Walking-adaptability therapy after stroke: results of a randomized controlled trial.

BACKGROUND: The ability to adapt walking to environmental properties and hazards, a prerequisite for safe ambulation, is often impaired in persons after stroke. RESEARCH QUESTION: The aim of this study was to compare the efficacy of two walking-adaptability interventions: a novel treadmill-based C-Mill therapy (using gait-dependent augmented reality) and the standard overground FALLS program (using physical context). We expected sustained improvements for both treatment groups combined but hypothesized better outcomes for C-Mill therapy than the FALLS program due to its expected greater amount of walking practice. METHODS: In this pre-registered single-centre parallel group randomized controlled trial, forty persons after stroke (≥ 3 months ago) with walking and/or balance deficits were randomly allocated to either 5 weeks of C-Mill therapy or the FALLS program. The primary outcome measure was the standard walking speed as determined with the 10-meter walking test (10MWT). Additionally, context-specific walking speed was assessed in environments enriched with either stationary physical context (10MWT context) or suddenly appearing visual images (Interactive Walkway obstacles). The walking-adaptability scores of those enriched walking tests served as secondary outcome measures. Furthermore, a cognitive task was added to all three assessments to evaluate dual-task performance in this context. Finally, the participants' experience and amount of walking practice were scored. The outcome measures were assessed at four test moments: pre-intervention (T0), post-intervention (T1), 5-week post-intervention retention (T2), and 1-year post-intervention follow-up (T3). RESULTS: No significant group differences were found between the interventions for the primary outcome measure standard walking speed, but we found a greater improvement in context-specific walking speed with stationary physical context of the C-Mill therapy compared to the FALLS program at the post-intervention test, which was no longer significant at retention. Both interventions were well received, but C-Mill therapy scored better on perceived increased fitness than the FALLS program. C-Mill therapy resulted in twice as many steps per session of equal duration than the FALLS program. The "change-over-time" analyses for participants of both interventions combined showed no significant improvements in the standard walking speed; however, significant improvements were found for context-specific walking speed, walking adaptability, and cognitive dual-task performance. SIGNIFICANCE: This study showed no between-group differences between the novel treadmill-based C-Mill therapy and the standard overground FALLS program with respect to the primary outcome measure standard walking speed. However, the greater amount of walking practice observed for the C-Mill group, an essential aspect of effective intervention programs after stroke, may underlie the reported increased perceived fitness and observed increased context-specific walking speed for the C-Mill group directly after the intervention. Although the "change-over-time" results for all participants combined showed no improvement in the standard walking speed, context-specific walking speed and walking adaptability showed sustained improvements after the interventions, underscoring the importance of including walking-adaptability training and assessment in rehabilitation post stroke. TRIAL REGISTRATION: The Netherlands Trial Register NTR4030 . Registered 11 June 2013.

[Clinical characteristics of sexually abused individuals with borderline intellectual functioning or mild intellectual disability: an overview of the literature]. / Klinische kenmerken van seksueel misbruikte mensen met een lichte verstandelijke beperking: een literatuuroverzicht.

BACKGROUND: Sexual abuse in individuals with (above) average iq is associated with a wide range of behavioural and psychological clinical characteristics, including characteristics regarding body experience. However, research on the clinical characteristics of sexually abused individuals with borderline intellectual functioning or mild intellectual disability (bif-mid) is scarce. OBJECTIVE To provide an overview of the literature on the clinical characteristics of sexually abused individuals with bif-mid.
METHOD: PubMed, Embase, PsycInfo, cinahl, Cochrane Library and Web of Science were searched for relevant publications using terms related to 'intellectual disability' and 'sexual abuse'.
RESULTS: Seven studies were included. The studies in question mostly reported behavioural and psychological characteristics such as challenging behaviour, sexualised behaviour or posttraumatic stress, anxiety or depressive symptoms associated with sexual abuse in individuals with bif-mid. None of the studies reported problems regarding body experience. CONCLUSIONS Sexual abuse in individuals with bif-mid is associated with a broad range of behavioural and psychological characteristics similar to that of individuals with (above) average iq. Whether sexually abused individuals with bif-mid have similar problems in body experience as sexually abused individuals with (higher than) average iq needs to be investigated.

Inter-individual differences in stride frequencies during running obtained from wearable data.

The purpose of the present study was to identify factors that underlie differences among runners in stride frequency (SF) as a function of running speed. Participants (N = 256; 85.5% males and 14.5% females; 44.1 ± 9.8 years; 181.4 ± 8.4 cm; 75.3 ± 10.6 kg; mean ± SD) shared their wearable data (Garmin Inc). Individual datasets were filtered to obtain representative relationships between stride frequency (SF) and speed per individual, representing in total 16.128 h of data. The group relationship between SF (72.82 to 94.73 strides · min-1) and running speed (V) (from 1.64 to 4.68 m · s-1) was best described with SF = 75.01 + 3.006 V. A generalised linear model with random effects was used to determine variables associated with SF. Variables and their interaction with speed were entered in a stepwise forward procedure. SF was negatively associated with leg length and body mass and an interaction of speed and age indicated that older runners use higher SF at higher speed. Furthermore, run frequency and run duration were positively related to SF. No associations were found with injury incidence, athlete experience or performance. Leg length, body mass, age, run frequency and duration were associated with SFs at given speeds. KEY POINTS On a group level, stride frequency can be described as a linear function of speed: SF (strides · min-1) = 75.01+ 3.006·speed (m · s-1) within the range of 1.64 to 4.68 m · s-1. On an individual level, the SF-speed relation is best described with a second order polynomial. Leg length and body mass were positively related to stride frequency while age was negatively related to stride frequency. Run frequency and run duration were positively related to stride frequency, while running experience, performance and injury incidence were unrelated.

An adaptive, real-time cadence algorithm for unconstrained sensor placement.

This paper evaluates a new and adaptive real-time cadence detection algorithm (CDA) for unconstrained sensor placement during walking and running. Conventional correlation procedures, dependent on sensor position and orientation, may alternately detect either steps or strides and consequently suffer from false negatives or positives. To overcome this limitation, the CDA validates correlation peaks as strides using the Sylvester's criterion (SC). This paper compares the CDA with conventional correlation methods. 22 volunteers completed 7 different circuits (approx. 140 m) at three gaits-speeds: walking (1.5 m s-1), running (3.4 m s-1), and sprinting (5.2 and 5.7 m s-1), disturbed by various gait-related activities. The algorithm was simultaneously evaluated for 10 different sensor positions. Reference strides were obtained from a foot sensor using a dedicated offline algorithm. The described algorithm resulted in consistent numbers of true positives (85.6-100.0%) and false positives (0.0-2.9%) and showed to be consistently accurate for cadence feedback across all circuits, subjects and sensors (mean ±â€¯SD: 98.9 ±â€¯0.2%), compared to conventional cross-correlation (87.3 ±â€¯13.5%), biased (73.0 ±â€¯16.2) and unbiased (82.2 ±â€¯20.6) autocorrelation procedures. This study shows that the SC significantly improves cadence detection, resulting in robust results for various gaits, subjects and sensor positions.

Effects of handrail hold and light touch on energetics, step parameters, and neuromuscular activity during walking after stroke.

BACKGROUND: Holding a handrail or using a cane may decrease the energy cost of walking in stroke survivors. However, the factors underlying this decrease have not yet been previously identified. The purpose of the current study was to fill this void by investigating the effect of physical support (through handrail hold) and/or somatosensory input (through light touch contact with a handrail) on energy cost and accompanying changes in both step parameters and neuromuscular activity. Elucidating these aspects may provide useful insights into gait recovery post stroke. METHODS: Fifteen stroke survivors participated in this study. Participants walked on a treadmill under three conditions: no handrail contact, light touch of the handrail, and firm handrail hold. During the trials we recorded oxygen consumption, center of pressure profiles, and bilateral activation of eight lower limb muscles. Effects of the three conditions on energy cost, step parameters and neuromuscular activation were compared statistically using conventional ANOVAs with repeated measures. In order to examine to which extent energy cost and step parameters/muscle activity are associated, we further employed a partial least squares regression analysis. RESULTS: Handrail hold resulted in a significant reduction in energy cost, whereas light touch contact did not. With handrail hold subjects took longer steps with smaller step width and improved step length symmetry, whereas light touch contact only resulted in a small but significant decrease in step width. The EMG analysis indicated a global drop in muscle activity, accompanied by an increased constancy in the timing of this activity, and a decreased co-activation with handrail hold, but not with light touch. The regression analysis revealed that increased stride time and length, improved step length symmetry, and decreased muscle activity were closely associated with the decreased energy cost during handrail hold. CONCLUSION: Handrail hold, but not light touch, altered step parameters and was accompanied by a global reduction in muscle activity, with improved timing constancy. This suggests that the use of a handrail allows for a more economic step pattern that requires less muscular activation without resulting in substantial neuromuscular re-organization. Handrail use may thus have beneficial effects on gait economy after stroke, which cannot be accomplished through enhanced somatosensory input alone.

Intended and unintended (sensory-)motor coupling between the affected and unaffected upper limb in complex regional pain syndrome.

BACKGROUND: Motor dysfunction in complex regional pain syndrome (CRPS) has been associated with bilateral malfunction of sensory and motor circuits, which hints at abnormal coupling between the affected and the contralateral unaffected limb. In addition, clinical observations suggest that motor performance may depend on the (voluntary or automatic) context in which movements are executed. The present study aimed to examine the role of voluntary and automatic aspects of interlimb coupling in CRPS. METHODS: Twenty patients with unilateral chronic CRPS and 40 healthy controls performed a set of unimanual and bimanual motor tasks that differed in the degree to which intended bilateral planning, intended afference-based error correction and unintended reflex-like entrainment were involved. RESULTS: Stability of interlimb coordination was reduced in CRPS patients compared to controls, especially for tasks involving active control of the affected side. In CRPS patients, intended coupling between the hands (planning, error correction) was markedly impaired, whereas unintended coupling between the hands (entrainment) appeared normal. CONCLUSIONS: Impaired motor control of the affected limb interfered with bimanual coordination, in particular for tasks involving voluntary (intended) as opposed to automatic (unintended) interlimb coupling. Our findings suggest inappropriate functioning of higher order centres involved in motor control of the affected limb, probably due to pain-related processes and impaired processing of proprioceptive information. Motor function of the affected limb may benefit from intended synchronization with movements of the unaffected contralateral limb, suggesting that bilateral training may be useful in patients with unilateral CRPS.

Can external lateral stabilization reduce the energy cost of walking in persons with a lower limb amputation?

The aim of this study was to examine whether impaired balance control is partly responsible for the increased energy cost of walking in persons with a lower limb amputation (LLA). Previous studies used external lateral stabilization to evaluate the energy cost for balance control; this caused a decrease in energy cost, with concomitant decreases in mean and variability of step width. Using a similar set-up, we expected larger decreases for LLA than able-bodied controls. Fifteen transtibial amputees (TT), 12 transfemoral amputees (TF), and 15 able-bodied controls (CO) walked with and without external lateral stabilization provided via spring like cords attached to the waist. Effects of this manipulation on energy cost, step parameters, and pelvic motion were evaluated between groups. TT (-5%) and CO (-3%) showed on average a small reduction in energy cost when walking with stabilization, whereas TF exhibited an increase in energy cost (+6.5%) The difference in the effect of stabilization was only significant between TT and TF. Step width, step width variability, and medio-lateral pelvic displacement decreased significantly with stabilization in all groups, especially in TT. Contrary to expectations, external lateral stabilization did not result in a larger decrease in the energy cost of walking for LLA compared to able-bodied controls, suggesting that balance control is not a major factor in the increased cost of walking in LLA. Alternatively, the increased energy cost with stabilization for TF suggests that restraining (medio-lateral) pelvic motion impeded necessary movement adaptations in LLA, and thus negated the postulated beneficial effects of stabilization on the energy cost of walking.

A benchmark test of accuracy and precision in estimating dynamical systems characteristics from a time series.

Characteristics of dynamical systems are often estimated to describe physiological processes. For instance, Lyapunov exponents have been determined to assess the stability of the cardio-vascular system, respiration, and, more recently, human gait and posture. However, the systematic evaluation of the accuracy and precision of these estimates is problematic because the proper values of the characteristics are typically unknown. We fill this void with a set of standardized time series with well-defined dynamical characteristics that serve as a benchmark. Estimates ought to match these characteristics, at least to good approximation. We outline a procedure to employ this generic benchmark test and illustrate its capacity by examining methods for estimating the maximum Lyapunov exponent. In particular, we discuss algorithms by Wolf and co-workers and by Rosenstein and co-workers and evaluate their performances as a function of signal length and signal-to-noise ratio. In all scenarios, the precision of Rosenstein's algorithm was found to be equal to or greater than Wolf's algorithm. The latter, however, appeared more accurate if reasonably large signal lengths are available and noise levels are sufficiently low. Due to its modularity, the presented benchmark test can be used to evaluate and tune any estimation method to perform optimally for arbitrary experimental data.

The effect of different inter-pad distances on the determination of active drag using the Measuring Active Drag system.

The Measuring Active Drag (MAD) system was developed to determine active drag in swimming by measuring the push-off force exerted at fixed pads placed below the waterline. The imposed inter-pad distance, which to date has been kept constant while using the MAD system, could affect the active drag because it requires the use of different stroke frequencies. The aim of the present study was therefore to determine the effect of inter-pad distance on active drag at a given speed. In particular, drag-velocity curves at three different inter-pad distances (1.25m, 1.35m and 1.45m) were determined using the MAD system for eleven competitive swimmers. Variation of 16% in inter-pad distance (14% change in stroke frequency) revealed no significant difference in calculated active drag between different inter-pad distances and a low (<5%) average coefficient of variation over different inter-pad distances was found. In addition, inter-test reliability, which was determined for the two 1.35m conditions only, was high (ICC>0.90) for measurements on two consecutive days. The results suggest that it may not be necessary to adapt the inter-pad distance of the MAD system based on anthropometric characteristics of the subject or the velocity-related stroke length in free swimming.

Assessing the stability of human locomotion: a review of current measures.

Falling poses a major threat to the steadily growing population of the elderly in modern-day society. A major challenge in the prevention of falls is the identification of individuals who are at risk of falling owing to an unstable gait. At present, several methods are available for estimating gait stability, each with its own advantages and disadvantages. In this paper, we review the currently available measures: the maximum Lyapunov exponent (λS and λL), the maximum Floquet multiplier, variability measures, long-range correlations, extrapolated centre of mass, stabilizing and destabilizing forces, foot placement estimator, gait sensitivity norm and maximum allowable perturbation. We explain what these measures represent and how they are calculated, and we assess their validity, divided up into construct validity, predictive validity in simple models, convergent validity in experimental studies, and predictive validity in observational studies. We conclude that (i) the validity of variability measures and λS is best supported across all levels, (ii) the maximum Floquet multiplier and λL have good construct validity, but negative predictive validity in models, negative convergent validity and (for λL) negative predictive validity in observational studies, (iii) long-range correlations lack construct validity and predictive validity in models and have negative convergent validity, and (iv) measures derived from perturbation experiments have good construct validity, but data are lacking on convergent validity in experimental studies and predictive validity in observational studies. In closing, directions for future research on dynamic gait stability are discussed.

Motor consequences of experimentally induced limb pain: a systematic review.

Compelling evidence exists that pain may affect the motor system, but it is unclear if different sources of peripheral limb pain exert selective effects on motor control. This systematic review evaluates the effects of experimental (sub)cutaneous pain, joint pain, muscle pain and tendon pain on the motor system in healthy humans. The results show that pain affects many components of motor processing at various levels of the nervous system, but that the effects of pain are largely irrespective of its source. Pain is associated with inhibition of muscle activity in the (painful) agonist and its non-painful antagonists and synergists, especially at higher intensities of muscle contraction. Despite the influence of pain on muscle activation, only subtle alterations were found in movement kinetics and kinematics. The performance of various motor tasks mostly remained unimpaired, presumably as a result of a redistribution of muscle activity, both within the (painful) agonist and among muscles involved in the task. At the most basic level of motor control, cutaneous pain caused amplification of the nociceptive withdrawal reflex, whereas insufficient evidence was found for systematic modulation of other spinal reflexes. At higher levels of motor control, pain was associated with decreased corticospinal excitability. Collectively, the findings show that short-lasting experimentally induced limb pain may induce immediate changes at all levels of motor control, irrespective of the source of pain. These changes facilitate protective and compensatory motor behaviour, and are discussed with regard to pertinent models on the effects of pain on motor control.

Validation of seat-off and seat-on in repeated sit-to-stand movements using a single-body-fixed sensor.

The identification of chair rise phases is a prerequisite for quantifying sit-to-stand movements. The aim of this study is to validate seat-off and seat-on detection using a single-body-fixed sensor against detection based on chair switches. A single sensor system with three accelerometers and three gyroscopes was fixed around the waist. Synchronized on-off switches were placed under the chair. Thirteen older adults were recruited from a residential care home and fifteen young adults were recruited among college students. Subjects were asked to complete two sets of five trials each. Six features of the trunk movement during seat-off and seat-on were calculated automatically, and a model was developed to predict the moment of seat-off and seat-on transitions. The predictions were validated with leave-one-out cross-validation. Feature extraction failed in two trials (0.7%). For the optimal combination of seat-off predictors, cross-validation yielded a mean error of 0 ms and a mean absolute error of 51 ms. For the best seat-on predictor, cross-validation yielded a mean error of -3 ms and a mean absolute error of 127 ms. The results of this study demonstrate that seat-off and seat-on in repeated sit-to-stand movements can be detected semi-automatically in young and older adults using a one-body-fixed sensor system with an accuracy of 51 and 127 ms, respectively. The use of the ambulatory instrumentation is feasible for non-technically trained personnel. This is an important step in the development of an automated method for the quantification of sit-to-stand movements in clinical practice.

Differential modulations of ipsilateral and contralateral beta (de)synchronization during unimanual force production.

Unilateral movement is usually accompanied by ipsilateral activity in the primary motor cortex (M1). It is still largely unclear whether this activity reflects interhemispheric 'cross-talk' of contralateral M1 that facilitates movement, or results from processes that inhibit motor output. We investigated the role of beta power in ipsilateral M1 during unimanual force production. Significant ipsilateral beta desynchronization occurred during continuous dynamic but not during static force production. Moreover, event-related time-frequency analysis revealed bilateral desynchronization patterns, whereas post-movement synchronization was confined to the contralateral hemisphere. Our findings indicate that ipsilateral activation is not merely the result of interhemispheric cross-talk but involves additional processes. Given observations of differential blood oxygen level-dependent responses in ipsilateral and contralateral M1, and the correlation between beta desynchronization and the firing rate of pyramidal tract neurons in contralateral M1 during movement, we speculate that beta desynchronization in contra- and ipsilateral M1 arises from distinct neural activation patterns.

Organization of voluntary stepping in response to emotion-inducing pictures.

The present experiment was conducted to examine the expectation that emotion stimuli influence the initiation and execution of voluntary stepping, a highly coordinated activity involving a sequence of medio-lateral and anterio-posterior weight shifts. Thirty participants made forward (approach) or backward (avoidance) steps on a forceplate in response to the valence of visual stimuli. Posturographic parameters of the steps, related to automatic stimulus evaluation, step initiation and step execution, were determined and analyzed as a function of stimulus valence and stimulus-response mapping. The results revealed marked effects of emotion on the step parameters of interest; unpleasant images caused an initial "freezing" response, and a tendency to move away from the stimuli. Pleasant stimuli, in contrast, were not found to induce approach tendencies. The results demonstrated that affect, especially negative emotions, and whole-body movements such as voluntary stepping are coupled.

Are fast interceptive actions continuously guided by vision? Revisiting Bootsma and van Wieringen (1990).

In an influential study, R. J. Bootsma and P. C. W. van Wieringen (1990) argued that 2 of their 5 participants used visual information continuously during the attacking forehand drive in table tennis, its brief duration vis-à-vis the visuomotor delay notwithstanding. The authors repeated Bootsma and van Wieringen's experiment and included a condition in which vision was obscured after drive initiation. The authors replicated most of Bootsma and van Wieringen's findings but found no significant differences between the full-vision and no-vision conditions, which goes against the interpretation of these findings as evidence for continuous visual guidance. A subsequent simulation study found that a single preprogrammed muscle stimulation pattern resulted in spatiotemporal convergence similar to that observed experimentally but not in other important behavioral characteristics. The results contain no indications that visual information that becomes available after drive initiation affects arm motion and suggest that a form of model-based predictive control is operative rather than continuous visual guidance.

Cortico-spinal synchronization reflects changes in performance when learning a complex bimanual task.

Motor performance is accompanied by neural activity in various cortical and sub-cortical areas. This intricate network has to be delicately orchestrated. We analyzed the role of beta synchronization in motor learning using magneto-encephalography combined with electromyography. Cortico-spinal synchronization in the beta band was found to be of particular importance in establishing bimanual movement patterns in the context of a 3:2 polyrhythmic (isometric) force production task. Its dynamics correlated highly with the learning of this complex bimanual motor skill. We submit that the cortical dynamics entrains the spinal motor system by which cortico-spinal beta synchrony serves higher-level motor control functions as primary means of information transfer along the neural axis.

Sway regularity reflects attentional involvement in postural control: effects of expertise, vision and cognition.

We examined the time varying (dynamic) characteristics of center-of-pressure (COP) fluctuations in a group of 14 preadolescent dancers and 16 age-matched non-dancers. The task involved maintaining balance for 20s with eyes open or eyes closed, and with or without performing an attention demanding cognitive task (word memorization). The main finding was that the time-dependent structure of the COP trajectories of dancers exhibited less regularity than that of non-dancers, as evidenced by a higher sample entropy (decreased statistical regularity). COP irregularity also increased during secondary task performance but decreased during standing with eyes closed. The combined findings indicate that the degree of attentional involvement in postural control - as reflected in the COP dynamics - varies along an automaticity continuum, and is affected by relatively stable subject characteristics (expertise) and more transient factors related to the attentional requirements of the task at hand.

Steady and transient coordination structures of walking and running.

We studied multisegmental coordination and stride characteristics in nine participants while walking and running on a treadmill. The study's main aim was to evaluate the coordination patterns of walking and running and their variance as a function of locomotion speed, with a specific focus on gait transitions and accompanying features like hysteresis and critical fluctuations. Stride characteristics changed systematically with speed in a gait-dependent fashion, but exhibited no hysteresis. Multisegmental coordination of walking and running was captured by four principal components, the first two of which were present in both gaits. Locomotion speed had subtle yet systematic differential effects on the relative phasing between the identified components in both walking and running and its variance, in particular in the immediate vicinity of gait transitions. Unlike the stride characteristics, the identified coordination patterns revealed clear evidence of both hysteresis and critical fluctuations around transition points. Overall, the results suggest that walking and running entail similar, albeit speed- and gait-dependent, coordination structures, and that gait transitions bear signatures of nonequilibrium phase transitions. Application of multivariate analyses of whole-body recordings appears crucial to detect these features in a reliable fashion.

Tapping with intentional drift.

When tapping a desired frequency, subjects tend to drift away from this target frequency. This compromises the estimate of the correlation between inter-tap intervals (ITIs) as predicted by the two-level model of Wing and Kristofferson which consists of an internal timer ('clock') and motor delays. Whereas previous studies on the timing of rhythmic tapping attempted to eliminate drift, we compared the production of three constant frequencies (1.5, 2.0, and 2.5 Hz) to the production of tapping sequences with a linearly decreasing inter-tap interval (ITI) (corresponding to an increase in tapping frequency from 1.5 to 2.5 Hz). For all conditions a synchronization-continuation paradigm was used. Tapping forces and electromyograms of the index-finger flexor and extensor were recorded and ITIs were derived yielding interval variability and model parameters, i.e., clock and motor variances. Electromyographic recordings served to study the influence of tapping frequency on the peripheral part of the tap event. The condition with an increasing frequency was more difficult to perform, as evidenced by an increase in deviation from the intended ITIs. In general, tapping frequency affected force level, inter-tap variability, model parameters, and muscle co-activation. Parameters for the condition with a decreasing ITI were comparable to those found in the constant frequency conditions. That is, although tapping with an intentional drift is different from constant tapping and more difficult to perform, the timing properties of both forms of tapping are remarkably similar and described well by the Wing and Kristofferson model.