Standing on wedges modifies side-specific postural control in the presence of lateral external perturbations

Trend change analysis in the assessment of body balance during posture adjustment in reaction to anterior-posterior ground perturbation

Postural adjustments (PA) occur to counteract predictable perturbations and can be impaired as a result of musculoskeletal and neurological dysfunctions. The most common way to detect PA is through electromyography measurements or center of pressure (COP) position measurements, where analysis in time domain and frequency domain are the most common. Aim of the research was to determine whether a new method of analyzing stabilographic measurements-the COP trend change analysis (TCI) of temporary posture corrections- can expand understanding of changes in balance strategy connected with PA. The study group involved 38 individuals (27women, 11men) aged 23±2.6 years. Measurements were performed using a stabilographic platform placed on a perturbation platform. The tests involved three measurements with forward and backward momentary movements of the platform. Participants were tested in three conditions-knowing the nature, time and direction of perturbation (Tr3), knowing only the nature of perturbation (Tr2) and without any information about the perturbation (Tr1). Statistically significant differences were revealed in the last second of Tr3 for the mean velocity of COP (p<0.05) and for two TCI parameters-TCI_dV (p<0.05) and TCI_dS (p<0.01). The increase in TCI_dV was related to the increase in the mean distance between trend changes (TCI_dS) and constant value of the mean time between trend changes (TCI_dT). The increase of the mean value of TCI_dS was the result of smaller number of posture corrections with the distance 0-2 mm and lager number with the distance 4-6 mm. Obtained results proved that the TCI analysis is a method enabling an extended analysis of PA, indicating the nature of changes occurring in posture corrections-longer momentary jumps of COP-related to a change in the strategy of maintaining balance before a known disorder, which has not been analyzed in this type of research so far.

The Effect of Virtual Reality Training on Anticipatory Postural Adjustments in Patients with Chronic Nonspecific Low Back Pain: A Preliminary Study

Objectives

This study is aimed at exploring the effects of virtual reality (VR) training on postural control, measured by anticipatory and compensatory postural adjustments (APAs and CPAs, respectively), in patients with chronic nonspecific low back pain (CNLBP) and the potential neuromuscular mechanism of VR training.

Methods

Thirty-four patients were recruited and randomly assigned to the VR group (n = 11), the motor control exercise group (MCE, n = 12) and the control group (CG, n = 11). The VR group received VR training using Kinect Xbox 360 systems and magnetic therapy. Besides magnetic therapy, the participants in the MCE group performed real-time ultrasound-guided abdominal drawing-in maneuver (ADIM) and four-point kneeling exercise. The CG only received magnetic therapy. Surface muscle electromyography (sEMG) was used to record the muscle activities of transverse abdominis (TrA), multifidus (MF), lateral gastrocnemius (LG), and tibialis anterior (TA) during ball-hitting tasks. The muscle activation time and integrals of the electromyography activities (IEMGs) during the APA and CPA stages were calculated and used in the data analysis. The visual analogue scale (VAS) and Oswestry dysfunction index (ODI) scores were also recorded.

Results

A significant interaction effect of time × group was observed on the activation time of TrA (p = 0.018) and MF (p = 0.037). The post-intervention activation time of the TrA was earlier in the VR group (p = 0.029). In contrast, the post-intervention activation time of the MF was significantly delayed in the VR group (p = 0.001). The IEMGs of TrA (p = 0.002) and TA (p = 0.007) during CPA1 significantly decreased only in the VR group after the intervention. The VAS scores of three group participants showed significant decreases after intervention (p < 0.001).

Conclusions

Patients with CNLBP showed reciprocal muscle activation patterns of the TrA and MF muscles after VR training. VR training may be a potential intervention for enhancing the APAs of the patients with CNLBP.

Effects of Ankle Angular Position and Standing Surface on Postural Control of Upright Stance

The purpose of the study was to investigate the effects of ankle angular position and standing surface type on static upright balance. Ten young adults stood on a force platform or on a firm wedge that induced 15° of either dorsiflexion or plantarflexion. In addition, a piece of foam was placed on top of the force platform and on the wedge. The center of pressure distance and velocity in the anteroposterior and mediolateral directions were calculated. Significantly larger magnitudes in most of the investigated variables were seen while standing with ankles in the dorsiflexion when compared with standing with the ankle joints in a natural position (p < .05). Plantarflexion increased the center of pressure anteroposterior velocity by 87% when compared with a natural stance (p < .05). Standing on the foam surfaces resulted in increases in all of the center of pressure measures by an average of 38% in all of the ankle conditions.

Characteristics of medial-lateral postural control while exposed to the external perturbation in step initiation

Controllability of posture in the medial-lateral direction is critical for balance maintenance, particularly in step initiation. The objective of the current study was to examine  the effects of external perturbation and landing orientation on medial-lateral control stability in step initiation. Eleven young healthy participants stood on the force platform and waited for the instruction of taking a step while experiencing a pendulum perturbation applied at the lateral side of the right shoulder. Eight experimental conditions were conducted by two levels of step side (right or left), two levels of perturbation (with or without), and two levels of landing orientation (forward or diagonal). The center of pressure (COP), pelvic movements, and muscle activities were recorded and analyzed as the onset of COP and pelvic movement, the COP displacement, and cocontraction and reciprocal muscle activation pattern. The temporal events of COP and pelvic movement were not significantly different in all experimental conditions. However, COP and pelvic movement were significantly later in the diagonal condition. Most of the segments showed reciprocal muscle activation patterns in relation to the perturbation released time. Subsequently, all segments showed cocontraction muscle activation patterns, which was significantly affected by step side, perturbation, and orientation. The results suggest that how the CNS initiated a step was identical with the COP then pelvic movement. The outcome highlights the importance of external perturbation and foot landing orientation effects on postural adjustments, which may provide a different approach to help step initiation.

Changes in the symmetry of external perturbations affect patterns of muscle activity during gait initiation

BACKGROUND

Gait initiation is associated with changes in the steady state and experiencing an external perturbation during initiation of gait could further threaten balance stability.

RESEARCH QUESTION

The aim of the study was to investigate if changes in the symmetry of the perturbations affect patterns of muscle activity during gait initiation.

METHODS

Eleven young health participants were instructed to stand on the force platform and wait for the instruction of taking a right step, left step or stand still while experiencing a pendulum perturbation applied to the back of both shoulders (symmetric), back of the right shoulder (asymmetric) or no perturbations. Bilateral electromyographic activity (EMG) of dorsal and ventral muscles, moments of the pendulum release and perturbation impact, center of pressure (COP) displacements and pelvic movements were recorded and analyzed before and after the onset of the perturbation.

RESULTS

Taking the right/left step in presence of symmetric perturbation did not affect the temporal sequence of COP and pelvic movements. The onset of COP and pelvic movement occurred before the perturbation impact at the shoulder levels. The factors of step and perturbation did not significantly affect integrals of bilateral muscles at the pendulum release. After the pendulum release, ventral and dorsal EMG integrals of the trunk, thigh, and shank segments increased or decreased corresponding to the swing and stance leg. Changes in muscle activities were also associated with the symmetric or asymmetric perturbations before and after the perturbation impact.

SIGNIFICANCE

The outcome of the study provides information about strategies used to coordinate the activity of muscles while body perturbations are induced during gait initiation.