Minimal detectable change of gait and balance measures in older neurological patients: estimating the standard error of the measurement from before-after rehabilitation data thanks to the linear mixed-effects models.

BACKGROUND: Tracking gait and balance impairment in time is paramount in the care of older neurological patients. The Minimal Detectable Change (MDC), built upon the Standard Error of the Measurement (SEM), is the smallest modification of a measure exceeding the measurement error. Here, a novel method based on linear mixed-effects models (LMMs) is applied to estimate the standard error of the measurement from data collected before and after rehabilitation and calculate the MDC of gait and balance measures. METHODS: One hundred nine older adults with a gait impairment due to neurological disease (66 stroke patients) completed two assessment sessions before and after inpatient rehabilitation. In each session, two trials of the 10-meter walking test and the Timed Up and Go (TUG) test, instrumented with inertial sensors, have been collected. The 95% MDC was calculated for the gait speed, TUG test duration (TTD) and other measures from the TUG test, including the angular velocity peak (ωpeak) in the TUG test's turning phase. Random intercepts and slopes LMMs with sessions as fixed effects were used to estimate SEM. LMMs assumptions (residuals normality and homoscedasticity) were checked, and the predictor variable ln-transformed if needed. RESULTS: The MDC of gait speed was 0.13 m/s. The TTD MDC, ln-transformed and then expressed as a percentage of the baseline value to meet LMMs' assumptions, was 15%, i.e. TTD should be < 85% of the baseline value to conclude the patient's improvement. ωpeak MDC, also ln-transformed and expressed as the baseline percentage change, was 25%. CONCLUSIONS: LMMs allowed calculating the MDC of gait and balance measures even if the test-retest steady-state assumption did not hold. The MDC of gait speed, TTD and ωpeak from the TUG test with an inertial sensor have been provided. These indices allow monitoring of the gait and balance impairment, which is central for patients with an increased falling risk, such as neurological old persons. TRIAL REGISTRATION: NA.

The social relevance and the temporal constraints of motor resonance in humans.

In humans, motor resonance effects can be tracked by measuring the enhancement of corticospinal excitability by action observation. Uncovering factors driving motor resonance is crucial for optimizing action observation paradigms in experimental and clinical settings. In the present study, we deepen motor resonance properties for grasping movements. Thirty-five healthy subjects underwent an action observation task presenting right-hand grasping movements differing from their action goal. Single-pulse transcranial magnetic stimulation was applied over the left primary motor cortex at 100, 200, or 300 ms from the onset of the visual stimulus depicting the action. Motor-evoked potentials were recorded from four muscles of the right hand and forearm. Results show a muscle-specific motor resonance effect at 200 ms after movement but selectively for observing a socially relevant grasp towards another human being. This effect correlates with observers' emotional empathy scores, and it was followed by inhibition of motor resonance at 300 ms post-stimulus onset. No motor resonance facilitation emerged while observing intransitive hand movement or object grasping. This evidence highlights the social side of motor resonance and its dependency on temporal factors.

Pay attention: you can fall! The Mini-BESTest scale and the turning duration of the TUG test provide valid balance measures in neurological patients: a prospective study with falls as the balance criterion.

Background: Balance, i.e., the ability not to fall, is often poor in neurological patients and this impairment increases their risk of falling. The Mini-Balance Evaluation System Test (Mini-BESTest), a rating scale, the Timed Up and Go (TUG) test, and gait measures are commonly used to quantify balance. This study assesses the criterion validity of these measures as balance measures. Methods: The probability of being a faller within nine months was used as the balance criterion. The Mini-BESTest, TUG (instrumented with inertial sensors), and walking test were administered before and after inpatient rehabilitation. Multiple and LASSO logistic regressions were used for the analysis. The diagnostic accuracy of the model was assessed with the area under the curve (AUC) of the receiver operating characteristic curve. Mobility measure validity was compared with the Akaike Information Criterion (AIC). Results: Two hundred and fourteen neurological patients (stroke, peripheral neuropathy, or parkinsonism) were recruited. In total, 82 patients fell at least once in the nine-month follow-up. The Mini-BESTest (AUC = 0.69; 95%CI: 0.62-0.76), the duration of the TUG turning phase (AUC = 0.69; 0.62-0.76), and other TUG measures were significant faller predictors in regression models. However, only the turning duration (AIC = 274.0) and Mini-BESTest (AIC = 276.1) substantially improved the prediction of a baseline model, which only included fall risk factors from the medical history (AIC = 281.7). The LASSO procedure selected gender, disease chronicity, urinary incontinence, the Mini-BESTest, and turning duration as optimal faller predictors. Conclusion: The TUG turning duration and the Mini-BESTest predict the chance of being a faller. Their criterion validity as balance measures in neurological patients is substantial.

Modulating motor resonance with paired associativestimulation: Neurophysiological and behavioral outcomes.

In the human brain, paired associative stimulation (PAS), a non-invasive brain stimulation technique based on Hebbian learning principles, can be used to model motor resonance, the inner activation of an observer's motor system by action observation. Indeed, the newly developed mirror PAS (m-PAS) protocol, through the repeatedly pairing of transcranial magnetic stimulation (TMS) pulses over the primary motor cortex (M1) and visual stimuli depicting index-finger movements, allows the emergence of a new, atypical pattern of cortico-spinal excitability. In the present study, we performed two experiments to explore (a) the debated hemispheric lateralization of the action-observation network and (b) the behavioral after-effects of m-PAS, particularly concerning a core function of the MNS: automatic imitation. In Experiment 1, healthy participants underwent two sessions of m-PAS, delivered over the right and left M1. Before and after each m-PAS session, motor resonance was assessed by recording motor-evoked potentials induced by single-pulse TMS applied to the right M1 while observing contralateral (left) and ipsilateral (right) index-finger movements or static hands. In Experiment 2, participants performed an imitative compatibility task before and after the m-PAS targeting the right M1. Results showed that only m-PAS targeting the right hemisphere, non-dominant in right-handed people, induced the emergence of motor resonance for the conditioned movement, absent before the stimulation. This effect is not present when m-PAS target the M1 of the left hemisphere. Importantly, the protocol also affects behavior, modulating automatic imitation in a strictly somatotopic fashion (i.e., influencing the imitation of the conditioned finger movement). Overall, this evidence shows that the m-PAS can be used to drive new associations between the perception of actions and their corresponding motor programs, measurable both at a neurophysiological and behavioral level. At least for simple, not goal-directed, movements, the induction of motor resonance and automatic imitation effects are governed by mototopic and somatotopic rules.

Action Observation Treatment for Upper Limb Rehabilitation in Patients With Stroke: Protocol for a Multicenter Randomized Controlled Trial.

BACKGROUND: In the last few years, new noninvasive strategies have emerged as rehabilitative treatments for patients with stroke. Action observation treatment (AOT) is a rehabilitation approach based on the properties of the mirror neuron system with a positive impact on modifying cortical activation patterns and improving the upper limb kinematics. AOT involves the dynamic process of observing purposeful actions with the intention of imitating and then practicing those actions. In recent years, several clinical studies suggested the effectiveness of AOT in patients with stroke to improve motor recovery and autonomy in activities of daily living. However, a deeper knowledge of the behavior of the sensorimotor cortex during AOT seems to be essential. OBJECTIVE: The aim of this clinical trial, conducted in 2 neurorehabilitation centers and in patients' homes, is to investigate the effectiveness of AOT in patients with stroke, confirming the translational power of a tailored treatment. Particular emphasis will be placed on the predictive value of neurophysiological biomarkers. In addition, the feasibility and impact of a home-based AOT program will be investigated. METHODS: A 3-arm, assessor-blinded, randomized controlled trial will be performed by enrolling patients with stroke in the chronic stage. A total of 60 participants will be randomly allocated to receive 15 sessions of AOT with different protocols (AOT at the hospital, AOT at home, and sham AOT), 3 sessions per week. The primary outcome will be assessed using the Fugl-Meyer Assessment-Upper Extremity scores. Secondary outcomes will be clinical, biomechanical, and neurophysiological assessment. RESULTS: The study protocol is part of a project (project code GR-2016-02361678) approved and funded by the Italian Ministry of Health. The study began with the recruitment phase in January 2022, and enrollment was expected to end in October 2022. Recruitment is now closed (December 2022). The results of this study are expected to be published in spring 2023. Upon completion of the analyses, we will examine the preliminary effectiveness of the intervention and neurophysiological outcomes. CONCLUSIONS: This study will be used to evaluate the effectiveness of 2 different AOT scenarios (ie, AOT at the hospital and AOT at home) in patients with chronic stroke and to assess the predictive value of neurophysiological biomarkers. Specifically, we will attempt to induce the functional modification of the cortical components by exploiting the features of the mirror neuron system, demonstrating relevant clinical, kinematic, and neurophysiological changes after AOT. With our study, we also want to provide, for the first time in Italy, the AOT home-based program while assessing its feasibility and impact. TRIAL REGISTRATION: ClinicalTrials.gov NCT04047134; https://clinicaltrials.gov/ct2/show/NCT04047134. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/42094.

Differential Item Functioning of the Mini-BESTest Balance Measure: A Rasch Analysis Study.

The Mini-Balance Evaluation Systems Test (Mini-BESTest), a 14-item scale, has high content validity for balance assessment. This study further examines the construct validity of the Mini-BESTest with an emphasis on its measurement invariance. The Mini-BESTest was administered to 292 neurological patients in two sessions (before and after rehabilitation) and evaluated with the Rasch analysis (Many-Facet Rating Scale Model: persons, items, sessions). Categories' order and fit to the model were assessed. Next, maps, dimensionality, and differential item functioning (DIF) were examined for construct validity evaluation. DIF was inspected for several clinically important variables, including session, diagnosis, and assistive devices. Mini-BESTest items had ordered categories and fitted the Rasch model. The item map did not flag severe construct underrepresentation. The dimensionality analysis showed that another variable extraneous to balance affected the score of a few items. However, this multidimensionality had only a modest impact on measures. Session did not cause DIF. DIF for assistive devices affected six items and caused a severe measurement artefact. The measurement artefact caused by DIF for diagnosis was negligible. The Mini-BESTest returns interval measures with robust construct validity and measurement invariance. However, caution should be used when comparing Mini-BESTest measures obtained with and without assistive devices.

The Falls Efficacy Scale International is a valid measure to assess the concern about falling and its changes induced by treatments.

OBJECTIVE: To test with the Rasch analysis the psychometric properties of the Falls Efficacy Scale International, a questionnaire for measuring concern about falling. DESIGN: Longitudinal observational study, before-after rehabilitation. SETTING: Inpatient rehabilitation. SUBJECTS: A total of 251 neurological patients with balance impairment. INTERVENTIONS: Physiotherapy and occupational therapy aimed at reducing the risk of falling. MAIN MEASURES: Participants (median age, first-third quartile: 74.0, 65.5-80.5 years; stroke and polyneuropathy: 43% and 21% of the sample, respectively) received a balance assessment (Falls Efficacy Scale International included) pre- and post-rehabilitation. Rasch analysis was used to evaluate the Falls Efficacy Scale International. Differential item functioning, which assesses the measures' stability in different conditions (e.g. before vs. after treatment) and in different groups of individuals, was tested for several variables. RESULTS: Patients suffered a moderate balance impairment (Mini-BESTest median score; first-third quartile: 15; 11-19), mild-moderate concern about falling (Falls Efficacy Scale International: 28; 21-37) and motor disability (Functional Independence Measure, motor domain: 70.0; 57.0-76.5). Falls Efficacy Scale International items fitted the Rasch model (range of infit and outfit mean square statistics: 0.8-1.32 and 0.71-1.45, respectively) and the questionnaire's reliability was satisfactory (0.87). No differential item functioning was found for treatment, gender, age and balance impairment. Differential item functioning was found for diagnosis and disability severity, but it is shown that it is not such as to bias measures. CONCLUSIONS: Falls Efficacy Scale International ordinal scores can be turned into interval measures, i.e. measures of the type of temperature. Being differential item functioning-free for treatment, these measures can be safely used to compare concern about falling before and after rehabilitation, such as when interested in assessing the rehabilitation effectiveness.

Effects of gait rehabilitation on motor coordination in stroke survivors: an UCM-based approach.

Post-stroke locomotion is usually characterized by asymmetrical gait patterns, compensatory movements of trunk and nonparetic limb, altered motor coordination, and wide inter-stride variability. This pilot study was designed to test a twofold hypothesis: post-stroke survivors can exploit the redundancy of the segmental angles to stabilize the 3D footpath trajectory during the swing phase, in accordance with the Uncontrolled Manifold (UCM) theory; an intense rehabilitative treatment improves both motor performance and outcomes of the UCM analysis. Ten stroke survivors underwent two evaluation sessions, before and after a conventional multidisciplinary intensive rehabilitation program, encompassing clinical tests and gait analysis, both overground and on treadmill. In addition, the UCM analysis was implemented to investigate whether variance of segmental angles is structured to minimize the inter-stride variability of the 3D footpath during the swing phase of treadmill locomotion. Both clinical and spatio-temporal parameters improved after the treatment, even if the statistical significance was reached for a limited set of them. The UCM analysis suggested that post-stroke survivors exploit the redundancy of lower limbs segmental angles mainly during the late swing, without significant differences between affected and unaffected sides. Thereafter, the main significant effects of the rehabilitative treatment consisted in strengthening the synergistic organization of the redundant segmental angles involving a more accurate control of the 3D footpath. Concluding, the UCM theory can be a promising tool to appraise the effects of a specific rehabilitative protocol on motor coordination in post-stroke survivors.

The McNemar Change Index worked better than the Minimal Detectable Change in demonstrating the change at a single subject level.

BACKGROUND AND OBJECTIVE: To assess the agreement between the Rasch Change Index (RCI), minimal detectable change (MDC), and McNemar Change Index (McCI), three statistics for demonstrating the patient's improvement/deterioration. METHODS: The Mini-Balance Evaluation Systems Test (Mini-BESTest (MB)) (a balance scale developed with the Rasch analysis) was administered before and after rehabilitation to 315 neurological patients. The MB RCI was chosen as the criterion standard for detecting the patient's improvement. Positive likelihood ratios and negative likelihood ratios (PLRs and NLRs, respectively) were used to evaluate the MDC and McCI accuracy in identifying the patient's improvement. Three different MB MDCs were assessed. RESULTS: One-hundred patients improved their MB in accordance with the RCI. All three MDCs and the McCI were solid in ruling out the patient's improvement (NLR <0.2). The McCI and the largest MDC were also good in detecting the patient's improvement (PLR>5), whereas the smaller MDCs were not. Of the four indices, McCI was the most robust in case of missing items. CONCLUSION: A patient stable in accordance with the MDCs or McCI is actually stable as per the criterion standard. To be reasonably sure that the patient is actually improved, larger MDC values or the McCI should be preferred, and the McCI is preferable if there are missing items.

Turning and sit-to-walk measures from the instrumented Timed Up and Go test return valid and responsive measures of dynamic balance in Parkinson's disease.

BACKGROUND: Balance impairment is a hallmark of Parkinson's disease with dramatic effects for patients (e.g. falls). Its assessment is thus of paramount importance. The aim of this work is to assess which measures from the instrumented Timed Up and Go test (recorded with inertial sensors) are valid balance measures in Parkinson's disease and evaluate their responsiveness to rehabilitation. METHODS: The Mini-BESTest (a criterion-standard balance measure) and the instrumented Timed Up and Go test (with inertial sensors secured to the trunk) were administered to 20 Parkinson's disease patients before and after inpatient rehabilitation (median [IQR]; 76.5 [8.25] years; 5 females; Hoehn and Yahr stage: 2.5 [0.5]). 81 parameters from the instrumented Timed Up and Go test were evaluated. Multiple factor analysis (a variant of principal component analysis for repeated measurements) and effect sizes were used to assess validity and responsiveness, respectively. FINDINGS: Only the first component of the multiple factor analysis correlated with the Mini-BESTest, and 21 measures from the instrumented Timed Up and Go test had large loadings on this component. However, only three of these 21 measures also directly correlated with the Mini-BESTest (trunk angular velocities from sit-to-walk and turning; r = 0.46 to 0.50, P = 0.021 to 0.038). Sit-to-walk angular velocity showed greater responsiveness than the Mini-BESTest, while turning showed slightly less. INTERPRETATION: Angular velocities from the turning and sit-to-walk phases of the Timed Up and Go test are valid balance measures in Parkinson's disease and are also responsive to rehabilitation.

Optical Magnetic Dipole Levitation Using a Plasmonic Surface.

Optically induced magnetic resonances in nonmagnetic media have unlocked magnetic light-matter interactions and led to new technologies in many research fields. Previous proposals for the levitation of nanoscale particles without structured illumination have worked on the basis of epsilon-near-zero surfaces or anisotropic materials, but these materials carry with them significant fabrication difficulties. We report the optical levitation of a magnetic dipole over a wide range of realistic materials, including bulk metals, thereby relieving these difficulties. The repulsion is independent of surface losses, and we propose an experiment to detect this force which consists of a core-shell nanoparticle, exhibiting a magnetic resonance, in close proximity to a gold substrate under plane wave illumination. We anticipate the use of this phenomenon in new nanomechanical devices.

Bringing spatiotemporal gait analysis into clinical practice: Instrument validation and pilot study of a commercial sensorized carpet.

BACKGROUND AND OBJECTIVE: We illustrate a low-cost platform easing the estimation of spatio-temporal parameters (GA-STP) ready for large-scale deployment in fall prevention. METHODS: We used a commercial sensorized carpet with a limited cost and a very coarse resolution. An instrument validation test was accomplished: the Wilcoxon test for paired samples and the correlation test with Spearman method were used to compare the values computed by the platform with reference ones. Hierarchical clustering using Ward's method and ROC curves have been used to assess the performance in a pilot study enrolling patients. RESULTS: Validation shows no significant difference between computed and reference values of gait speed (ρ-value:0.99; p-value:2.2E-16), step number (ρ-value:0.91; p-value:5.8E-16) and stride-length (ρ-value:0.92; p-value:7.5E-9). The clinical pilot study confirms that the platform may also be used to track the improvements occurring during a rehabilitation program. CONCLUSIONS: We believe that the use of a commercial carpet makes the solution proposed ready to be deployed on a large scale for effectively bringing GA into the clinical practice.

Responsiveness to rehabilitation of balance and gait impairment in elderly with peripheral neuropathy.

Elderly people with peripheral neuropathy of the lower limbs (PNLL) demonstrate a typical balance and gait impairment because of sensory ataxia. There is evidence that rehabilitation produces important gains on balance and gait. However, responsiveness to rehabilitation of balance and gait measures is unknown in PNLL. Aim of the current work is to evaluate the responsiveness to rehabilitation of balance, gait and sensory ataxia measures in elderly with PNLL. Twenty-five elderly with PNLL attending physiotherapy and occupational therapy during inpatient rehabilitation were recruited. Balance and gait measures (including static posturography, TUG test and the 10 m walking test) were administered on admission and discharge. An accelerometer secured to the trunk was used for TUG recording and static balance assessment. Static balance was tested with open and closed eyes, so as to assess sensory ataxia. Following rehabilitation, patients improved gait [admission vs discharge, mean(SD): 0.86(0.33) vs 0.98(0.32) m/s], TUG [18.7(7.8) vs 15.1(5.2) s] and turning [46.2(15.3) vs 53.3(15.3) °/s]. However, none of 12 static balance parameters derived from trunk acceleration significantly changed. Principal component analysis showed that before training, eyes closed and eyes open balance correlated with orthogonal components (one and two vs. three and four). After training, eyes open and eyes closed balance were more similar to each other being both correlated with component one. Responsiveness to rehabilitation is larger for gait than static balance measured by trunk acceleration. However, exercise can also have a beneficial effect on sensory ataxia by making eyes closed balance more similar to eyes open balance.

Experimental demonstration of linear and spinning Janus dipoles for polarisation- and wavelength-selective near-field coupling.

The electromagnetic field scattered by nano-objects contains a broad range of wavevectors and can be efficiently coupled to waveguided modes. The dominant contribution to scattering from subwavelength dielectric and plasmonic nanoparticles is determined by electric and magnetic dipolar responses. Here, we experimentally demonstrate spectral and phase selective excitation of Janus dipoles, sources with electric and magnetic dipoles oscillating out of phase, in order to control near-field interference and directional coupling to waveguides. We show that by controlling the polarisation state of the dipolar excitations and the excitation wavelength to adjust their relative contributions, directionality and coupling strength can be fully tuned. Furthermore, we introduce a novel spinning Janus dipole featuring cylindrical symmetry in the near and far field, which results in either omnidirectional coupling or noncoupling. Controlling the propagation of guided light waves via fast and robust near-field interference between polarisation components of a source is required in many applications in nanophotonics and quantum optics.

How do patients improve their timed up and go test? Responsiveness to rehabilitation of the TUG test in elderly neurological patients.

BACKGROUND: The timed up and go (TUG) test is widely used for assessing treatments effectiveness on elderly mobility. Although the TUG test consists of different tasks (e.g. walking and turning), the total TUG duration (TTD) is usually the only outcome measure, with TTD shortening indicating the patient's improvement. RESEARCH QUESTION: Does TTD shortening reflect the improvement of each TUG tasks or does it reflect the improvement of only some of them? METHODS: This retrospective study recruited 120 elderly patients (mean, SD: 76.9, 6.6 years) admitted to inpatient rehabilitation because of an acute or chronic neurological disease (acute patients, AP; chronic patients, CP). TTD and TUG tasks duration was measured on admission and discharge (five trials/session) by means of the instrumental TUG test (ITUG). Likelihood ratios (LRs) were used for inferring TUG tasks improvement from TTD improvement. TTD and TUG tasks have improved if at least four measurements on discharge were shorter than the shortest measurement on admission. RESULTS: TTD improvement per se is not enough to claim that all the TUG tasks have improved (LR+AP = 1.32; LR+CP = 1.85). Conversely, if TTD has not improved, not even a single TUG task has improved (LR-AP = 0.13; LR-CP = 0.19). If TTD has improved, there is at least one TUG task that actually improved (LR+AP = 3.17; LR+CP = 9.54). The improvement of all TUG tasks can be only inferred in the (unusual) event of a large TTD shortening (AP: >39%, LR+AP = 6.26; CP: >30%, LR+CP = 9.0). SIGNIFICANCE: In most cases, TTD improvement is not associated with the improvement of all TUG tasks. Moreover, when TTD has improved there is at least a TUG task that has improved, but that remains unknown. To actually understand how treatments ameliorate patients' mobility, ITUG with TUG task duration measurement should be preferred to TTD.

Directional scattering from particles under evanescent wave illumination: the role of reactive power.

Study of photonic spin-orbital interactions, which involves control of the propagation and spatial distributions of light via its polarization, is not only important at the fundamental level but also has significant implications for functional photonic applications that require active tuning of directional light propagation. Many of the experimental demonstrations have been attributed to the spin-momentum locking characteristic of evanescent waves. In this Letter, we show another property of evanescent waves: the polarization-dependent direction of the imaginary part of the Poynting vector, i.e., reactive power. Based on this property, we propose a simple and robust way to tune the directional far-field scattering from nanoparticles near a surface under evanescent wave illumination by controlling its polarization and direction of the incident light.

Janus and Huygens Dipoles: Near-Field Directionality Beyond Spin-Momentum Locking.

Unidirectional scattering from circularly polarized dipoles has been demonstrated in near-field optics, where the quantum spin-Hall effect of light translates into spin-momentum locking. By considering the whole electromagnetic field, instead of its spin component alone, near-field directionality can be achieved beyond spin-momentum locking. This unveils the existence of the Janus dipole, with side-dependent topologically protected coupling to waveguides, and reveals the near-field directionality of Huygens dipoles, generalizing Kerker's condition. Circular dipoles, together with Huygens and Janus sources, form the complete set of all possible directional dipolar sources in the far- and near-field. This allows the designing of directional emission, scattering, and waveguiding, fundamental for quantum optical technology, integrated nanophotonics, and new metasurface designs.

Criterion validity of the instrumented Timed Up and Go test: A partial least square regression study.

The Timed Up and Go (TUG) test is a common mobility measure in rehabilitation. With the instrumental TUG test (ITUG; i.e. the TUG measured by inertial measurement units, IMUs), several movement measures are newly available. However, the clinical meaning of these new measures is not totally clear. Aim of the current work is to evaluate the validity of different ITUG parameters as a measure of balance. Neurological patients (n = 122; 52 females; 89 older than 65 years) completed the TUG test with IMUs secured to their back. IMUs signals were used to split the TUG test in five phases (sit-to-stand, walk1, turn1, walk2 and turn-and-sit) and twelve movement parameters were obtained. Experienced clinicians administered the Mini-BESTest (MB) scale, a sound balance measure. The partial least square regression (PLSR) was used to explore the association between the ITUG variables and the MB measure. A PLSR model with twelve ITUG variables had satisfactory fit parameters (RMSEP: 11%; R2: 0.41, 95% CI: 0.28-0.54; regression line: 1, 95% CI: 0.78-1.22). Three ITUG variables (i.e. turn1 vertical angular velocity, turn1 duration and turn2 vertical angular velocity) were found to be the most important predictors of the MB measure. A PLSR model with the turning variables only had fit parameters comparable to that of the twelve variables model. Turning parameters from the TUG test are good predictors of the MB scale. The mean angular velocity during turning and the duration of the turning phase are thus proposed as a valid, ratio-level measures of balance in neurological patients.