Gait Variability as a Potential Motor Marker of Cerebellar Disease-Relationship between Variability of Stride, Arm Swing and Trunk Movements, and Walking Speed.

Excessive stride variability is a characteristic feature of cerebellar ataxias, even in pre-ataxic or prodromal disease stages. This study explores the relation of variability of arm swing and trunk deflection in relationship to stride length and gait speed in previously described cohorts of cerebellar disease and healthy elderly: we examined 10 patients with spinocerebellar ataxia type 14 (SCA), 12 patients with essential tremor (ET), and 67 healthy elderly (HE). Using inertial sensors, recordings of gait performance were conducted at different subjective walking speeds to delineate gait parameters and respective coefficients of variability (CoV). Comparisons across cohorts and walking speed categories revealed slower stride velocities in SCA and ET patients compared to HE, which was paralleled by reduced arm swing range of motion (RoM), peak velocity, and increased CoV of stride length, while no group differences were found for trunk deflections and their variability. Larger arm swing RoM, peak velocity, and stride length were predicted by higher gait velocity in all cohorts. Lower gait velocity predicted higher CoV values of trunk sagittal and horizontal deflections, as well as arm swing and stride length in ET and SCA patients, but not in HE. These findings highlight the role of arm movements in ataxic gait and the impact of gait velocity on variability, which are essential for defining disease manifestation and disease-related changes in longitudinal observations.

Personalizing Deep Brain Stimulation Using Advanced Imaging Sequences.

OBJECTIVE: With a growing appreciation for interindividual anatomical variability and patient-specific brain connectivity, advanced imaging sequences offer the opportunity to directly visualize anatomical targets for deep brain stimulation (DBS). The lack of quantitative evidence demonstrating their clinical utility, however, has hindered their broad implementation in clinical practice. METHODS: Using fast gray matter acquisition T1 inversion recovery (FGATIR) sequences, the present study identified a thalamic hypointensity that holds promise as a visual marker in DBS. To validate the clinical utility of the identified hypointensity, we retrospectively analyzed 65 patients (26 female, mean age = 69.1 ± 12.7 years) who underwent DBS in the treatment of essential tremor. We characterized its neuroanatomical substrates and evaluated the hypointensity's ability to predict clinical outcome using stimulation volume modeling and voxelwise mapping. Finally, we determined whether the hypointensity marker could predict symptom improvement on a patient-specific level. RESULTS: Anatomical characterization suggested that the identified hypointensity constituted the terminal part of the dentatorubrothalamic tract. Overlap between DBS stimulation volumes and the hypointensity in standard space significantly correlated with tremor improvement (R2  = 0.16, p = 0.017) and distance to hotspots previously reported in the literature (R2  = 0.49, p = 7.9e-4). In contrast, the amount of variance explained by other anatomical atlas structures was reduced. When accounting for interindividual neuroanatomical variability, the predictive power of the hypointensity increased further (R2  = 0.37, p = 0.002). INTERPRETATION: Our findings introduce and validate a novel imaging-based marker attainable from FGATIR sequences that has the potential to personalize and inform targeting and programming in DBS for essential tremor. ANN NEUROL 2022;91:613-628.

Functional connectivity maps of theta/alpha and beta coherence within the subthalamic nucleus region.

The subthalamic nucleus (STN) is a primary target for deep brain stimulation in Parkinson's disease (PD). Although small in size, the STN is commonly partitioned into sensorimotor, cognitive/associative, and limbic subregions based on its structural connectivity profile to cortical areas. We investigated whether such a regional specialization is also supported by functional connectivity between local field potential recordings and simultaneous magnetoencephalography. Using a novel data set of 21 PD patients, we replicated previously reported cortico-STN coherence networks in the theta/alpha and beta frequency ranges, and looked for the spatial distribution of these networks within the STN region. Although theta/alpha and beta coherence peaks were both observed in on-medication recordings from electrode contacts at several locations within and around the STN, sites with theta/alpha coherence peaks were situated at significantly more inferior MNI coordinates than beta coherence peaks. Sites with only theta/alpha coherence peaks, i.e. without distinct beta coherence, were mostly located near the border of sensorimotor and cognitive/associative subregions as defined by a tractography-based atlas of the STN. Peak coherence values were largely unaltered by the medication state of the subject, however, theta/alpha peaks were more often identified in recordings obtained after administration of dopaminergic medication. Our findings suggest the existence of a frequency-specific topography of cortico-STN coherence within the STN, albeit with considerable spatial overlap between functional networks. Consequently, optimization of deep brain stimulation targeting might remain a trade-off between alleviating motor symptoms and avoiding adverse neuropsychiatric side effects.

Connectivity profile of thalamic deep brain stimulation to effectively treat essential tremor.

Essential tremor is the most prevalent movement disorder and is often refractory to medical treatment. Deep brain stimulation offers a therapeutic approach that can efficiently control tremor symptoms. Several deep brain stimulation targets (ventral intermediate nucleus, zona incerta, posterior subthalamic area) have been discussed for tremor treatment. Effective deep brain stimulation therapy for tremor critically involves optimal targeting to modulate the tremor network. This could potentially become more robust and precise by using state-of-the-art brain connectivity measurements. In the current study, we used two normative brain connectomes (structural and functional) to show the pattern of effective deep brain stimulation electrode connectivity in 36 patients with essential tremor. Our structural and functional connectivity models were significantly predictive of postoperative tremor improvement in out-of-sample data (P < 0.001 for both structural and functional leave-one-out cross-validation). Additionally, we segregated the somatotopic brain network based on head and hand tremor scores. These resulted in segregations that mapped onto the well-known somatotopic maps of both motor cortex and cerebellum. Crucially, this shows that slightly distinct networks need to be modulated to ameliorate head versus hand tremor and that those networks could be identified based on somatotopic zones in motor cortex and cerebellum. Finally, we propose a multi-modal connectomic deep brain stimulation sweet spot that may serve as a reference to enhance clinical care, in the future. This spot resided in the posterior subthalamic area, encroaching on the inferior borders of ventral intermediate nucleus and sensory thalamus. Our results underscore the importance of integrating brain connectivity in optimizing deep brain stimulation targeting for essential tremor.

Instrumental Assessment of Stepping in Place Captures Clinically Relevant Motor Symptoms of Parkinson's Disease.

Fluctuations of motor symptoms make clinical assessment in Parkinson's disease a complex task. New technologies aim to quantify motor symptoms, and their remote application holds potential for a closer monitoring of treatment effects. The focus of this study was to explore the potential of a stepping in place task using RGB-Depth (RGBD) camera technology to assess motor symptoms of people with Parkinson's disease. In total, 25 persons performed a 40 s stepping in place task in front of a single RGBD camera (Kinect for Xbox One) in up to two different therapeutic states. Eight kinematic parameters were derived from knee movements to describe features of hypokinesia, asymmetry, and arrhythmicity of stepping. To explore their potential clinical utility, these parameters were analyzed for their Spearman's Rho rank correlation to clinical ratings, and for intraindividual changes between treatment conditions using standard response mean and paired t-test. Test performance not only differed between ON and OFF treatment conditions, but showed moderate correlations to clinical ratings, specifically ratings of postural instability (pull test). Furthermore, the test elicited freezing in some subjects. Results suggest that this single standardized motor task is a promising candidate to assess an array of relevant motor symptoms of Parkinson's disease. The simple technical test setup would allow future use by patients themselves.

Shorter pulse width reduces gait disturbances following deep brain stimulation for essential tremor.

OBJECTIVE: Gait disturbances are frequent side effects occurring during chronic thalamic deep brain stimulation (DBS) in patients with essential tremor (ET). Adapting stimulation settings to shorter pulse widths has been shown to reduce side effects of subthalamic DBS. Here, we assess how a reduction of pulse width changes gait performance of affected patients. METHODS: Sensor-based gait assessment was performed to record spatiotemporal gait parameters in 10 healthy subjects (HS) and 7 patients with ET with gait disturbances following thalamic DBS. Patients were tested during standard DBS, after 72 hours of stimulation withdrawal and at least 30 days after adjusting DBS settings to a shorter pulse width of 40 µs (DBS40PW). RESULTS: Patients with ET on standard DBS showed significantly higher variability of several spatiotemporal gait parameters compared with HS. Variability of stride length and range of motion of the shanks significantly decreased OFF DBS as compared with standard DBS. This improvement was maintained over 30 days with DBS40PW while providing effective tremor suppression in six out of seven patients. CONCLUSION: Shorter pulse widths may reduce gait disturbances in patients with ET that are induced by DBS while preserving a level of tremor suppression equal to standard stimulation settings.

Pallidal low-frequency activity in dystonia after cessation of long-term deep brain stimulation.

OBJECTIVE: This study investigates the association between pallidal low-frequency activity and motor sign severity in dystonia after chronic deep brain stimulation for several months. METHODS: Local field potentials were recorded in 9 dystonia patients at 5 timepoints (T1-T5) during an OFF-stimulation period of 5 to 7 hours in parallel with clinical assessment using Burke-Fahn-Marsden Dystonia Rating Scale. A linear mixed effects model was used to investigate the potential association of motor signs with local field potential activity in the low frequency (3-12 Hz) and beta range (13-30 Hz). RESULTS: A significant association of Burke-Fahn-Marsden Dystonia Rating Scale scores with low-frequency activity (3-12 Hz; b = 4.4; standard error = 1.5, degrees of freedom = 43, P = 0.006, 95% confidence interval, 1.3-7.5), but not beta activity (13-30 Hz) was revealed within participants across timepoints. CONCLUSION: Low-frequency activity is associated with dystonic motor sign severity, even months after chronic deep brain stimulation. Our findings corroborate the pathophysiological role of low-frequency activity in dystonia and highlight the potential utility as a biomarker for adaptive neuromodulation. © 2019 International Parkinson and Movement Disorder Society.

Motor Cortical Plasticity Relates to Symptom Severity and Clinical Benefit From Deep Brain Stimulation in Cervical Dystonia.

OBJECTIVE: To investigate the relationship between motor cortical plasticity, intracortical inhibition, and clinical response to pallidal deep brain stimulation (DBS) in patients with cervical dystonia (CD). MATERIALS AND METHODS: Response to paired associative stimulation (PAS) and short interval intracortical inhibition (SICI) were assessed in patients with CD before and after three months of DBS and correlated with severity of dystonic symptoms as assessed by Toronto-Western-Spasmodic Torticollis Rating Scale (TWSTRS) severity score. Relations of electrophysiological parameters with clinical improvement were explored with correlation analysis. RESULTS: Patients with higher levels of plasticity before surgery showed higher symptom severity (R = 0.83, p = 0.008) but had also the larger clinical benefit following DBS (R = 0.88, p = 0.003). This correlation was independent from preoperative (preOP) TWSTRS motor score as revealed by partial correlation analysis. Intracortical inhibition was not altered in CD and not related to clinical outcome after DBS. CONCLUSIONS: Our findings indicate that a high degree of preOP plasticity is associated with higher symptom severity, underlining the role of abnormal plasticity in the pathophysiology of dystonia. At the same time individual degree of plasticity may drive reestablishment of normal motor programs, leading to better clinical outcome with DBS. The latter suggests that individual PAS-response may indicate the susceptibility for neuromodulatory processes as an important factor for clinical DBS effects. It might therefore serve as a neurophysiological marker to predict outcome and guide patient selection.

Kinematic Effects of Combined Subthalamic and Dorsolateral Nigral Deep Brain Stimulation in Parkinson's Disease.

Background: Additional stimulation of the substantia nigra (SNr) has been proposed to target axial symptoms and gait impairment in patients with Parkinson's disease (PD). Objective: This study aimed to characterize effects of combined deep brain stimulation (DBS) of the subthalamic nucleus (STN) and SNr on gait performance in PD and to map stimulation sites within the SNr. Methods: In a double-blinded crossover design, 10 patients with PD and gait impairment underwent clinical examination and kinematic assessment with STN DBS, combined STN+SNr DBS and OFF DBS 30 minutes after reprogramming. To confirm stimulation within the SNr, electrodes, active contacts, and stimulation volumes were modeled in a common space and overlap with atlases of SNr was computed. Results: Overlap of stimulation volumes with dorsolateral SNr was confirmed for all patients. UPDRS III, scoring of freezing during turning and transitioning, stride length, stride velocity, and range of motion of shank, knee, arm, and trunk as well as peak velocities during turning and transitions and turn duration were improved with STN DBS compared to OFF. On cohort level, no further improvement was observed with combined STN+SNr DBS but additive improvement of spatiotemporal gait parameters was observed in individual subjects. Conclusions: Combined high frequency DBS of the STN and dorsolateral SNr did not consistently result in additional short-term kinematic or clinical benefit compared to STN DBS. Stimulation intervals, frequency, and patient selection for target symptoms as well as target region within the SNr need further refinement in future trials.

Long-term effects of pallidal deep brain stimulation in tardive dystonia: a follow-up of 5-14 years.

INTRODUCTION: Pallidal DBS is an established treatment for severe isolated dystonia. However, its use in disabling and treatment-refractory tardive syndromes (TS) including tardive dyskinesia and tardive dystonia (TD) is less well investigated and long-term data remain sparse. This observational study evaluates long-term effects of deep brain stimulation (DBS) of the globus pallidus internus (GPi) in patients with medically refractory TS. METHODS: We retrospectively analyzed a cohort of seven TD patients with bilateral GPi-DBS. Involuntary movements, dystonia and disability were rated at long-term follow-up (LT-FU) after a mean of 122 ± 33.2 SD months (range 63-171 months) and compared to baseline (BL), short-term (ST-FU; mean 6 ± 2.0 SD months) and 4-year follow-up (4y-FU; mean 45 ± 12.3 SD months) using the Abnormal Involuntary Movement Scale (AIMS) and the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS), respectively. Quality of life and mood were evaluated using the SF36 and Beck Depression Index (BDI) questionnaires, respectively. RESULTS: At LT-FU patients had improved by 73% ± 14.2 SD in involuntary movements and 90% ± 1.0 SD in dystonia. Mood had improved significantly whereas quality of life remained unchanged compared to baseline. No serious long-lasting stimulation-related adverse events (AEs) were observed. Three patients of this cohort presented without active stimulation and ongoing symptom relief at long-term follow-up after 3-10 years of continuous DBS. CONCLUSION: Pallidal DBS is a safe and effective long-term TD treatment. Even more interesting, three of our patients could stop stimulation after several years of DBS without serious relapse. Larger studies need to explore the phenomenon of ongoing symptom relief after DBS cessation.

Overnight unilateral withdrawal of thalamic deep brain stimulation to identify reversibility of gait disturbances.

BACKGROUND: Gait disturbances are frequent side effects related to chronic thalamic deep brain stimulation (DBS) that may persist beyond cessation of stimulation. OBJECTIVE: We investigate the temporal dynamics and clinical effects of an overnight unilateral withdrawal of DBS on gait disturbances. METHODS: 10 essential tremor (ET) patients with gait disturbances following thalamic DBS underwent clinical and kinematic gait assessment ON DBS, after instant and after an overnight unilateral withdrawal of DBS of the hemisphere corresponding to the non-dominant hand. The effect of stimulation withdrawal on gait performance was quantitatively assessed using clinical rating and inertial sensors and compared to gait kinematics from 10 additional patients with ET but without subjective gait impairment. DBS leads were reconstructed and active contacts were visualized in relation to surrounding axonal pathways and nuclei. RESULTS: Patients with gait deterioration following DBS exhibited greater excursion of sagittal trunk movements and greater variability of stride length and shank range of motion compared to ET patients without DBS and without subjective gait impairment. Overnight but not instant unilateral withdrawal of DBS resulted in significant reduction of SARA axial subscore and stride length variability, while tremor control of the dominant hand was preserved. Cerebellothalamic, striatopallidofugal and corticospinal fibers were in direct vicinity of transiently deactivated contacts. CONCLUSION: Non-dominant unilateral cessation of VIM DBS may serve as a therapeutic option as well as a diagnostic intervention to identify stimulation-induced gait disturbances that is applicable in ambulatory settings due to preserved functionality of the dominant hand.

Rodent models for gait network disorders in Parkinson's disease - a translational perspective.

Gait impairments in Parkinson's disease remain a scientific and therapeutic challenge. The advent of new deep brain stimulation (DBS) devices capable of recording brain activity from chronically implanted electrodes has fostered new studies of gait in freely moving patients. The hope is to identify gait-related neural biomarkers and improve therapy using closed-loop DBS. In this context, animal models offer a wealth of opportunities to investigate gait network impairments at multiple biological scales and address unresolved questions from clinical research. Yet, the contribution of rodent models to the development of future neuromodulation therapies will rely on translational validity. In this review, we summarize the most effective strategies to model parkinsonian gait in rodents. We discuss how clinical observations have inspired targeted brain lesions in animal models, and whether resulting motor deficits and network oscillations match recent findings in humans. We conclude that future research should incorporate behavioral tests with increased cognitive demands to potentially uncover episodic gait impairments in rodents. Additionally, we expect that basic research will benefit from the implementation of evolving signal processing strategies from clinical research. This coevolution of translational research may contribute to the future optimization of gait therapy in Parkinson's disease.

Proposal for Post Hoc Quality Control in Instrumented Motion Analysis Using Markerless Motion Capture: Development and Usability Study.

BACKGROUND: Instrumented assessment of motor symptoms has emerged as a promising extension to the clinical assessment of several movement disorders. The use of mobile and inexpensive technologies such as some markerless motion capture technologies is especially promising for large-scale application but has not transitioned into clinical routine to date. A crucial step on this path is to implement standardized, clinically applicable tools that identify and control for quality concerns. OBJECTIVE: The main goal of this study comprises the development of a systematic quality control (QC) procedure for data collected with markerless motion capture technology and its experimental implementation to identify specific quality concerns and thereby rate the usability of recordings. METHODS: We developed a post hoc QC pipeline that was evaluated using a large set of short motor task recordings of healthy controls (2010 recordings from 162 subjects) and people with multiple sclerosis (2682 recordings from 187 subjects). For each of these recordings, 2 raters independently applied the pipeline. They provided overall usability decisions and identified technical and performance-related quality concerns, which yielded respective proportions of their occurrence as a main result. RESULTS: The approach developed here has proven user-friendly and applicable on a large scale. Raters' decisions on recording usability were concordant in 71.5%-92.3% of cases, depending on the motor task. Furthermore, 39.6%-85.1% of recordings were concordantly rated as being of satisfactory quality whereas in 5.0%-26.3%, both raters agreed to discard the recording. CONCLUSIONS: We present a QC pipeline that seems feasible and useful for instant quality screening in the clinical setting. Results confirm the need of QC despite using standard test setups, testing protocols, and operator training for the employed system and by extension, for other task-based motor assessment technologies. Results of the QC process can be used to clean existing data sets, optimize quality assurance measures, as well as foster the development of automated QC approaches and therefore improve the overall reliability of kinematic data sets.

Clinical Presentation and Causes of Non-traumatic Spinal Cord Injury: An Observational Study in Emergency Patients.

Introduction: Diagnosing non-traumatic spinal cord injury (NTSCI) is often challenging. However, clear discrimination from non-spinal pathologies, e.g., "myelopathy-mimics" (MMs), is critical in preventing long-term disability and death. In this retrospective study we (1) investigated causes of NTSCI, (2) identified clinical markers associated with NTSCI and (3) discuss implications for NTSCI management. Methods: Our sample consisted of 5.913 consecutive neurological and neurosurgical patients who were treated in our emergency department during a one-year period. Patients with a new or worsened bilateral sensorimotor deficit were defined as possible NTSCI. We then compared clinical and imaging findings and allocated patients into NTSCIs and MMs. Results: Of ninety-three included cases, thirty-six (38.7%) were diagnosed with NTSCI. Fifty-two patients (55.9%) were classified as MMs. In five patients (5.4%) the underlying pathology remained unclear. Predominant causes of NTSCI were spinal metastases (33.3%), inflammatory disorders (22.2%) and degenerative pathologies (19.4%). 58.6% of NTSCI patients required emergency treatment. Presence of a sensory level (p = <0.001) and sphincter dysfunction (p = 0.02) were the only significant discriminators between NTSCI and MMs. Conclusion: In our study, one-third of patients presenting with a new bilateral sensorimotor deficit had NTSCI. Of these, the majority required emergency treatment. Since there is a significant clinical overlap with non-spinal disorders, a standardized diagnostic work-up including routine spinal MRI is recommended for NTSCI management, rather than an approach that is mainly based on clinical findings.

Determining an efficient deep brain stimulation target in essential tremor - Cohort study and review of the literature.

INTRODUCTION: Deep brain stimulation (DBS) is a highly efficacious treatment for essential tremor (ET). Still, the optimal anatomical target in the (sub)thalamic area is a matter of debate. The aim of this study was to determine the optimal target of DBS for ET regarding beneficial clinical outcome and impact on activities of daily living as well as stimulation-induced side effects and compare it with previously published coordinates. METHODS: In 30 ET patients undergoing bilateral DBS, severity of tremor was assessed by blinded video ratings before and at 1-year follow-up with DBS ON and OFF. Tremor scores and reported side effects and volumes of tissue activated were used to create a probabilistic map of DBS efficiency and side effects. RESULTS: DBS was effective both in tremor suppression as well as in improving patient reported outcomes, which were positively correlated. The "sweet spot" for tremor suppression was located inferior of the VIM in the subthalamic area, close to the superior margin of the zona incerta. The Euclidean distance of active contacts to this spot as well as to 10 of 13 spots from the literature review was predictive of individual outcome. A cluster associated with the occurrence of ataxia was located in direct vicinity of the "sweet spot". CONCLUSION: Our findings suggest the highest clinical efficacy of DBS in the posterior subthalamic area, lining up with previously published targets likely representing the dentato-rubro-thalamic tract. Side effects may not necessarily indicate lead misplacement, but should encourage clinicians to employ novel DBS programing options.

Association Between Fatigue and Motor Exertion in Patients With Multiple Sclerosis-a Prospective Study.

Background: Fatigue in multiple sclerosis (MS) is conceived as a multidimensional construct. Objectives: This study aims to describe the changes of balance and gait parameters after 6 min of walking (6 MW) as potential quantitative markers for perceptions of state fatigue and trait fatigue in MS. Methods: A total of 19 patients with MS (17 with fatigue) and 24 healthy subjects underwent static posturography, gait analysis, and ratings of perceived exertion before and after 6 MW. Results: 6 MW was perceived as exhaustive, but both groups featured more dynamic comfortable speed walking after 6 MW. Shorter stride length at maximum speed and increased postural sway after 6 MW indicated fatigability of balance and gait in MS group only. While most changes were related to higher levels of perceived exertion after 6 MW (state fatigue), higher fatigue ratings (trait fatigue) were only associated with less increase in arm swing at comfortable speed. Further analysis revealed different associations of trait fatigue and performance fatigability with disability and motor functions. Performance fatigability was most closely related to the Expanded Disability Status Scale, while for trait fatigue, the strongest correlations were seen with balance function and handgrip strength. Conclusions: Fatigability of performance was closely related to perceptions of exertion after 6 MW (state fatigue) and disability in MS but distinct from fatigue ratings, conceived as trait fatigue. Our study identified postural sway, arm swing during gait, and hand grip strength as unexpected potential motor indicators of fatigue ratings in MS.

Less Is More - Estimation of the Number of Strides Required to Assess Gait Variability in Spatially Confined Settings.

Background: Gait variability is an established marker of gait function that can be assessed using sensor-based approaches. In clinical settings, spatial constraints and patient condition impede the execution of longer distance walks for the recording of gait parameters. Turning paradigms are often used to overcome these constraints and commercial gait analysis systems algorithmically exclude turns for gait parameters calculations. We investigated the effect of turns in sensor-based assessment of gait variability. Methods: Continuous recordings from 31 patients with movement disorders (ataxia, essential tremor and Parkinson's disease) and 162 healthy elderly (HE) performing level walks including 180° turns were obtained using an inertial sensor system. Accuracy of the manufacturer's algorithm of turn-detection was verified by plotting stride time series. Strides before and after turn events were extracted and compared to respective average of all strides. Coefficient of variation (CoV) of stride length and stride time was calculated for entire set of strides, segments between turns and as cumulative values. Their variance and congruency was used to estimate the number of strides required to reliably assess the magnitude of stride variability. Results: Non-detection of turns in 5.8% of HE lead to falsely increased CoV for these individuals. Even after exclusion of these, strides before/after turns tended to be spatially shorter and temporally longer in all groups, contributing to an increase of CoV at group level and widening of confidence margins with increasing numbers of strides. This could be attenuated by a more generous turn excision as an alternative approach. Correlation analyses revealed excellent consistency for CoVs after at most 20 strides in all groups. Respective stride counts were even lower in patients using a more generous turn excision. Conclusion: Including turns to increase continuous walking distance in spatially confined settings does not necessarily improve the validity and reliability of gait variability measures. Specifically with gait pathology, perturbations of stride characteristics before/after algorithmically excised turns were observed that may increase gait variability with this paradigm. We conclude that shorter distance walks of around 15 strides suffice for reliable and valid recordings of gait variability in the groups studied here.