Walking with eyes closed is easier than walking with eyes open without visual cues: The Romberg task versus the goggle task.

Background: The Romberg test, with the subject standing and with eyes closed, gives diagnostic arguments for a proprioceptive disorder. Closing the eyes is also used in balance rehabilitation as a main way to stimulate neural plasticity with proprioceptive, vestibular and even cerebellar disorders. Nevertheless, standing and walking with eyes closed or with eyes open in the dark are certainly 2 different tasks.

In healthy subjects, the sitting position can be used to validate the postural effects induced by wearing a lumbar lordosis brace.

Aim Of The Study: To assess the validity of the sitting position when testing lumbar braces for the maintenance of lordosis.

Patients And Methods: Twelve young adult subjects participated in the experiment, in which they were seated on force platform. The four experimental conditions (with or without a brace and with or without enforced lordosis) were chosen in order to distinguish between the roles played by lordosis and the brace, respectively.

Age-related changes in posture control are differentially affected by postural and cognitive task complexity.

The simple postural task of quiet standing, which requires minimal attentional resources, is generally paired with cognitive activity. Competition for attentional resources is a consequence of simultaneously performing balance tasks and cognitive tasks, and impairment of attentional resource allocation with aging leads to increased risks of fall. We investigated age-related changes in posture control during dual task performance, using a paradigm that crossed a static (quiet standing) and a dynamic (keeping balance on a translational force plate) postural task and cognitive tasks of low demand (mental arithmetic) and high demand (spatial memory).

Can tactile plantar stimulation improve postural control of persons with superficial plantar sensory deficit?

Background And Aims: Complex interactions between visual, vestibular and somatosensory information and the cerebellar system are involved in the maintenance of upright posture. Previous studies have shown that normal aging and pathologies may lead to deterioration of the control of upright standing posture.

Methods: In order to investigate postural control during quiet standing in the elderly, the center of pressure (CoP) was analysed on two force platforms in three different groups.

Quiet postural control of patients with total hip arthroplasty following joint arthritis.

To assess the postural strategies developed by patients after total hip arthroplasty (THA), 14 patients were measured 12 days after surgery. The respective role played by both sound and prosthetic legs and the compensatory mechanisms were assessed through a separate measure of the center-of-pressure (CP) trajectories under each foot. The movements of the center-of-gravity (CG) were estimated from those of the resultant CP to determine postural performance.

[What compensatory motor strategies do patients with multiple sclerosis develop for balance control?].

Introduction: One of the main features of multiple sclerosis (MS) is the deterioration of motor pathway axons, and in some cases, sensory system axons. Consequently, experimental sensori-motor testing with the undisturbed upright stance paradigm might be useful. It can be hypothesized that the postural strategies could be differently affected depending on the degree of dysfunction of both sensory and motor tracts.

Biomechanical assessment of the sitting posture maintenance in patients with stroke.

Background And Purpose: Regaining control of sitting posture is one of the first goals in the rehabilitation of patients with stroke. So, it requires a precise quantification of this postural behaviour. The purpose of the present investigation was thus to assess postural control during sitting in people with hemiparesis through a biomechanical analysis.

[Performing saccadic eye movements modifies postural control organisation].

Aims Of The Study: To assess to which extent performing saccadic eye movements modifies the postural strategies aimed at maintaining balance.

Materials And Methods: Twelve healthy adults were tested on a force platform in several conditions including one in which they were required to stare a visual target and four in which small and larger saccadic eyes movements were performed vertically and horizontally. The displacements of the centre of pressure (CP) were then processed through frequency analysis and modelled as fractional Brownian motion (fBm).

[Effects of rigid-ankle and ankle-foot orthoses in the control of asymetrical undisturbed upright stance].

Objective: To limit sensorimotor impairment associated with various diseases, devices aimed at easing such impairment are usually prescribed. A better knowledge of the specific effects of these devices in healthy subjects should help to assess the prescription.

Materials And Methods: Sixteen young healthy individuals were required to stand still on a double-force platform with an asymmetrical body weight distribution over the 2 legs and to reduce as much as possible their motions.

Recalibration of somesthetic plantar information in the control of undisturbed upright stance maintenance.

To assess the effects of changes in somesthetic plantar information on upright quiet stance, a rotary plantar massage was applied under the feet of healthy subjects for ten minutes. The controlling variable, the centre of pressure (CP) displacements, were recorded, before and after massage, through a force platform and decomposed into two elementary motions: the vertical projection of the centre of gravity (CG(v)) and the difference between the latter and the CP (CP-CG(v)) along medio-lateral ML and antero-posterior AP directions. These motions were processed through frequency analysis and modelled as fractional Brownian motion.

Modifying the gain of the visual feedback affects undisturbed upright stance control.

Objective: To assess the effects of visual feedback gain, which express the amplitudes of the displacements of the centre of pressure displayed on a computer screen.

Design: The controlling variable, the centre of pressure trajectories, recorded using a force platform, were decomposed into two elementary motions: (1) the horizontal displacements of the centre of gravity and (2) the vertical projection of the difference between centre of pressure and the centre of gravity. These motions were processed through frequency analysis and modelled as fractional Brownian motion to assess their spatio-temporal linkage and their degree of control.

[Postural control in idiopathic scoliosis: comparison between healthy and scoliotic subjects].

Purpose Of The Study: To assess the effects of idiopathic scoliosis on undisturbed postural control in young female teenagers.

Material And Methods: The centre of pressure (CP) displacements, measured through a force platform, were decomposed into two elementary components in order to differentiate the net postural performance, as revealed by the horizontal motions of the centre of gravity (CGh) and the level of muscular activity expressed by the vertical difference CP-CGv. The CG horizontal displacements were estimated from those of the CP with a low pass filter taking into account the subjects' anthropometry.

How postural behaviour in undisturbed upright stance can be used to assess the physical characteristics of various models of ankle orthoses.

Objectives: To assess various ankle orthoses presenting different physical characteristics.

Design: The postural performance in bi-pedal stance of 14 healthy adults was assessed during four different ankle orthoses conditions.

Background: Resultant ankle stiffness is an important component in undisturbed upright postural regulation.

The influence of gender and body characteristics on upright stance.

Background: Morphologic characteristics such as height and body weight determine body inertia, an important factor related to postural stability. However, whilst investigations have classically analysed these parameters separately, global morphology has been poorly researched. Secondly, the influence of gender on postural stability demonstrates opposing trends, some authors observing that men sway less than women, and others noting the contrary.

[Adaptation of control mechanisms involved in upright undisturbed stance maintenance during prolonged darkness].

Aims Of The Study: To assess to which extent the non visual somato-sensorial information may, through a recalibration process, induce a reorganisation by the central nervous system to control undisturbed upright stance.

Materials And Methods: Ten healthy adults were placed in complete darkness for a 24 min period. Their postural performance was recorded through a force platform on which they were required to stand still at regular intervals.

Visual feedback induces opposite effects on elementary centre of gravity and centre of pressure minus centre of gravity motions in undisturbed upright stance.

Objective: To evaluate the instantaneous effects of visual feedback on undisturbed stance control mechanisms.

Design: The controlling variable, the centre of pressure trajectories, recorded using a force platform, were decomposed into two elementary motions: (1) the horizontal displacements of the centre of gravity and (2) the vertical projection of the difference between centre of pressure and the centre of gravity. These motions were processed through frequential analysis and modelled as fractional Brownian motion.

[Influence of visual cues on upright postural control: differentiated effects of eyelids closure].

In most protocols aimed at testing balance abilities, patients are generally required to close their eyes in order to gain insight about proprioceptive cues and the way the central nervous system (CNS) uses this information. However, one should not exclude possible interaction with the physiological mechanisms involved in eyelid closure, thus leading to a biased neurological evaluation. To assess this possible involvement, 15 healthy adults were required to keep their eyes open in the dark (YOn), to close normally (YF) and forcibly their eyelids (YFF), respectively in random order.

[How mirror feedback improves undisturbed upright stance control].

Objective: To evaluate, in normal and healthy adults, the postural effects induced by a protocol of body sway mirror feedback.

Materials And Methods: Two experimental conditions, one consisting in staring eyes open (EO) and one consisting in mirror feedback (MFB), are randomly proposed. Displacements of the centre of pressure (CP), issued from a force platform, are advantageously decomposed along medio-lateral ML and antero-posterior AP directions into two elementary components: the horizontal motions of the centre of gravity (CG(h)) and the difference CP-CG(v).

[A forward leaning posture affects more the amplitudes of the centre of pressure displacements than those of the centre of gravity].

Objective: An ordinary and practical method to assess the postural control mechanisms is to measure, through a force platform, the point of application of the resultant reaction forces. The recorded signal, the centre of pressure CP, is used to compute the motions of the vertical projection of the centre of gravity (CG(v)) and those of the difference CP-CG(v). The former is considered in this postural task as the controlled variable whereas the latter is thought to express the ankle resultant stiffness.

Backward and forward leaning postures modelled by an fBm framework.

Body leaning effects on postural control have been assessed by recording the centre of pressure (CP) displacements in healthy subjects under three experimental conditions (REF, BWD and FWD corresponding to upright, backward leaning and forward leaning of the body, respectively). The CP displacements were used to compute the motions of the vertical projections of the centre of gravity (CG(v)) and those of the difference CP-CG(v). A frequential analysis shows that the main effect takes place on CP-CG(v) motions, suggesting increased muscular activity in these leaning postures.