Posturography

Stress influences performance: Insights into designing high cognitive load rehab tasks

The objective of this study was to investigate the effect of induced stress on the performance of each task during high cognitive load situations(HCLS). We hypothesized that induced stress leads to performance decrements during HCLS. In this study, the HCLS included standing while completing a secondary task(wire maze). The wire maze was composed of a metal wire path(maze) and a single ring, held in one hand that was moved over the maze without contacting the maze itself. Stress was induced through a loud buzzer when the ring contacted the maze. Participants were asked to randomly stand 1)quietly, or while completing the wire maze 2)with or 3)without the buzzer. Trials were three-minute long. A sample of 18 healthy young participants, (24.76±3.56 years) were randomly recruited. Perceived stress was obtained after each trial. Regularity of ground-reaction-force (GRF) in anterior-posterior and medial-lateral directions as well as wire maze error (ring-to-path contact) were calculated as primary and secondary task performance. GRF was more irregular during quietly standing compared to HCLS with and without the buzzer in both the AP and ML directions(p=0.02, p=0.001, respectively in anterior-posterior,η^2=0.28)&(p=0.004, p<0.0001, respectively in medial-lateral, η^2=0.39). Perceived stress was significantly lower during quietly standing compared to HCLS with(p=0.001, η^2=0.45) and without buzzer(p=0.007) conditions. Overall, the hypothesis was supported partially; during the most stressful HCLS, the high level of perceived stress coincided with less wire maze errors(P<0.0001, d= 0.72). Identifying the strategies underlying task prioritization can help clinicians design appropriate interventions to challenge patients appropriately to improve performance during HCLS.
Listed In: Biomechanical Engineering, Biomechanics, Physical Therapy, Posturography


An Investigation of Factors Affecting Dynamic Postural Stability in Collegiate Cross Country Runners

Injury could lead to impaired postural stability which is commonly assessed during return-to-sport rehabilitation. The Dynamic Postural Stability Index (DPSI) estimates variability in tri-axial ground reaction forces. DPSI is higher in injured runners and predicts performance in soccer players. DPSI has also been related to ankle range of motion (ROM) and strength in military personnel. PURPOSE: To explore relationship between previous injury, ankle ROM and strength with DPSI in collegiate runners. METHODS: Twenty-seven Division I collegiate cross country athletes (19.8±1.3 years) participated. Athletes jumped over a hurdle on to an AMTI force plate and landed on a single leg for DPSI estimation. Three trials were performed bilaterally. Ankle ROM was assessed via active dorsiflexion and gastrocnemius length measurement. Ankle and hip strength were measured using a handheld dynamometer. An independent samples t-test was used to compare DPSI between injured (IG – those injured in the past 3 years) and uninjured (UG) groups. Pearson’s correlation coefficients were determined between DPSI and other variables. RESULTS: No significant difference was found for DPSI on left (IG: 0.30±0.03 vs. UG: 0.32±0.04) and right (IG: 0.30± 0.03 vs. UG: 0.31±0.03) sides. There was a significant moderate negative correlation between dorsiflexion ROM and DPSI (right side r= -0.605, p= 0.001; left side r= -0.452, p= 0.001). There were no correlations between strength and DPSI except for right inversion strength and right DPSI (r= 0.446, p=0.020). CONCLUSION: DPSI seems to be influenced to a greater extent by ankle dorsiflexion than strength or previous injury in a collegiate runners.
Listed In: Biomechanics, Physical Therapy, Posturography, Sports Science


Synchronization of EEG Activity with Body Balance During Cognitive Visual Exercises

When evaluation cognition, there is a certain complexity surrounding electroencephalographic (EEG) recordings, which would greatly benefit from being supplemented by secondary recordings, such as those from a force platform. Currently, there is also a lack of evidence supporting the need to implement creative exercise on analytical coursework, specifically in STEM degrees where there is gaining momentum to incorporate the arts [3]. This pilot study aims to correlate electroencephalography (EEG, Brain Vision) and postural sway (AMTI AccuSway) data to verify cognitive changes. This study hypothesizes that participants will have 1) increased EEG alpha activity and 2) increased postural sway when participating in iterations of a problem-solving tasks administered after the participant engages in creative activities. The study will use human-subject data gathered from electroencephalography (Brain Vision) and postural sway (AMTI AccuSway) to quantify the cognitive engagement of participants during the learning of new concepts in a unique manner that allows the participants to think about them visually. The hypothesis is that the teaching methods introduced will encourage participants to have increased cognitive attention. Two participants were evaluated on their postural sway and EEG activity during the answering of Raven’s Progressive Matrices tests before and after artistic viewing and drawing activities. The data generated by this study by these means will show that increased cognition is apparent when concepts are presented in a visual manner, fortifying a philosophy that engineering curricula would benefit from artistic additions.
Listed In: Neuroscience, Posturography


Standing steadiness and variability of older adults on a step ladder

MOTIVATION: Ladder fall injury rates are highest among older adults. While standing stability has been quantified using center of pressure (COP) to classify general fall risk of older adults, it has not been applied to older adults’ balance and performance on ladders. This study investigates the standing stability of older adults while performing a task on a ladder. METHODS: One-hundred four older adults completed the Physiological Profile Assessment (PPA) to classify fall risk and climbed to the second step of a household step ladder to change a light bulb. Force plates under the step ladder were used to calculate the COP. COP parameters were extracted to assess stability on the step ladder including path length (time-normalized), RMS and elliptical area. Task time and COP parameters were compared between 10 participants with the highest fall risk and 10 participants with the lowest fall risk based on the PPA. RESULTS: Task time was 8.4 seconds (63.9%) longer for the high fall risk group. Time-normalized path lengths were similar between the two groups. The high fall risk group showed an increase in RMS by 18.1% and elliptical area by 44.6%. CONCLUSIONS: Differences in tasks time, RMS and elliptical area were observed between low and high fall risk groups. Larger RMS values and elliptical area indicate more movement away from the average COP location. This suggests high fall risk older adults to be more variable than low fall risk older adults in their standing stability when completing a task on a step ladder.
Listed In: Biomechanical Engineering, Biomechanics, Posturography


The effect of a specific fatigue protocol in force propulsion and postural sway in female handball athletes

Fatigue is a case of interaction between different factors and is characterized by the increase in the perceived effort to exercise and produce force. However, the effect on balancing tasks are not completely understood, especially the time course of the postural sway parameters during the recovery phase. Twenty female handball athletes participated in this study. They stood upright in a one-leg posture supported by the non-dominant limb on a force plate. The center of pressure (COP) and the maximum propulsion force (FMAX) were obtained at baseline, immediately after the exhaustion due to the fatigue protocol and every minute during the first 10 min of the recovery phase. For the postural-sway measures, participants stood on the force plate for 30 s with eyes opened looking to a target. Based on the COP displacement, the ellipse area containing 95% of the COP data points (Area) was computed. The FMAX was measured during a countermovement jump. Specific handball actions composed the fatigue protocol in the format of a circuit with the gradual increment of laps. The force decreased ~9.5% after the fatigue protocol (p = 0.01) and returned to baseline values during the recovery phase at the fifth minute. For the postural sway, the Area decreased during the recovery phase until the fourth minute (p = 0.007). The fatigue protocol affected postural sway and force variables, which returned to baseline values after four minutes of the protocol. Therefore, we suggest that future fatigue analyses should be tested during this time window.
Listed In: Biomechanics, Posturography, Sports Science


Balancing sensory inputs: Sensory reweighting of vision and ankle proprioception during a bipedal posture task

Multisensory integration is driven by a process of sensory reweighting during which each input is assigned a weight depending on the current functional state of a particular sensory system, the task itself and the context in which it is being performed. The primary aim of this study was to determine which of the two inputs between ankle proprioception and vision is upweighed during a postural control task when the two inputs provide conflicting information pertaining to direction of body sway. Achilles tendon vibration and visual flow were used to create sensory conflict, which produced center of pressure (COP) sway in opposite directions when applied independently. The baseline conditions (1) consisted of eyes open quiet stance condition, eyes closed with vibration applied on the Achilles tendons (2) and eyes open with visual flow (3). The experimental condition simultaneously combined vibration and visual flow. COP excursions were recorded in 10 healthy young adults to evaluate the magnitude and direction of sway produced by vibration and/or visual flow. Additionally, lower body joint kinematics were evaluated to understand the multi-segmental strategies and their adaptation to the various sensory manipulations. The results showed that visual flow moderated the extent of backward COP and ankle angular displacement produced when vibration was applied independently. Additionally, visual flow was also found to reduce the extent of predominant hip strategy generated by ankle vibration. The findings show that visual input plays a significant role in maintaining stability and that ankle proprioception is downweighed during conflicts between vision and proprioception. This has important implication for balance training using controlled visual flow in patients with balance disorders and elderly.
Listed In: Biomechanics, Neuroscience, Posturography


Locomotor Stability Control and Vestibular Function among Older Adults: Implications for Falls Prevention and Research

In the following project, we explored the relationships between age, vestibulopathy and stability control, in order to determine the age and vestibulopathy-related effects on stability control, and to establish if a relationship existed between static and dynamic stability task performance. The first study examined the response to repeated trip perturbations of healthy middle aged adults and vestibulopathy patients, the second examined feedforward adaptation of gait in young, middle aged and older adults to a sustained mechanical perturbation and the third examined the relationship between standing balance and recovery following a tripping perturbation in vestibulopathy patients. The results showed that vestibulopathy is related to a diminished ability to control and recover gait stability after an unexpected perturbation, and to a deficient reactive adaptation potential. With ageing, the ability to recalibrate locomotor commands to control stability is preserved, although this recalibration may be slower in old age compared to middle and young age. Given that a decline in vestibular function is seen with increasing age, we suggest that assessment of vestibular function may be necessary when investigating locomotor stability and falls risk in both research and clinical settings. Finally, despite static balance tasks and parameters being commonly used in clinical settings, we did not find a consistent relationship between static and dynamic stability task performance, indicating the importance of dynamic stability tests when assessing falls risk in clinical settings.
Listed In: Biomechanics, Gait, Posturography


ESTIMATION OF OPTIMAL STIMULUS AMPLITUDE FOR BALANCE TRAINING USING ELECTRICAL STIMULATION OF THE VESTIBULAR SYSTEM

Sensorimotor changes such as postural and gait instabilities can affect the functional performance of astronauts after gravitational transitions. When astronauts are trained before flight with supra-threshold noisy, stochastic vestibular stimulation (SVS), the central nervous system can be trained to reweight sensory information by using veridical information from other sensory inputs (such as vision and proprioception) for postural and gait control. This reweighting, in turn, can enhance functional performance in novel gravitational environments. However, the optimal maximum amplitude of stimulation has not yet been identified that can simulate the effect of deterioration in vestibular inputs for preflight training or for evaluating vestibular contribution in functional tests in general. Most studies have used arbitrary but fixed maximum current amplitudes from 3 to 5 mA in the mediolateral (ML) direction to disrupt balance function in both ML and anterior-posterior directions in healthy adults. The goal of this study was to determine the minimum SVS level that yields an equivalently degraded balance performance. Fourteen subjects stood on a compliant surface with their eyes closed and were instructed to maintain a stable upright stance. Measures of stability of the head, trunk, and whole body were quantified in the ML direction. Objective perceptual motion thresholds were estimated ahead of time by having subjects sit on a chair with their eyes closed and giving 1-Hz bipolar binaural sinusoidal electrical stimulation at various current amplitudes. Results from the balance task suggest that using stimulation amplitudes of 280% of motion-perceptual threshold (~2.2 mA on average) significantly degraded balance performance.


Listed In: Biomechanics, Neuroscience, Posturography


Acute Effects of Lateral Ankle Sprains on Range of Motion, Single Limb Balance, and Self-Reported Function

One in three individuals who suffer a lateral ankle sprain (LAS) subsequently develop chronic ankle instability. However, our inability to properly treat acute LAS is not surprising given our limited understanding of post-LAS consequences. 12 patients (21.6±2.9yrs; 172.9±13.1cm; 79.1±21.4kg) with an acute LAS participated. All participants were evaluated for dorsiflexion range of motion (DFROM), time-to-boundary (TTB) in single limb balance (SLB), and self-reported function (SRF) at 1-week, 2-weeks, 4-weeks, 6-weeks, and 8-weeks post injury. Both the involved and uninvolved limbs were measured during the patients first test session. DFROM was assessed using the weight-bearing lunge test and all participants performed 3, 10s of single limb stance with eyes open on a force plate to measure their single limb balance. SRF was measured using the Foot and Ankle Ability Measure (FAAM) and FAAM-Sport (FAAM-S). Post injury time points were compared to a control condition using multivariate ANOVAs (α=0.05). Relative to the control condition, FAAM and FAAM-S were significantly lower at 1-week and 2-weeks post injury. The FAAM-S was also significantly lower score compare to control condition at 4-weeks post-injury. Both FAAM and FAAM-S were not significant different at 6-weeks post-injury. Post-injury TTB measures and DFROM were not significantly different from the control condition. Non-significant declines in DFROM and TTB were observed as in this sample of acute LAS and appear to present with unique recovery patterns. Different recovery patterns among the tested outcomes indicate the need for further research with a larger cohort and for a longer post-injury duration.


Listed In: Biomechanics, Physical Therapy, Posturography, Sports Science


Sensory contributions to standing balance in unilateral vestibulopathy

Patients with unilateral peripheral vestibular disorder (UPVD) have diminished postural stability and therefore the aim of this study was to examine the contribution of multiple sensory systems to postural control in UPVD. Seventeen adults with UPVD and 17 healthy controls participated in this study. Centre of pressure (COP) trajectories were assessed using a force plate during six standing tasks: Forwards and backwards leaning, and standing with and without Achilles tendon vibration, each with eyes open and eyes closed. Postural stability was evaluated over 30s by means of: total COP excursion distance (COPPath) and the distances between the most anterior and posterior points of the COPPath and the anterior and posterior anatomical boundaries of the base of support (COPAmin and COPPmin). In addition, the corrected COPAmin and COPPmin was assessed by taking the corrected base of support boundaries into account using the anterior and posterior COP data from the leaning tasks. UPVD patients showed a tendency for smaller limits of stability during the leaning tasks in both directions. Subject group and task condition effects were found (P<0.05) for COPPath, (i.e. higher values for patients compared to controls). UPVD patients showed lower (P<0.05) COPPmin values compared to the control group for all conditions (more pronounced with the corrected COPPmin). Disturbance of the visual system alone lead to a distinct postural backward sway in both subject groups which became significantly more pronounced in combination with Achilles tendon vibration. The individual limits of stability should be considered in future research when conducting posturographic measurements.
Listed In: Biomechanics, Neuroscience, Physical Therapy, Posturography