Technical noteEstimating the centre of gravity of the body on the basis of the centre of pressure in standing posture
Abstract
This study proposes to estimate the horizontal positions of the body's centre of gravity (CoG) in a standing posture, on the basis of the horizontal positions of the centre of pressure (CoP). The latter were measured with a force plate, and using a low-pass filter defined by a mathematical relationship of the relative magnitude of the CoG with respect to the magnitude of the CoP, as a function of the frequency oscillations (Brenière, 1996, Journal of Motor Behaviour 28, 291–298). This relationship was computed from the angular momentum equation applied to the whole body with respect to the CoG using the inverse dynamics approach and force plate recordings, and considering the CoP and CoG oscillations as simple periodic functions. Five subjects were asked to perform voluntary oscillations along medio-lateral and antero-posterior axes, keeping their bodies straight, and without moving their feet. The CoG accelerations measured by the force plate were compared with the CoG accelerations derived from the estimated CoG positions. The average root-mean-square difference between these accelerations was very small, confirming the accuracy of this method. This simplified way to calculate the CoG positions, rarely measured in standing, allows a comparative assessment of motion performance. This method could also be applied to other kinds of movement such as walking.
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Cited by (157)
A new approach to body balance analysis based on the eight-phase posturographic signal decomposition
2022, Biomedical Signal Processing and ControlStatic posturography possesses a significant, although undiscovered to date, diagnostic potential hidden in the subtle oscillations which represent individual muscle contractions regulating body balance when standing still. This paper presents the principles of a new approach to posturographic signal analysis. First, the Center of Mass path (xCoM) is estimated from Center of Pressure (xCoP) signal using digital filtering. The difference xCoPM = xCoP − xCoM approximately corresponds to the corrective muscle impulses. Then, the velocities and accelerations of xCoM and xCoPM paths (vCoM, aCoM, vCoPM, aCoPM) are calculated. Next, 8 phases of body balance regulation are defined based on the combination of instantaneous signs of vCoM, aCoM and vCoPM. Finally, 16 phase transitions are defined which represent different special instants of body balance regulation. They may be divided into 3 main types: Zero Crossing (ZC), Turning Back (TB) and Impulse Extremum (IE). They can be subsequently divided into Forward and Backward subtypes.
Based on the presented decomposition 822 new parameters have been analyzed. The exemplary analysis including 23 young healthy subjects (eyes open vs. eyes closed condition) indicated that a number of new parameters showed a higher discrimination power than the standard parameters analyzed to date. Advanced big data methods, such as neural networks or decision trees, should be applied in the future to the extracted parameters in order to evaluate the possible diagnostic potential of the new method of analysis.
Contribution of posturography to balance assessment in elderly people
2021, Pratique Neurologique - FMCLa compréhension des mécanismes permettant de se maintenir en équilibre est un enjeu de santé globale. Avec une prévalence plus élevée et des conséquences plus graves, la chute de la personne âgée est une problématique qui peut être vue sous le prisme de l’analyse du contrôle moteur afin de mieux comprendre la relation qui existe entre les capacités d’équilibration de l’individu, d’une part, et le contexte qui inscrit cette personne dans un environnement qui la conduira à une chute, d’autre part. Nous présentons dans cet article l’apport de la posturographie statique dans la compréhension du lien entre posture et chute, notamment chez les personnes fragiles. Au-delà d’une pathologie spécifique, la personne âgée présente une modification de son contrôle postural qui conduit à des stratégies motrices moins efficientes en cas de déstabilisation. Au regard du manque de performance des tests cliniques dans la détection des personnes les plus à risque de chute, la posturographie se positionne comme une solution dans la quantification des oscillations posturales au repos. Cette méthode d’analyse de la stabilité humaine a poussé les cliniciens et les chercheurs à élaborer des modèles biomécaniques et neurophysiologiques pour expliciter les tracés obtenus sur plateforme de force. Les variables extraites de ces enregistrements sont dorénavant exploitées dans la prédiction de la chute. Bien que les scores de prédiction résultant de cet examen semblent élevés, des challenges demeurent dans son exploitation clinique en pratique courante.
Understanding the mechanisms people use to maintain balance is a global health issue. Because of their high prevalence and serious consequences, falls in the elderly can be seen as a serious problem amendable to motor control analysis that would afford a better understanding of the relationship between an individual's capacity for equilibration and an environmental context favoring falls. In this article, we discuss the contribution of static posturography to our understanding of the link between posture and falls, particularly in frail people. Beyond specific pathological conditions, elderly people present a modification of their postural control which leads to less efficient motor strategies to cope with destabilizing situations. Considering that clinical tests are unable to detect people most at risk of falling, posturography would be a useful alternative for quantifying postural sway at rest. This method of analyzing human stability has led clinicians and researchers to develop biomechanical and neurophysiological models to explain the trajectories recorded on force platforms. The variables extracted from these recordings are now being used in fall prediction. Although the prediction scores resulting from this examination seem high, posturography remains a challenging clinical test widely used in routine practice.
The effects of pain and a secondary task on postural sway during standing
2021, Human Movement SciencePain impairs available cognitive resources and somatosensory information, but its effects on postural control during standing are inconclusive. The aim of this study was to investigate whether postural sway is affected by the presence of pain and a secondary task during standing.
Sixteen healthy subjects stood as quiet as possible at a tandem stance for 30s on a force platform at different conditions regarding the presence of pain and a secondary task. Subjects received painful stimulations on the right upper arm or lower leg according to a relative pain threshold [pain 7 out 10 on a Visual Analog Scale (VAS) - 0 representing “no pain” and 10 “worst pain imaginable”] using a computer pressurized cuff. The secondary task consisted of pointing to a target using a head-mounted laser-pointer as visual feedback. Center of Pressure (COP) sway area, velocity, mean frequency and sample entropy were calculated from force platform measures.
Compared to no painful condition, pain intensity (leg: VAS = 7; arm VAS = 7.4) increased following cuff pressure conditions (P < .01). Pain at the leg decreased COP area (P < .05), increased COP velocity (P < .05), mean frequency (P < .05) and sample entropy (P < .05) compared with baseline condition regardless the completion of the secondary task. During condition with pain at the leg, completion of the secondary task reduced COP velocity (P < .001) compared with condition without secondary task.
Pain in the arm did not affect postural sway. Rather, postural adaptations seem dependent on the location of pain as pain in the lower leg affected postural sway. The completion of a secondary task affected postural sway measurements and reduced the effect of leg pain on postural sway. Future treatment interventions could benefit from dual-task paradigm during balance training aiming to improve postural control in patients suffering from chronic pain.
Fronto-Parietal Brain Areas Contribute to the Online Control of Posture during a Continuous Balance Task
2019, NeuroscienceNeuroimaging studies have provided evidence for the involvement of frontal and parietal cortices in postural control. However, the specific role of these brain areas for postural control remains to be known. Here, we investigated the effects of disruptive transcranial magnetic stimulation (TMS) over supplementary motor areas (SMA) during challenging continuous balance task in healthy young adults. We hypothesized that a virtual lesion of SMA will alter activation within the brain network identified using electroencephalography (EEG) and impair performance of the postural task. Twenty healthy young adults received either continuous theta burst stimulation (cTBS) or sham stimulation over SMA followed by the performance of a continuous balance task with or without somatosensory input distortion created by sway-referencing the support surface. cTBS over SMA compared to sham stimulation showed a smaller increase in root mean square of center of pressure as the difficulty of continuous balance task increased suggestive of altered postural control mechanisms to find a stable solution under challenging sensory conditions. Consistent with earlier studies, we found sources of EEG activation within anterior cingulate (AC), cingulate gyrus (CG), bilateral posterior parietal regions (PPC) during the balance task. Importantly, cTBS over SMA compared to sham stimulation altered EEG power within the identified fronto-parietal regions. These findings suggest that the changes in activation within distant fronto-parietal brain areas following cTBS over SMA contributed to the altered postural behavior. Our study confirms a critical role of AC, CG, and both PPC regions in calibrating online postural responses during a challenging continuous balance task.
Postural control in healthy young adults using a double seesaw device
2019, Journal of BiomechanicsPostural control on single and double seesaws was investigated in young healthy adults required to stand as still as possible on two side-by-side seesaws favoring pitch motion and lying on two separate force platforms. The device offers the possibility to get associated or dissociated seesaws and, if dissociated, to induce asymmetric patterns for the centers-of-pressure (CP) under both left and right feet by using different radii for the two seesaws. Substituting a parallelepiped volume to one seesaw offering a firm contact to one foot is also possible. The results indicated that dissociating the two seesaws led to increased resultant CP (CPRes) and vertically projected center-of-gravity movements (CGv) only along the mediolateral axis, whereas a slight decreasing tendency characterized these movements along the antero-posterior axis. When standing on two independent seesaws with different radii, significantly larger CP displacements were seen along the antero-posterior axis under the foot lying on the more stable support, i.e., the seesaw with the longer radius or the parallelepiped volume. In these two asymmetrical conditions, the CPRes output results from a compensatory mechanism, i.e. larger movements under one foot to compensate for the decreased movements occurring under the opposite foot. This postural control strategy is aimed at allowing sufficient CPRes displacements in order to appropriately secure balance. Because of the complex sensorimotor coordination induced, involving differentially in certain cases both legs, the double seesaw device can be viewed as a possible tool for challenging postural control by inducing asymmetrical patterns between left and right feet CP movements.
Interaction between postural asymmetry and visual feedback effects in undisturbed upright stance control in healthy adults
2017, Neurophysiologie CliniqueCitation Excerpt :In recording CP displacements under each foot separately, our objective was to assess the likely compensatory mechanisms used to secure appropriate CPRes displacements in stance control. For the estimation of CGv movements, and therefore CPRes-CGv, it was hypothesized that CPRes displacements operating at high frequencies would not incur appreciable CGv movements due to the huge inertia of the upright body [4]. Fig. 2 highlights the different steps involved in the estimation of the CGv movements.
The technique of additional visual feedback has been shown to significantly decrease the center of pressure (CP) displacements of a standing subject. Body-weight asymmetry is known to increase postural instability due to difficulties in coordinating the reaction forces exerted under each foot and is often a cardinal feature of various neurological and traumatic diseases. To examine the possible interactions between additional visual feedback and body-weight asymmetry effects, healthy adults were recruited in a protocol with and without additional visual feedback, with different levels of body-weight asymmetry.
CP displacements under each foot were recorded and used to compute the resultant CP displacements (CPRes) and to estimate vertically projected center of gravity (CGv) and CPRes-CGv displacements. Overall, six conditions were randomly proposed combining two factors: asymmetry with three BW percentage distributions (50/50, 35/65 and 20/80; left/right leg) and feedback (with or without additional VFB).
The additional visual feedback technique principally reduces CGv displacements, whereas asymmetry increases CPRes-CGv displacements along the mediolateral axis. Some effects on plantar CP displacements were also observed, but only under the unloaded foot. Interestingly, no interaction between additional visual feedback and body-weight asymmetry was reported.
These results suggest that the various postural effects that ensue from manipulating additional visual feedback parameters, shown previously in healthy subjects in various studies, could also apply independently of the level of asymmetry.
Visual feedback effects could be observed in patients presenting weight-bearing asymmetries.
Il a été précédemment montré que la rétroaction additionnelle visuelle permettait de réduire les déplacements du centre des pressions (CP) d’un individu debout. Une asymétrie de répartition du poids est connue pour faciliter l’instabilité posturale, de par des difficultés de coordination des forces de réaction exercées sous chaque pied. Cette asymétrie constitue une caractéristique importante de diverses pathologies neurologiques ou traumatologiques. Afin d’examiner les possibles interactions entre les effets de cette rétroaction et de l’asymétrie, un protocole incluant des sujets adultes sains a été mis en place comprenant des conditions avec ou non-présence de rétroaction et différents niveaux d’asymétries de répartition.
Les déplacements du CP sous chacun des pieds sont utilisés pour calculer le centre des pressions résultant (CPRes) et par estimation la projection verticale du centre de gravité (CGv) et la différence CPRes-CGv. Six conditions ont été proposées aléatoirement combinant plusieurs niveaux d’asymétries (50/50, 35/65 et 20/80) et la présence ou non de rétroaction.
La rétroaction additionnelle réduit principalement les mouvements du CGv alors que l’asymétrie accroît ceux de CPRes-CGv selon l’axe médio-latéral. Des effets sur les déplacements plantaires du pied allégé sont aussi observés. Aucune interaction entre la rétroaction et l’asymétrie n’est trouvée.
Ces résultats suggèrent que les effets précédemment observés en manipulant diverses variables de la rétroaction chez des sujets sains puissent être retrouvés, ceci indépendamment du niveau d’asymétrie.
Les effets de rétroaction peuvent être observés chez des patients montrant une asymétrie de répartition de poids.