Vertical Posture Research Articles

Long-term follow-up after vertical extraocular muscle surgery to correct abnormal vertical head posture

ABSTRACTPurpose: To report outcomes of vertical extraocular muscle surgery to correct abnormal vertical head posture in children with horizontal infantile nystagmus.Methods: Retrospective case series of seven patients evaluated at one institution with abnormal vertical head position (chin-up or chin-down) in the setting of horizontal infantile nystagmus. All patients underwent bilateral vertical extraocular muscle surgery with the same surgeon. Pre- and postoperative vertical head position under binocular viewing conditions was the primary outcome measure. Secondary outcomes included visual acuity, stereopsis, degree of cyclotorsion, and residual ocular alignment.Results: Seven children with infantile nystagmus syndrome, ranging in age from 4 months to 5 years at presentation, underwent extraocular muscle surgery to correct chin-down or chin-up head position associated with a null position in the setting of horizontal nystagmus. Five children had other ocular pathology (albinism, n = 4; cone-rod dystrophy, n = 1). Five of the seven patients had combined vertical recti and oblique muscle surgery. Three of the patients had additional extraocular muscle surgery to correct horizontal misalignment (exotropia, n = 2; esotropia, n = 1). One patient underwent a separate Kestenbaum procedure (bilateral horizontal resection/recession) to correct concomitant horizontal face turn. Median postoperative follow-up was 8.0 years (range 1–9.5 years). Postoperatively, three patients had complete resolution of their abnormal head position, and three had an improvement in their head posture, with a mean reduction in original vertical head position of 25 degrees. One of these patient had a reversal of their head position from a chin-up to a small chin-down position. Only one patient had no clinically significant improvement in their head position. No patients had signs or symptoms of cyclotorsion postoperatively.Conclusion: Combined vertical recti and oblique muscle surgery can successfully improve and even resolve vertical head posture, and prevents cyclorotary disorders postoperatively.

Objectification of motor disorders in children with cerebral palsy: what we know so far

This study provides an overview of the recent literature regarding the assessment methods of the functional state of the locomotor system in children with cerebral palsy. The objective methods of quantitative assessment of motor disorders in cerebral palsy are presented, including the measurement of stability, biomechanical assessment of walking, and video analysis of movements. The influence of the cognitive load on the ability to maintain the vertical posture in children with cerebral palsy as well as the changes in the stability of the vertical posture with closed eyes were observed. Changes in the walking parameters with an increase in the speed were also recorded in children with cerebral palsy.
 Methods that assess hand motion in children with cerebral palsy include tests involving the moving of objects, tests for speed assessment in joint movements, and video analysis of motions.
 The methods and tests for such an evaluation require to be valid and reliable, allowing an objective assessment of the severity of motor disorders in cerebral palsy.

Stability of vertical posture explored with unexpected mechanical perturbations: synergy indices and motor equivalence.

We explored the relations between indices of mechanical stability of vertical posture and synergy indices under unexpected perturbations. The main hypotheses predicted higher posture-stabilizing synergy indices and higher mechanical indices of center of pressure stability during perturbations perceived by subjects as less challenging. Healthy subjects stood on a force platform and held in fully extended arms a bar attached to two loads acting downward and upward. One of the loads was unexpectedly released by the experimenter causing a postural perturbations. In different series, subjects either knew or did not know which of the two loads would be released. Forward perturbations were perceived as more challenging and accompanied by co-activation patterns among the main agonist-antagonist pairs. Backward perturbation led to reciprocal muscle activation patterns and was accompanied by indices of mechanical stability and of posture-stabilizing synergy which indicated higher stability. Changes in synergy indices were observed as early as 50-100ms following the perturbation reflecting involuntary mechanisms. In contrast, predictability of perturbation direction had weak or no effect on mechanical and synergy indices of stability. These observations are interpreted within a hierarchical scheme of synergic control of motor tasks and a hypothesis on the control of movements with shifts of referent coordinates. The findings show direct correspondence between stability indices based on mechanics and on the analysis of multi-muscle synergies. They suggest that involuntary posture-stabilizing mechanisms show synergic organization. They also show that predictability of perturbation direction has strong effects on anticipatory postural adjustment but not corrective adjustments. We offer an interpretation of co-activation patterns that questions their contribution to postural stability.

Systemic effects of deep brain stimulation on synergic control in Parkinson’s disease

ObjectiveWe explored effects of deep brain stimulation (DBS) in patients with Parkinson’s disease (PD) on the synergic control of fingers in a multi-finger force production task and of muscles in a task involving vertical posture. MethodsThe finger task involved the four fingers of a hand producing accurate total force followed by a targeted quick force pulse. The postural task involved releasing a load from extended arms. The analysis of synergies was performed within the framework of the uncontrolled manifold hypothesis. ResultsDBS led to no significant changes in indices of stability during steady-state phases. In contrast, DBS improved indices of agility, quantified as anticipatory synergy adjustments that reduced stability of salient performance variables in preparation to their quick change. There were moderate-to-strong correlations between indices of both stability and agility measured in the multi-finger force production and multi-muscle whole-body action. ConclusionsOur results point at systemic changes in synergic control in PD. They show that DBS is effective in improving only one components of synergic control related to agility in performance being relatively ineffective for the stability component. SignificanceThe results show systemic brain mechanisms of synergies and suggest differential effects of DBS on indices of stability and agility.

The Search for the Intersection of Form and Function: Looking for Clues into What Has Determined How, Why, and When Animals Came to Move the Way They Do.

The Search for the Intersection of Form and Function: Looking for Clues into What Has Determined How, Why, and When Animals Came to Move the Way They Do.

Quantification of Myosin Heavy Chain Isoform mRNA Transcripts in the Supraspinatus Muscle of Vertical Clinger Primates

Vertical clinging is a specialized form of locomotion characteristic of the primate family Callitrichidae. Vertical clinging requires these pronograde primates to maintain a vertical posture, so the protraction of their forelimbs must resist gravity. Since pronograde primates usually move as horizontal quadrupeds, we hypothesized that the supraspinatus muscle of vertical clingers would present specific characteristics related to the functional requirements imposed on the shoulder area by vertical clinging. To test this hypothesis, we quantified by real-time quantitative polymerase chain reaction the mRNA transcripts of myosin heavy chain (MHC) isoforms in the supraspinatus muscle of 15 species of pronograde primates, including vertical clingers. Our results indicate that the supraspinatus of vertical clingers has a specific expression pattern of the MHC isoforms, with a low expression of the transcripts of the slow MHC-I isoform and a high expression of the transcripts of the fast MHC-II isoforms. We conclude that these differences can be related to the particular functional characteristics of the shoulder in vertical clingers, but also to other anatomical adaptations of these primates, such as their small body size.

Control of vertical posture while standing on a sliding board and pushing an object.

Voluntary pushing or translation perturbation of the support surface each induces a body perturbation that affects postural control. The objective of the study was to investigate anticipatory (APA) and compensatory (CPA) postural adjustments when pushing an object (that induces self-initiated perturbation) and standing on a sliding board (that induces translational perturbation). Thirteen healthy young participants were instructed to push a handle with both hands while standing on a sliding board that was either free to move in the anterior-posterior direction or stationary. Electromyographic activity (EMG)of trunk and lower extremity muscles, center of pressure (COP) displacements, and the forces exerted by the hand were recorded and analyzed during the APA and CPA phases. When the sliding board was free to move during pushing (translation perturbation), onsets of activity of ventral leg muscles and COP displacement were delayed as compared to pushing when standing on a stationary board. Moreover, magnitudes of shank muscle activity and the COP displacement were decreased. When pushing heavier weight, magnitudes of muscle activity, COP displacement, and pushing force increased. The magnitude of activity of the shank muscles during the APA and CPA phases in conditions with translational perturbation varied with the magnitude of the pushing weight. The outcome of the study suggests that the central nervous system prioritizes the pushing task while attenuates the source of additional perturbation induced by translation perturbation. These results could be used in the development of balance re-training paradigms involving pushing weight while standing on a sliding surface.

Maintenance of Human Vertical Posture upon Asymmetric Leg Loading and Fixation of the Knee Joint of One Leg

Maintenance of a vertical posture was studied in standing subjects with a fixed knee joint of one leg and a different weight distribution between the legs. Knee fixation on one leg did not affect the speed of movements of the common center of pressure (CP) at any weight distribution between the legs, and the stability of vertical posture was therefore unchanged. However, the relative contributions of the legs to the posture control changed when knee movements of one leg were restricted. The speed of CP movements of the free leg was independent of the weight loading on the leg. The speed of CP movements of the leg with the knee fixed depended on the weight distribution and was higher when the leg was loaded. Thus, the leg with the fixed knee joint made a greater contribution to maintaining vertical posture when the leg was loaded. Yet its contribution was comparable with that of the unloaded free contralateral leg even in this case, as was evident from lack of differences in CP movements between the two legs. It was assumed that the leg with the free knee joint played a major role in maintaining equilibrium of vertical posture, while the leg with the fixed knee joint mostly acted to more finely adjust the body position.

Changes in the characteristics of voluntary movements after long duration spaceflight

Changes in the characteristics of voluntary movements after long duration spaceflight

Chapter 3 - Gravity estimation and verticality perception

Gravity is a defining force that governs the evolution of mechanical forms, shapes and anchors our perception of the environment, and imposes fundamental constraints on our interactions with the world. Within the animal kingdom, humans are relatively unique in having evolved a vertical, bipedal posture. Although a vertical posture confers numerous benefits, it also renders us less stable than quadrupeds, increasing susceptibility to falls. The ability to accurately and precisely estimate our orientation relative to gravity is therefore of utmost importance. Here we review sensory information and computational processes underlying gravity estimation and verticality perception. Central to gravity estimation and verticality perception is multisensory cue combination, which serves to improve the precision of perception and resolve ambiguities in sensory representations by combining information from across the visual, vestibular, and somatosensory systems. We additionally review experimental paradigms for evaluating verticality perception, and discuss how particular disorders affect the perception of upright. Together, the work reviewed here highlights the critical role of multisensory cue combination in gravity estimation, verticality perception, and creating stable gravity-centered representations of our environment.

Evaluation of vestibular function among individuals with visual impairment

The vestibular system functions more actively in individuals who are visually impaired in vertical posture maintenance as a compensation for the lack of visual stimuli. This compensation is a result of the special role played by the vestibular and labyrinthine reflex due to the absence of visual sensory signal. The literature contains inconclusive and limited results on the possibility of compensating for balance in individuals with visual impairment. Hence the current study was carried out to strengthen the literature.

Alterations in the ability to maintain balance as a result of stochastic resonance whole body vibration in women.

PurposeA vertical posture makes it difficult to maintain balance especially in the elderly. Loss of balance leads to falls and injuries. In the present study, we evaluated whether balance maintenance can be improved with the use of stochastic resonance whole body vibration (SR-WBV).MethodsAn examination of balance, involving 187 women aged 19–74 years, was conducted using double-plate posturography pre and post SR-WBV. The SR-WBV trainings were performed using the SRT Zeptor Medical-plus noise device. The entire study lasted 6 weeks, with a total of 12 training sessions, each consisting of nine 45 second series, with a 45 second pause between them.ResultsPost SR-WBV there was a reduction in the value of: the resultant mean velocity (MV) of the movement of COP (centre of pressure) for both lower limbs (B) and in the right lower limb (R) during the test with eyes closed (EC), the mean velocity and mean amplitude (MA) of the movement of COP along the x-axis (ML) of the left lower limb (L) during the test with eyes open (EO) and closed and some additional parameters. Negative correlations between age/index of improvement of MV-EC-B, MV-EC-L and MVML-EC-L, and BMI/index of improvement of MV-EC-B, MVML-EC-B appeared. Height correlated positively with the index of improvement of MV-EC-B and MVML-EC-B.ConclusionsAs a result of SR-WBV, the left leg is more stable along the x-axis and the disproportion between the stability of both legs is reduced. Consequently, body stability is higher. The SR-WBV is more effective in younger, taller and slimmer women. SR-WBV parameters should be optimized so that the training is more beneficial for elderly and shorter women, and for women with a higher BMI.

Role of point of application of perturbation in control of vertical posture.

The role of point of application of perturbation in the anticipatory (APAs) and compensatory (CPAs) postural control was studied. Twelve healthy participants stood on a sliding board (that was either locked and as such motionless or unlocked and as such free to move in the anterior-posterior direction). The body perturbations were applied either to the shoulders (by a pendulum impact) or the feet (by the movement of the sliding board). Electromyographic activity (EMG) of the trunk and lower extremity muscles was recorded. Latencies, integrals of EMG and muscle co-contraction (C) and reciprocal (R) activation indices were calculated and analyzed within the intervals typical for the APAs and CPAs. Higher EMG integrals were seen in the APAs phase when perturbation was applied to the shoulders. Reciprocal activation of muscles was seen in the APAs phase in the shoulders perturbationcondition, while co-contraction was seen in the feet perturbationcondition. Co-contraction was observed within the CPA phase in both experimental conditions. Higher C values were found in the feet perturbation condition in the CPA phase. The results suggest that different motor control strategies are employed by the central nervous system when encounter perturbations of similar magnitude but applied to different parts of the body. The outcome highlights the importance of investigation of the role of the point of application of the perturbation.

Impact of Orientation on the Vitamin D Weighted Exposure of a Human in an Urban Environment.

The vitamin D3-weighted UV exposure of a human with vertical posture was calculated for urban locations to investigate the impact of orientation and obstructions on the exposure. Human exposure was calculated by using the 3D geometry of a human and integrating the radiance, i.e., the radiant energy from the direct solar beam and the diffuse sky radiation from different incident and azimuth angles. Obstructions of the sky are derived from hemispherical images, which are recorded by a digital camera with a fisheye lens. Due to the low reflectivity of most surfaces in the UV range, the radiance from obstructed sky regions was neglected. For spring equinox (21 March), the exposure of a human model with winter clothing in an environment where obstructions cover 40% of the sky varies by up to 25%, depending on the orientation of the human model to the sun. The calculation of the accumulated vitamin D3-weighted exposure of a human with winter clothing walking during lunch break shows that human exposure is reduced by the obstruction of buildings and vegetation by 40%.

Effectiveness of vertical posture recovery after external pushing impact in athletes specialized in different sports

The ability of athletes with different training specializations to recover vertical posture after an external pushing impact was studied. Athletes engaged in cyclic exercise sports (jogging, n = 7) and complex coordinate sports (wrestling, n = 10) and nonathletes (control, n = 10) were the subjects of this study. The recovery of vertical position after a small external pushing impact on the arms extended forward was assessed using stabilography. We determined the maximum amplitude (Amp-m) of deviation from the general center of pressure, the reaction time (RT) and the velocity of reaction (V-r), as well as the variance and mean velocity of vertical posture oscillations before and after an impact. It was found that, although no differences were observed in the vertical posture stability before pushing, the Amp-m was lower in the wrestlers than in the control group (by 17.5%, p = 0.018 under the eye-open conditions; by 27.3%, p = 0.002 under the eye-closed conditions). The deprivation of visual information about the pushing moment increases the Amp-m and V-r and had no effect on the RT in all groups. Under the eye-closed conditions, an increase in Amp-m as a result of pushing was significantly lower in the wrestlers (p = 0.033) than in the control group. Under the eye-closed conditions, the accuracy of the recovery of the initial vertical position after pushing was higher in the wrestlers than in the control group (p = 0.027). The indicators of postural stability, displacement of the center of pressure, and vertical posture sway and recovery after pushing did not differ between the runners and other groups. Therefore, compared to cyclic exercises, training in complex coordinating sports more effectively improves the ability to maintain vertical posture in response to its perturbation.

Design of optimized soft soles for humanoid robots

We describe a methodology to design foot soles for a humanoid robot given walking gait parameters (i.e. given center-of-mass and zero-moment-point trajectories). In order to obtain an optimized compliant sole, we devised a shape optimization framework which takes — among other inputs, an initial rough (simplified) shape of the sole and refines it through successive optimization steps under additional constraints and a cost function. The shape is optimized based on the simulation of the sole deformation during an entire walking step, taking time dependent input of the walking pattern generator into account. Our shape optimization framework is able to minimize the impact of the foot with the ground during the heel-strike phase and to limit foot rotation in case of perturbations. Indeed, low foot rotation enforces a vertical posture and secures the balance of the humanoid robot. Moreover, weight restriction (formulated as a constraint on the sole volume) is added to our optimization problem.

Human body modeling method to simulate the biodynamic characteristics of spine in vivo with different sitting postures.

The aim of this study is to model the computational model of seated whole human body including skeleton, muscle, viscera, ligament, intervertebral disc, and skin to predict effect of the factors (sitting postures, muscle and skin, buttocks, viscera, arms, gravity, and boundary conditions) on the biodynamic characteristics of spine. Two finite element models of seated whole body and a large number of finite element models of different ligamentous motion segments were developed and validated. Static, modal, and transient dynamic analyses were performed. The predicted vertical resonant frequency of seated body model was in the range of vertical natural frequency of 4 to 7Hz. Muscle, buttocks, viscera, and the boundary conditions of buttocks have influence on the vertical resonant frequency of spine. Muscle played a very important role in biodynamic response of spine. Compared with the vertical posture, the posture of lean forward or backward led to an increase in stress on anterior or lateral posterior of lumbar intervertebral discs. This indicated that keeping correct posture could reduce the injury of vibration on lumbar intervertebral disc under whole-body vibration. The driving posture not only reduced the load of spine but also increased the resonant frequency of spine.

Control of vertical posture while elevating one foot to avoid a real or virtual obstacle.

The purpose of this study is to investigate the control of vertical posture during obstacle avoidance in a real versus a virtual reality (VR) environment. Ten healthy participants stood upright and lifted one leg to avoid colliding with a real obstacle sliding on the floor toward a participant and with its virtual image. Virtual obstacles were delivered by a head mounted display (HMD) or a 3D projector. The acceleration of the foot, center of pressure, and electrical activity of the leg and trunk muscles were measured and analyzed during the time intervals typical for early postural adjustments (EPAs), anticipatory postural adjustments (APAs), and compensatory postural adjustments (CPAs). The results showed that the peak acceleration of foot elevation in the HMD condition decreased significantly when compared with that of the real and 3D projector conditions. Reduced activity of the leg and trunk muscles was seen when dealing with virtual obstacles (HMD and 3D projector) as compared with that seen when dealing with real obstacles. These effects were more pronounced during APAs and CPAs. The onsets of muscle activities in the supporting limb were seen during EPAs and APAs. The observed modulation of muscle activity and altered patterns of movement seen while avoiding a virtual obstacle should be considered when designing virtual rehabilitation protocols.

Functional Neuroanatomy for Posture and Gait Control.

Here we argue functional neuroanatomy for posture-gait control. Multi-sensory information such as somatosensory, visual and vestibular sensation act on various areas of the brain so that adaptable posture-gait control can be achieved. Automatic process of gait, which is steady-state stepping movements associating with postural reflexes including headeye coordination accompanied by appropriate alignment of body segments and optimal level of postural muscle tone, is mediated by the descending pathways from the brainstem to the spinal cord. Particularly, reticulospinal pathways arising from the lateral part of the mesopontine tegmentum and spinal locomotor network contribute to this process. On the other hand, walking in unfamiliar circumstance requires cognitive process of postural control, which depends on knowledges of self-body, such as body schema and body motion in space. The cognitive information is produced at the temporoparietal association cortex, and is fundamental to sustention of vertical posture and construction of motor programs. The programs in the motor cortical areas run to execute anticipatory postural adjustment that is optimal for achievement of goal-directed movements. The basal ganglia and cerebellum may affect both the automatic and cognitive processes of posturegait control through reciprocal connections with the brainstem and cerebral cortex, respectively. Consequently, impairments in cognitive function by damages in the cerebral cortex, basal ganglia and cerebellum may disturb posture-gait control, resulting in falling.

Effect of unstable shoes on trunk posture during standing and gait in chronic low back pain

Chronic low back pain (CLBP) is a common painful condition affecting particularly medical hospital staff. Wearing unstable shoes could be proposed as an alternative treatment as a pain decrease was observed in a recent study. A six-week treatment showed pain decrease that could be linked to a more vertical trunk posture. Therefore, the aim of this study was to evaluate if unstable shoes allow a more vertical posture of the trunk in the sagittal plane explaining this decrease in pain after six weeks of wearing. Forty CLBP hospital employees were randomly distributed in intervention (IG, n = 17) and control group (CG, n = 16) wearing respectively unstable and stable shoes. Gait and orthostatic trunk kinematics were recorded before and after six weeks in barefoot and shoes conditions. IG participants were defined responders (R-IG, n = 8) if a pain reduction ≥ 2 points (difference in values obtained with a visual analogue scale pain scale (VAS) before and after 6 weeks) was observed; otherwise, IG participants were defined non-responders (NR-IG, n = 9) (pain reduction < 2). IG had a tendency to show a trunk more vertical than CG in orthostatic position and R-IG had a tendency to show a trunk more vertical than NR-IG during gait. Due to the small observed differences, it is difficult to conclude on the effect of unstable shoes on trunk posture and gait of CLBP patients after six weeks of wearing.