Effects of Stroboscopic Vision on Depth Jump Motor Control: A Biomechanical Analysis.

Researchers commonly use the 'free-fall' paradigm to investigate motor control during landing impacts, particularly in drop landings and depth jumps (DJ). While recent studies have focused on the impact of vision on landing motor control, previous research fully removed continuous visual input, limiting ecological validity. The aim of this investigation was to evaluate the effects of stroboscopic vision on depth jump (DJ) motor control. Ground reaction forces (GRF) and lower-extremity surface electromyography (EMG) were collected for 20 young adults (11 male; 9 female) performing six depth jumps (0.51 m drop height) in each of two visual conditions (full vision vs. 3 Hz stroboscopic vision). Muscle activation magnitude was estimated from EMG signals using root-mean-square amplitudes (RMS) over specific time intervals (150 ms pre-impact; 30-60 ms, 60-85 ms, and 85-120 ms post-impact). The main effects of and interactions between vision and trial number were assessed using two-way within-subjects repeated measures analyses of variance. Peak GRF was 6.4% greater, on average, for DJs performed with stroboscopic vision compared to full vision (p = 0.042). Tibialis anterior RMS EMG during the 60-85 ms post-impact time interval was 14.1% lower for DJs performed with stroboscopic vision (p = 0.020). Vastus lateralis RMS EMG during the 85-120 ms post-impact time interval was 11.8% lower for DJs performed with stroboscopic vision (p = 0.017). Stroboscopic vision altered DJ landing mechanics and lower-extremity muscle activation. The observed increase in peak GRF and reduction in RMS EMG of the tibialis anterior and vastus lateralis post-landing may signify a higher magnitude of lower-extremity musculotendinous stiffness developed pre-landing. The results indicate measurable sensorimotor disruption for DJs performed with stroboscopic vision, warranting further research and supporting the potential use of stroboscopic vision as a sensorimotor training aid in exercise and rehabilitation. Stroboscopic vision could induce beneficial adaptations in multisensory integration, applicable to restoring sensorimotor function after injury and preventing injuries in populations experiencing landing impacts at night (e.g., military personnel).

Step edge highlighters and illuminance changes influence stair descent in a real-world setting.

Studies investigating the effect of tread edge highlighters on descent speed differ, but collectively report the potential benefit of reduced fall risk. Here we examine the impact of adding high-contrast black vinyl striping to the front edge of each step's tread and its impact on descending gait speed (intervention), while controlling for illumination. Descending gait speed was estimated from 5,824 video observations using the stairway length and entry and exit times. A second stairway was unaltered (control) to compare to the intervention. Stair users were primarily 18-30 years old with a small percentage being middle-aged and older adults. Descending gait speed was significantly slower on the intervention stairway (Linear mixed effects model: standardised coefficient = -0.07, 95% CI = [-0.12, -0.02], p = .010) compared to the control and may be impacted by illuminance. We propose that the slowed gait speed could be due to changes in gait kinematics (e.g. foot clearance) and may reduce fall-risk. Practitioner summary: Tread-edge contrast enhancement could be a low-cost means to reduce fall-risk on stairways, but its impact on gait kinematics is not well understood. We found that contrast enhancement reduced descending gait speed, but descending gait speed's impact on fall risk reduction ultimately requires further investigation.

Safe stairway negotiation: Role of distractions and handrail use.

INTRODUCTION: This study sought to examine stairway safety by identifying associations between fall-related events on stairways, distractions, gait speed, drifting, as well as handrail use and proximity. METHOD: Video recordings captured 11,137 observations of stair users in two public stairways and recorded distractions (e.g., looking at a mobile device, talking on a mobile device, using earbuds or headphones, holding a mobile device, or talking with a peer), gait speed (m/s), drifting (change of direction), as well as handrail use and proximity to a handrail. RESULTS: In our sample, consisting of primarily young adults (observed 18-40 years old), we found that when a distraction was present, gait speed was reduced (p <.001), drifting increased (p <.001), and handrail use negatively impacted (p <.001) compared to stair users who were not distracted. CONCLUSIONS: These results indicate that distractions, such as mobile devices, used during stair negotiation can reduce handrail use and increase behaviors associated with fall-related events. PRACTICAL APPLICATIONS: Mobile device use during stairway negotiation increases the likelihood of distraction-induced events. Stair users should be encouraged to limit or avoid mobile device use in public stairway environments. Mobile manufacturers and mobile app developers could aim to develop strategies or mobile app alerts to reduce the impact of distractions (e.g., mobile device use) during stair negotiation to lessen the health and financial burden associated with fall-related events on stairways.

Pickleball for Inactive Mid-Life and Older Adults in Rural Utah: A Feasibility Study.

Many diseases, disabilities, and mental health conditions associated with aging can be delayed or prevented through regular exercise. Several barriers to exercise, many of which are exacerbated in rural communities, prevent mid-life and older adults from accessing its benefits. However, recently, a racquet sport named pickleball has become popular among older adults, and it appears to overcome some of these barriers. We conducted a feasibility study to evaluate the impact of a six-week pickleball intervention on measures of muscle function, cognitive function, perceived pain, and cardio-metabolic risk, as well as several psychosocial factors contributing to adherence in sedentary rural participants. Participants improved their vertical jump, cognitive performance, and reported a decrease in self-reported pain, suggesting improved physical and cognitive health across the sample. Participants also reported high levels of satisfaction and demonstrated good adherence over the duration of the study. Perhaps of greatest value was the overwhelmingly positive response from participants to the intervention and follow-up interviews reporting a desire to continue pickleball play beyond the study period. Overall, pickleball appears to be a promising intervention to, (1) elicit functional- and cognitive-related improvements, and (2) motivate mid-life and older adults to adhere to exercise sufficiently long to benefit their health.

Relationship between Speed of Response Inhibition and Ability to Suppress a Step in Midlife and Older Adults.

In young adults, performance on a test of response inhibition was recently found to be correlated with performance on a reactive balance test where automated stepping responses must occasionally be inhibited. The present study aimed to determine whether this relationship holds true in older adults, wherein response inhibition is typically deficient and the control of postural equilibrium presents a greater challenge. Ten participants (50+ years of age) completed a seated cognitive test (stop signal task) followed by a reactive balance test. Reactive balance was assessed using a modified lean-and-release system where participants were required to step to regain balance following perturbation, or suppress a step if an obstacle was present. The stop signal task is a standardized cognitive test that provides a measure of the speed of response inhibition called the Stop Signal Reaction Time (SSRT). Muscle responses in the legs were compared between conditions where a step was allowed or blocked to quantify response inhibition of the step. The SSRT was significantly related to leg muscle suppression during balance recovery in the stance leg. Thus, participants that were better at inhibiting their responses in the stop signal task were also better at inhibiting an unwanted leg response in favor of grasping a supportive handle. The relationship between a seated cognitive test using finger responses and leg muscle suppression when a step was blocked indicates a context-independent, generalized capacity for response inhibition. This suggests that a simple cognitive test such as the stop signal task could be used clinically to predict an individual's capacity for adapting balance reactions and fall risk. The present results provide support for future studies, with larger samples, to verify this relationship between stop signal reaction time and leg response during balance recovery.

Vestibular attenuation to random-waveform galvanic vestibular stimulation during standing and treadmill walking.

The ability to move and maintain posture is critically dependent on motion and orientation information provided by the vestibular system. When this system delivers noisy or erred information it can, in some cases, be attenuated through habituation. Here we investigate whether multiple mechanisms of attenuation act to decrease vestibular gain due to noise added using supra-threshold random-waveform galvanic vestibular stimulation (GVS). Forty-five participants completed one of three conditions. Each condition consisted of two 4-min standing periods with stimulation surrounding a 1-h period of either walking with stimulation, walking without stimulation, or sitting quietly. An instrumented treadmill recorded horizontal forces at the feet during standing and walking. We quantified response attenuation to GVS by comparing vestibular stimulus-horizontal force gain between conditions. First stimulus exposure caused an 18% decrease in gain during the first 40 s of standing. Attenuation recommenced only when subjects walked with stimulation, resulting in a 38% decrease in gain over 60 min that did not transfer to standing following walking. The disparity in attenuation dynamics and absent carry over between standing and walking suggests that two mechanisms of attenuation, one associated with first exposure to the stimulus and another that is task specific, may act to decrease vestibulomotor gain.

Promoting Generalized Learning in Balance Recovery Interventions.

Recent studies have shown balance recovery can be enhanced via task-specific training, referred to as perturbation-based balance training (PBT). These interventions rely on principles of motor learning where repeated exposure to task-relevant postural perturbations results in more effective compensatory balance responses. Evidence indicates that compensatory responses trained using PBT can be retained for many months and can lead to a reduction in falls in community-dwelling older adults. A notable shortcoming with PBT is that it does not transfer well to similar but contextually different scenarios (e.g., falling sideways versus a forward trip). Given that it is not feasible to train all conditions in which someone could fall, this limited transfer presents a conundrum; namely, how do we best use PBT to appropriately equip people to deal with the enormous variety of fall-inducing scenarios encountered in daily life? In this perspective article, we draw from fields of research that explore how general learning can be promoted. From this, we propose a series of methods, gleaned from parallel streams of research, to inform and hopefully optimize this emerging field where people receive training to specifically improve their balance reactions.

Absence of Nonlinear Coupling Between Electric Vestibular Stimulation and Evoked Forces During Standing Balance.

The vestibular system encodes motion and orientation of the head in space and is essential for negotiating in and interacting with the world. Recently, random waveform electric vestibular stimulation has become an increasingly common means of probing the vestibular system. However, many of the methods used to analyze the behavioral response to this type of stimulation assume a linear relationship between frequencies in the stimulus and its associated response. Here we examine this stimulus-response frequency linearity to determine the validity of this assumption. Forty-five university-aged subjects stood on a force-plate for 4 min while receiving vestibular stimulation. To determine the linearity of the stimulus-response relationship we calculated the cross-frequency power coupling between a 0 and 25 Hz bandwidth limited white noise stimulus and induced postural responses, as measured using the horizontal forces acting at the feet. Ultimately, we found that, on average, the postural response to a random stimulus is linear across stimulation frequencies. This result supports the use of analysis methods that depend on the assumption of stimulus-response frequency linearity, such as coherence and gain, which are commonly used to analyze the body's response to random waveform electric stimuli.

Which Exercise Interventions Can Most Effectively Improve Reactive Balance in Older Adults? A Systematic Review and Network Meta-Analysis.

BACKGROUND: Reactive balance is the last line of defense to prevent a fall when the body loses stability, and beneficial effects of various exercise-based interventions on reactive balance in older adults have been reported. However, their pooled evidence on the relative effects has yet to be described. OBJECTIVE: To review and evaluate the comparative effectiveness of various exercise-based interventions on reactive balance in older adults. METHODS: Nine electronic databases and reference lists were searched from inception to August 2021. Eligibility criteria according to PICOS criteria were as follows: (1) population: older adults with the mean age of 65 years or above; (2) intervention and comparison: at least two distinct exercise interventions or one exercise intervention with a no-exercise controlled intervention (NE) compared in each trial; (3) outcome: at least one measure of reactive balance; (4) study: randomized controlled trial. The main network meta-analysis was performed on data from the entire older adult population, involving all clinical conditions as well as healthy older adults. Subgroup analyses stratified by characteristics of participants (healthy only) and reactive balance outcomes (simulated slip or trip while walking, simulated forward falls, being pushed or pulled, and movable platform) were also conducted. RESULTS: Thirty-nine RCTs (n = 1388) investigating 17 different types of exercise interventions were included in the network meta-analysis. Reactive balance training as a single intervention presented the highest probability (surface under the cumulative ranking (SUCRA) score) of being the best intervention for improving reactive balance and the greatest relative effects vs. NE in the entire sample involving all clinical conditions [SUCRA = 0.9; mean difference (95% Credible Interval): 2.7 (1.0 to 4.3)]. The results were not affected by characteristics of participants (i.e., healthy older adults only) or reactive balance outcomes. SUMMARY/CONCLUSION: The findings from the NMA suggest that a task-specific reactive balance exercise could be the optimal intervention for improving reactive balance in older adults, and power training can be considered as a secondary training exercise.

Variance based weighting of multisensory head rotation signals for verticality perception.

We tested the hypothesis that the brain uses a variance-based weighting of multisensory cues to estimate head rotation to perceive which way is up. The hypothesis predicts that the known bias in perceived vertical, which occurs when the visual environment is rotated in a vertical-plane, will be reduced by the addition of visual noise. Ten healthy participants sat head-fixed in front of a vertical screen presenting an annulus filled with coloured dots, which could rotate clockwise or counter-clockwise at six angular velocities (1, 2, 4, 6, 8, 16°/s) and with six levels of noise (0, 25, 50, 60, 75, 80%). Participants were required to keep a central bar vertical by rotating a hand-held dial. Continuous adjustments of the bar were required to counteract low-amplitude low-frequency noise that was added to the bar's angular position. During visual rotation, the bias in verticality perception increased over time to reach an asymptotic value. Increases in visual rotation velocity significantly increased this bias, while the addition of visual noise significantly reduced it, but did not affect perception of visual rotation velocity. The biasing phenomena were reproduced by a model that uses a multisensory variance-weighted estimate of head rotation velocity combined with a gravito-inertial acceleration signal (GIA) from the vestibular otoliths. The time-dependent asymptotic behaviour depends on internal feedback loops that act to pull the brain's estimate of gravity direction towards the GIA signal. The model's prediction of our experimental data furthers our understanding of the neural processes underlying human verticality perception.

Virtual signals of head rotation induce gravity-dependent inferences of linear acceleration.

KEY POINTS: Considerable debate exists regarding whether electrical vestibular stimuli encoded by vestibular afferents induce a net signal of linear acceleration, rotation or a combination of the two. This debate exists because an isolated signal of head rotation encoded by the vestibular afferents can cause perceptions of both linear and angular motion. We recorded participants' perceptions in different orientations relative to gravity and predicted their responses by modelling the effect of electrical vestibular stimuli on vestibular afferents and a current model of central vestibular processing. We show that, even if electrical vestibular stimuli are encoded as a net signal of head rotation, participants perceive both linear acceleration and rotation motions, provided the electrical stimulation-induced rotational vector has a component orthogonal to gravity. The emergence of a perception of linear acceleration from a single rotational input signal clarifies the origins of the neural mechanisms underlying electrical vestibular stimulation. ABSTRACT: Electrical vestibular stimulation (EVS) is an increasingly popular biomedical tool for generating sensations of virtual motion in humans, for which the mechanism of action is a topic of considerable debate. Contention surrounds whether the evoked vestibular afferent activity encodes a signal of net rotation and/or linear acceleration. Central processing of vestibular self-motion signals occurs through an internal representation of gravity that can lead to inferred linear accelerations in absence of a true inertial acceleration. Applying this model to virtual signals of rotation evoked by EVS, we predict that EVS will induce behaviours attributed to both angular and linear motion, depending on the head orientation relative to gravity. To demonstrate this, 18 subjects indicated their perceived motion during sinusoidal EVS when in one of four head/body positions orienting the gravitational vector parallel or orthogonal to the EVS rotation vector. During stimulation, participants selected one simulated movement from seven that corresponded best to what they perceived. Participants' responses in each orientation were predicted by a model combining the influence of EVS on vestibular afferents with known mechanisms of vestibular processing. When the EVS rotation vector had a component orthogonal to gravity, human perceptual responses were consistent with a non-zero central estimate of interaural or superior-inferior linear acceleration. The emergence of a perception of linear acceleration from a single rotational input signal clarifies the origins of the neural mechanisms underlying EVS, which has important implications for its use in human biomedical or sensory augmentation applications.

Cerebellar Degeneration Increases Visual Influence on Dynamic Estimates of Verticality.

Our perception of verticality relies on combining sensory information from multiple sources. Neuronal recordings in animals implicate the cerebellum in the process, yet disease of the human cerebellum was not found to affect this perception. Here we show that a perceptual disturbance of verticality is indeed present in people with a genetically determined and pure form of cerebellar degeneration (spinocerebellar ataxia type 6; SCA 6), but is only revealed under dynamic visual conditions. Participants were required to continuously orient a visually displayed bar to vertical while the bar angle was perturbed by a low-frequency random signal and a random dot pattern rotated in their visual periphery. The random dot pattern was rotated at one of two velocities (4°/s and 16°/s), traveling with either coherent or noisy motion. Perceived vertical was biased by visual rotation in healthy participants, particularly in a more elderly group, but SCA 6 participants were biased more than both groups. The bias was reduced by visual noise, but more so for SCA 6 participants than young controls. Distortion of verticality by visual rotation stems from the stimulus creating an illusion of self-rotation. We modeled this process using a maximum-likelihood sensory cue-combination model operating on noisy visual- and vestibular-rotation signals. The observed effects of visual rotation and visual noise could be compellingly explained by cerebellar degeneration, and to a lesser extent aging, causing an increase in central vestibular noise. This is consistent with the human cerebellum operating on dynamic vestibular signals to inform the process that estimates which way is up.

Forecast or Fall: Prediction's Importance to Postural Control.

To interact successfully with an uncertain environment, organisms must be able to respond to both unanticipated and anticipated events. For unanticipated events, organisms have evolved stereotyped motor behaviors mapped to the statistical regularities of the environment, which can be trigged by specific sensory stimuli. These "reflexive" responses are more or less hardwired to prevent falls and represent, maybe, the best available solution to maintaining posture given limited available time and information. With the gift of foresight, however, motor behaviors can be tuned or prepared in advance, improving the ability of the organism to compensate for, and interact with, the changing environment. Indeed, foresight's improvement of our interactive capacity occurs through several means, such as better action selection, processing, and conduction delay compensation and by providing a prediction with which to compare our actual behaviors to, thereby facilitating error identification and learning. Here we review the various roles foresight (prediction) plays in maintaining our postural equilibrium. We start by describing some of the more recent findings related to the prediction of instability. Specifically, we cover recent advancements in the understanding of anticipatory postural behaviors that are used broadly to stabilize volitional movement and compensate for impending postural disturbances. We also describe anticipatory changes in the state, or set, of the nervous system that may facilitate anticipatory behaviors. From changes in central set, we briefly discuss prediction of postural instability online before moving into a discussion of how predictive mechanisms, such as internal models, permit us to tune, perhaps our highest level predictive behaviors, namely the priming associated with motor affordances. Lastly, we explore methods best suited to expose the contribution of prediction to postural equilibrium control across a variety of contexts.

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.

Comparison of motor skill learning, grip strength and memory recall on land and in chest-deep water.

Immersion in chest-deep water may augment explicit memory in healthy adults however, there is limited information on how this environment might affect implicit memory or motor learning. The purpose of this study was to compare the speed and accuracy for learning a motor skill on land and in chest-deep water. Verbal word recall and grip strength were included to gain a more complete understanding of the intervention. Sixty-two younger adults (age = 23.3 ± 3.59 yrs.) were randomly assigned to either a water group immersed to the xiphoid or a land group. Participants in both groups completed the same eight practice trials of a mirror-drawing task on two separate days. Outcome measures for this task included time and error numbers to complete each drawing. The number of words recalled using a 12 word recall test, and peak grip strength using a hand dynamometer were measured each day of testing. The influence of environment and repeated practice on each outcome measure were assessed with an analysis of variance and effect sizes (ES). Time and errors for both groups significantly decreased with practice (p < 0.01, ES = 0.11-0.28), however the drawing time was greater in water than on land for trials 1, 5, and 6 (ES = 0.50-0.55). There was a 7% increase in words recalled (9.24 ± 1.19 vs 8.60 ± 1.19) and a 16% increase in grip strength (405 ± 104 vs 342 ± 83) for water than land groups (ES 0.54-0.64). Healthy adults in chest-deep water and on land display comparable mirror-drawing speed and accuracy after minimal practice. Curiously, water immersion may augment verbal word recall and grip strength abilities.

Down regulation of vestibular balance stabilizing mechanisms to enable transition between motor states.

The neural control of transition between posture and movement encompasses the regulation of reflex-stabilizing mechanisms to enable motion. Optimal feedback theory suggests that such transitions require the disengagement of one motor control policy before the implementation of another. To test this possibility, we investigated the continuity of the vestibular control of balance during transitions between quiet standing and locomotion and between two standing postures. Healthy subjects initiated and terminated locomotion or shifted the distribution of their weight between their feet, while exposed to electrical vestibular stimuli (EVS). The relationship between EVS and ground reaction forces was quantified using time-frequency analyses. Discontinuities corresponding to null coherence periods were observed preceding the onset of movement initiation and during the step preceding locomotion termination. These results show humans interrupt the vestibular balance stabilizing mechanisms to transition between motor states, suggesting a discrete change between motor control policies, as predicted by optimal feedback theory.

Rapid limb-specific modulation of vestibular contributions to ankle muscle activity during locomotion.

KEY POINTS: The vestibular influence on human walking is phase-dependent and modulated across both limbs with changes in locomotor velocity and cadence. Using a split-belt treadmill, we show that vestibular influence on locomotor activity is modulated independently in each limb. The independent vestibular modulation of muscle activity from each limb occurs rapidly at the onset of split-belt walking, over a shorter time course relative to the characteristic split-belt error-correction mechanisms (i.e. muscle activity and kinematics) associated with locomotor adaptation. Together, the present results indicate that the nervous system rapidly modulates the vestibular influence of each limb separately through processes involving ongoing sensory feedback loops. These findings help us understand how vestibular information is used to accommodate the variable and commonplace demands of locomotion, such as turning or navigating irregular terrain. ABSTRACT: During walking, the vestibular influence on locomotor activity is phase-dependent and modulated in both limbs with changes in velocity. It is unclear, however, whether this bilateral modulation is due to a coordinated mechanism between both limbs or instead through limb-specific processes that remain masked by the symmetric nature of locomotion. Here, human subjects walked on a split-belt treadmill with one belt moving at 0.4 m s-1 and the other moving at 0.8 m s-1 while exposed to an electrical vestibular stimulus. Muscle activity was recorded bilaterally around the ankles of each limb and used to compare vestibulo-muscular coupling between velocity-matched and unmatched tied-belt walking. In general, response magnitudes decreased by ∼20-50% and occurred ∼13-20% earlier in the stride cycle at the higher belt velocity. This velocity-dependent modulation of vestibular-evoked muscle activity was retained during split-belt walking and was similar, within each limb, to velocity-matched tied-belt walking. These results demonstrate that the vestibular influence on ankle muscles during locomotion can be adapted independently to each limb. Furthermore, modulation of vestibular-evoked muscle responses occurred rapidly (∼13-34 strides) after onset of split-belt walking. This rapid adaptation contrasted with the prolonged adaptation in step length symmetry (∼128 strides) as well as EMG magnitude and timing (∼40-100 and ∼20-70 strides, respectively). These results suggest that vestibular influence on ankle muscle control is adjusted rapidly in sensorimotor control loops as opposed to longer-term error correction mechanisms commonly associated with split-belt adaptation. Rapid limb-specific sensorimotor feedback adaptation may be advantageous for asymmetric overground locomotion, such as navigating irregular terrain or turning.

Vestibular contribution to balance control in the medial gastrocnemius and soleus.

The soleus (Sol) and medial gastrocnemius (mGas) muscles have different patterns of activity during standing balance and may have distinct functional roles. Using surface electromyography we previously observed larger responses to galvanic vestibular stimulation (GVS) in the mGas compared with the Sol muscle. However, it is unclear whether this difference is an artifact that reflects limitations associated with surface electromyography recordings or whether a compensatory balance response to a vestibular error signal activates the mGas to a greater extent than the Sol. In the present study, we compared the effect of GVS on the discharge behavior of 9 Sol and 21 mGas motor units from freely standing subjects. In both Sol and mGas motor units, vestibular stimulation induced biphasic responses in measures of discharge timing [11 ± 5.0 (mGas) and 5.6 ± 3.8 (Sol) counts relative to the sham (mean ± SD)], and frequency [0.86 ± 0.6 Hz (mGas), 0.34 ± 0.2 Hz (Sol) change relative to the sham]. Peak-to-trough response amplitudes were significantly larger in the mGas (62% in the probability-based measure and 160% in the frequency-based measure) compared with the Sol (multiple P < 0.05). Our results provide direct evidence that vestibular signals have a larger influence on the discharge activity of motor units in the mGas compared with the Sol. More tentatively, these results indicate the mGas plays a greater role in vestibular-driven balance corrections during standing balance.