Since my first ISPGR World Conference in Fort Lauderdale in 2017, I have seen many studies on functional near-infrared spectroscopy (fNIRS). Whilst its use is still controversial, research has demonstrated that fNIRS assessments are feasible, and their results not only reinforce previous theories related to motor control but also bring new hypotheses regarding the involvement of cortical areas in balance and gait tasks, shedding light on a better understanding of fall risk. It was a great pleasure to have received the ISPGR Emerging Scientist Award 2023 because of my work in this emerging scientific field. Below, I summarise my research findings using fNIRS to examine complex balance and gait.

In a series of studies, I examined older adults at low and high fall risk and people with Parkinson’s disease (PD). These participants performed a range of stepping tests (simple choice stepping reaction time test (CSRT), CSRT with inhibitory response (iCSRT) and a Stroop version of CSRT (SST)), along with an adaptive walking test. The cortical areas examined were the prefrontal cortex (PFC), supplementary motor area (SMA) and premotor cortex (PMC). Older adults at high fall risk exhibited increased PFC activity and stepping response variability when completing the SST test compared to older adults at low fall risk and compared to the CSRT test [1]. In PD, the pattern of cortical activity differed. Whilst older adults increased their cortical activity (PFC, SMA and PMC) to handle more complex stepping tests (iCSRT and SST), people with PD exhibited a “slowdown” phenomenon, demonstrating reduced cortical activity in the same areas [2]. Finally, during adaptive gait, people with PD had little or no additional PFC, SMA, and PMC capacity beyond what they needed for simple walking and, therefore, presented with a more conservative gait pattern than their healthy peers [3].

Altogether, these results elucidate that older adults may not cope with task demands, relying heavily on their cortical resources, which reflects their increased risk of falling. Moreover, this increased cortical activity seems to reflect a compensatory process for deficits in postural control or a degree of neural inefficiency in those at high fall risk. In PD, the reduced cortical activity during complex stepping tests might reflect multiple pathways and/or subcortical damage, resulting in deficient use of cognitive and motor resources and poor overall motor behavior.  Finally, the cortical activity and behavior exhibited by people with PD during adaptive gait appear consistent with concepts of compensatory over-activation and capacity limitation.

Publications

[1]  Paulo H S Pelicioni, Stephen R Lord, Daina L Sturnieks, Bethany Halmy, Jasmine C Menant. Cognitive and Motor Cortical Activity During Cognitively Demanding Stepping Tasks in Older People at Low and High Risk of Falling. Front Med (Lausanne). 2021; 8: 554231. doi: 10.3389/fmed.2021.554231

[2]  Paulo H S Pelicioni, Stephen R Lord, Yoshiro Okubo, Daina L Sturnieks, Jasmine C Menant. People With Parkinson’s Disease Exhibit Reduced Cognitive and Motor Cortical Activity When Undertaking Complex Stepping Tasks Requiring Inhibitory Control. Neurorehabil Neural Repair. 2020 Dec;34(12):1088-1098. doi: 10.1177/1545968320969943.

[3]  Paulo H S Pelicioni, Stephen R Lord, Yoshiro Okubo, Jasmine C Menant. Cortical activation during gait adaptability in people with Parkinson’s disease. Gait Posture. 2022 Jan:91:247-253. doi: 10.1016/j.gaitpost.2021.10.038.

About the Author

By Kaylena Ehgoetz Martens

Freezing of gait is characterised by a sudden inability to initiate or continue walking which significantly impacts quality of life in people living with Parkinson’s disease. Since dopaminergic replacement therapy only partially ameliorates freezing of gait, other non-dopaminergic contributions may play a role in freezing of gait. There is evidence that sympathetic arousal increases prior to a freezing episode, particularly when freezing is triggered by stress. This highlights a potential neural mechanism to underpin the relationship between anxiety and freezing of gait. Despite a growing body of evidence that suggests anxiety may be a crucial contributor to freezing of gait, no research study has investigated changes in functional network architecture as a result of induced-anxiety which often triggers freezing of gait. Here, we aimed to investigate how anxiety-inducing contexts might ‘set the stage for freezing’, through the ascending arousal system, by examining an anxiety-inducing virtual reality gait paradigm inside functional magnetic resonance imaging (fMRI).

We used a virtual reality gait paradigm to navigate a virtual plank that has been validated to elicit anxiety, whilst simultaneously collecting task-based fMRI data from individuals with idiopathic Parkinson’s disease with confirmed freezing of gait. First, we established that the threatening condition (i.e., navigating across a narrow plank above a deep pit) provoked more freezing when compared to the non-threatening condition. We established that the threatening condition was associated with heightened network integration. By utilizing a dynamic connectivity analysis, we identified patterns of increased ‘cross-talk’ within and between motor, limbic and cognitive networks in the threatening conditions. The sympathetic nature of this phenomenon was demonstrated by an increase in pupil dilation during the anxiety-inducing condition of the virtual reality gait paradigm outside of the MRI scanner.

Figure 1: Screenshots of the virtual-reality paradigm A) non-threatening and B) threatening walking conditions. C) Graphical representation of the noradrenergic Locus Coeruleus and its influence on pupil dilation. D) ‘Cross-talk’ model depicted graphically, with “cross-talk” visualized through heightened connectivity/network integration represented by the orange boldened lines, and its subsequent influences on the Striatum, which inhibits Globus Pallidus Internus (GPi), which inhibits the Mesencephalic Locomotor Regions (‘MLR’), leading to freezing of gait.

This work reveals a potential explanation for how anxiety could lead to freezing of gait. Heightened sympathetic arousal related to anxiety could increase ‘cross-talk’ between distributed cortical networks that ultimately manifest as episodes of freezing of gait. This research advances our understanding of a symptom that affects many people living with Parkinson’s disease and opens new avenues to explore for better clinical management.

Publication: Taylor, N.L., Wainstein, G., Quek, D., Lewis, S.J.G., Shine, J.M., Ehgoetz Martens, K.A. (2022) The contribution of noradrenergic activity to anxiety-induced freezing of gait. Movement Disorders, 37(7):1432-1443. DOI: 10.1002/mds.28999

About the Author

By Steven Phu

Slips and trips are the most common causes of falls in ambulant older people, with the rapid activation and coordination of muscles being essential to recover balance following such postural disturbances. For falls prevention, balance (e.g. standing on one leg, tandem walking) and strengthening exercises are highly effective but often lack task specificity. In comparison, reactive balance training directly practices fall circumstances by inducing repeated perturbations such as slips and trips. Although there is accumulating evidence that these more task-specific interventions also prevent falls in older people, the underlying mechanisms remain unclear. For example, we do not know whether postural responses after an unpredictable perturbation are delayed with ageing and if these postural responses can be improved by exercise and/or reactive balance training interventions. Therefore, we performed a systematic review to determine the impact of ageing and interventions (both exercise and reactive balance training) on postural responses following unpredictable perturbations.

After searching the literature for studies assessing delay in muscle activation (onset latency) following an unpredictable perturbation, we compared postural responses of young versus older adults, regular exercisers versus non exercisers and the effects of interventions with (randomised control trials) and without (uncontrolled clinical trials) a control group (Figure 1). Through meta-analysis, we found evidence for significant delays in postural responses in older versus young adults. We also found evidence for faster postural response in regular exercisers (i.e. those who reported continued participation in exercise for at least a year). Finally, in data from controlled trials, we found postural responses were improved after medium (2 to 6 weeks) and long term (≥6 weeks) interventions regardless of the training mode (exercise or reactive balance training). In contrast, short-term interventions over one or two days did not improve postural responses.

In summary, our systematic review and meta-analysis provided evidence for age-related decline and exercise-induced improvement in postural responses following unpredictable perturbations. There was insufficient evidence to determine the ideal modality of intervention (exercise or reactive balance training) to improve postural responses, however, the data suggested interventions lasting at least 2 weeks were required to achieve improvements.

Figure 1. Summary of meta-analysis findings examining onset latency (milliseconds) in response to postural perturbations

Publication

Phu S, Sturnieks DL, Lord SR, Okubo Y. Impact of ageing, fall history and exercise on postural reflexes following unpredictable perturbations: A systematic review and meta-analyses. Mech Ageing Dev. 2022;203:111634. doi: 10.1016/j.mad.2022.111634

https://doi.org/10.1016/j.mad.2022.111634

About the Author

By Duangporn Suriyaamarit and Sujitra Boonyong

Sit-to-stand movements, where an individual rises from a chair to a standing position, are common daily functional actions. Previous research has demonstrated that the design and dimensions of the chair used can influence the performance of the sit-to-stand task. For instance, getting up from a chair with higher height and an anterior tilted seat surface is usually easier. No evidence has been presented to date, however, in children with cerebral palsy for whom sit-to-stand movements are a constant challenge. This research therefore sought to draw comparisons between performance levels in terms of mechanical work, movement time, kinematics, and kinetics while getting up from chairs with varying seat angles and heights, for children with cerebral palsy.

Experiments were carried out involving 12 children with cerebral palsy under three conditions. The control condition used a low and horizontal seat (low-flat). The other two conditions were a low seat with anterior inclination (low-tilted), and a high horizontal seat (high-flat). Under both low-tilted and high-flat conditions, there was a significant reduction in movement time and mechanical work during sit-to-stand, in comparison to the low-flat control condition. We also found that at the start of the sit-to-stand movement in the low-tilted, there was better trunk alignment, and reduced pelvic motion. Meanwhile, the high-flat showed a reduction in the range of movement for the knee, hip, and ankle joints, and in the maximal hip and knee extension moments in comparison to the low-flat.

Our findings indicate that both a high seat and anterior inclination can improve sit-to-stand performance in children with cerebral palsy, although these two chair types provide different benefits. The low-tilted chair improves trunk alignment with the pelvis as the sit-to-stand task commences. Anterior inclination should therefore be employed for children with cerebral palsy whose primary problem lies in trunk and pelvis alignment even though they have sufficient muscle strength in the lower legs to facilitate standing. We also found that the high-flat chair reduced hip, knee, and ankle joint excursion and lowered the maximal hip and knee extension moment. A higher chair may therefore be helpful for children with cerebral palsy whose primary problems concern the lower extremities, or who are still in the initial stages of training for sit-to-stand movements. The findings presented here may help clinicians determine which type of chair design is more appropriate for a specific child with cerebral palsy.

Figure: The three different chairs and corresponding movement time and mechanical work during the sit-to-stand task.

Publication

Suriyaamarit, D., & Boonyong, S. (2020). Comparison of the effects of chair height and anterior seat inclination on sit-to-stand ability in children with spastic diplegic cerebral palsy. Journal of Biomechanics, 113, 110098. https://doi.org/10.1016/j.jbiomech.2020.110098

About the Author

By Lotte Grevendonk and Christopher McCrum

There are many benefits of habitual physical activity, exercise and sports participation for older people. However, the extent to which these influence one of the most common causes of injuries in older age, namely falls, is unclear. In this study, we assessed the influence of age on various metabolic and mobility-related outcomes, accounting for physical activity levels. We also evaluated the additional effects of more extensive exercise or sports participation in old age. In this blog post, we focus on our motion-capture derived gait outcomes.

We investigated walking characteristics of 12 younger adults (~24y) versus 13 healthy older adults (~71y) with approximately the same habitual physical activity levels (~10,000 steps per day, 2.6% and 2.2% of waking time in high intensity physical activity). We also compared the same healthy older adults with 15 exercise-trained older adults (~68y, ~14,000 steps per day, 5.3% of waking time in high intensity physical activity, mostly endurance or mixed endurance and resistance-based exercise training).

We first compared spatiotemporal step parameters and their variability between the groups when participants walked on a treadmill at a range of speeds. In these conditions, most gait variables were not affected by age (young vs. old) and none were affected by exercise training (older healthy vs. older trained). These findings indicated that perhaps decline in steady-state walking is slowed with suitable physical activity levels, but not further enhanced by exercise training.

Using repeated treadmill belt acceleration perturbations, we compared groups on stability (first perturbation) and adaptability (repeated perturbations). Despite similar physical activity levels, older adults responded less effectively to the first perturbation compared to their younger peers (Figure 1, top left panel; larger deviation from, and more steps to return to, baseline Anteroposterior Margin of Stability). However, adaptability was not significantly different between age groups (Figure 1, top right panel). We found no clear differences between the healthy and trained older adults in these outcomes (Figure 1, bottom panels).

In conclusion, older people can broadly preserve their spatiotemporal step parameters during unperturbed walking with sufficient physical activity but the ability to cope with large balance disturbances remains less effective initially (adaptability was not affected by age). High levels of exercise training beyond that recommended by the World Health Organisation in old age do not seem to provide further benefit for either aspect of walking stability, but this should be further investigated in larger future studies.

Figure 1. Mean and SD of the anteroposterior margins of stability for the younger versus older participants (Y and O) and for the older versus trained older participants (TO) during the first and ninth perturbations (Pert1R and Pert9L) including unperturbed walking prior to each perturbation (Base), the final step prior to each perturbation (Pre) and the first eight recovery steps following the perturbations (Post1 – 8). A significant group effect from a two-way repeated measures ANOVA was found only for the Y vs. O comparison at Pert1R. *: Significant difference to Base within the group (p < 0.05; adjusted using Dunnett’s multiple comparisons test). #: significant difference between groups (p < 0.05; adjusted using Šídák’s multiple comparisons test).

Publication

Grevendonk L, Connell NJ, McCrum C, Fealy CE, Bilet L, Bruls YMH, Mevenkamp J, Schrauwen-Hinderling VB, Jörgensen JA, Moonen-Kornips E, Schaart G, Havekes B, de Vogel-van den Bosch J, Bragt MCE, Meijer K, Schrauwen P, and Hoeks J. Impact of aging and exercise on skeletal muscle mitochondrial capacity, energy metabolism, and physical function. Nature Communications 12: 4773, 2021. doi: 10.1038/s41467-021-24956-2

About the Author

By Dr Erika Pliner

Ladder use is a hazardous activity and the leading cause of fatal falls from a height. Older adults are at highest risk of experiencing a ladder fall during household activities, such as clearing a roof gutter. Climbing (foot and body position, handhold force) and environmental (climb direction, ladder angle) factors are known to affect ladder fall risk, but little is known about individual characteristics that may predispose someone to a ladder fall. Therefore, we conducted a study to determine individual factors that contribute to effective ladder use.

We recruited 100 older adults and asked them to clear a gutter using a straight ladder in the laboratory (Figure 1). The gutter was 2.1 m above the ground, 5.8 m in length, and filled with tennis balls. The straight ladder was partially fixed to the experimental setup that supported the gutter, simulating a straight ladder leaning against a wall. The ladder was easily moved laterally along the wall to the desired location. To completely clear the length of the gutter, participants had to move and climb the ladder multiple times. We recorded time to complete this task as the outcome measure.

For each participant, we assessed individual metrics of strength, upper limb control, balance, cognition, and propensity for risk-taking. To determine which individual factors are related to effective ladder use, we performed regression analysis with the individual metrics on task completion time. Our results showed that the time taken to clear the gutter was predicted by multiple individual factors. Specifically, participants with greater quadriceps strength, better upper limb coordination, more controlled leaning balance, and a greater propensity for taking risks completed the gutter clearing task faster, suggesting these participants to be more effective ladder users.

Knowledge of individual factors that are associated with effective ladder use can be used to direct ladder fall interventions. Ladder users who take longer to complete ladder tasks (increasing their ladder use exposure and fall risk) may be identified and warned of their fall risk through screening tools and targeted for strength and balance training interventions to reduce their fall risk. Further, this knowledge can guide ladder design and safety instruction. Specifically, ladders could be designed to reduce the need for superior balance control and quadriceps strength with a greater base-of-support at lower rungs commonly used for working heights. Safety instructions may be updated to inform users to utilize additional tools to avoid strenuous postures that require greater upper limb coordination. Future work is needed to assess the trade-off between efficient ladder use (faster task completion times) and risky ladder use (completing the task near or outside stability limits).

Figure 1. Experimental set-up

Pliner, E.M., Sturnieks, D.L., Lord, S.R. (2020). Individual factors that influence task performance on a straight ladder in older people. Experimental Gerontology, 142: 111127. https://doi.org/10.1016/j.exger.2020.111127

About the Author

By Dr Tarun Arora, Dr Alison Oates and Dr Kristin Musselman

After someone has injured their spinal cord, the communication between their brain and body is disrupted, which can make movement challenging. In more than half of spinal cord injuries (SCI), the spinal cord is not completely damaged (i.e., an “incomplete” injury ). The majority of individuals with an incomplete SCI (iSCI) are able to walk. Unfortunately, about three-quarters of people with an iSCI report at least one fall per year. This risk of falling is similar or even higher than other populations who are prone to falls such as older adults (33%) or those living with stroke (73%) and Parkinson’s disease (68%). Research shows that individuals with iSCI walk slower, take shorter steps, and spend more time in double support which improves their mechanical stability. Thus, they are less likely to lose their balance during walking, but can they recover once their balance is perturbed? Our research studied reactive responses to an unexpected slip perturbation in people with an iSCI.

We brought 20 individuals with iSCI and 15 age-and-sex matched individuals without SCI (niSCI) to the Biomechanics of Balance and Movement Lab at the University of Saskatchewan. A slip device embedded into the floor becomes highly slippery (comparable to that of clean ice at 0 deg. celsius!) when unlocked (Figure 1). Without knowing when the slip device will be unlocked, participants walked for several “normal walking” trials. Then we unlocked the slip device for an “unexpected slip”without telling them  (click here for videos). The velocity of the slipping heel was used to categorize the severity of the slip as hazardous (>1m/s) or non-hazardous. Using 3-D motion capture, we measured stability at the first compensatory step after the slip. We also measured when and how much the muscles in the leg activated in reaction to slip.

Both groups had similar proportions of hazardous and non-hazardous slips suggesting a comparable slip severity. The iSCI group could not regain as much stability as the niSCI group using a compensatory step. Also, the iSCI group demonstrated lower calf muscle activation compared to the niSCI group.

Using the unexpected slip paradigm, we demonstrated some important limitations in the reactive balance of individuals with iSCI. This research highlights the importance of evaluating reactive balance during clinical balance evaluations in individuals with iSCI. Clinicians should consider evaluating reactive balance evaluation (e.g., mini-BESTest) in their practice.

Figure 1. Slip device and schematic lab setup for data collection (modified from Arora T et al., PM&R 2019)

Note: this study was a part of a larger research project that was funded by the Saskatchewan Health Research Foundation (awarded to AO and KEM).

Publication

Arora T, Musselman KE, Lanovaz JL, Linassi G, Arnold C, Milosavljevic S, Oates A. (2020) Reactive balance responses to an unexpected slip perturbation in individuals with incomplete spinal cord injury. Clin Biomech (Bristol, Avon), 78:105099. https//doi.org/10.1016/j.clinbiomech.2020.105099

About the Author

By Kelly Robb

Plantar intrinsic foot muscles are commonly described as acting as one ‘functional unit’. However, previous human studies of EMG recordings of abductor hallucis and flexor digitorum brevis during walking  have revealed that these muscles have unique onset/offset patterns during the gait cycle. This suggests that they may function more independently than once thought. To our knowledge, there has been no report of EMG recording of the transverse head of adductor hallucis, another plantar intrinsic foot muscle, during walking. In this study, we therefore aimed to 1) develop a fine-wire EMG technique to record EMG of the transverse head of adductor hallucis during gait, and 2) examine this muscle’s functional role during walking.

We recorded bipolar fine-wire EMG of the transverse head of adductor hallucis in 19 feet of 10 young adults during walking. Under ultrasound guidance, we inserted fine-wire electrodes into the transverse head of adductor hallucis muscle via a dorsal forefoot insertional approach. Participants then completed a series of level walking trials over a custom-made walking platform, designed to allow for manipulation of the flooring surface compliance between hard and soft foam. This flooring compliance change modified the muscular demands of the transverse head of adductor hallucis during the stance phase of the gait cycle. We compared and reported the ensemble averages between both flooring surfaces and typical phasic EMG activity of the transverse head of adductor hallucis during level walking.

We found that the transverse head of adductor hallucis appears to contract, neutralizing the role of the tibialis anterior, and acting as a forefoot stabilizer during the propulsive phase of gait. Even more intriguing, the demands of this muscle appear to change when varying the flooring compliance (Figure). These preliminary insights into the functional role of the transverse head of adductor hallucis during walking may prove informative to clinicians treating common forefoot pathologies, including hallux valgus and metatarsalgia symptoms. These results may also be useful for the design of foot orthoses and/or footwear to alleviate the muscular demands of the transverse head of adductor hallucis during walking. Future researchers are encouraged to adopt this fine-wire technique and advance transverse head of adductor hallucis EMG literature across different foot shapes and participants experiencing pathological forefoot deformities.

Figure: Representative data of the EMG bursting pattern of the transverse head of adductor hallucis during walking. When walking on a hard surface (top), peak activity occurs at approximately 15% and 60% of the gait cycle, corresponding to initial contact and propulsion phases of gait. When walking on the softer foam (bottom), there is an absence of EMG activity at initial contact, with the retention of similar bursts in EMG at propulsion.

Publication

Robb, Kelly A., Melady, Hope D. & Perry, Stephen D. (2021) Fine-wire electromyography of the transverse head of adductor hallucis during locomotion. Gait & Posture, 85, 7-13. https://doi.org/10.1016/j.gaitpost.2020.12.020

About the Author

By Dr Sudeshna Chatterjee

In the past several years, studies have shown that the prefrontal cortex — which has a crucial role in the control of executive functions including attention, working memory, and motor planning — is also involved in the neural control of walking. Mobile brain imaging approaches, such as functional near-infrared spectroscopy, allow us to measure prefrontal cortical activation during the performance of various walking tasks. While this is extremely valuable, an important yet unresolved challenge in the measurement and interpretation of brain activity during walking is the influence of inter-individual differences on brain activation. In our study, we address important knowledge gaps by investigating the extent to which prefrontal cortical activation during an obstacle negotiation task relative to typical steady state walking is explained by inter-individual differences in age, executive function, and sex in older adults. Furthermore, we present a novel perspective on the interpretation of prefrontal activation during walking based on a conceptual model of brain aging, the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH). Developed by Reuter-Lorenz and Cappell (2008), CRUNCH is a broader conceptual framework that consolidates several brain aging models including neural inefficiency, neural compensation, and capacity limitation.

We found that age, executive function, and their interaction are significant predictors of prefrontal activation during obstacle negotiation in older adults. Consistent with CRUNCH, among older adults of a younger age (< 75 years), lower executive function was associated with neural inefficiency where greater recruitment of prefrontal activation was observed during obstacle negotiation compared to their peers with higher executive function (Panel A). In contrast, older adults of an advanced age (≥ 75 years) exhibited a ceiling effect of brain recruitment resources during obstacle negotiation regardless of executive function level (Panel B). Panels C and D show the conceptual interpretation of our data based on the CRUNCH framework. Finally, we found evidence of compensatory overactivation, where greater prefrontal activation was associated with a smaller drop in obstacle negotiation speed compared to typical steady state walking.

Our findings demonstrate that the interaction between task demands and individual characteristics may influence the functional range of brain activity available during complex walking and this should be considered by studies designed to intervene on brain activation efficiency to enhance walking ability in older adults. We suggest that future studies should measure activity from additional brain regions; design walking tasks with multiple gradations of difficulty; and include genetics and lifestyle as these variables may protect against or worsen mobility decline in older adults.

Figure 1: Panels A and B show the prefrontal activity data during typical steady state walking (Typical) and obstacle negotiation (Obstacles) in the early and late aging groups. Panels C and D show the conceptual interpretation of our data based on the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH) framework. EF denotes executive function. ΔO2Hb denotes the change in prefrontal activity during the walking period compared to the reference period for each task. ΔPFR denotes the change in prefrontal recruitment during Obstacles compared to Typical. Group differences in ΔPFR are reported as Cohen’s d.

This research was supported by a NIH/NIA R21 grant awarded to Dr. David J. Clark, Associate Professor at the University of Florida (The UPfront Walking Study).

Publication

Chatterjee SA, Seidler RD, Skinner JW, Lysne PE, Sumonthee C, Wu SS, Cohen RA, Rose DK, Woods AJ, Clark DJ. Obstacle negotiation in older adults: prefrontal activation interpreted through conceptual models of brain aging. Innov Aging. 2020;4(4):1-12. doi: 10.1093/geroni/igaa034.

About the Author

By Dr Tiphanie Raffegeau, Dr Brad Fawver and Dr William Young

Fear of falling profoundly affects a person’s balance control and walking, and paradoxically, might increase their risk of falling. The influence of such mobility-related anxiety is often tested by having people stand on the edge of an elevated platform. Based on this approach, our team developed a virtual reality (VR) program to induce mobility-related anxiety and examine the effects of simulated balance threats on balance and walking behavior.

Working in collaboration with software developers in the Spencer S. Eccles Health Science Library at the University of Utah led by Ben Engel, we created a simulation inspired by a popular game: “Richies Plank Experience.” Designed with Unity3D software (Unity Technologies, San Francisco, CA. USA ), a realistic rendering of a local outdoor setting was incorporated to deliver an anxiety-inducing ‘plank-walking’ simulation (Figure 1). The program has a plank-matching feature which uses the handheld controllers to capture four locations at each corner of any straight walkway. The spatial coordinates match the dimensions of the real and virtual walkways so what people see in VR is the same as what they feel when their feet touch the real platform edges. The feeling is enhanced by wearing a pair of virtual sneakers (system accessories worn around the ankle) that track their foot motion in the VR simulation. Finally, the program features an ‘elevator’ function, that raises the walkway level at customizable height and speed.

The effectiveness of the VR height illusion, shown by performance changes from low to high VR heights, is documented in slower turning behavior and direction-dependent standing balance (see Raffegeau et al., 2020a, 2020b). The success of the VR height illusion is supported by increased self-reported cognitive (e.g., worry) and somatic (e.g., tension) anxiety, more mental effort dedicated to the task, and less confidence in one’s ability to complete the task at VR high heights (Raffegeau et al., 2020a). We also detected increased heart rate variability (Coefficient of Variation) when participants stood at high elevations using a commercial heart rate monitor (Polar M430) (Raffegeau et al., 2020b) providing more support for the effectiveness of our paradigm.

In the future, we plan to improve the VR height illusion by determining the best method of delivering the experiment (e.g., timing, transportation to height, etc.) and scaling the virtual foot representation to each person. Future experiments will include obstacles to avoid and added cognitive tasks to study anxiety-related detriments to everyday mobility demands.

The program is accessible through Ben Engel’s github (see Raffegeau et al., 2020a).

Figure 1: Top: Progression of VR program development/design from initial version 1 (left) to current realistic version 2 (right) designed to represent an outdoor location in Park City, Utah. Note, the researcher’s user interface is shown. Bottom: the HTC Vive VR system equipment (left), a person fitted with the VR head mounted display walking on our path (middle), and the real-world path that is matched in the virtual world using the plank matching feature (right).

Low height VR walk video:

High height VR walk video:

Publications

Raffegeau, T.E., Fawver, B., Young, W. R., Williams, A. M., Lohse, K. R., and Fino, P. C. (2020a) The direction of postural threat alters standing balance control when standing at virtual elevation, Experimental Brain Research, 238(11), 2653 2663. https://www.sciencedirect.com/science/article/pii/S0966636220300072?via%3Dihub

Raffegeau, T.E., Fawver, B., Clark, M., Engle, B., Young, W. R., Williams, A. M., Lohse, K. R., and Fino, P. C. (2020b) The feasibility of using virtual reality to induce mobility-related anxiety during turning, Gait & Posture, 77, 6-13. https://doi.org/10.1016/j.gaitpost.2020.01.006

About the Author