject to suppress vestibular input causing lateral body sway only in the lower frequency range (here at 0.2 and 0.3 Hz). This evidence of vestibular contribution to postural control in the lateral plane is consistent with the response characteristics of the vestibulo-ocular reflex.

Adolescent↗

PubMed1985

Afferent control of human stance and gait: evidence for blocking of group I afferents during gait.

The cerebral potentials (c.p.) evoked by electrical stimulation of the tibial nerve during stance and in the various phases of gait of normal subjects were compared with the c.p. and leg muscle e.m.g. responses evoked by perturbations of stance and gait. Over the whole step cycle of gait the c.p. evoked by an electrical stimulus were of smaller amplitude (3 microV and 9 microV, respectively) than that seen in the stance condition, and appeared with a longer latency (mean times to first positive peak: 63 and 43 ms, respectively). When the electrical stimulus was applied during stance after ischaemic blockade of group I afferents, the c.p. were similar to those evoked during gait. The c.p. evoked by perturbations were larger in amplitude than those produced by the electrical stimulus, but similar in latencies in both gait and stance (mean 26 microV and 40 microV; 65 ms and 42 ms, respectively) and configurations. The large gastrocnemius e.m.g. responses evoked by the stance and gait perturbations arose with a latency of 65 to 70 ms. Only in the stance condition was a smaller, shorter latency (40 ms) response seen. It is concluded that during gait the signals of group I afferents are blocked at both segmental and supraspinal levels which was tested by tibial nerve stimulation. It is suggested that the e.m.g. responses induced in the leg by gait perturbations are evoked by group II afferents and mediated via a spinal pathway. The c.p. evoked during gait most probably reflect the processing of this group II input by supraspinal motor centres for the coordination of widespread arm and trunk muscle activation, necessary to restablish body equilibrium.

Adult↗

PubMed1992

Visually induced destabilization of human stance: neuronal control of leg muscles.

With subjects standing on a treadmill both the treadmill and an optical flow pattern were moved sinusoidally (0.25 Hz) and the effect of delaying the presentation of the image with respect to treadmill movement was analysed. Around the posterior turning point of treadmill movement a modulation of the tibialis anterior EMG was observed, the onset, duration and amplitude of which were dependent upon the phase-shift between the movements of the legs and the image. At times around the anterior turning point a corresponding modulation, but only of EMG amplitude, occurred in the extensor muscles. Little adaptational changes in EMG activity were seen during successive cycles. Consequently during a specific sensitive phase of the sinus tibialis anterior EMG, responses are evoked in which strength depended on the velocity of the optical flow pattern. The modulation of the extensor activity is necessary for a 'resetting' of the neutral body position.

Adaptation, Physiological↗

PubMed1999

Lateral balance organisation in human stance in response to a random or predictable perturbation.

The effect of the predictability of perturbation to standing balance was evaluated in terms of the muscle activity and response dynamics of five subjects exposed to horizontal forces at the pelvis producing sideways or forward sway. Rapid (EMG onset latencies of 70-80 ms recorded from the left gluteus medius and gastrocnemius) and qualitatively different patterns of response were produced by forward pushes and pushes to either side. However, the EMG response to left push was constant in pattern and timing, whether the push direction was constant and, therefore, predictable over a block of trials or whether the left push trials were interleaved randomly with right push or forward push trials. Moreover, there were no systematic effects of perturbation direction uncertainty on the latency and rate of increase of ground reaction forces. We conclude that prior information does not speed postural responses that differ quantitatively according to the direction of perturbation to balance.

Adult↗

PubMed1997

Human stance stability improves with the repetition of the task: effect of foot position and visual condition.

The effects of repetition of quiet stance trials on body sway, recorded through a stabilometric platform, were studied in 12 normal subjects. With feet together, both with eyes open (EO) and closed (EC), a progressive shift forward of the centre of foot pressure (CFP) occurred with repetition. In addition, with EC, but not with EO, a significant progressive reduction in sway area (SA) and sway path (SP) occurred. With feet 10 cm apart, initial SA and SP values were significantly smaller than with feet together, regardless of the visual condition, but repetition of trials induced no significant effects on either position of CFP or body sway under either visual condition. Results indicate the occurrence of a learning phenomenon in this simple postural task, whereby the body shifts towards a 'safer' position with a minimum energy expenditure due to reduced corrections of sway. Forward leaning and decrease in sway are two independently-occurring processes, each possibly due to a better central integration of proprioceptive input with repetition of trials.

Adolescent↗

PubMed1993

Gating of reflexes in ankle muscles during human stance and gait.

Holding the body's centre of gravity steady represents the crucial variable for the stabilization of posture in upright stance in man. Results from two experimental approaches suggest that force-dependent receptors are required, in addition to the well-known systems involved in sway stabilization, for equilibrium control. One approach concerns bilateral leg muscle activation during stance. Unilateral or bilateral leg displacements were induced while subjects stood on a treadmill with split belts. A unilateral displacement induced a bilateral EMG response. During bilateral displacements the EMG activity was linearly summed or subtracted, depending on whether the legs were displaced in the same or opposite directions. Both legs acted in a cooperative manner: each limb affected the strength of muscle activation and the time-space behaviour of the other. This interlimb coordination is suggested to be mediated by spinal interneuronal circuits, which are themselves under supraspinal (e.g., cerebellar) control. The other approach concerns the modulation of postural reflexes under stimulated "microgravity" ir. water immersion. An approximately linear relationship was found between contact forces and impulse-directed EMG response amplitudes in the leg muscles. Out of water loading of the subjects resulted in no further increase of the response amplitude. It was concluded that the function of proprioceptive reflexes involved in the stabilization of posture depends on the presence of contact forces opposing gravity. Extensor load receptors are thought to signal changes of the projection of body's centre of mass with respect to the feet. The interaction of the afferent input from these receptors with the other systems involved in postural control is not yet fully understood.

Ankle↗

PubMed1991

Compensation of human stance perturbations: selection of the appropriate electromyographic pattern.

Perturbations of stance evoke purposive EMG patterns which are directed to hold the body's centre of gravity over the feet. Dorsiflexing rotation of the feet is followed by a monosynaptic stretch reflex response in the gastrocnemius muscle, succeeded by a late compensatory tibialis anterior activation. Backward translation of the feet elicits only a compensatory polysynaptic EMG response in the gastrocnemius muscle, while an early gastrocnemius response is absent. The amplitude modulation of the gastrocnemius H-reflex has been investigated during the early part of the two modes of perturbation. Only during translational perturbation a progressive decrease in gastrocnemius H-reflex amplitude started within 5 ms after onset of displacement. The degree of the reduction in amplitude in the former perturbation was dependent on the displacement velocity. Only the contact forces (torques) differed between the two modes of perturbations within the first 10 ms after onset of perturbations. It is suggested that signals from pressure receptors within the body are responsible for the early change in H-reflex amplitude during translational perturbations and it is concluded that the simplest spinal reflex is under very rapid and powerful moment-to-moment control by changes in peripheral feedback. In view of a strong reciprocal modulation of monosynaptic and polysynaptic reflex responses, the later purposive EMG responses may be determined by early changes in presynaptic inhibition of group I afferents.

Adult↗

PubMed1993

Human stance on a sinusoidally translating platform: balance control by feedforward and feedback mechanisms.

With subjects standing on a treadmill moving sinusoidally backward and forward, recordings of electromyographic (EMG) leg and trunk muscle activity, head and joint movements and platform torque were made with the subjects' eyes open or closed. The sinusoidal frequency was changed, stepwise and randomly, between 0.5, 0.3 and 0.25 Hz. The amplitude of the deflection was constant at +/- 12 cm. During an adapted sinus cycle, the maximum leg muscle EMG activity was recorded in the tibialis anterior around the posterior turning point and in the gastrocnemius around the anterior turning point in the treadmill cycle. This activity was associated with a forward inclination of the body around the posterior point and a straightening of the body at the anterior point. Both the degree of body inclination and the corresponding EMG activity were dependent upon the sinusoidal frequency. The programmed adjustment of the body inclination was such that the result of inertial and gravitational forces acting on the body coincided with the axis of the body at the posterior turning point. At the anterior point, the adjustment was achieved mainly by strong activation of the leg extensors. The latencies of the compensatory muscle responses to a change in treadmill frequency were significantly shorter at the posterior point for the gastrocnemius than for the tibialis anterior, and at the anterior point for the tibialis anterior than for the gastrocnemius. No correlated changes were seen in the corresponding head and joint movements. The difference in latency can best be attributed to the different body postures during the sinusoid. Early activation of the gastrocnemius is required due to the forward-directed impulse to the inclined body at the posterior point, and of the tibialis anterior muscle due to the backward-directed impulse to the erect body at the anterior point. It is suggested that afferent input from extensor load receptors provides information about the position of the body's centre of gravity relative to the support surface and determines the generation of the EMG responses. Adaptation of both the EMG and biomechanical patterns to a new sinusoidal frequency of the treadmill occurred within four cycles after the change. Biomechanically, this was reflected as a change in the body posture. Vision did not significantly affect these changes. In conclusion, standing on a sinusoidally moving platform, the nervous system acts to control the position of the body's centre of gravity relative to the feet. Body posture is adjusted in such a way that the forces acting on the body during the treadmill movements become minimised.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1989

Interlimb coordination of leg-muscle activation during perturbation of stance in humans.

1. Electromyographic (EMG) responses were recorded in both legs, along with corresponding joint movements, after uni- and bilateral perturbations during stance on a treadmill with split belts. Displacements were directed forward, backward, or in opposing directions. They were induced by randomly timed ramp impulses at one of four different rates of treadmill acceleration. 2. Unilateral perturbations directed backward were followed by a bilateral gastrocnemius-EMG response, forward-directed perturbations by a bilateral tibialis anterior-EMG response. The amplitude of these responses was dependent on the rate of treadmill acceleration. Relative to the response of the displaced leg, the amplitude of the EMG response on the nondisplaced side was smaller when a gastrocnemius EMG response was induced, and about equal when the tibialis anterior muscle was activated. The onset latencies were shorter on the displaced side (displaced leg 75-96 ms, non-displaced leg 93-112 ms). 3. Bilateral perturbations in one direction were followed by larger EMG responses in both legs (in the gastrocnemius for backward-directed impulses, in the tibialis anterior for forward-directed impulses). For a given acceleration rate, their amplitude was about equal to the sum of the EMG amplitude of the displaced leg and that of the nondisplaced leg obtained during unilateral displacement. The inverse result was obtained when the legs were simultaneously displaced in opposite directions: EMG responses in both legs were significantly smaller than those obtained after unilateral displacement. 4. It is concluded that a unilateral displacement evokes reflex EMG responses in the synergistic muscles of both legs, which are graded according to the size of the proprioceptive input from the primarily displaced joint. During bilateral displacements, the activity induced by the respective contralateral leg is linearly summed or subtracted, depending on whether the legs are displaced in the same or in opposite directions. In view of the short latencies of these bilateral responses, it would seem that they are mediated by a spinal mechanism. 5. Distinct differences in the behavior of the antagonistic leg muscles were observed: 1) the coactivation of the contralateral leg muscle was significantly smaller when the gastrocnemius was stretched unilaterally, whereas it was about equal for the tibialis anterior; and 2) the gastrocnemius EMG responses were closely correlated with the displacement velocity, whereas the tibialis anterior response was more closely correlated with acceleration, i.e., the tibialis anterior response was more dynamic in nature.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed2004

Does hypnotizability affect human upright stance?

Subjects highly (Highs) and low susceptible to hypnosis (Lows) show different imagery and attentional capabilities and also peculiar somatomotor, vegetative and electroencephalographic differences in basal and task conditions. Since attention is one of the main component of hypnotic susceptibility and also a relevant factor for postural control, the aim of the experiment was to study actual differences between Highs and Lows at the eyes closure during upright stance. Visual and motor imagery as well as attentional/disattentional capabilities were evaluated through psychological tests. Posture was monitored though Elite systems during upright stance with open and closed eyes. At the eyes closure, Highs and Lows exhibited a different body sway modulation. Possible different compensation mechanisms are suggested for the two groups and interactions between attentional/arousal systems responsible of hypnotic phenomenology and postural control are underlined.

Adolescent↗

PubMed2003

A multisensory posture control model of human upright stance.

We present a multisensory postural control model based on experiments where the balance in normal subjects and vestibular loss patients was perturbed by application of external torque produced by force-controlled pull stimuli. The stimuli were applied while subjects stood on a stationary or body-sway-referenced motion platform with eyes closed and auditory cues masked. Excursions of the center of mass (COM) and the center of pressure (COP) were analyzed using a systems analysis approach. The results were compared to an 'inverted pendulum' model of posture control. The model receives input from four sensors: ankle proprioceptors, semicircular canals, otoliths, and plantar pressure sensors (somatosensory graviceptors). Sensor fusion mechanisms are used to yield separate internal representations of foot support motion, gravity, and external torque (pull). These representations are fed as global set point signals into a local control loop based on ankle proprioceptive negative feedback. This set point control upgrades the proprioceptive body-on-foot (support) stabilization into a body-in-space control which compensates for support tilt, gravity, and contact forces. This compensation occurs even when the stimuli are combined or a voluntary lean is superimposed. Model simulations paralleled our experimental findings.

Adult↗