ANKLE TORQUE VARIANCE IS A BETTER INDICATOR OF BALANCE CONTROL PERFORMANCE THAN PLANTAR PERCEPTUAL SENSITIVITY THRESHOLD.

We explored whether ankle torque variability or plantar perceptual threshold explains human balance control more effectively. We hypothesized that ankle torque variance is a better indicator of center of pressure (COP) velocity variance than plantar perceptual sensitivity. Two conditions were tested: loaded (23 kg vest added) and unloaded, as loading should diminish plantar sensitivity and increase COP velocity variability. We created a linear feedback model to assess the noise change in the sensorimotor loop induced by loading. Plantar sensitivity was quantified using a psychophysical approach while participants stood barefoot. A linear motor applied a force impulse on the participant's heel. A 'yes-no' method of limits was selected to identify plantar sole sensory thresholds in both conditions. We observed reduced plantar sensitivity in loaded compared to unloaded conditions. In the loaded condition, participants exhibited greater COP velocity variance, with significant positive Pearson's correlations confirming a substantial association between ankle torque and COP velocity variances for both loaded (variance accounted for (VAR): r2 = 44.56%, p = 0.018) and unloaded conditions (VAF: r2 = 58.83 %, p = 0.004). No significant correlation existed between COP velocity variance and plantar sensitivity threshold for both loaded (VAF: r2 = 0.002 %, p = 0.99) and unloaded conditions (VAF: r2 = 21.81%, p = 0.35). The model confirmed a ~88% rise in sensorimotor loop noise in the loaded condition. Ankle torque variance assesses the precision of non-perceptual and perceptual detection mechanisms in evaluating whole-body motions and the accuracy in converting sensory cues into ankle torque.

The relationship between back handspring step out performance and take-off technique in female gymnasts.

Although the back handspring step out (BHS) is a foundational skill in balance beam routines, it can be performed using different take-off techniques. Back injuries are highly prevalent in the BHS due to the combination of high spine extension and joint loading. However, it is unclear which technique minimises injury risk or leads to better BHS performance. The purpose of the study was to identify techniques used for the BHS take-off and analyse the resulting BHS performance. Gymnasts were found to use either: Simultaneous Flexion-trunk and knees flex at the same time; Sequential Flexion-trunk reaches its maximum flexion followed by knee flexion; or Double-Bounce-knees and trunk both flex and then the knees extend and flex again. To assess performance, point deductions were calculated, and dynamic balance, ground reaction forces (GRFs) and relevant joint angles were analysed. The techniques had no differences in point deductions or dynamic balance, but there were differences in GRFs, spine extension and knee flexion. The Sequential Flexion technique had the lowest spine extension, which potentially reduces back injuries and the lowest knee flexion, which is a BHS requirement. These results support the use of Sequential Flexion technique when performing the BHS.

Single session of direction-specific training using auditory cues improves anticipatory postural adjustments to lateral perturbations.

When exposed to a predictable external perturbation, humans typically generate anticipatory postural adjustments (APAs) to minimize potential body disturbance. After a single session of training, individuals demonstrated the ability to rely solely on an auditory cue to elicit appropriate APAs in response to an external postural perturbation. However, whether the generation of APAs requires directional specific training remains unclear. The aim of this study was to assess whether directional-specific training with auditory cues is necessary for the generation of appropriate APA responses. Ten young adults were exposed to external perturbations targeting either their left or right shoulders, with or without an auditory cue prior to the physical impact. Electromyography (EMG) activities of sixteen trunk and leg muscles and center-of-pressure (COP) displacements were recorded and analyzed during the anticipatory and compensatory phases of postural control. Outcome measures included the latencies and integrals of muscle activities, COP displacements, and indices of co-contraction and reciprocal activation of muscles. The results revealed that, after training with right-side perturbations accompanied by an auditory cue, young adults exhibited earlier and more efficient APA responses to right-side perturbations relying only on the auditory cue. Additionally, they displayed earlier APA responses in some muscles to left-side perturbations, although these responses were less efficient. Our findings suggest that young adults could generate effective APAs to external perturbations relying on an auditory cue after a single training session; however, these responses were directional specific.

Are changes in pain intensity related to changes in balance control in individuals with chronic non-specific low back pain? A systematic review and meta-analysis.

PURPOSE: The aim of this study is to summarize the evidence regarding whether pain reduction in individuals with chronic non-specific low back pain (CNSLBP) following conservative interventions is related to corresponding improvements in balance control. METHODS: Randomized controlled trials were identified from 5 databases (MEDLINE, Cochrane Library, Embase, Web of Science, and PsycINFO). Two reviewers independently screened and identified relevant studies that investigated the effects of nonsurgical or nonpharmacological CNSLBP treatments on both pain intensity and balance control. Meta-regression analyses were performed to establish the associations between post-treatment changes in these 2 variables. RESULTS: 31 studies involving 1280 participants with CNSLBP were included. Moderate-quality evidence suggested that pain reduction was associated with and explained 34%-45% of decreases in body sway, as measured by center-of-pressure (CoP) area and CoP velocity with eyes open. However, no significant association was observed between pain reduction and CoP area or velocity in anteroposterior/mediolateral directions. Similarly, there was no significant association between pain reduction and CoP distance or radius. Low-quality evidence indicated that pain relief explained a 15% improvement in one-leg stance with eyes open but not in the eyes-closed condition. Additionally, very low-quality evidence suggested that pain relief explained a 44% decrease in the static anteroposterior stability index with eyes closed but not in the eyes-open, mediolateral, or overall conditions. Furthermore, low-quality evidence indicated that reduced pain was associated with and accounted for 25%-43% of the improved composite and posteromedial scores of the star-excursion balance test, rather than the anterior and posterolateral scores. CONCLUSION: Depending on the type of balance assessment, pain relief following conservative interventions may slightly to moderately enhance balance control in individuals with CNSLBP. Clinicians should pay close attention to the balance control in patients with CNSLBP, particularly among older adults.

Gray Matter Volumes Mediate the Relationship Between Disease Duration and Balance Control Performance in Chronic Ankle Instability.

The relationship between structural changes in the cerebral gray matter and diminished balance control performance in patients with chronic ankle instability (CAI) has remained unclear. This paper aimed to assess the difference in gray matter volume (GMV) between participants with CAI and healthy controls (HC) and to characterize the role of GMV in the relationship between disease duration and balance performance in CAI. 42 participants with CAI and 33 HC completed the structural brain MRI scans, one-legged standing test, and Y-balance test. Regional GMV was measured by applying voxel-based morphometry methods. The result showed that, compared with HC, participants with CAI exhibited lower GMV in multiple brain regions (familywise error [FWE] corrected p < 0.021). Within CAI only, but not in HC, lower GMV in the thalamus (ß = -0.53, p = 0.003) and hippocampus (ß = -0.57, p = 0.001) was associated with faster sway velocity of the center of pressure (CoP) in eyes closed condition (i.e., worse balance control performance). The GMV in the thalamus (percentage mediated [PM] = 32.02%; indirect effect ß = 0.119, 95% CI = 0.003 to 0.282) and hippocampus (PM = 33.71%; indirect effect ß = 0.122, 95% CI = 0.005 to 0.278) significantly mediated the association between the disease duration and balance performance. These findings suggest that the structural characteristics of the supraspinal elements is critical to the maintenance of balance control performance in individuals suffering from CAI, which deserve careful consideration in the management and rehabilitation programs in this population.

Reliability and validity of the ratings of perceived stability scale as a measure of balance exercise intensity in persons with multiple sclerosis.

PURPOSE: The study aimed to determine the test-retest reliability and concurrent validity of the Ratings of Perceived Stability (RPS) scale as a measure of balance exercise intensity in persons with multiple sclerosis (MS). METHODS: Twenty participants with MS (mean age: 58.1 ± 15.29; 60% female) performed 14 balance tasks on two separate occasions wearing body-worn inertial sensors and rated their perceived stability for each task. Sensor data included sway velocity and angle, gait speed, turn velocity, and lean angle. Intraclass correlation coefficients (ICC) and Spearman rank correlations (rs) were employed to assess reliability and validity, respectively. RESULTS: The RPS showed good to excellent test-retest reliability (ICC> 0.75) on 12 out of the 14 tasks. The stability ratings revealed moderate relationships with postural sway outcomes in static balance tasks (rs: 0.49 to 0.77) and weak to moderate associations with gait speed (rs: -0.69 to -0.14). Ratings of stability were also strongly related to turn velocity (rs= -0.77) and moderately related to lean angle (rs= 0.58). CONCLUSIONS: The RPS scale offers a promising clinical tool to measure balance exercise intensity for persons with MS. This standardized scale allows for tailored balance training with a novel means for exercise monitoring and progression in this population.

The Ratings of Perceived Stability (RPS) scale is a reliable and valid measure for determining balance exercise intensity in persons with multiple sclerosis.The RPS scale can contribute to clear evaluation, description, and replication of balance training intensity in future balance interventions.

Identifying neural correlates of balance impairment in traumatic brain injury using partial least squares correlation analysis.

Objective.Balance impairment is one of the most debilitating consequences of traumatic brain injury (TBI). To study the neurophysiological underpinnings of balance impairment, the brain functional connectivity during perturbation tasks can provide new insights. To better characterize the association between the task-relevant functional connectivity and the degree of balance deficits in TBI, the analysis needs to be performed on the data stratified based on the balance impairment. However, such stratification is not straightforward, and it warrants a data-driven approach.Approach.We conducted a study to assess the balance control using a computerized posturography platform in 17 individuals with TBI and 15 age-matched healthy controls. We stratified the TBI participants into balance-impaired and non-impaired TBI usingk-means clustering of either center of pressure (COP) displacement during a balance perturbation task or Berg Balance Scale score as a functional outcome measure. We analyzed brain functional connectivity using the imaginary part of coherence across different cortical regions in various frequency bands. These connectivity features are then studied using the mean-centered partial least squares correlation analysis, which is a multivariate statistical framework with the advantage of handling more features than the number of samples, thus making it suitable for a small-sample study.Main results.Based on the nonparametric significance testing using permutation and bootstrap procedure, we noticed that the weakened theta-band connectivity strength in the following regions of interest significantly contributed to distinguishing balance impaired from non-impaired population, regardless of the type of stratification:left middle frontal gyrus, right paracentral lobule, precuneus, andbilateral middle occipital gyri. Significance.Identifying neural regions linked to balance impairment enhances our understanding of TBI-related balance dysfunction and could inform new treatment strategies. Future work will explore the impact of balance platform training on sensorimotor and visuomotor connectivity.

Reciprocal Inhibition and Coactivation of Ankle Muscles in Low- and High-Velocity Forward and Backward Perturbations.

Reciprocal inhibition and coactivation are strategies of the central nervous system used to perform various daily tasks. In automatic postural responses (APR), coactivation is widely investigated in the ankle joint muscles, however reciprocal inhibition, although clear in manipulative motor actions, has not been investigated in the context of APRs. The aim was to identify whether reciprocal inhibition can be observed as a strategy in the recruitment of gastrocnemius Medialis (GM), Soleus (So) and Tibialis Anterior (TA) muscles in low- and high-velocity forward and backward perturbations. We applied two balance perturbations with a low and a high velocity of displacement of the movable platform in forward and backward conditions and we evaluated the magnitude and latency time of TA, GM and So activation latency, measured by electromyography (EMG). In forward perturbations, coactivation of the three muscles was observed, with greater activation amplitude of the GM and lesser amplitude of the So and TA muscles. For backward, the pattern of response observed was activation of the TA muscle, a decrease in the EMG signal, which characterizes reciprocal inhibition of the GM muscle and maintenance of the basal state of the So muscle. This result indicates that backward perturbations are more challenging.

Multimodal training protocols on unstable rather than stable surfaces better improve dynamic balance ability in older adults.

BACKGROUND: There has been growing interest in using unstable devices in training protocols. This study aimed to assess the effectiveness of two multimodal exercise interventions (i.e., on stable and unstable surfaces) on dynamic balance control and lower limb strength in older adults. METHODS: Sixty-two older adults were randomly assigned to two intervention groups (N = 20, stable group; N = 19, unstable group), and to a control group (N = 18). In this single-blinded randomized controlled study, the two intervention groups underwent a 12-week training program twice a week for 45 min, consisting of strength and balance exercises. The stable (ST) group performed the training program over stable surfaces, while the unstable (UNST) group over unstable surfaces. Dynamic balance was assessed by computing the center of pressure (CoP) trajectory while a driven movable platform induced an unexpected perturbation of the base of support. Specifically, we considered the following CoP-related parameters within a 2.5-s temporal window from the beginning of the perturbation: displacement (Area95), mean velocity (Unit Path), anterior-posterior first peak (FP), post perturbation variability (PPV), and maximal oscillations (ΔCoPMax). The dominant quadriceps strength was measured through an isometric maximal voluntary contraction on an instrumented chair. RESULTS: Four out of five CoP-related parameters (i.e., Area95, Unit Path, ΔCoPMax, and PPV) significantly improved in the UNST group from a minimum of 14.28% (d = 0.44) to a maximum of 52.82% (d = 0.58). The ST group significantly improved only in two (i.e., ΔCoPMax, and PPV) out of five CoP-related parameters with an enhancement of 12.48% (d = 0.68) and 19.10% (d = 1.06). Both intervention groups increased the maximal isometric quadriceps strength (UNST:17.27%, d = 0.69; ST:22.29%, d = 0.98). The control group did not show changes in any of the parameters considered. CONCLUSIONS: Stable surfaces promoted faster increments of muscular strength. Unstable surfaces were more effective in enhancing dynamic balance efficiency. These findings suggested the employment of multimodal training on unstable rather than stable surfaces to potentially lower the incidence of falls in older adults. TRIAL REGISTRATION: NCT05769361, retrospectively registered 13 March 2023, https://clinicaltrials.gov/study/NCT05769361?lat=45.3661864&lng=11.8209139&locStr=Padova,%20Italy&distance=50&page=11&rank=107 .

Differences in left and right lower limb control strategies in coping with visual tracking tasks during bipedal standing.

Introduction: Differences in motor control between the lower limbs may influence the risk of sports injury and recovery from rehabilitation. In this study, differences in the visual feedback ability of the left and right lower limbs were assessed using visual target tracking tasks. Methods: Thirty-four healthy young subjects (aged 20.4 ± 1.2 years) were asked to move their bodies back and forth while tracking a visual target displayed on a monitor in front of them for 30 s. The two target motions were sinusoidal (i.e., predictable patterns) and more complex (random) patterns. To assess the ability of the lower limbs to follow visual target tracking, antero-posterior CoP (right limb, CoPap-r; left limb, CoPap-l) and medio-lateral CoP (right limb, CoPml-r; left limb, CoPml-l) data were measured using a stabilometer. Tracking ability by visual feedback ability was calculated as the difference in displacement between the target signal and the trajectories of the right and left pressure centers as trapezoidal areas, and a smaller sum of area (SoA) over the entire measurement time was defined as a greater tracking ability. Results: Regarding the SoA in the anterior-posterior CoP, the mean SoA in the sinusoidal and random tasks was significantly lower in the CoP-r data than in the CoP-l data, indicating that the right lower limb had a more remarkable ability to follow visual target tracking. Regarding the SoA in the medial-lateral direction (CoP), the mean SoA in the sinusoidal and random tasks did not significantly differ between the two legs. Discussion: The right lower limb may have a tracking function activated by the target signal when responding to visual stimuli. Identifying the motor strategies of each lower limb in response to visual stimuli will not only help identify potential differences between each lower limb but also suggest the possibility of enhancing the role of each lower limb in balance control.

Trunk Instability in the Pitch, Yaw, and Roll Planes during Clinical Balance Tests: Axis Differences and Correlations to vHIT Asymmetries Following Acute Unilateral Vestibular Loss.

BACKGROUND: Clinical dynamic posturography concentrates on the pitch and roll but not on the yaw plane instability measures. This emphasis may not represent the axis instability observed in clinical stance and gait tasks for patients with balance deficits in comparison to healthy control (HC) subjects, nor the expected instability based on correlations with vestibulo-ocular reflex (VOR) deficits. To examine the axis stability changes with vestibular loss, we measured trunk sway in all three directions (pitch, roll, and yaw) during the stance and gait tasks of patients with acute unilateral vestibular neuritis (aUVN) and compared the results with those of HC. Concurrent changes in VORs were also examined and correlated with trunk balance deficits. METHODS: The results of 11 patients (mean age of 61 years) recorded within 6 days of aUVN onset were compared within those of 8 age-matched healthy controls (HCs). All subjects performed a two-legged stance task-standing with eyes closed on foam (s2ecf), a semi-gait task-walking eight tandem steps (tan8), and four gait tasks-walking 3 m with head rotating laterally, pitching, or eyes closed (w3hr, w3hp, w3ec), and walking over four barriers 24 cm high, spaced 1 m apart (barr). The tasks' peak-to-peak yaw, pitch and roll angles, and angular velocities were measured with a gyroscope system (SwayStarTM) mounted at L1-3 and combined into three, axis-specific, balance control indexes (BCI), using angles (a) for the tandem gait and barriers task, and angular velocities (v) for all other tasks, as follows: axis BCI = (2 × 2ecf)v + 1.5 × (w3hr + w3hp + w3ec)v + (tan8 + 12 × barr)a. RESULTS: Yaw and pitch BCIs were significantly (p ≤ 0.004) greater (88 and 30%, respectively) than roll BCIs for aUVN patients. For HCs, only yaw but not pitch BCIs were greater (p = 0.002) than those of roll (72%). The order of BCI aUVN vs. HC differences was pitch, yaw, and roll at 55, 44, and 31%, respectively (p ≤ 0.002). This difference with respect to roll corresponded to the known greater yaw plane than roll plane asymmetry (40 vs. 22%) following aUVN based on VOR responses. However, the lower pitch plane asymmetry (3.5%) in VOR responses did not correspond with the pitch plane instability observed in the balance control tests. The increases in pitch plane instability in UVL subjects were, however, highly correlated with those of roll and yaw. CONCLUSIONS: These results indicate that greater yaw than pitch and roll trunk motion during clinical balance tasks is common for aUVN patients and HCs. However, aUVN leads to a larger increase in pitch than yaw plane instability and a smaller increase in roll plane instability. This difference with respect to roll corresponds to the known greater yaw plane than roll plane asymmetry (40 vs. 22%) following aUVN observed in VOR responses. However, the lower pitch plane asymmetry (3.5%) in VOR responses does not correspond with the enhanced movements in the pitch plane, observed in balance control tasks. Whether asymmetries in vestibular-evoked myogenic potentials (Vemps) are better correlated with the deficits in pitch plane balance control remains to be investigated. The current results provide a strong rationale for the clinical testing of directional specific balance responses, especially yaw and pitch, and the linking of balance results for yaw and roll to VOR asymmetries.

Exploring the effect of human-drone communication modality on safety and balance control in virtual construction environments.

This study examines the impact of Human-Drone Interaction (HDI) modalities on construction workers' safety and balance control within virtual environments. Utilising virtual reality (VR) simulations, the study explored how gesture and speech-based communications influence workers' physical postures and balance, contrasting these modalities with a non-interactive control group. One hundred participants were recruited, and their movements and balance control were tracked using motion sensors while they interacted with virtual drones through either gesture, speech, or without communication. Results showed that interactive modalities significantly improved balance control and reduced the risk of falls, suggesting that advanced HDI can enhance safety on construction sites. However, speech-based interaction increased cognitive workload, highlighting a trade-off between physical safety and mental strain. These findings underscore the potential of integrating intuitive communication methods into construction operations, although further research is needed to optimise these interactions for long-term use and in diverse noise environments.

This study examines the impact of Human-Drone Interaction (HDI) modalities on construction workers' safety and balance control within virtual environments with a human subject experiment. Results showed that interactive modalities significantly improved balance control and reduced the risk of falls.

Balance Control Deficits are Associated With Diminished Ankle Force Sense, Not Position Sense, in Athletes with Chronic Ankle Instability.

OBJECTIVES: To compare balance control and ankle proprioception between athletes with and without chronic ankle instability (CAI). A further objective was to explore the relationship between balance control performance and ankle proprioception in athletes with CAI. DESIGN: Cross-sectional study. SETTINGS: Sports Rehabilitation Laboratory. PARTICIPANTS: Eighty-eight recreational athletes (47 CAI and 41 healthy control) were recruited. INTERVENTIONS: No applicable. MAIN OUTCOME MEASURES: Balance control performance was assessed using the sway velocity of the center of the pressure during the one-leg standing tasks. Ankle proprioception, including joint position sense and force sense, were tested using absolute error (AE) associated with joint position reproduction and force reproduction tasks in 4 directions, that is, plantarflexion, dorsiflexion, inversion, and eversion. RESULTS: Athletes with CAI performed significantly worse than those without CAI in balance control tasks. In addition, CAI athletes showed significantly worse joint position sense and force sense in all 3 movement directions tested (plantarflexion, inversion, and eversion). Correlation analysis showed that the AE of the plantarflexion force sense was significantly moderately correlated with medial-lateral sway velocity in the one-leg standing with eyes open and closed conditions (r=.372-.403, P=.006-.012), and the AE of inversion force sense was significantly moderately correlated with medial-lateral sway velocity in the one-leg standing with eyes open (r=.345, P=.018) in athletes with CAI, but the joint position sense measures were not (all P>0.05). CONCLUSIONS: Athletes with CAI showed significantly impaired balance control performance and diminished ankle proprioception. Deficit in force sense was deemed as a moderate predictor of one-leg standing balance control deficits in athletes with dominant-side injury CAI, whereas ankle position sense may be a small predictor.

How older adults maintain lateral balance while walking on narrowing paths.

BACKGROUND: Older adults have difficulty maintaining side-to-side balance while navigating daily environments. Losing balance in such circumstances can lead to falls. We need to better understand how older adults adapt lateral balance to navigate environment-imposed task constraints. RESEARCH QUESTION: How do older adults adjust mediolateral balance while walking along continually-narrowing paths, and what are the stability implications of these adjustments? METHODS: Eighteen older (71.6±6.0 years) and twenty younger (21.7±2.6 years) healthy adults traversed 25 m-long paths that gradually narrowed from 45 cm to 5 cm. Participants switched onto an adjacent path when they chose. We quantified participants' lateral center-of-mass dynamics and lateral Margins of Stability (MoSL) as paths narrowed. We quantified lateral Probability of Instability (PoIL) as the probability that participants would take a laterally unstable (MoSL<0) step as they walked. We also extracted these outcomes where participants switched paths. RESULTS: As paths narrowed, all participants exhibited progressively smaller average MoSL and increasingly larger PoIL. However, their MoSL variability was largest at both the narrowest and widest path sections. Older adults exhibited consistently both larger average and more variable MoSL across path widths. Taken into account together, these resulted in either comparable or somewhat larger PoIL as paths narrowed. Older adults left the narrowing paths sooner, on average, than younger. As they did so, older adults exhibited significantly larger average and more variable MoSL, but somewhat smaller PoIL than younger. SIGNIFICANCE: Our results directly challenge the predominant interpretation that larger average MoSL indicate "greater stability", which we argue is inconsistent with the principles underlying its derivation. In contrast, analyzing step-to-step gait dynamics, together with estimating PoIL allows one to properly quantify instability risk. Furthermore, the adaptive strategies uncovered using these methods suggest potential targets for future interventions to reduce falls in older adults.

Cross-frequency modulation of postural fluctuations and scalp EEG in older adults: error amplification feedback for rapid balance adjustments.

Virtual error amplification (VEA) in visual feedback enhances attentive control over postural stability, although the neural mechanisms are still debated. This study investigated the distinct cortical control of unsteady stance in older adults using VEA through cross-frequency modulation of postural fluctuations and scalp EEG. Thirty-seven community-dwelling older adults (68.1 ± 3.6 years) maintained an upright stance on a stabilometer while receiving either VEA or real error feedback. Along with postural fluctuation dynamics, phase-amplitude coupling (PAC) and amplitude-amplitude coupling (AAC) were analyzed for postural fluctuations under 2 Hz and EEG sub-bands (theta, alpha, and beta). The results revealed a higher mean frequency of the postural fluctuation phase (p = .005) and a greater root mean square of the postural fluctuation amplitude (p = .003) with VEA compared to the control condition. VEA also reduced PAC between the postural fluctuation phase and beta-band EEG in the left frontal (p = .009), sensorimotor (p = .002), and occipital (p = .018) areas. Conversely, VEA increased the AAC of posture fluctuation amplitude and beta-band EEG in FP2 (p = .027). Neither theta nor alpha band PAC or AAC were affected by VEA. VEA optimizes postural strategies in older adults during stabilometer stance by enhancing visuospatial attentive control of postural responses and facilitating the transition of motor states against postural perturbations through a disinhibitory process. Incorporating VEA into virtual reality technology is advocated as a valuable strategy for optimizing therapeutic interventions in postural therapy, particularly to mitigate the risk of falls among older adults.

Impact of visual rotations on heading direction and center of mass control during steady-state gait.

Visual information is essential to navigate the environment and maintain postural stability during gait. Visual field rotations alter the perceived heading direction, resulting in gait trajectory deviations, known as visual coupling. It is unclear how center of mass (CoM) control relative to a continuously changing base of support (BoS) is adapted to facilitate visual coupling. This study aimed to characterize mediolateral (ML) balance control during visual coupling in steady-state gait. Sixteen healthy participants walked on an instrumented treadmill, naive to sinusoidal low-frequency (0.1 Hz) rotations of the virtual environment around the vertical axis. Rotations were continuous with 1) high or 2) low amplitude or were 3) periodic with 10-s intervals. Visual coupling was characterized with cross-correlations between CoM trajectory and visual rotations. Balance control was characterized with the ML margin of stability (MoSML) and by quantifying foot placement control as the relation between CoM dynamics and lateral foot placement. Visual coupling was strong on a group level (continuous low: 0.88, continuous high: 0.91, periodic: 0.95) and moderate to strong on an individual level. Higher rotation amplitudes induced stronger gait trajectory deviations. The MoSML decreased toward the deviation direction and increased at the opposite side. Foot placement control was similar compared with regular gait. Furthermore, pelvis and foot reorientation toward the rotation direction was observed. We concluded that visual coupling was facilitated by reorientating the body and shifting the extrapolated CoMML closer to the lateral BoS boundary toward the adjusted heading direction while preserving CoM excursion and foot placement control.NEW & NOTEWORTHY Healthy, naive participants were unaware of subtle, low-frequency rotations of the visual field but still coupled their gait trajectory to a rotating virtual environment. In response, participants decreased their margin of stability toward the new heading direction, without changing the center of mass excursion magnitude and foot placement strategy.

Sensory integration and segmental control of posture during pregnancy.

BACKGROUND: Approximately 25% of pregnant people fall, yet the underlying mechanisms of this increased fall-risk remain unclear. Prior studies examining pregnancy and balance have utilized center of pressure analyses and reported mixed results. The purpose of this study was to examine sensory and segmental contributions to postural control throughout pregnancy using accelerometer-based measures of sway. METHODS: Thirty pregnant people (first trimester: n = 10, second trimester: n = 10, third trimester: n = 10) and 10 healthy, nonpregnant control people stood quietly for one minute in four conditions: eyes open on a firm surface, eyes closed on a firm surface, eyes open on a foam pad, and eyes closed on foam. Postural sway was quantified using the root mean square accelerations in the anterior-posterior and medial-lateral directions from an inertial sensor at the lumbar region. Sensory sway ratios, segmental coherence and co-phase, were calculated to assess sensory contributions and segmental control, respectively. FINDINGS: Pregnant people did not display greater sway compared to healthy, nonpregnant controls. There were no group differences in vestibular, visual, or somatosensory sway ratios, and no significant differences in balance control strategies between pregnant and nonpregnant participants across sensory conditions. INTERPRETATION: The small effects observed here contrast prior studies and suggest larger, definitive studies are needed to assess the effect of pregnancy on postural control. This study serves as a preliminary exploration of pregnant sensory and segmental postural control and highlights the need for future to hone the role of balance in fall risk during pregnancy.

Brain and brawn in balance: Central processing speed and muscle torque development speed are independently associated with the ability to recover balance with feet-in-place.

BACKGROUND: Stepping thresholds, i.e. the maximum perturbation one can withstand without taking a step, predict falls in older people. This ability requires fast central processing of sensory information followed by rapid execution of adequate motor responses, both of which are affected by age. However, there is limited evidence on their combined effect on stepping thresholds. RESEARCH QUESTION: Are cognitive and motor speeds important for stepping thresholds and do they interact, allowing for compensation? METHODS: Two-hundred forty-two people (mean age: 80 years, standard deviation 4; 110 women) underwent a series of waist-pulls of increasing magnitude to assess stepping thresholds in anterior, posterior and mediolateral directions. Cognitive function was assessed as simple hand reaction time and trail making test performance, and muscle function was assessed as isometric peak and rate of torque development of dominant leg muscles. Principal component analysis reduced these variables to four factors: peak muscle strength, muscle torque development speed (motor speed), executive function and central processing speed (cognitive speed). These factors were used in univariable and multivariable regression models to determine their association with stepping thresholds. RESULTS: Faster central processing speed (beta:2.69; 95 %CI:1.49-3.88) and faster muscle torque development speed (beta:2.60, 95 %CI:0.63-4.57) were associated with higher stepping thresholds. These associations remained in a multivariable model. No interaction was found between cognitive and motor speed on stepping thresholds (p = 0.602). SIGNIFICANCE: Central processing speed and muscle torque development speed affect stepping thresholds independently from each other and may both be important age-related motor impairment targets for preventing falls in older people.

The impact of backpack load on adolescent's stair descent gait.

This study investigates the impact of increasing backpack load on the gait of adolescents during stair descent. Sixteen healthy male students (age = 12.9 ± 0.6 years) were required to descend the stairs in 4 loaded conditions. The kinematic, kinetic, and EMG data were collected synchronously and gait parameters, especially indicators of balance control, were analyzed. The posterior tilt angles (COM-COP IA in the sagittal plane) (0 %-42 %, 48 %-53 %, 58 %-91 %, p < 0.01), trunk anterior tilt angles (9-33 %, 51-65 %, p < 0.01), and CV of stride length (p < 0.01) increased with the backpack load. The COM-Step edge separation decreased with the increased backload (p < 0.01). In addition, the hip flexion torque (25-40 %, 45-51 %, p < 0.01), the rectus femoris activation, and the hip stiffness increased significantly as the load up to 15 % Body Weight (BW)and 20 % BW. The increasing backpack load may affect adolescent's stair descent gait. Especially as the load was up to 15 % BW, the adolescents' bodies tended to tilt backwards relative to the support foot during the single stance phase. They may activate the hip flexors and tilt forward the trunk to recover from the balance perturbation, which was associated with increased hip flexion torques. This adjustment was more pronounced with the increasing backpack load. However, excessive forward flexion may increase the risk of forward falls. The boundaries of adjustment need further research in the future. Findings from this study provide baseline information on the intrinsic mechanisms of balance control during stair descent.

Tai Chi counteracts age-related somatosensation and postural control declines among older adults.

Objective: To investigate the effect of a 16-week Tai Chi practice on strength, tactile sensation, kinesthesia, and static postural control among older adults of different age groups. Methods: This is a quasi-experimental study. Thirteen participants aged 60-69 years (60-69yr), 11 aged 70-79 years (70-79yr), and 13 aged 80-89 years (80-89yr) completed 16 weeks of 24-form Tai Chi practice. Their ankle and hip peak torque, tactile sensation, ankle and knee kinesthesia, and the root mean square of the center of pressure (Cop-RMS) were measured before (week 0) and after (week 17) practice. Results: 80-89yr showed less ankle plantar/dorsiflexion and hip abduction peak torques (p = 0.003, p < 0.001, p = 0.001), and a greater ankle plantar/dorsiflexion kinesthesia (p < 0.001, p = 0.002) than 60-69yr and 70-79yr. Greater ankle plantar/dorsiflexion and hip abduction torques (p = 0.011, p < 0.001, p = 0.045), improved arch and heel tactile sensation (p = 0.040, p = 0.009), and lower knee flexion/extension kinesthesia (p < 0.001, p = 0.044) were observed at week 17. The significant group*practice interaction for the fifth metatarsal head tactile sensation (p = 0.027), ankle plantar/dorsiflexion kinesthesia (p < 0.001, p = 0.004), and the CoP-RMS in the mediolateral direction (p = 0.047) only in 80-89yr revealed greater improvement at week 17. Conclusion: Tai Chi practice increased strength, tactile sensation, kinesthesia, and static postural control among older adults. Tai Chi practice improved tactile, kinesthesia sensations, and static postural control among older adults over 80, who presented with worse strength and kinesthesia than their younger counterparts. Tai Chi practice offers a safe exercise option for those aged over 80 to encourage improvements in sensorimotor control.