Task-specific training for improving propulsion symmetry and gait speed in people in the chronic phase after stroke: a proof-of-concept study.

BACKGROUND: After stroke, some individuals have latent, propulsive capacity of the paretic leg, that can be elicited during task-specific gait training. The aim of this proof-of-concept study was to investigate the effect of five-week robotic gait training for improving propulsion symmetry by increasing paretic propulsion in chronic stroke survivors. METHODS: Twenty-nine individuals with chronic stroke and impaired paretic propulsion (≥ 8% difference in paretic vs. non-paretic propulsive impulse) were enrolled. Participants received ten 60-min sessions of individual robotic gait training targeting paretic propulsion (five weeks, twice a week), complemented with home exercises (15 min/day) focusing on increasing strength and practicing learned strategies in daily life. Propulsion measures, gait kinematics and kinetics, self-selected gait speed, performance of functional gait tasks, and daily-life mobility and physical activity were assessed five weeks (T0) and one week (T1) before the start of intervention, and one week (T2) and five weeks (T3) after the intervention period. RESULTS: Between T0 and T1, no significant differences in outcomes were observed, except for a marginal increase in gait speed (+ 2.9%). Following the intervention, propulsion symmetry (+ 7.9%) and paretic propulsive impulse had significantly improved (+ 8.1%), whereas non-paretic propulsive impulse remained unchanged. Larger gains in propulsion symmetry were associated with more asymmetrical propulsion at T0. In addition, following the intervention significantly greater paretic trailing limb angles (+ 6.6%) and ankle plantarflexion moments (+ 7.1%) were observed. Furthermore, gait speed (+ 7.2%), 6-Minute Walk Test (+ 6.4%), Functional Gait Assessment (+ 6.5%), and daily-life walking intensity (+ 6.9%) had increased following the intervention. At five-week follow-up (T3), gains in all outcomes were retained, and gait speed had further increased (+ 3.6%). CONCLUSIONS: The post-intervention gain in paretic propulsion did not only translate into improved propulsion symmetry and gait speed, but also pertained to performance of functional gait tasks and daily-life walking activity levels. These findings suggest that well-selected chronic stroke survivors may benefit from task-specific targeted training to utilize the residual propulsive capacity of the paretic leg. Future research is recommended to establish simple baseline measures for identification of individuals who may benefit from such training and confirm benefits of the used training concepts in a randomized controlled trial. TRIAL REGISTRATION: Registry number ClinicalTrials.gov ( www.clinicaltrials.gov ): NCT04650802, retrospectively registered 3 December 2020.

Effect of assist-as-needed robotic gait training on the gait pattern post stroke: a randomized controlled trial.

BACKGROUND: Regaining gait capacity is an important rehabilitation goal post stroke. Compared to clinically available robotic gait trainers, robots with an assist-as-needed approach and multiple degrees of freedom (AANmDOF) are expected to support motor learning, and might improve the post-stroke gait pattern. However, their benefits compared to conventional gait training have not yet been shown in a randomized controlled trial (RCT). The aim of this two-center, assessor-blinded, RCT was to compare the effect of AANmDOF robotic to conventional training on the gait pattern and functional gait tasks during post-stroke inpatient rehabilitation. METHODS: Thirty-four participants with unilateral, supratentorial stroke were enrolled (< 10 weeks post onset, Functional Ambulation Categories 3-5) and randomly assigned to six weeks of AANmDOF robotic (combination of training in LOPES-II and conventional gait training) or conventional gait training (30 min, 3-5 times a week), focused on pre-defined training goals. Randomization and allocation to training group were carried out by an independent researcher. External mechanical work (WEXT), spatiotemporal gait parameters, gait kinematics related to pre-defined training goals, and functional gait tasks were assessed before training (T0), after training (T1), and at 4-months follow-up (T2). RESULTS: Two participants, one in each group, were excluded from analysis because of discontinued participation after T0, leaving 32 participants (AANmDOF robotic n = 17; conventional n = 15) for intention-to-treat analysis. In both groups, WEXT had decreased at T1 and had become similar to baseline at T2, while gait speed had increased at both assessments. In both groups, most spatiotemporal gait parameters and functional gait tasks had improved at T1 and T2. Except for step width (T0-T1) and paretic step length (T0-T2), there were no significant group differences at T1 or T2 compared to T0. In participants with a pre-defined goal aimed at foot clearance, paretic knee flexion improved more in the AANmDOF robotic group compared to the conventional group (T0-T2). CONCLUSIONS: Generally, AANmDOF robotic training was not superior to conventional training for improving gait pattern in subacute stroke survivors. Both groups improved their mechanical gait efficiency. Yet, AANmDOF robotic training might be more effective to improve specific post-stroke gait abnormalities such as reduced knee flexion during swing. Trial registration Registry number Netherlands Trial Register ( www.trialregister.nl ): NTR5060. Registered 13 February 2015.

Estimating ankle torque and dynamics of the stabilizing mechanism: No need for horizontal ground reaction forces.

Changes in human balance control can objectively be assessed using system identification techniques in combination with support surface translations. However, large, expensive and complex motion platforms are required, which are not suitable for the clinic. A treadmill could be a simple alternative to apply support surface translations. In this paper we first validated the estimation of the joint stiffness of an inverted pendulum using system identification methods in combination with support surface translations, by comparison with the joint stiffness calculated using a linear regression method. Second, we used the system identification method to investigate the effect of horizontal ground reaction forces on the estimation of the ankle torque and the dynamics of the stabilizing mechanism of 12 healthy participants. Ankle torque and resulting frequency response functions, which describes the dynamics of the stabilizing mechanism, were calculated by both including and excluding horizontal ground reaction forces. Results showed that the joint stiffness of an inverted pendulum estimated using system identification is comparable to the joint stiffness estimated by a regression method. Secondly, within the induced body sway angles, the ankle torque and frequency response function of the joint dynamics calculated by both including and excluding horizontal ground reaction forces are similar. Therefore, the horizontal ground reaction forces play a minor role in calculating the ankle torque and frequency response function of the dynamics of the stabilizing mechanism and can thus be omitted.

Effectiveness of rehabilitation interventions to improve paretic propulsion in individuals with stroke - A systematic review.

BACKGROUND: Stroke survivors often show reduced walking velocity and gait asymmetry. These gait abnormalities are associated with reduced propulsion of the paretic leg. This review aimed to provide an overview of the potential effectiveness of post-stroke rehabilitation interventions to improve paretic propulsion, ankle kinetics and walking velocity. METHODS: A systematic search was performed in Pubmed, Web of Science, Embase, and Pedro. Studies were eligible if they reported changes in propulsion measures (impulse, peak value and symmetry ratios) or ankle kinetics (moment and power) following intervention in stroke survivors (group size ≥10). Study selection, data extraction and quality assessment were performed independently by two authors. FINDINGS: A total of 28 studies were included, of which 25 studies applied exercise interventions, two studies focused on surgical interventions, and one on non-invasive brain stimulation. The number of high-quality trials was limited (N = 6; score Downs and Black scale ≥19). Propulsion measures were the primary outcome in eight studies. In general, mixed results were reported with 14 interventions yielding improvements in propulsion and ankle kinetics. In contrast, gains in walking velocity were observed in the vast majority of studies (N = 20 out of 23). INTERPRETATION: Interventions that yielded gains in propulsion appeared to have in common that they challenged and/or enabled the utilization of latent propulsive capacity of the paretic leg during walking. Walking speed generally increased, regardless of the observed change in propulsion, suggesting the use of compensatory mechanisms. Findings should, however, be interpreted with some caution, as the evidence base for this emerging focus of rehabilitation is limited.

Excessive short-latency stretch reflexes in the calf muscles do not cause postural instability in patients with hereditary spastic paraplegia.

OBJECTIVE: To identify the role of hyperexcitable short-latency stretch reflexes (SLRs) on balance control in people with hereditary spastic paraplegia (PwHSP). METHODS: Sixteen PwHSP with triceps surae spasticity and 9 healthy control subjects were subjected to toes-up support-surface perturbations. EMG data were recorded from gastrocnemius, soleus and tibialis anterior. Furthermore, center-of-mass trajectories were recorded. RESULTS: PwHSP were less able to withstand the perturbations. Triceps surae SLRs (40-80 ms post perturbation) in PwHSP were increased compared to healthy subjects. Furthermore, a sustained triceps surae EMG activity at 220-320 ms post perturbation was observed in PwHSP, whereas control subjects demonstrated suppression of triceps surae activity. Center of mass trajectories started to diverge between PwHSP and controls only after ∼500 ms, with greater excursions being observed in the PwHSP. CONCLUSIONS: The present results confirm that balance control is impaired in PwHSP. However, the late instant of center of mass divergence argues against a direct, causative role of hyperexcitable SLRs in the triceps surae. SIGNIFICANCE: We postulate that enhanced short-latency stretch reflexes of the triceps surae do not underlie poor balance control in PwHSP. Instead, we suggest the lack of suppression of later triceps surae activity to be the main cause.

Immediate after-effects of robot-assisted gait with pelvic support or pelvic constraint on overground walking in healthy subjects.

BACKGROUND: Recovery of walking is a primary rehabilitation goal of most stroke survivors. Control of pelvic movements is one of the essential determinants of gait, yet surprisingly, conventional robot-assisted gait trainers constrain pelvic movements. Novel robot-assisted gait trainers, such as LOPES II, are able to support pelvic movements during gait. The aim of this cross-over study was to investigate the immediate after-effects of pelvic support (PS) or pelvic constraint (PC) gait training with LOPES II on overground walking in healthy subjects. METHODS: Thirteen able-bodied subjects (22.8 ± 2.1 years) participated in two 20-min gait training sessions with LOPES II; one with PS and one with PC. During the PS-training, the LOPES II actively guided the lateral displacement of the pelvis, while pelvic rotations were free. During the PC-condition, both lateral displacement and pelvic rotations were constrained and reduced to a minimum. The training sessions were separated by a 30-min resting period. Lateral displacement of the pelvis, hip and knee kinematics, and spatiotemporal parameters during overground walking were determined at baseline and immediately following the training using 3D gait analysis. RESULTS: During the PS-condition in LOPES II the lateral pelvic displacement was significantly greater (105.6 ± 0 .5 mm) than during the PC-condition (10.8 ± 0 .7 mm; p < 0.001). Analysis of the first five steps of overground walking immediately following PC-condition showed significantly smaller lateral displacements of the pelvis (32.3 ± 12.0 mm) compared to PS-condition (40.1 ± 9 .8 mm; p < 0.01). During the first five steps, step width was significantly smaller after PC-condition (0.17 ± 0. 04 m) compared to PS-condition (0.20 ± 0.04 m; p = 0.01) and baseline (0.19 ± 0. 03 m; p = 0.01). Lateral displacement of the pelvis and step width post training returned to baseline levels within 10 steps. PC- nor PS-condition affected kinematics, gait velocity, cadence, stride length or stance time. CONCLUSIONS: In healthy subjects, robot-assisted gait training with pelvic constraint had immediate negative after-effects on the overground walking pattern, as compared to robot-assisted gait training with pelvic support. Gait training including support of the lateral displacement of the pelvis better resembles the natural gait pattern. It remains to be identified whether pelvic support during robot-assisted gait training is superior to pelvic constraint to promote gait recovery in individuals with neurological disorders.

Assessment of the underlying systems involved in standing balance: the additional value of electromyography in system identification and parameter estimation.

BACKGROUND: Closed loop system identification (CLSIT) is a method to disentangle the contribution of underlying systems in standing balance. We investigated whether taking into account lower leg muscle activation in CLSIT could improve the reliability and accuracy of estimated parameters identifying the underlying systems. METHODS: Standing balance behaviour of 20 healthy young participants was measured using continuous rotations of the support surface (SS). The dynamic balance behaviour obtained with CLSIT was expressed by sensitivity functions of the ankle torque, body sway and muscle activation of the lower legs to the SS rotation. Balance control models, 1) without activation dynamics, 2) with activation dynamics and 3) with activation dynamics and acceleration feedback, were fitted on the data of all possible combinations of the 3 sensitivity functions. The reliability of the estimated model parameters was represented by the mean relative standard errors of the mean (mSEM) of the estimated parameters, expressed for the basic parameters, the activation dynamics parameters and the acceleration feedback parameter. To investigate the accuracy, a model validation study was performed using simulated data obtained with a comprehensive balance control model. The accuracy of the estimated model parameters was described by the mean relative difference (mDIFF) between the estimated parameters and original parameters. RESULTS: The experimental data showed a low mSEM of the basic parameters, activation dynamics parameters and acceleration feedback parameter by adding muscle activation in combination with activation dynamics and acceleration feedback to the fitted model. From the simulated data, the mDIFF of the basic parameters varied from 22.2-22.4% when estimated using the torque and body sway sensitivity functions. Adding the activation dynamics, acceleration feedback and muscle activation improved mDIFF to 13.1-15.1%. CONCLUSIONS: Adding the muscle activation in combination with the activation dynamics and acceleration feedback to CLSIT improves the accuracy and reliability of the estimated parameters and gives the possibility to separate the neural time delay, electromechanical delay and the intrinsic and reflexive dynamics. To diagnose impaired balance more specifically, it is recommended to add electromyography (EMG) to body sway (with or without torque) measurements in the assessment of the underlying systems.

Estimating severity of sideways fall using a generic multi linear regression model based on kinematic input variables.

Many research groups have studied fall impact mechanics to understand how fall severity can be reduced to prevent hip fractures. Yet, direct impact force measurements with force plates are restricted to a very limited repertoire of experimental falls. The purpose of this study was to develop a generic model for estimating hip impact forces (i.e. fall severity) in in vivo sideways falls without the use of force plates. Twelve experienced judokas performed sideways Martial Arts (MA) and Block ('natural') falls on a force plate, both with and without a mat on top. Data were analyzed to determine the hip impact force and to derive 11 selected (subject-specific and kinematic) variables. Falls from kneeling height were used to perform a stepwise regression procedure to assess the effects of these input variables and build the model. The final model includes four input variables, involving one subject-specific measure and three kinematic variables: maximum upper body deceleration, body mass, shoulder angle at the instant of 'maximum impact' and maximum hip deceleration. The results showed that estimated and measured hip impact forces were linearly related (explained variances ranging from 46 to 63%). Hip impact forces of MA falls onto the mat from a standing position (3650±916N) estimated by the final model were comparable with measured values (3698±689N), even though these data were not used for training the model. In conclusion, a generic linear regression model was developed that enables the assessment of fall severity through kinematic measures of sideways falls, without using force plates.

Dynamic stability during level walking and obstacle crossing in persons with facioscapulohumeral muscular dystrophy.

Patients with FSHD suffer from progressive skeletal muscle weakness, which is associated with an elevated fall risk. To obtain insight into fall mechanisms in this patient group, we aimed to assess dynamic stability during level walking and obstacle crossing in patients at different disease stages. Ten patients with at least some lower extremity weakness were included, of whom six were classified as moderately affected and four as mildly affected. Ten healthy controls were also included. Level walking at comfortable speed was assessed, as well as crossing a 10 cm high wooden obstacle. We assessed forward and lateral dynamic stability, as well as spatiotemporal and kinematics variables. During level walking, the moderately affected group demonstrated a lower walking speed, which was accompanied by longer step times and smaller step lengths, yet dynamic stability was unaffected. When crossing the obstacle, however, the moderately affected patients demonstrated reduced forward stability margins during the trailing step, which was accompanied by an increased toe clearance and greater trunk and hip flexion. This suggests that during level walking, the patients effectively utilized compensatory strategies for maintaining dynamic stability, but that the moderately affected group lacked the capacity to fully compensate for the greater stability demands imposed by obstacle crossing, rendering them unable to maintain optimal stability levels. The present results highlight the difficulties that FSHD patients experience in performing this common activity of daily living and may help explain their propensity to fall in the forward direction.

Incorporating in vivo fall assessments in the simulation of femoral fractures with finite element models.

Femoral fractures are a major health issue. Most experimental and finite element (FE) fracture studies use polymethylmethacrylate cups on the greater trochanter (GT) to simulate fall impact loads. However, in vivo fall studies showed that the femur is loaded distally from the GT. Our objective was to incorporate in vivo fall data in FE models to determine the effects of loading position and direction, and size of simulated impact site on the fracture load and fracture type for a healthy and an osteoporotic femur. Twelve sets of loading position and angles were applied through 'near point loads' on the models. Additional simulations were performed with 'cup loads' on the GT, similar to the literature. The results showed no significant difference between fracture loads from simulations with near point loads distally from the GT and those with cup loads on the GT. However, simulated fracture types differed, as near point loads distally from the GT generally resulted in various neck fractures, whilst cup load simulations predicted superior neck and trochanteric fractures only. This study showed that incorporating in vivo fall assessments in FE models by loading the models distally from the GT results in prediction of realistic fracture loads and fracture types.

Gait propulsion in patients with facioscapulohumeral muscular dystrophy and ankle plantarflexor weakness.

Facioscapulohumeral muscular dystrophy is a slowly progressive hereditary disorder resulting in fatty infiltration of eventually most skeletal muscles. Weakness of trunk and leg muscles causes problems with postural balance and gait, and is associated with an increased fall risk. Although drop foot and related tripping are common problems in FSHD, gait impairments are poorly documented. The effect of ankle plantarflexor involvement on gait propulsion has never been addressed. In addition to ankle plantarflexion, gait propulsion is generated through hip flexion and hip extension. Compensatory shifts between these propulsion sources occur when specific muscles are affected. Such a shift may be expected in patients with FSHD since the calves may show early fatty infiltration, whereas iliopsoas and gluteus maximus muscles are often spared for a longer time. In the current study, magnetic resonance imaging was used to assess the percentage of unaffected calf, iliopsoas and gluteus maximus muscles. Joint powers were analyzed in 10 patients with FSHD at comfortable and maximum walking speed to determine the contribution of ankle plantarflexor, hip flexor and hip extensor power to propulsion. Associations between muscle morphology, power generation and gait speed were assessed. Based on multivariate regression analysis, ankle plantarflexor power was the only factor that uniquely contributed to the explained variance of comfortable (R(2)=80%) and maximum (R(2)=86%) walking speed. Although the iliopsoas muscles were largely unaffected, they appeared to be sub-maximally recruited. This submaximal recruitment may be related to poor trunk stability, resulting in a disproportionate effect of calf muscle affliction on gait speed in patients with FSHD.

A gait paradigm reveals different patterns of abnormal cerebellar motor learning in primary focal dystonias.

Accumulating evidence points to a role of the cerebellum in the pathophysiology of primary dystonia. The aim of this study was to investigate whether the abnormalities of cerebellar motor learning in primary dystonia are solely detectable in more pure forms of cerebellum-dependent associative motor learning paradigms, or whether these are also present in other motor learning paradigms that rely heavily on the cerebellum but in addition require a more widespread sensorimotor network. Twenty-six patients with various forms of focal dystonia and 10 age-matched healthy controls participated in a motor learning paradigm on a split-belt treadmill. By using reflective markers, three-dimensional kinematics were recorded using a 6-camera motion analysis system. Adaptation walking parameters were analyzed offline, comparing the different dystonia groups and healthy controls. Patients with blepharospasm and writer's cramp were significantly impaired on various adaptation walking parameters. Whereas results of cervical dystonia patients did not differ from healthy controls in terms of adaptation walking parameters, differences in parameters of normal gait were found. We have here demonstrated abnormal sensorimotor adaptation with the split-belt paradigm in patients with blepharospasm and writer's cramp. This reinforces the current concept of cerebellar dysfunction in primary dystonia, and that this extends beyond more pure forms of cerebellum-dependent associative motor learning paradigms. However, the finding of normal adaptation in cervical dystonia patients indicates that the pattern of cerebellar dysfunction may be slightly different for the various forms of primary focal dystonia, suggesting that actual cerebellar pathology may not be a primary driving force in dystonia.

Trunk muscle involvement is most critical for the loss of balance control in patients with facioscapulohumeral muscular dystrophy.

BACKGROUND: Although it is known that muscle weakness is a major cause of postural instability and leads to an increased incidence of falls in patients with neuromuscular disease, the relative contribution of lower extremity and trunk muscle weakness to postural instability has not been studied well. METHODS: We determined the relationship between muscle fatty infiltration and sagittal-plane balance in ten patients with facioscapulohumeral muscular dystrophy. Sagittal-plane platform translations were imposed in forward and backward directions on patients with facioscapulohumeral muscular dystrophy and healthy controls. Stepping thresholds were determined and kinematic responses and center-of-mass displacements were assessed using 3 dimensional motion analysis. In the patients, magnetic resonance imaging was used to determine the amount of fatty infiltration of trunk and lower extremity muscles. FINDINGS: Stepping thresholds in both directions were decreased in patients compared to controls. In patients, significant correlations were found for fatty infiltration of ventral muscles with backward stepping threshold and for fatty infiltration of dorsal muscles with forward stepping threshold. Fatty infiltration of the rectus abdominis and the back extensors explained the largest part of the variance in backward and forward stepping thresholds, respectively. Center-of-mass displacements were dependent on intensity and direction of perturbation. Kinematic analysis revealed predominant ankle strategies, except in patients with lumbar hyperlordosis. INTERPRETATION: These findings indicate that trunk muscle involvement is most critical for loss of sagittal-plane postural balance in patients with facioscapulohumeral muscular dystrophy. This insight may help to develop rehabilitation strategies to prevent these patients from falling.

Obstacle course training can improve mobility and prevent falls in people with intellectual disabilities.

BACKGROUND: Persons with intellectual disabilities (ID) constitute a special-needs population at high risk of falling. This is the first study to evaluate whether obstacle course training can improve mobility and prevent falls in this population. METHODS: The intervention was implemented as part of an institution-wide health care improvement plan aimed at reducing falls at a residential facility for people with ID. It comprised an annual screening of each resident for his or her individual fall risk. Subsequently, the group of ambulatory persons with a moderate to high fall risk (n = 39) were offered 10-session obstacle course training to improve their balance and gait abilities. Mobility was assessed pre-intervention, mid-term and post-intervention with the Performance Oriented Mobility Assessment (POMA), the Timed Up and Go (TUG) and the 10-meter walking test. The number of falls was compared between the year before and after intervention. RESULTS: The number of falls decreased by 82% (P < 0.001). POMA scores significantly improved from pre-intervention to mid-term (mean difference ± SD, 1.8 ± 2.9, P = 0.001), from mid-term to post-intervention (2.0 ± 2.9, P < 0.001), and from pre-intervention to post-intervention (3.8 ± 4.3, P < 0.001). Participants completed the 10-meter walking test faster at the post-intervention compared with the pre-intervention assessment (difference ± SD, 2.1 ± 5.1 s, P = 0.022). TUG scores did not improve significantly. CONCLUSIONS: The present study provides preliminary evidence for the effectiveness of obstacle course training in improving mobility and preventing falls in people with ID. As falls are a significant health concern in this population, further research is advocated to provide conclusive evidence for the suggested beneficial effects of exercise interventions.

Are postural responses to backward and forward perturbations processed by different neural circuits?

Startle pathways may contribute to rapid accomplishment of postural stability. Here we investigate the possible influence of a startling auditory stimulus (SAS) on postural responses. We formulated four specific questions: (1) can a concurrent SAS shorten the onset of automatic postural responses?; and if so (2) is this effect different for forward versus backward perturbations?; (3) does this effect depend on prior knowledge of the perturbation direction?; and (4) is this effect different for low- and high-magnitude perturbations? Balance was perturbed in 11 healthy participants by a movable platform that suddenly translated forward or backward. Each participant received 160 perturbations, 25% of which were combined with a SAS. We varied the direction and magnitude of the perturbations, as well as the prior knowledge of perturbation direction. Perturbation trials were interspersed with SAS-only trials. The SAS accelerated and strengthened postural responses with clear functional benefits (better balance control), but this was only true for responses that protected against falling backwards (i.e. in tibialis anterior and rectus femoris). These muscles also demonstrated the most common SAS-triggered responses without perturbation. Increasing the perturbation magnitude accelerated postural responses, but again with a larger acceleration for backward perturbations. We conclude that postural responses to backward and forward perturbations may be processed by different neural circuits, with influence of startle pathways on postural responses to backward perturbations. These findings give directions for future studies investigating whether deficits in startle pathways may explain the prominent backward instability seen in patients with Parkinson's disease and progressive supranuclear palsy.

Loading enhances the occurrence of startle responses in leg muscles.

INTRODUCTION: The startle reflex is an involuntary reaction to sudden sensory input and consists of a generalized flexion response. Startle responses in distal leg muscles occur more frequently during standing compared to sitting. We hypothesized that sensory input from load receptors modulates the occurrence of startle responses in leg muscles. METHODS: We administered sudden startling auditory stimuli (SAS) to 11 healthy subjects while (1) sitting relaxed, (2) standing relaxed, (3) standing while bearing 60% of their weight on the right leg, (4) standing while bearing 60% of their weight on the left leg, and (5) standing with 30% body weight support ('bilateral unloaded'). The requested weight distribution for each condition was verified using force plates. Electromyography data were collected from both tibialis anterior (TA) and the left sternocleidomastoid muscles. RESULTS: In the TA, startle responses occurred much more frequently during normal standing (26% of trials) compared to both sitting (6% of trials, p<0.01) and bilateral unloading (3% of trials, p<0.01). In the asymmetrical stance conditions, startle responses in the TA were more common in the loaded leg (21% of trials) compared to the unloaded leg (10% of trials, p<0.05). DISCUSSION: The occurrence of startle responses in the leg muscles was strongly influenced by load. Hence, it is likely that information from load receptors influences startle response activity. We suggest that, in a stationary position, startling stimuli result in a descending volley from brainstem circuits, which is gated at the spinal level by afferent input from load receptors.

Split-belt locomotion in Parkinson's disease with and without freezing of gait.

BACKGROUND: Parkinson's disease (PD) patients have an increased gait asymmetry and variability, which is most pronounced in patients with freezing of gait (FOG). We examined if stride time variability and deficits in interlimb coordination between the upper and lower limbs would increase during split-belt locomotion in PD, and particularly so in patients with FOG. METHODS: Fourteen PD patients (seven with FOG, matched for disease severity with the seven non-freezers) and 10 healthy controls walked on a treadmill with split belts at different speeds (2 versus 3km/h). Gait was recorded by means of a video motion analysis system. Outcome measures were stride length asymmetry and variability, stride time asymmetry and variability, ipsilateral and contralateral interlimb coordination, and phase coordination index. RESULTS: Both PD subjects and controls were able to adapt to split-belt walking by modulating their stride length. However, freezers showed a larger increase in stride time asymmetry and stride time variability due to split-belt walking compared to non-freezers. Furthermore, contralateral interlimb coordination improved in control subjects during split-belt walking, but not in PD patients (freezers and non-freezers). Phase coordination index did not change differently across the three groups. CONCLUSIONS: The ability to walk under split-belt conditions was preserved in PD. Non-freezers and controls compensated for the experimentally increased stride length asymmetry by decreasing their stride time asymmetry. This ability was lost in freezers, who in fact increased their stride time asymmetry during split-belt walking. As a result, stride time variability also increased in freezers. These findings support the hypothesis that FOG is related to gait asymmetries and to gait timing deficits.

Falls in older persons with intellectual disabilities: fall rate, circumstances and consequences.

BACKGROUND: Falling is a common cause of injuries and reduced quality of life. Persons with intellectual disabilities (ID) are at increased risk for falls and related injuries. As the number of elderly persons with ID is growing rapidly, it is imperative to gain insight into the quantity of the problem of falling, the circumstances that precipitate falls and to better understand their aetiology in persons with ID. This is the first study to prospectively investigate fall rate, circumstances and fall consequences in older adults with mild to moderate ID. METHOD: Eighty-two individuals with mild to moderate ID, 50 years and over [mean age 62.3 (SD = 7.6), 34 male], participated in this study, which was conducted at three service providers for persons with ID in the Netherlands. Falls were registered for 1 year with monthly fall registration calendars to determine the fall rate (mean number of falls per person per year). Information on fall circumstances and consequences was obtained from questionnaires completed by caregivers and study participants after each fall. RESULTS: We determined that the fall rate in this sample was 1.00 fall per person per year. Thirty-seven participants reported at least one fall (range 1-6). Sex and age were not related to falls. Most falls occurred while walking (63.3%), outside (61.7%) and in familiar environments (88.9%). Importantly, 11.5% of falls resulted in severe injuries, approximately half of which were fractures. CONCLUSION: The circumstances and consequences of falls in persons with ID are comparable to those of the general elderly population, but the rate is substantially higher. As such, appropriate fall prevention strategies must be developed for individuals with ID.

Can martial arts techniques reduce fall severity? An in vivo study of femoral loading configurations in sideways falls.

Sideways falls onto the hip are a major cause of femoral fractures in the elderly. Martial arts (MA) fall techniques decrease hip impact forces in sideways falls. The femoral fracture risk, however, also depends on the femoral loading configuration (direction and point of application of the force). The purpose of this study was to determine the effect of fall techniques, landing surface and fall height on the impact force and the loading configuration in sideways falls. Twelve experienced judokas performed sideways MA and Block ('natural') falls on a force plate, both with and without a judo mat on top. Kinematic and force data were analysed to determine the hip impact force and the loading configuration. In falls from a kneeling position, the MA technique reduced the impact force by 27%, but did not change the loading configuration. The use of the mat did not change the loading configuration. Falling from a standing changed the force direction. In all conditions, the point of application was distal and posterior to the greater trochanter, but it was less distal and more posterior in falls from standing than from kneeling position. The present decrease in hip impact force with an unchanged loading configuration indicates the potential protective effect of the MA technique on the femoral fracture risk. The change in loading configuration with an increased fall height warrant further studies to examine the effect of MA techniques on fall severity under more natural fall circumstances.

Development and Process Evaluation of a 5-Week Exercise Program to Prevent Falls in People after Stroke: The FALLS Program.

Falls are a common complication after stroke, with balance and gait deficits being the most important risk factors. Taking into account the specific needs and capacities of people with stroke, we developed the FALLS program (FALL prevention after Stroke), based on the "Nijmegen falls prevention program" (a proven-effective 5-week exercise program designed for community-dwelling elderly people). The program was tested in twelve community-dwelling persons with stroke, and a process evaluation was conducted with patients, trainers, health care professionals, and managers. The FALLS program was considered suitable and feasible by people with stroke in the study and relevant health care professionals, and recommendations for implementation in clinical practice have been suggested.