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PubMed2000

Anticipatory EMG patterns associated with preferred and non-preferred arm pointing movements.

Rapid arm movements generate balance perturbations, which are anticipated and counteracted by postural adjustments. The effect of lateral preference on the control of the postural preparation to maximal velocity upperlimb pointing movements was investigated in right-handers. The muscular activities characterizing the postural adjustments were compared for preferred and non-preferred upper-limb movements. Movements were performed in two sitting conditions differing by their stability ("full on seat" and "edge of seat"). The electromyographic activity of the arm-movement prime mover and of several trunk and hip muscles involved in postural control was recorded with surface electrodes. Results indicate the presence of a reproducible pattern of anticipatory postural adjustments (APAs) involving trunk and hip muscles preceding the activation of the prime mover. In the "full on seat" condition, APAs started earlier and movement velocity was higher for preferred than for non-preferred arm movements. In the "edge of seat" condition, maximal velocity of movement did not differ significantly between both sides, but a higher excitation level of postural muscles was required to achieve this similar performance when the non-preferred upper limb was used. These findings are consistent with the hypothesis that handedness involves differences in the postural control associated with upperlimb movements, in other words that lateral preference is associated with a postural laterality.

Adaptation, Physiological↗
PubMed2001

Abnormal vestibular control of gaze and posture in a strain of a waltzing rat.

The waltzing behavior is usually attributed to vestibular dysfunction. However, the vestibular control of gaze and posture has not yet been measured quantitatively in any waltzing mutant. Therefore, this study was aimed at investigating the relationship between inner-ear morphology, the circling behavior, and the vestibular control of gaze and posture in a new strain of waltzing rats. Light- and electron-microscopy studies of these mutants did not reveal any structural abnormalities of the vestibular neural epithelia. In addition, the expression of Calretinin and 200-kD phosphorylated and non-phosphorylated neurofilaments was also found to be normal in the vestibular neural epithelia and ganglion cells. In contrast, the mutants showed severe dysfunctions of the vestibular control of gaze and posture. The skeletal geometry of the alert unrestrained animals was studied using cineradiography. At rest, waltzing rats held their heads tilted down: the horizontal semicircular-canal's plane was near the earth-horizontal's plane, instead of being tilted up as in Long Evans control rats. In addition, their cervical column was pitched more forward (33.6 degrees) than in the control group (6.9 degrees). The circling behavior was observed frequently, and the rats had episodes of circling in both directions. The episodes of circling amounted to an average of 17 turns, and the average angular velocity of the circling was 645 degrees/s. Unilateral labyrinthectomy induced the same postural and oculomotor syndromes in the waltzing and control groups. This indicates that the mutant vestibular nerve had a significant resting discharge before the lesion. Eye movements were recorded using acutely implanted search coils. Although waltzing rats were able to perform normal spontaneous eye movements, they showed a complete deficit of the horizontal vestibulo-ocular reflex (HVOR) and an impairment of the maculo-ocular reflex (MOR) during constant velocity, off-vertical axis rotation (OVAR). These results show, for the first time, that deficient transduction and/or processing of the horizontal-canal- and macular-related information can be causally related to the circling behavior and abnormal posture, respectively.

Animals↗
PubMed1990

The control of limb geometry in cat posture.

1. The aim of this study is to address the problem of the controlled variable in quadrupedal stance. In particular, we considered whether the projection of the centre of mass of the body on the support surface or the joint torques or the geometrical configuration of the limbs are primarily controlled. 2. Cats were trained to stand freely on a platform which could be tilted in the sagittal plane by up to +/- 20 deg. The normal and tangential components of the contact forces at each paw were measured by means of load cells. The position of limb joints was recorded by means of the ELITE system. 3. The projection of the centre of body mass on the platform, as well as the orientation and length of limb axes, varied to only a limited extent with tilt angle. In particular, the limb axes were closely lined up with the vertical, as were the vectors of the contact forces at the paws. As a result, the torques at the proximal joints (scapula and hip) were close to zero and the torques at the other joints varied little with table tilt. 4. In order to test the different hypotheses on postural control, an external load (10-20% of the animal weight) was applied to the cat forequarters. The projected centre of mass consistently shifted forwards, contrary to the hypothesis that this parameter is controlled in stance. Instead, the geometry of limb posture remained unmodified after load application, even though the torques at forelimb joints were much greater than in the control. 5. This postural behaviour showed no sign of adaptation over a period of 24 h of continuous load application. 6. It is concluded that limb geometry is primarily controlled in stance. The results are discussed in the context of current notions on hierarchical control and body scheme.

Animals↗
PubMed2004

Does postural chain mobility influence muscular control in sitting ramp pushes?

This study was conducted under the hypothesis that voluntary movement involves a perturbation of body balance and that a counter-perturbation has to be developed to limit the perturbation effects, which is a condition necessary to perform the movement efficiently. The stabilising action is produced in body segments that constitute the "postural" chain, and the voluntary movement by the segments said to constitute the "focal" chain. In order to deepen the understanding of how the postural chain contributes to the motor act, isometric transient efforts were considered. Seven adults in a sitting posture were instructed to exert bilateral horizontal pushes on a dynamometric bar, as rapidly as possible, up to their maximal force (Fx). Two sitting conditions were considered: full ischio-femoral contact (100 BP) and one-third ischio-femoral contact (30 BP), the latter being known to yield greater pelvis and spine mobility, that is greater postural mobility. Each session consisted of ten maximal pushes for each sitting condition. In order to explore the influence of postural mobility on muscular control and push force, surface EMGs of 14 postural and focal muscles were recorded. In addition, reaction forces (Rx) and displacement (Xp) of the centre of pressure (along the anteroposterior axis) were measured, as well as iliac crest acceleration (xh and zh, along the anteroposterior and vertical axes, respectively). The results showed that push force varied abruptly during the task ramp effort. When the ischio-femoral contact was limited, push force was enhanced, as well as the rate of push force rise (Fx/Deltat, Deltat being the force rise duration), suggesting a greater perturbation to balance. Also, there were significant increases in the Rx reaction forces, indicating body segment acceleration: "dynamic" phenomena occurred in the articulated body chain in response to increases in Fx. In addition, even though muscular contraction was isometric, postural EMGs, as well as focal EMGs, were phasic, a feature which characterises transient force exertion. The Rx reaction forces were associated with backward displacement of the centre of pressure, Xp. The centre of pressure displacement was interpreted as a backward pelvis rotation, an interpretation which was confirmed by backward and upward iliac crest accelerations. When ischio-femoral contact was reduced, the backward pelvis rotation was significantly increased, resulting from an increased pelvis and spine mobility. Distinct focal and postural EMG sequences were found to be associated with the effort. Two different sets of muscles were observed when considering recruitment order, the focal and the postural muscles. The ankle muscles were activated before the pelvis, the back and the scapular girdle, with the upper limb muscles activated only after the onset of the primum movens of push action (serratus anterior): the activation process followed a distal to proximal progression order. Moreover, the postural EMG sequence was anticipatory, that is there were anticipatory postural adjustments (APAs). Modifying the ischio-femoral contact did not induce a change in either the postural muscle set or in the recruitment order. There were significant increases in the level of activation (integrated EMG) of the postural muscles when ischio-femoral contact was reduced. They did not result from an increase in EMG duration but only from a modulation of EMG amplitude, suggesting that postural control for different ischio-femoral contacts involves adapting the motor program according to the postural requirements, rather than changing the postural strategy. Moreover, as APA amplitude was increased when ischio-femoral contact was reduced, it could be assumed that the postural chain is programmed in relation to postural chain mobility. In addition, the increase in postural EMGs was interpreted as an increased counter-perturbation opposed to an increased push force. It is concluded that greater mobility of the postural chain favours a greater dynamic counter-perturbat chain favours a greater dynamic counter-perturbation, which, in turn, allows the development of a greater push force; the ability to develop such a counter-perturbation (termed PKC: posturo-kinetic capacity) is enhanced when postural chain mobility is greater. Postural chain mobility appears to be a task parameter, and postural control appears to involve adapting the motor program according to the postural requirements, rather than changing the postural strategy.

Biomechanical Phenomena↗
PubMed2006

Responsiveness to terrestrial optic flow in infancy: does locomotor experience play a role?

Human infants show a peak in postural compensation to optic flow at approximately nine months of age. The current experiment tested whether the magnitude of visual-postural coupling in 9-month-olds increases when terrestrial optic flow is added to a moving room. A secondary objective was to explore whether locomotor experience plays any role in enhancing responsiveness to the additional terrestrial information. Ninety-one infants (experienced creepers, nascent creepers, and prelocomotors) were exposed to two conditions of optic flow: global optic flow (G) and global optic flow minus terrestrial optic flow (G-T). The additional terrestrial optic flow led to significantly higher visual-postural coupling. Consistent with previous findings, locomotor experience had no effect on responsiveness to the G-T condition, though there was weak evidence that the nascent creepers were more strongly influenced by the difference between flow conditions than the other infants. Unexpectedly, the prelocomotor females showed significantly lower visual-postural coupling than the prelocomotor males. These findings support the notion that the ground provides an important source of information for the control of posture and locomotion. The findings also suggest that locomotor experience most likely helps to functionalize smaller (partial), rather than larger (global), optic flow fields for postural control.

Female↗
PubMed1998

The origin and relief of common pain.

Where pain of the musculoskeletal system is present, commonly, this pain is without objective evidence of disease, trauma, or disorder. Absence of an apparent cause for common pain prompts the consideration of mechanical stress as a contributing factor. The principal stress of the musculoskeletal system is postural. By posture it is usually meant the distribution of body mass with respect to gravity. Past efforts to predict chronic pain by postural analysis or to reduce such pain by strengthening, conscious control or splinting of posture has had marginal success. Past failure to relate posture to pain is attributable to (1) ubiquity of sub-optimal posture that precludes clinical comparison to those with optimal posture; (2) presupposition that the causal relation between posture and pain is of the observational class of causality rather than the manipulable kind; (3) a definition of posture that is too narrow to complete the picture; and (4) inadequate methods for reduction of postural asymmetry to an extent that is sufficient to elicit a significant and enduring effect on sub-optimal posture and related pain. Posture can be defined more broadly as the stance of the body performing within the boundaries of posture and which is mediated by the Postural Control System towards greatest stability (Fx. 1). The stance of the body is the arrangement of the body with respect to gravity and other accelerative forces. The postural boundaries are the set of forces that resist acceleration and thereby provide the limits within which one functions stably, and this resistance is currently approximated by six principal sources of resistance to acceleration: viscous, elastic, neuromuscular, rigid, viscoelastic, and inertial. The Postural Control System is located in the brainstem and modulates body stance to more economically and stably effect and resist acceleration. The rigid boundaries can be so with respect to compressive, tractive, or tensile qualities that permits three kinds of motion: translation, rotation and oscillation. An example of postural boundaries that are rigid with respect to compression and tensile character are the bones that bear weight. In contrast, ligaments provide a tractive rigidity and musculotendons a relatively elastic boundary. Joint surfaces are considered boundaries that are rigid but not perfectly so. Of fundamental importance are those joints that arc lowermost in a column of the musculoskeletal system namely: (1) the feet and ankles that support the entirety of the musculoskeletal system and; (2) the base of the sacrum that supports the vertebral spine. This broadened definition of posture leads to a greatly enhanced manipulability of posture in the upright stance and alleviation of more than two-thirds of common pain by the coherent combination of (1) manual manipulation to reduce somatic dysfunction; (2) foot orthotics to optimize the amplitude of the arches of the feet and vertically align the ankle; (3) a heel lift to level the sacral base; (4) and a group of therapeutic postures configured to minimize restriction of peripheral soft tissue reflective of the earlier posture, all aimed to optimize posture. Mediated by the postural control system, manipulation of postural boundaries accordingly modifies the structure and function of the entire musculoskeletal system. Typically, this relief is maintained by foot orthotic and heel lift alone without maintenance by manual manipulation, medication, or exercise.

Back Pain↗
PubMed2003

Implementation of the Vienna Hydrotherapy Group for Laryngectomees--a pilot study.

GOALS: Laryngectomy involves several problems for the individual, such as the need to cope with a stoma, adjustment to tracheostomal breathing, and the formation of a voice. Contact with water, resulting in aspiration, may prove fatal for laryngectomized patients in the absence of appropriate aids. The aim of this pilot study was to conduct a hydrotherapy group for laryngectomized patients and to evaluate its feasibility and outcome in relation to the goals of therapy. PATIENTS AND METHODS: Six male patients who had undergone laryngectomy were included in a pilot study. The patients underwent a structured hydrotherapy rehabilitation program (three times a week for 8 weeks), using a special underwater therapy device. The patients' posture was controlled by posturography and their endurance capacity by standard ergometry and the 6-min walk. The parameters of fatigue, expectoration, mobility, elasticity/flexibility, postural control/coordination, and general well being were registered on a visual analog scale (VAS). Quality of life was assessed by having the patients fill out the German version of the SF-36 Health Survey. MAIN RESULTS: Posturograpy findings showed an improvement of two subtests ( p<0.028). Exercise testing showed an improved endurance capacity ( p<0.028). The patients were able to walk a greater distance in the 6-min walking test ( p<0.028). The VAS also showed an improvement of endurance capacity ( p<0.028), fatigue ( p<0.028), expectoration ( p<0.043), mobility of the neck and shoulder ( p<0.027), flexibility ( p<0.027), postural control and coordination ( p<0.028), and general well being ( p<0.028). On the SF-36 Health Survey, the patients were improved in the items "Physical functioning" ( p<0.027), "Vitality" ( p<0.027) "Role-physical" ( p<0.026), and "Social functioning" ( p<0.043). CONCLUSIONS: A hydrotherapy group for laryngectomized patients proved to be safe, feasible, and effective in this pilot study.

Activities of Daily Living↗
PubMed1989

A control systems framework for understanding normal and abnormal posture.

This paper presents a brief overview of a control systems framework for understanding normal and abnormal posture, with a special emphasis on postural control during arm movements. The need for meaningful and valid definitions of postural output is discussed. A distinction is drawn between the joint posture and balance outputs of the system. The roles of commands and perturbing inputs in controlling and disturbing joint posture and balance are described. The effects of initial conditions on command inputs and postural outputs are considered. Mechanisms for correcting postural errors are described, with a major focus on active closed-loop and open-loop control processes. The method of objectively describing system behavior by the gains, time delays, and thresholds of input-output functions is presented. All concepts are developed in relation to their clinical implications.

Arm↗
PubMed1988

Postural adjustments induced by simulated motion of differently structured environments.

We have investigated how visual information of a scene, moving along the line of sight of a subject, affects postural readjustments made by a subject when instructed to maintain an upright posture. Two different types of stimulus patterns were presented each inducing a different optic flow field. In one case an optic flow field was induced by simulating motion of a subject relative to a wall and in the second case by stimulating motion of a subject through a tunnel. In both cases clear effects on postural balance were observed. It suggests that postural responses are invariant for the structure of the moving environment. The amplitude of the postural responses did not depend on the velocity of the simulated motion, and therefore did not depend on the absolute magnitude of the optic flow components. The amount of texture in the moving scene proved to be an important factor. In addition, it was found that the control of postural balance is not exclusively dominated by information provided by the peripheral part of the subject's visual field. Moreover, the results indicate that the divergence component in the optic-flow field alone is not sufficient to control posture in forward/backward direction.

Humans↗
PubMed1997

Effect of physical training on head-hip co-ordinated movements during unperturbed stance.

A cross-correlation analysis between head and hip lateral accelerations has been used to analyse the effects of sport training (in experts in judo or classical dance as compared to controls) on postural strategies during unperturbed stance. Subjects were standing in the sharpened Romberg position on either a hard or foam rubber support. The main results were: (1) several non-visual and ankle-like strategies (head-hip movements in the same sense) were used by both groups on both supports; (2) two types of lateral hip strategies (head-hip movements in opposite sense) were seen in controls on soft support only, and were mainly modulated by vision. Training appears to result in a shift from a visual to a proprioceptive dominance in the regulation of postural control in unperturbed stance.

Adolescent↗
PubMed1999

Sensory and motor interdependence in postural adjustments.

The sensory reafference from a movement depends upon the movement, and the movement chosen depends upon the available senses, as demonstrated by vestibular patients who abandon certain movements. Often, one variable is assumed to be dependent whereas the other is independent; however, sensory and motor dynamics in posture are interdependent as conditions upon each other. This paper applies conditional dynamics to characterize the global structure of interdependence between sensory states and motor strategies in fast postural adjustments. The mathematical formalism incorporates rich but disparate experimental, clinical, and theoretical results about sensory and motor control of posture. The control structures presented include relatively stable anatomical, physiological, and functional structures, both continuous and discrete, leading to a composite functional logic for the coordination of these structures in sensorimotor control. Results include sensorimotor control structures for postural adjustments for healthy subjects and certain types of vestibular patients. The sensorimotor control structures for patients with absent vestibular function suggest implications for management of the deficit.

Adaptation, Physiological↗