Gait & Posture

Markerless motion capture offers a practical approach to biomechanical assessment in clinical populations outside of controlled laboratory environments. The purpose of this study was to evaluate the utility of markerless motion capture for quantifying static postural control impairment in individuals with stroke. Participants with subacute stroke (n=26) and healthy controls (n=171) performed a 30-second quiet standing task across three data collection sites in Kingston, Ontario, Canada. Video data were processed using Theia3D, and pelvis center of mass (COM) trajectories were extracted. Five discrete COM parameters were computed and transformed into Z-scores using normative models developed from the healthy population. An overall Task Score was calculated by aggregating parameter Z-scores. Forty-six percent of participants with stroke were identified as impaired on the task (Task Score > 95th percentile of the healthy distribution). At the parameter level, impairments were more prevalent in the mediolateral (ML) than anteroposterior (AP) direction (root-mean-square distance: 50% impaired ML vs. 12% impaired AP; mean velocity: 46% impaired ML vs. 35% impaired AP). Task scores and several task parameters demonstrated significant correlations with Berg Balance Scale scores (r = -0.64 to -0.81) and Functional Independence Measure Motor Sub-Scale scores (r = -0.62 to -0.77), with poorer performance associated with lower clinical scores. These findings demonstrate the utility of markerless motion capture for quantifying static postural control impairment following stroke. Future work should extend this framework to evaluate impairment in more dynamic postural control and gait tasks.

Background: Safely walking through complex environments requires the use of visual information to plan and regulate steps, while managing competing cognitive demands. Age-related changes in visual control of gait and executive function may contribute to unsafe stepping behaviour, particularly under cognitive load. Route previewing may support visual motor planning, but its effects under dual task conditions in older adults are not well understood. Research Question: Does cognitive dual tasking influence gait and gaze behaviour during adaptive walking in older adults, and does previewing the walking route before gait initiation mitigate these effects? Methods: Thirty nine community dwelling older adults (Mage=73.4 years, SD=8.1; 14 male) completed four adaptive walking conditions, combining single and dual-task walking with and without previewing. Per condition, participants completed six trials across different 8-m long coloured walking routes. Gait characteristics were assessed using an instrumented walkway and video-analysis, while gaze behaviour was recorded using mobile eye tracking. Cognitive load was manipulated using a serial subtraction task. Gait and gaze outcomes were evaluated using linear mixed effects models. Results: Dual task performance significantly increased stepping errors, cross-steps, and double limb support, while reducing stride length (p < .001). It also significantly increased the number and duration of task irrelevant fixations (p < .001). After previewing, participants exhibited more efficient gaze behaviour, as evidenced by looking further ahead (larger forward gaze transitions) and fewer irrelevant gaze fixations (p < .002). Significant Task-by-Preview interactions revealed that previewing mitigated the negative effects of dual-tasking on stepping errors and cross steps (p < .001). Significance: Route previewing prior to gait initiation attenuates negative effects of cognitive load on adaptive gait in older adults, likely by supporting visual motor planning. These findings highlight the potential value of simple visual planning interventions for improving adaptive gait in older adults.

Balance is fundamental to mobility and independence, yet it remains difficult to measure in a way that is both clinically meaningful and feasible for widespread adoption. There is a need for more quantitative, objective, and accessible balance assessments. To this end, we created the Stanford Balance Level Evaluation (StaBLE), a battery of 18 balance-challenging tasks and accompanying digital performance metrics computed from video that aimed to capture widely ranging balance abilities across 180 participants. We validated the StaBLE score against existing clinical scales and found that it correlated with age ({rho} = -0.76, p<0.001), the Activities-Specific Balance Confidence Scale ({rho} = 0.60, p<0.001), a Mini-Balance Evaluation Systems Test task ({tau}=0.55, p<0.001), 4-Stage Balance Test ({tau} = 0.55, p<0.001), and Short Physical Performance Battery ({tau} =0.57, p<0.001). StaBLE overcame ceiling effects in these existing scales and had a different underlying distribution for those identified at risk of falling and not (KS: 0.67, p<0.001). To reduce the time it takes to perform the test, we identified subsets of balance tasks that best predicted the StaBLE score across different populations. Together, our dataset, balance assessment protocol, and performance-based score demonstrate the validity of digital measures of balance.

Introduction: Knee muscle coactivation is elevated after anterior cruciate ligament reconstruction (ACLR), contributing to altered joint loading and post-traumatic osteoarthritis. Existing methods average coactivation within predefined gait phases and require priori designation of muscles roles, limiting the resolution for when differences occur. Objective: Characterize knee joint coactivation and dynamics throughout gait in individuals with ACLR using statistical parametric mapping. Methods: Ten individuals with unilateral ACLR and ten healthy matched controls performed overground walking at their preferred speed, while kinematics, kinetics, and electromyography of the quadriceps, hamstring, and gastrocnemius muscles were recorded. Coactivation was quantified using time-varying, multi-muscle coactivation, and was compared using a one-tailed statistical parametric mapping (SPM) t-test. Knee joint angle, angular speed, and moment were compared using SPM Hotelling's T2 tests with Bonferroni-adjusted post hoc comparisons (= 0.05). Results: Coactivation was greater in the ACLR group at 0.01%-6.14%, 35.23%-40.94%, 69.73-71.99%, 72.12-77.31%, 77.89-78.05%, and 94.63%-95.87% (p < 0.0001) of stride. The ACLR group also demonstrated greater knee internal-external rotation angle at 0.01%-47.34%, 52.14%-61.87%, and 66.47%-100% (p <0.0001) and lower knee flexion angle at 55.79%-65.93% (p = 0.004) of stride, than healthy controls. Finally, a smaller knee flexion-extension moment was observed in the ACLR group at 57.43%-62.18% (p = 0.005) of stride. Conclusions: Coactivation after ACLR is elevated at loading response, late mid-stance, terminal stance and early push-off phase. Greater coactivation was observed during weight-acceptance phases, whereas lower knee moments characterized initial swing. These alterations are localized rather than uniformly distributed, supporting phase-targeted rehabilitation.

Background: Gait propulsion (anterior ground reaction force) is commonly impaired after stroke. Force plates and wearable sensors can quantify propulsion but are not routinely available in clinical settings. Walking speed alone does not adequately capture the heterogeneity of propulsion deficits. Objective: To determine whether standardized clinical measures can estimate post-stroke propulsion metrics and classify propulsion impairment. Methods: Forty individuals post-stroke participated: 33 for model development and cross-validation (11 with repeated observations for longitudinal validation) and 7 for independent-cohort validation. Clinical measures included the 6-Minute Walk Test (6MWT), comfortable walking speed (CWS), Functional Gait Assessment (FGA), Fugl-Meyer Assessment of the Lower Extremity (FMA-LE), Short Physical Performance Battery (SPPB), Timed Up and Go test (TUG), and stroke chronicity. Regression models were developed to estimate three propulsion metrics: paretic propulsion peak and impulse, and interlimb propulsion symmetry. Model performance was evaluated using R2 and RMSE. Propulsion impairment was classified from symmetry estimates using a prespecified cutoff of 31.5%, with classification accuracy reported. Results: Models using the 6MWT, SPPB, TUG, and chronicity estimated paretic propulsion peak (R2 = 0.77, RMSE = 3.00 %body weight) and impulse (R2 = 0.81, RMSE = 0.65 %body weight {middle dot} %stance phase). FMA-LE, SPPB, TUG, and chronicity estimated propulsion symmetry (R2 = 0.75, RMSE = 8.56%) and classified propulsion impairment with 84.8% accuracy. Classification accuracy was 91.7% in longitudinal validation and 85.7% in independent-cohort validation. Conclusions: A multidomain clinical assessment framework may support practical and accurate estimation and classification of post-stroke propulsion impairment in clinical settings where specialized instrumentation is unavailable.

BackgroundTrunk flexor and extensor measurement tools are useful for measuring progress throughout the identification, treatment and management of spinal pathologies. Handheld dynamometry is popular amongst clinicians due to its convenience. However, poor standardisation of the testing position can lead to suboptimal intra-rater reliability, which consequently reduces the validity of the results. The VALD ForceFrame Strength Testing System is a portable and standardized hybrid strength-assessment system that quantifies strength and power outputs. ObjectiveThis study aims to assess the test-retest reliability of isometric trunk flexion and extension strength using the ForceFrame testing technology. MethodsA total of 29 healthy participants undertook two testing sessions, each requiring them to perform maximal isometric trunk flexion and extension using the ForceFrame. Test re-test reliability was assessed using the Intraclass Correlation Coefficient (ICC), and the standard error of measure (SEM) was used to calculate the minimum detectable change. ResultsExcellent reliability was observed for both trunk flexion (ICC 0.92; 95% CI 0.83-0.96) and extension (ICC 0.93; 95% CI 0.86-0.97) tests, and the minimum detectable changes observed were 71.35N and 101.20N, respectively. ConclusionsThe results from this study suggest that the VALD force frame offers clinicians a reliable method of assessing change in trunk flexor and extensor strength.

Gait impairments are a major contributor to disability in patients with Parkinson's disease despite dopaminergic and neuromodulation therapies. External cues (e.g., visual targets, rhythmic auditory sounds) are commonly used to improve gait quality and reduce freezing of gait (FOG), yet their effectiveness varies across patients and contexts. Improved understanding of the neural mechanisms of cueing benefits is essential to personalize rehabilitation strategies and improve outcomes. We use mobile electroencephalography (EEG) to test the hypothesis that cues improve gait through engagement of voluntary motor control mechanisms to compensate for impaired gait automaticity. In addition, we investigate whether this mechanism is related to cueing benefits or freezing status. Eighteen PD patients with a history of freezing (PD-F), 21 patients without freezing (PD-NF) and 19 age-matched healthy controls (HC) walked overground under three conditions: normal walking, synchronizing to auditory cues, and stepping over visual cues. Stride-locked beta band (13-30 Hz) power dynamics in sensorimotor cortex were used to measure cortical control of stepping. Spatiotemporal gait parameters improved with cues in all groups. However, PD-F had smaller cue-related gains in speed and stride length when compared with PD-NF for both cue types, and did not improve gait speed with visual cues. EEG revealed greater contralateral sensorimotor cortex swing-phase beta suppression in PD-F than PD-NF patients, with visual cues eliciting the most robust response. In contrast, beta suppression with cues was less pronounced in PD-NF and HC, despite greater behavioral gains. In addition, engagement of sensorimotor cortex during visual cueing was associated with divergent gait effects across PD subgroups: In PD-NF greater beta suppression was associated with less gait improvement, whereas in PD-F the opposite was observed. These findings suggest distinct sensorimotor control mechanisms for cue utilization in PD-F and PD-NF, and indicate that engagement of voluntary motor control circuits may underlie cueing benefits primarily in PD-F.

Background: Post-stroke spasticity is commonly assessed using the Modified Ashworth Scale (MAS), despite its limited objectivity and variable reliability. This study introduces ScoreE, a novel isokinetic dynamometry-derived metric designed to quantify elbow and wrist flexor hyper-resistance by comparing patients torque-angle profiles with a healthy reference corridor. Methods: Thirty-five post-stroke patients and twenty-one healthy controls were included. Elbow and wrist hyper-resistance was assessed using the MAS and an isokinetic dynamometer in two testing conditions: seated on the dynamometer chair (ergo chair) and seated in the patient wheelchair. Two dynamometer-derived metrics were analyzed: ScoreE and peak torque (PeakT). Feasibility, inter-rater and test-retest reliability, and associations with MAS grades were assessed. Exploratory PRE-POST changes following a 10-min local vibration session were also described. Results: ScoreE showed good to excellent inter-rater and test-retest reliability across joints and testing conditions. Inter-rater ICCs ranged from 0.81 to 0.89, and test-retest ICCs from 0.76 to 0.93. PeakT showed moderate to good reliability. In contrast, MAS agreement was lower and more variable. ScoreE showed moderate associations with MAS grades, particularly at the elbow, with weaker and less consistent associations at the wrist. MAS assessment was faster, but all assessments were well tolerated, with median pain ratings of 0/10 in all testing conditions. PRE-POST vibration changes were small and heterogeneous, preventing formal assessment of responsiveness. Conclusion: ScoreE provides a reliable, objective, and visually interpretable quantification of post-stroke elbow and wrist flexor hyper-resistance. By comparing the full torque-angle profile with normative data, this approach preserves information on both the magnitude and angular span of abnormal resistance, supporting its potential for targeted longitudinal monitoring.

BackgroundPersistent postural-perceptual dizziness (PPPD) is a chronic functional dizziness disorder characterized by unsteadiness, hypersensitivity to motion and visually complex environments. Although increasingly investigated, the role of the different factors involved remains unclear. This study aims to comprehensively characterize PPPD across clinical, biological, and behavioral domains. MethodsData from 18 PPPD patients and 20 age- and sex-matched healthy control volunteers (HC) were analyzed, including clinical and psychological questionnaires, a neuropsychological battery, salivary markers, posturography under different conditions, and gait analysis under single- and dual-task demands. ResultsPatients reported greater depressive symptoms, higher perceived stress, and reduced quality of life than HC, but showed no neuropsychological deficits and comparable past psychological trauma and personality traits. Salivary stress marker levels were similar to HC. Gait analysis revealed a slower, cautious gait in patients, which worsened without vision, with no differences in automaticity (stride time variability). Postural assessments showed greater sway and enhanced low-frequency oscillations, exacerbated by absence of visual input in PPPD. Visual reliance for postural control correlated negatively with subjective symptom severity, but not other symptom-related measures. ConclusionPPPD patients have lower mood and increased perceived stress, with no increase in biological stress markers compared to HC. Cognition, personality, and exposure to past trauma might be less relevant than previously hypothesized. Patients show visual dependence for gait and postural control, likely a maladaptive compensatory mechanism. These findings support interventions targeted at reducing visual dependence and at improving mood, rather than interventions focusing on psychological trauma. SummaryO_LIWhat is already known on this topic - PPPD (Persistent Perceptual Postural Dizziness) is a functional dizziness disorder characterized by different biopsychosocial factors, often investigated in isolation. C_LIO_LIWhat this study adds - PPPD patients have higher depression and perceived stress scores, lower quality of life, but show no differences in past trauma, personality traits, and biological stress markers, compared to healthy controls. They also show a reliance on vision both for gait and for postural control, with increased low-frequency oscillations in the anteroposterior direction. Visual dependence is likely maintained by its perceived role in symptom reduction. C_LIO_LIHow this study might affect research, practice or policy - These findings support rehabilitation strategies aimed at reducing reliance on vision and increasing reliance on vestibular inputs, but not interventions focusing on past traumatic experiences. C_LI

Aims: Our primary aim was to determine the immediate effects of using a supported stepping device on the real-time locomotor behavior of pre-walking infants with Down syndrome (DS). Our secondary aim was to characterize the role of the caregiver in facilitating infant locomotor behavior by quantifying infant-initiated and caregiver-initiated walker movement, and to test whether walker movement encourages stepping behavior. Methods: Pre-walking infants with DS played with their caregiver in two conditions--with and without assistance from a wheeled suspension walker. To examine changes across development, we recorded infants across one to four sessions from 10 to 19 months of age. Results: Across developmental stages, we found that suspension walkers robustly increased infants' locomotor behavior: The walker increased upright time, percent time stepping, stepping rate, upright bout rate, percent time locomoting, and total bout rate. Most walker movement was initiated by caregivers, and infants stepped more while the walker was moving compared to stationary. Conclusions: Even without practice, pre-walking infants with DS were able to take advantage of the suspension walker to increase their locomotor behavior. Caregivers facilitated infants' activity by moving the walker. Future work will examine the potential of overground suspension walkers for home-based intervention.

Targeted stepping requires coordinating limb transport, preparatory postural adjustments, and accurate foot placement while maintaining balance under competing speed and accuracy demands. Although Fitts' law robustly describes speed-accuracy trade-offs (SATs) in upper-limb movements, its applicability to whole-body stepping remains unclear due to additional postural and visuomotor constraints. This study investigates how instructional emphasis and spatial demands modulate SAT regulation and pre-step postural dynamics during stepping. Twenty-four healthy young adults will perform a multidirectional stepping task across two directions (0 degrees and 45 degrees) and two distances (45% and 80% of leg length) under three instruction conditions: Fast, Accurate, and Fast & Accurate. Kinematic and force-plate data will quantify movement time, foot-placement error, and pre-step center-of-pressure dynamics. We hypothesize that instructional emphasis and increased postural demands will systematically alter stepping strategies and produce deviations from classical Fitts-type scaling, particularly during diagonal stepping.

Objective: The aim of the current study was to evaluate the feasibility of a multi-channel distributed wearable ultrasound (D-WUS) system capable of simultaneously probing dynamic muscle activity across multiple anatomical sites to assess neuromuscular coordination during physical activity. Methods: Twenty NCAA Division I women athletes (8 with prior knee injury) performed countermovement jumps (CMJs) on dual force plates while wearing a four-channel D-WUS system targeting the vastus lateralis (VL) and vastus medialis oblique (VMO) in both limbs. Real-time M-mode ultrasound data were processed using a composite factorization approach integrating nonnegative matrix factorization and principal component analysis (CF-PCA) to extract dominant muscle-contraction patterns. Correlation and timing metrics between VL and VMO were compared across injury status. Results: CMJ performance metrics (jump height, RSImod) did not differ between groups (p > 0.05). However, D-WUS revealed significant differences in muscle coordination in the right limb: VL-VMO correlation (p = 0.029) and timing symmetry (p = 0.019) were reduced in participants with prior knee injury; left-limb differences were not significant. Right-limb timing symmetry was negatively correlated with SMFA score (rho = -0.48, p = 0.033). Functional survey scores (SMFA) also differed significantly (p = 0.001), while VISA-P scores did not. Conclusion: These preliminary findings provide feasibility-level evidence that distributed wearable ultrasound can detect limb-specific neuromuscular coordination differences not reflected in force-plate biomechanics, motivating larger prospective studies to establish reliability and clinical utility. Significance: With further validation, this approach may offer a scalable, objective means of monitoring muscle contraction during rehabilitation.

Background: Wearable sensing and machine learning can support objective assessment of Parkinson's disease (PD), but performance depends on sensor placement, modality, and analysis, and studies often target selected motor tasks, whereas clinical assessment integrates multiple standardized movements. How discriminative information is distributed across tasks and modalities remains unclear, limiting comparability and translation. Objectives: To quantify standardized Movement Disorder Society Unified Parkinson's Disease Rating Scale Part III (MDS-UPDRS III) tasks across complementary modalities, determine task- and modality-specific contributions to discrimination, and identify complementary, stable candidate digital biomarkers. Methods: Thirty-one participants with PD (Hoehn and Yahr stages I-III) and 30 age- and sex-matched healthy controls performed seven MDS-UPDRS III tasks (items 3.4-3.8, 3.10, 3.15). Unilateral surface electromyography from task-specific muscles and full-body inertial motion capture were acquired, which drove subject-specific musculoskeletal simulations. A leakage-free classification pipeline (in-fold feature selection, repeated cross-validation, permutation testing) was applied by task and modality, followed by sparse task fusion and stability-based biomarker selection. Results: Discrimination was concentrated in four upper-limb tasks, with pronation-supination (3.6) performing best (ROC-AUC 0.94; balanced accuracy 0.92). Multitask multimodal fusion maintained discrimination (ROC-AUC 0.93; balanced accuracy 0.92; sensitivity 0.87; specificity 0.97), retaining finger tapping (3.4), hand movements (3.5), pronation-supination (3.6), and postural tremor (3.15). Eighteen stable candidate biomarkers captured complementary alterations in movement execution, muscle activation, coordination, tremor, and proximal stabilization. Conclusions: In this cohort, discriminative information converged on a four-task upper-limb assessment and a physiologically interpretable multimodal biomarker profile. These findings support shorter, clinically anchored digital motor assessment, pending independent clinical validation.

Conventional clinical assessment of upper limb kinematics relies on goniometry or visual estimation, methods that provide limited information on multi-segment 3D kinematics and can have poor inter-rater reliability. Inertial measurement units (IMUs) represent a viable alternative; however, extracting anatomically meaningful joint angles from skin-mounted sensors remains challenging owing to sensor-to-segment misalignment, soft-tissue artefact, and suboptimal orientation estimation under dynamic conditions. This study developed and validated a multi-segment IMU-based framework for upper limb kinematic assessment, addressing three stages of the measurement pipeline: (i) sensor fusion gain optimisation as a function of task mean segment angular velocity; (ii) accuracy of an anatomical landmark registration-based alignment method; and (iii) comparative evaluation of landmark-based alignment against manual and neutral-pose alignment approaches. Twenty participants with typical shoulder function performed clinical and functional upper limb tasks, recorded simultaneously with an optoelectronic motion capture system and six IMUs tracking the thorax, clavicle, scapula, humerus, forearm, and hand. Orientation estimation used a gradient-descent complementary filter with velocity-dependent gain modulation. Sensor-to-segment alignment was achieved via manual, neutral-pose, and landmark registration methods. Mean sensor orientation errors ranged from 1.5 to 3 degrees across segments/tasks and increased with angular velocity. Landmark registration produced substantially lower joint angle errors than manual and neutral-pose alignment across all joints (root mean square error range: 3.7-7.8 degrees; manual: 8.3-24.2 degrees; neutral: 15.5-35.5 degrees). These results indicate that IMU-derived kinematic accuracy is context-dependent, varying with joint and movement type, suggesting that accuracy should be established for the specific movements and joints relevant to each clinical application.

Background: Knee osteoarthritis (OA) is characterized by progressive joint degradation and altered gait biomechanics. Inter-limb load asymmetry during daily living tasks may accelerate joint deterioration, particularly when combined with physical fatigue. This study investigates the relationship between daily physical fatigue and inter-limb load asymmetry patterns during functional activities in individuals with unilateral knee OA. Objective: To evaluate the impact of fatigue on inter-limb load asymmetry and joint loading rates during daily living tasks in patients with unilateral knee osteoarthritis, and to identify biomechanical and clinical factors associated with load distribution patterns. Methods: One hundred eighteen participants with unilateral knee OA (mean age 62.6 (SD 7.4) years, BMI 29.9 (SD 4.2) kg/m2) completed biomechanical assessments during non-fatigued and fatigued conditions. Ground reaction force measurements were obtained during functional tasks including stair climbing, sit-to-stand transitions, and level walking. Load asymmetry was quantified as the inter-limb difference in peak vertical ground reaction forces. Statistical analysis was conducted using Python (v3.9), including paired t-tests, analysis of variance, and linear regression modeling. Results: Participants demonstrated significantly increased load asymmetry under fatigue conditions (mean difference 8.7% (SD 12.3) %, p < 0.001). Fatigue-induced asymmetry was task-dependent, with stair negotiation showing the greatest increase (11.2% (SD 14.1) %). Peak loading rates on the affected knee were inversely correlated with time-to-peak load during fatigued conditions (r = -0.68, p < 0.001). Disease severity (WOMAC score) and age significantly predicted asymmetry changes (R2 = 0.52, p < 0.001). Conclusions: Physical fatigue exacerbates inter-limb load asymmetry in unilateral knee OA, potentially accelerating joint degeneration. Task-specific interventions targeting fatigue management and load redistribution may improve long-term outcomes. Future longitudinal studies should examine the temporal relationship between acute biomechanical changes and progressive structural joint damage. Keywords: Knee osteoarthritis, load asymmetry, fatigue, biomechanics, ground reaction forces, functional tasks.

Altered walking mechanics in individuals with obesity can contribute to knee osteoarthritis. The gait deviations may become more pronounced during obstacle crossing. In women, body fat distribution may further influence knee load, especially when excess fat accumulates in the thighs and hips. However, relatively little is known about how regional fat distribution affects gait in women with obesity. This study investigated how obesity and, among women, different fat distributions (Apple: more abdominal fat; Pear: more lower-limb fat) influence knee biomechanics during walking with and without obstacle crossing. Participants were 15 controls without obesity (NB) and 27 with obesity (OB). Within female participants, 10 without obesity (fNB) were compared with 20 with obesity, stratified by waist-hip ratio (Apple:10, Pear:10). Speed-adjusted statistical parametric mapping applied a general linear model (NB vs. OB) and an analysis of covariance (fNB vs. Apple vs. Pear). OB exhibited a significantly greater late-stance knee extension moment than NB across all tasks, and this difference persisted among fNB, Apple, and Pear in obstacle tasks (p<0.05). OB walked with reduced knee flexion during the early-stance leading limb after crossing a medium-height obstacle (p=0.048) and a high-height obstacle (p=0.008) compared to NB. There were significant body-shape effects (p<0.05), and post-hoc comparisons confirmed that Pear had lower knee angles than fNB in both leading-limb conditions after crossing medium- and high-height obstacles (p=0.008 and p=0.001, respectively). These findings suggest that obstacle crossing helps illuminate how excess weight influences knee biomechanics, and how regional fat distribution modulates the degree of this alteration.

Reduced visibility is a common contributor to falls in older adults, but the neural processes that support safe locomotion under low lighting are not well established. In this study, 22 young (mean age = 22.5) and 20 older (mean age = 70.9) adults walked along a pathway under bright, ambient and dark lighting conditions while stepping over expected and unexpected obstacles projected on the floor. Mobile electroencephalography (EEG), combined with motion capture, was used to quantify spectral power changes during obstacle crossing preparation and the post-crossing phases, relative to a standing baseline. We identified that reduced lighting conditions elicited a widespread increase in cortical engagement, predominantly in the alpha band, during both preparation and reset phases. Obstacle negotiation recruited a distributed sensorimotor network, with reduced theta-alpha-beta desynchronisation during preparation and a robust post-movement beta rebound during the post-crossing reset phase. Expectation effects were modest, with unexpected obstacles inducing greater transient alpha-beta desynchronisation relative to expected obstacles, suggesting additional cortical resources are recruited under uncertainty. Age effects were minimal and limited to reduced frontal alpha desynchronisation in older adults compared to young adults during the preparation phase, possibly reflecting differences in walking speed rather than differences in neural control. In conclusion, environmental features such as low lighting and obstacle presence exert a stronger influence on cortical dynamics during walking than age and expectation effects alone. This provides a foundation for future work examining how these processes may differ in older adults at increased risk of falls.

Background: Tremor is a repetitive, oscillatory movement with multiple subtypes requiring accurate characterization for diagnosis and treatment. While frequency, amplitude, and context are routinely used to describe tremor, recent recommendations have emphasized oscillation shape and regularity. However, these descriptors lack strict operational definitions, and differences in how clinicians interpret them introduce inconsistency into tremor classification. Objective: We quantified inter-rater reliability for commonly used tremor descriptors and determined which objectively measured signal parameters: peak amplitude, peak frequency, and frequency variability best explained inconsistency in rater assessments. Methods: We developed the Tremor Waveform Morphology Questionnaire (TWMQ) and obtained standardized video recordings of 34 individuals with upper-extremity tremor performing rest, postural, and kinetic tasks, with simultaneous kinematic recordings using an inertial sensor. Movement disorder experts rated tremor presence, shape, symmetry, regularity, rhythmicity, and diagnosis. We assessed inter-rater reliability, cross-feature dependencies, and modeled the influence of objective signal parameters on each subjective rating. Results: Tremor presence and symmetry showed high agreement, whereas jerkiness, rhythmicity, amplitude stability, and clinical diagnosis showed lower reliability. Modeling revealed that peak amplitude primarily influenced judgments of tremor presence, jerkiness, and diagnosis, while frequency variability drove ratings of rhythmicity and amplitude stability. Conclusions: Morphology-based descriptors remain subjective, but disagreement systematically reflects measurable signal properties. Objective definitions based on peak amplitude and frequency variability may improve the reliability and reproducibility of tremor characterization.

Standing balance relies on the continuous detection of body motion across a wide range of amplitudes and frequencies. According to Weber's law, sensory discrimination should degrade in proportion to stimulus amplitude, yet vestibular self-motion perception deviates from this prediction. Whether this deviation extends to the vestibular control of posture remains unknown. To test this hypothesis, we delivered amplitude-increasing electrical vestibular stimulation (EVS, 0-2 mA) at four frequencies (0.1, 0.2, 0.5, and 1 Hz) to 10 healthy young adults, and quantified balance discrimination thresholds (DTs) from the gain and inter-trial variability of the lateral ground reaction force, using signal detection theory. Balance control DTs increased sublinearly with EVS amplitude at all frequencies, deviating from Weber's law. Both balance-correcting response gain and variability accounted for this deviation: gain decreased more slowly than the strictly inverse relationship that would have alone produced strict adherence to Weber's law, while variability exhibited an initial increase followed by saturation at higher EVS amplitudes, a signal-dependent structure necessary to reproduce the observed DT pattern. EVS frequency modulated the shape of this deviation but affected neither overall DT nor the signal-to-noise ratio of the balance-correcting response, which instead remained similar across frequencies. This study revealed a particular property of postural control discrimination by extending the psychophysical and neural deviations from Weber's law previously reported for vestibular perception. Overall, these results provide a better understanding of the balance control discrimination process and provide potential additional assessment criteria for vestibular impairments.

Background Parkinson disease (PD) is associated with increased sedentary time and reduced cardiorespiratory fitness, making exercise an important component of disease management. Although exercise improves cardiorespiratory fitness, individuals with PD vary substantially in their response to exercise. Sedentary time may contribute to this variability, yet whether sedentary time modifies the response to intervention and varying exercise intensities within an intervention is unknown. We examined whether sedentary time interacted with 6 months of moderate-intensity or high-intensity aerobic exercise on maximal oxygen consumption (VO2max) in individuals with PD. Methods This secondary analysis used data from the SPARX phase 2 randomized clinical trial including 128 de novo PD patients assigned to high- or moderate-intensity treadmill exercise, or usual care for 6 months. Interactions between randomized group and post-randomization 6-months average sedentary time were assessed for associations with 6-month change in VO2max by using linear regression models corresponding to Analysis of Covariance (ANCOVA) models with interaction. Results The interaction between exercise intensity and sedentary behavior on 6-month change in VO2max in the moderate-intensity group compared with usual care was not significant ({beta}: -1.78, 95% CI: -3.76 to 0.20, p-value: 0.08), although the sensitivity analysis restricted to complete cases showed a significant interaction where each 10% increase in 6-months average sedentary time was associated with a 2.51 mL/kg/min decrease in VO2max change in the moderate-intensity group compared with usual care ({beta}: -2.51, 95% CI: -4.53 to -0.48, p-value: 0.02). There was no significant interaction between exercise intensity and sedentary behavior on 6-month change in VO2max in the high-intensity group compared with usual care ({beta}: -1.46, 95% CI: -4.74 to 1.83, p-value: 0.38). The sensitivity analysis showed similar results. Conclusions These hypothesis-generating, preliminary findings suggest that sedentary time may modify the response to exercise among individuals participating in moderate-intensity aerobic exercise. Future adequately powered randomized controlled trials are needed to confirm these findings and determine whether sedentary behavior should be considered when prescribing exercise for individuals with PD.