Effects of Galvanic Vestibular Stimulation on Visual Verticality and Standing Posture Differ Based on the Polarity of the Stimulation and Hemispheric Lesion Side in Patients With Stroke

Introduction: There is growing evidence supporting the relationship of vertical misperception and poor balance control with asymmetrical standing posture in patients with stroke. Although the vestibular system has been shown to be responsible for vertical misperception and balance disorders, the effect of galvanic vestibular stimulation (GVS) on both vertical misperception and postural asymmetry after stroke remains elusive. The aim of this study was to investigate the effects of GVS on visual verticality and postural asymmetry after stroke and to clarify whether the effects differ depending on the polarity of the stimulation and hemispheric lesion side.Methods: We measured the subjective visual vertical (SVV) and body weight distribution on each foot in an upright stance in 24 patients with a hemispheric stroke (10 with a left hemisphere lesion and 14 with a right hemisphere lesion) and nine age-matched healthy controls. During the measurements, bipolar GVS (1.5 mA) was applied over the bilateral mastoid processes in three stimulation conditions: contralesional-anodal and ipsilesional-cathodal vestibular stimulation, ipsilesional-anodal and contralesional-cathodal vestibular stimulation, and no stimulation. To examine whether GVS modulates visual verticality and standing posture, SVV and weight-bearing in the three conditions were analyzed.Results: During no stimulation, the SVV deviated to the contralesional side in patients with a right hemisphere lesion, while more weight-bearing was observed on the ipsilesional limb than on the contralesional limb in both patient groups than in the controls. The SVV was modulated by reversing the polarity of GVS in all the groups when the cathodal stimulus side was either ipsilateral or contralateral to the lesion while the ipsilesional-cathodal vestibular stimulation reduced weight-bearing asymmetry in only the patients with a right hemisphere lesion.Conclusions: These findings demonstrate that the effects of GVS on the SVV and standing posture differ depending on the polarity of GVS and the hemispheric lesion side. Patients with a right hemisphere lesion have difficulty maintaining their preferred standing posture under visual verticality modulation evoked by GVS. The application of GVS may clarify whether the vestibular system has neural redundancy after stroke to suppress any effects of the stimulation, including modulation of the visual verticality, on balance.

Left-right side-specific endocrine signaling complements neural pathways to mediate acute asymmetric effects of brain injury

Brain injuries can interrupt descending neural pathways that convey motor commands from the cortex to spinal motoneurons. Here, we demonstrate that a unilateral injury of the hindlimb sensorimotor cortex of rats with completely transected thoracic spinal cord produces hindlimb postural asymmetry with contralateral flexion and asymmetric hindlimb withdrawal reflexes within 3 hr, as well as asymmetry in gene expression patterns in the lumbar spinal cord. The injury-induced postural effects were abolished by hypophysectomy and were mimicked by transfusion of serum from animals with brain injury. Administration of the pituitary neurohormones β-endorphin or Arg-vasopressin-induced side-specific hindlimb responses in naive animals, while antagonists of the opioid and vasopressin receptors blocked hindlimb postural asymmetry in rats with brain injury. Thus, in addition to the well-established involvement of motor pathways descending from the brain to spinal circuits, the side-specific humoral signaling may also add to postural and reflex asymmetries seen after brain injury.

Static postural differences between male and female equestrian riders on a riding simulator

This study aimed to compare static posture of male and female riders on a riding simulator. Ten female and five male riders underwent a 5 min standardised exercise programme on the simulator, they were then videoed for 10 s from each the left, right, and rear views whilst stationary on the simulator. Two-dimensional kinematic analysis of the videos showed that male riders had a more neutrally positioned pelvis in the sagittal plane (median left: 6.47°, right: 5.24°) with females demonstrating a posterior pelvic tilt (L: 14.04°, R: 13.55°). Females showed significantly greater pelvic obliquity (median female: 1.99°, male: 0.73°), trunk lean (F: 1.60°, M: 0.43°), and shoulder tilt (F: 1.79°, M: 0.57°) in the frontal plane, demonstrating an overall greater postural asymmetry. Previous studies of elite riders have shown a more anteriorly rotated pelvis to be more desirable. Symmetry of riding position is favourable as it allows movements to be performed with ease and ensures even force distribution through the saddle to the horse. Male riders may therefore have a biomechanical advantage over females when it comes to maintaining a desirable riding position. This research should now be extended to study riders on the horse in motion.

Motor strategy during postural control is not muscle fatigue joint-dependent, but muscle fatigue increases postural asymmetry

The aim of this study was to investigate the effects of ankle and hip muscle fatigue on motor adjustments (experiment 1) and symmetry (experiment 2) of postural control during a quiet standing task. Twenty-three young adults performed a bipedal postural task on separate force platforms, before and after a bilateral ankle and hip muscle fatigue protocol (randomized). Ankle and hip muscles were fatigued separately using a standing calf raise protocol (ankle fatigue) on a step and flexion and extension of the hip (hip fatigue) sitting on a chair, at a controlled movement frequency (0.5Hz), respectively. In both experiments, force, center of pressure, and electromyography parameters were measured. The symmetry index was used in experiment 2 to analyze the postural asymmetry in the parameters. Our main findings showed that muscle fatigue impaired postural stability, regardless of the fatigued muscle region (i.e., ankle or hip). In addition, young adults used an ankle motor strategy (experiment 1) before and after both the ankle and hip muscle fatigue protocols. Moreover, we found increased asymmetry between the lower limbs (experiment 2) during the quiet standing task after muscle fatigue. Thus, we can conclude that the postural motor strategy is not muscle fatigue joint-dependent and a fatigue task increases postural asymmetry, regardless of the fatigued region (hip or ankle). These findings could be applied in sports training and rehabilitation programs with the objective of reducing the fatigue effects on asymmetry and improving balance.

Association Between Scapular Posture and Two Different Pectoralis Minor Length Tests in Adolescents

Postural asymmetry due to the alterations in scapular posture is typically considered to be associated with injury. Pectoralis minor (PM) has played a crucial role in scapular posture, but limited knowledge exists that shows the possible effect of PM length on static scapular positioning in adolescents. The aim of this study was to investigate the association between static scapular positioning and two different PM length measurements in adolescents. Pearson rank test demonstrated that direct measurements of the PM length significantly and strongly inversely correlated to scapular anterior tilting (p = .01; r = −.592)and significantly and moderately inversely correlated to scapular internal rotation (p = .013; r = −.465) and scapular downward rotation (p = .028; r = −.416). However, indirect measurement of the PM length was not related to scapular posture. No significant correlation was found between direct and indirect PM length measurements. Direct measurement of PM length presents more information regarding alterations of the static scapular positioning.

Factors of Postural Asymmetry (FPA) At The Pre- and Subclinical Stages of the Develop-ment of 3D Deformity of the Vertebral Complex

In the pathogenesis of typical scoliosis, as a three-dimensional deformation, the process of formation of its horizontal component is of particular interest. From the point of view of the functional anatomy of the vertebral complex, appearance of this component is directly related to the work of the transverso-spinal muscles. Thus, their contraction on the left side results in a rotational displacement of the vertebral bodies to the right, and the same phenomenon on the right causes a left-sided rotation of the main bone elements of the supporting column of the spine. It has already been shown that longterm asymmetric contraction of these muscles is a key at the subclinical stage of the transition of a healthy spine to the “scoliotic” status [1-3]. The method of blood serum bioassay (BT SC) has confirmed our assumption that among the participants in the pathogenesis of progressive scoliosis there are so-called neuropeptide factors of postural asymmetry (FPA), which have an ability to lateralize the activity of motor neurons in the spinal cord. These were natural regulators - oxytocin and arginine-8-vasopressin, and this ability appears in a case of a multiple increase in their concentration. Determination of their quantitative characteristics using ELISA showed high correlations between the levels of these factors and the process of spinal column deformation at the pre-and subclinical stages of scoliosis development.