Decoding Sensorimotor Rhythms during Robotic-Assisted Treadmill Walking for Brain Computer Interface (BCI) Applications.

Locomotor malfunction represents a major problem in some neurological disorders like stroke and spinal cord injury. Robot-assisted walking devices have been used during rehabilitation of patients with these ailments for regaining and improving walking ability. Previous studies showed the advantage of brain-computer interface (BCI) based robot-assisted training combined with physical therapy in the rehabilitation of the upper limb after stroke. Therefore, stroke patients with walking disorders might also benefit from using BCI robot-assisted training protocols. In order to develop such BCI, it is necessary to evaluate the feasibility to decode walking intention from cortical patterns during robot-assisted gait training. Spectral patterns in the electroencephalogram (EEG) related to robot-assisted active and passive walking were investigated in 10 healthy volunteers (mean age 32.3±10.8, six female) and in three acute stroke patients (all male, mean age 46.7±16.9, Berg Balance Scale 20±12.8). A logistic regression classifier was used to distinguish walking from baseline in these spectral EEG patterns. Mean classification accuracies of 94.0±5.4% and 93.1±7.9%, respectively, were reached when active and passive walking were compared against baseline. The classification performance between passive and active walking was 83.4±7.4%. A classification accuracy of 89.9±5.7% was achieved in the stroke patients when comparing walking and baseline. Furthermore, in the healthy volunteers modulation of low gamma activity in central midline areas was found to be associated with the gait cycle phases, but not in the stroke patients. Our results demonstrate the feasibility of BCI-based robotic-assisted training devices for gait rehabilitation.

Using Actual and Imagined Walking Related Desynchronization Features in a BCI.

Recently, brain-computer interface (BCI) research has extended to investigate its possible use in motor rehabilitation. Most of these investigations have focused on the upper body. Only few studies consider gait because of the difficulty of recording EEG during gross movements. However, for stroke patients the rehabilitation of gait is of crucial importance. Therefore, this study investigates if a BCI can be based on walking related desynchronization features. Furthermore, the influence of complexity of the walking movements on the classification performance is investigated. Two BCI experiments were conducted in which healthy subjects performed a cued walking task, a more complex walking task (backward or adaptive walking), and imagination of the same tasks. EEG data during these tasks was classified into walking and no-walking. The results from both experiments show that despite the automaticity of walking and recording difficulties, brain signals related to walking could be classified rapidly and reliably. Classification performance was higher for actual walking movements than for imagined walking movements. There was no significant increase in classification performance for both the backward and adaptive walking tasks compared with the cued walking tasks. These results are promising for developing a BCI for the rehabilitation of gait.

Arm movements can increase leg muscle activity during submaximal recumbent stepping in neurologically intact individuals.

Facilitation of leg muscle activity by active arm movements during locomotor tasks could be beneficial during gait rehabilitation after spinal cord injury. The present study explored the effects of arm movements on leg muscle activity during submaximal recumbent stepping. Healthy subjects exercised on a recumbent stepping machine both with and without arm movements. Activity of five leg muscles was recorded and compared for stepping with and without arm movements. To determine which arm movements are optimal for leg muscle facilitation, subjects were instructed to step with 1) mechanically coupled vs. decoupled arm and leg movements, 2) synchronous vs. asynchronous arm movements, and 3) at 50 vs. 70 RPM. Leg muscle activity was increased by active arm movements in all muscles, except the vastus lateralis muscle. Activity of other extensors (soleus, medial gastrocnemius, and biceps femoris) was primarily increased during the extension phase, whereas activity of flexors (tibialis anterior) was also increased during the flexion phase. Facilitation was more or less consistent for both frequencies and for synchronous and asynchronous movements. For coupled arm movements, facilitation tended to be diminished or absent. The observed facilitation in the present study is probably of neuromuscular rather than biomechanical origin, since the arms are probably hardly involved in postural control or weight-bearing during recumbent stepping. Further studies in patients should explore the possibility to integrate neuromuscular facilitation in rehabilitation programs.

CNS effects of indomethacin: should patients be cautioned about decreased mental alertness and motor coordination?

AIMS: In many European countries as well as in the USA, the leaflet, or even the packaging of indomethacin, contains a specific warning to refrain from activities requiring mental alertness and motor coordination, such as driving a car. In this placebo-controlled randomized study with a crossover design we attempted to find evidence for that warning. METHODS: Indomethacin 75 mg slow release or a visually identical placebo with similar flavour was taken orally twice daily for 2.5 days. It was suggested that indomethacin affects the motor coordination required to avoid obstacles successfully during walking and that this effect will be even stronger when simultaneously performing a cognitive task that puts mental alertness to the test. Nineteen healthy middle-aged individuals (60 ± 4.7 years, eight female) performed an obstacle avoidance task on a treadmill), combined with a cognitive secondary task. Biceps femoris (BF) muscle response times, obstacle avoidance failure rates and composite scores ((100 × accuracy)/verbal response time) were used to evaluate the data. RESULTS: No differences between indomethacin and placebo were found on the outcome measures regarding motor coordination, avoidance failure rates (P = 0.81) and BF response times (P = 0.47), nor on the performance on the secondary cognitive task (P = 0.12). CONCLUSIONS: Even though surrogate methods were used, the current study provides evidence to suggest that there might be no need to caution patients who experience CNS side effects after indomethacin use to avoid activities requiring quick and adequate reactions, such as walking under challenging circumstances and maybe also driving a car.

Dual-tasking interferes with obstacle avoidance reactions in healthy seniors.

Dual-tasking can lead to falls, as does a deterioration of obstacle avoidance (OA) skills. Hence, it is expected that a combination of both would be even more detrimental, especially when OA is time-critical. Previous studies confirmed this expectation, however, due to several limitations in their design it is yet too early to draw any definitive conclusions on the allocation of attentional resources in OA under dual-task conditions. Therefore, attentionally demanding primary and secondary tasks were used with the instruction to perform as well as possible on both tasks. Nineteen healthy senior individuals (60±4.7 years, 8 females) performed an OA task on a treadmill while walking at 3 km/h as a single task and combined with an auditory Stroop task. Biceps femoris (BF) muscle response times, OA failure rates and composite scores were used to evaluate the data. Increased OA failure rates (3%, p=0.03) and delayed BF response times (21 ms, p<0.001) were found under dual-task conditions. Composite scores were reduced during (p<0.001) and just after obstacle crossing (p=0.003). In conclusion, dual-tasking during time-critical OA affects the motor as well as the cognitive task when subjects are instructed to keep up performance on both tasks. This adds to the evidence indicating an increased risk of tripping or falling when attention is divided during walking in the presence of unexpected obstacles.

Unraveling the association between SSRI use and falls: an experimental study of risk factors for accidental falls in long-term paroxetine users.

Selective serotonin reuptake inhibitors (SSRIs) are widely used to treat depression and are also associated with an increased falls risk. However, the biological mechanism underlying accidental falls with SSRI intake has yet to be elucidated. The present experimental study was designed to investigate whether obstacle avoidance skills in long-term (>90 days), senior paroxetine users (61 ± 5.8 years) are affected during gait, simple and challenging postural balance tasks, as well as during manual reaction time tasks. The performance of the paroxetine users was compared with healthy group-matched controls (60 ± 4.8 years). The results demonstrated impaired postural balance in the paroxetine users, especially during one-legged stance or under various dual-task conditions. Although the deficit in one-legged stance could indicate vestibular involvement, this was deemed unlikely because performance of standing on compliant surface with closed eyes remained unaffected. Paroxetine use also failed to affect manual reaction times or obstacle avoidance performance. It is suggested that paroxetine affects attentional capacities particularly in conjunction with balance control. Compared with healthy seniors, long-term senior users of paroxetine seem to be at an increased risk of falling due to impairments in balance control, especially when attention has to be divided between 2 concurrent activities.

Plantar pressure with and without custom insoles in patients with common foot complaints.

BACKGROUND: Although many patients with foot complaints receive customized insoles, the choice for an insole design can vary largely among foot experts. To investigate the variety of insole designs used in daily practice, the insole design and its effect on plantar pressure distribution were investigated in a large group of patients. MATERIALS AND METHODS: Mean, peak, and pressure-time-integral per sensor for 204 subjects with common foot complaints for walking with and without insoles was measured with the footscan® insole system (RSscan International). Each insole was scanned twice (precision3D), after which the insole height along the longitudinal and transversal cross section was calculated. Subjects were assigned to subgroups based on complaint and medial arch height. Data were analyzed for the total group and for the separate subgroups (forefoot or heel pain group and flat, normal or high medial arch group). RESULTS: The mean pressure significantly decreased under the metatarsal heads II-V and the calcaneus and significantly increased under the metatarsal bones and the lateral foot (p<0.0045) due to the insoles. However, similar redistribution patterns were found for the different foot complaints and arch heights. There was a slight difference in insole design between the subgroups; the heel cup was significantly higher and the midfoot support lower for the heel pain group compared to the forefoot pain group. The midfoot support was lowest in the flat arch group compared to the high and normal arch group (p<0.05). CONCLUSION: Although the insole shape was specific for the kind of foot complaint and arch height, the differences in shape were very small and the plantar pressure redistribution was similar for all groups. CLINICAL RELEVANCE: This study indicates that it might be sufficient to create basic insoles for particular patient groups.

The effect of a non-steroidal anti-inflammatory drug on two important predictors for accidental falls: postural balance and manual reaction time. A randomized, controlled pilot study.

Accidental falls in older individuals are a major health and research topic. Increased reaction time and impaired postural balance have been determined as reliable predictors for those at risk of falling and are important functions of the central nervous system (CNS). An essential risk factor for falls is medication exposure. Amongst the medications related to accidental falls are the non-steroidal anti-inflammatory drugs (NSAIDs). About 1-10% of all users experience CNS side effects. These side effects, such as dizziness, headaches, drowsiness, mood alteration, and confusion, seem to be more common during treatment with indomethacin. Hence, it is possible that maintenance of (static) postural balance and swift reactions to stimuli are affected by exposure to NSAIDs, indomethacin in particular, consequently putting older individuals at a greater risk for accidental falls. The present study investigated the effect of a high indomethacin dose in healthy middle-aged individuals on two important predictors of falls: postural balance and reaction time. Twenty-two healthy middle-aged individuals (59.5 ± 4.7 years) participated in this double-blind, placebo-controlled, randomized crossover trial. Three measurements were conducted with a week interval each. A measurement consisted of postural balance as a single task and while concurrently performing a secondary cognitive task and reaction time tasks. For the first measurement indomethacin 75 mg (slow-release) or a visually identical placebo was randomly assigned. In total, five capsules were taken orally in the 2.5 days preceding assessment. The second measurement was without intervention, for the final one the first placebo group got indomethacin and vice versa. Repeated measures GLM revealed no significant differences between indomethacin, placebo, and baseline in any of the balance tasks. No differences in postural balance were found between the single and dual task conditions, or on the performance of the dual task itself. Similarly, no differences were found on the manual reaction time tasks. The present study showed that a high indomethacin dose does not negatively affect postural balance and manual reaction time in this healthy middle-aged population. Although the relatively small and young sample limits the direct ability to generalize the results to a population at risk of falling, the results indicate that indomethacin alone is not likely to increase fall risk, as far as this risk is related to above mentioned important functions of the CNS, and not affected by comorbidities.

Even low alcohol concentrations affect obstacle avoidance reactions in healthy senior individuals.

BACKGROUND: Alcohol is a commonly used social drug and driving under influence is a well-established risk factor for traffic accidents1. To improve road safety, legal limits are set for blood alcohol concentration (BAC) and driving, usually at 0.05% (most European countries) or 0.08% (most US states, Canada and UK). In contrast, for walking there are no legal limits, yet there are numerous accounts of people stumbling and falling after drinking. Alcohol, even at these low concentrations, affects brain function and increases fall risk. An increased fall risk has been associated with impaired obstacle avoidance skills. Low level BACs are likely to affect obstacle avoidance reactions during gait, since the brain areas that are presumably involved in these reactions have been shown to be influenced by alcohol. Therefore we investigated the effect of low to moderate alcohol consumption on such reactions.Thirteen healthy senior individuals (mean(SD) age: 61.5(4.4) years, 9 male) were subjected to an obstacle avoidance task on a treadmill after low alcohol consumption. Fast stepping adjustments were required to successfully avoid suddenly appearing obstacles. Response times and amplitudes of the m. biceps femoris, a prime mover, as well as avoidance failure rates were assessed. FINDINGS: After the first alcoholic drink, 12 of the 13 participants already had slower responses. Without exception, all participants' biceps femoris response times were delayed after the final alcoholic drink (avg ± sd:180 ± 20 ms; p < 0.001) compared to when participants were sober (156 ± 16 ms). Biceps femoris response times were significantly delayed from BACs of 0.035% onwards and were strongly associated with increasing levels of BAC (r = 0.6; p < 0.001). These delays had important behavioural consequences. Chances of hitting the obstacle were doubled with increased BACs. CONCLUSIONS: The present results clearly show that even with BACs considered to be safe for driving, obstacle avoidance reactions are inadequate, late, and too small. This is likely to contribute to an increased fall risk. Therefore we suggest that many of the alcohol-related falls are the result of the disruptive effects of alcohol on the online corrections of the ongoing gait pattern when walking under challenging conditions.

Evidence for bilaterally delayed and decreased obstacle avoidance responses while walking with a lower limb prosthesis.

OBJECTIVE: To examine whether the increased failure rates in obstacle avoidance of patients with lower limb amputation can be understood on the basis of increased delay and/or decreased amplitudes of obstacle avoidance responses. METHODS: Subjects performed obstacle avoidance on a treadmill while EMG recordings were made of several major muscles of the leg. RESULTS: It was found that subjects with a lower limb amputation have delayed responses (e.g. delays of 20 ms for the Biceps Femoris) and have decreased response amplitudes (36-41% smaller). Furthermore, such changes were observed not only on the prosthetic side, but also on the sound side. The decreased amplitudes were associated with increased failure rates in the obstacle avoidance task. CONCLUSIONS: It is concluded that the bilaterally delayed and reduced responses in persons with a lower limb prosthesis reflect a basic reorganization within the central nervous system aimed at providing synchronized activity in both lower limbs, even though the peripheral deficit involves only one limb. SIGNIFICANCE: The present results on obstacle avoidance responses can be used to evaluate future prosthetic training involving obstacle crossings for amputee rehabilitation.

Exercise training can improve spatial characteristics of time-critical obstacle avoidance in elderly people.

Fall prevention programs have rarely been evaluated by quantitative movement analysis methods. Quantitative movement analyses could provide insight into the mechanisms underlying the effects of training. A treadmill obstacle avoidance task under time pressure has recently been used to evaluate a fall prevention exercise program for community-dwelling elderly people and it showed that participants improved their obstacle avoidance success rates. The mechanism, by which the increased success rates were achieved, however, remained to be determined. Participants were elderly who had fallen at least once in the year prior to participation. They were assigned to either the exercise or the control group. The control group did not receive any specific treatment. The exercise group was administered a five week exercise program, which consisted of exercises on a functionally oriented obstacle course, walking exercises, and practice of fall techniques. Pre- and post-intervention laboratory obstacle avoidance tests were conducted. Three possible determinants of success were investigated, namely avoidance reaction times, the distribution of avoidance strategies, and three spatial parameters (toe distance, foot clearance and heel distance). Analysis yielded significant TimexGroup interactions in heel distances. The exercise group increased heel distance, while the control group did not. Increased heel distance may result in reduced risk of heel contact with the obstacle and, consequently, larger success rates. The remaining parameters showed no effect of training. In conclusion, the training program was effective in improving time-critical obstacle avoidance skills. In every day life, these effects of training may contribute to less obstacle-related fall incidents in elderly. In addition, these findings could indicate that the execution of other time-critical events, like an actual fall, could also be improved by training.

Posturographic assessment of sitting balance recovery in the subacute phase of stroke.

Although early sitting balance is a well-known predictor of functional outcome after stroke, it is still unknown which aspects of normal upright sitting balance are most sensitive to subsequent recovery. This study used an adjustable chair mounted on a force platform to assess the recovery of quiet-sitting balance in 16 patients with a first supratentorial stroke during their inpatient rehabilitation. The patients underwent three posturographic assessments at 6-week intervals from the moment of their admission, on average 5.6 weeks after stroke. Each quiet-sitting balance assessment consisted of two series of four 30-s test conditions: sitting with eyes open and closed, on both a stable and unstable (air cushion) surface. The RMS of the center-of-pressure (COP) velocities was used as the primary measure of lateral and anteroposterior balance control. It was found that, compared to 10 healthy elderly, lateral balance was more affected by stroke than balance in the anteroposterior direction, especially during visual deprivation, and most sensitive to subsequent functional changes induced by spontaneous recovery or rehabilitation. Furthermore, lateral balance control showed the strongest association with the Berg Balance Scale as a clinical measure of balance capacity. Hence, (lateral) trunk control seems to be a primary target for rehabilitation. Since an unstable support was necessary to obtain significant effects of stroke, recovery and visual deprivation, it may be important to use an unstable support during sitting balance training as well.

Is the modified Tardieu scale in semi-standing position better associated with knee extension and hamstring activity in terminal swing than the supine Tardieu?

The aim of this study was to investigate whether the modified Tardieu scale (MTS) in a semi-standing position, used for the assessment of hamstrings spasticity, was better associated with knee extension and hamstrings activity in terminal swing than the MTS in a supine position in children with cerebral palsy (CP). Seven children diagnosed with spastic CP (Gross Motor Function Classification System Levels I-II) and seven healthy comparison children participated in the study. An instrumented MTS in supine and semi-standing position and an instrumented gait assessment were conducted. Results showed that spasticity-related outcomes of the semi-standing MTS do not show better associations with terminal swing characteristics of gait than the same outcomes of the supine MTS in children with spastic CP. Only the passive restricted knee angle from the supine MTS was strongly associated with the maximum knee extension during gait (r(s)=0.99; p <0.001), suggesting that hamstrings length is more important for terminal swing behaviour than hamstrings spasticity.

The relation between postural stability and weight distribution in healthy subjects.

Knowledge of the effects of leg-loading asymmetry on postural control and control asymmetry during quiet upright standing in healthy young and middle-aged subjects is necessary before these relationships in patients with lateralized disorders can be assessed and understood. A posturographic procedure was developed, using a dual-plate force platform, during which 10 younger and 10 middle-aged healthy individuals were required to adopt various degrees of (a) symmetrical weight distributions (0, 5, 10, 20 and 30% of extra body weight loaded onto either leg). Postural control and control asymmetry were quantified by centre of pressure (CP) fluctuations in the lateral (LAT) and anterior-posterior (AP) directions under both feet together and individually. Subsequently, the relationship between weight distribution on one hand and postural control and control asymmetry on the other hand, was calculated. Results demonstrated that with increasing weight-bearing asymmetry (WBA), the overall control of postural sway velocity increased mainly in the LAT direction, where a first-order polynomial function fitted best. The asymmetry of control of postural sway velocity increased with increasing weight-bearing asymmetry in favour of the more loaded leg in LAT and AP directions. A first-order polynomial was used for both AP and LAT direction. Effects of weight-bearing asymmetry on postural control and control asymmetry are due to changes in the biomechanical constraints of upright standing. It was suggested that through increasing weight-bearing asymmetry the postural instability increased by reducing the efficiency of hip load/unload mechanisms and increasing the (compensatory) ankle moments.

Age-related deficits in early response characteristics of obstacle avoidance under time pressure.

BACKGROUND: Obstacles in the travel path are a frequent cause of falls among elderly persons. In obstacle avoidance under time pressure, elderly persons have been reported to be less successful than young persons, but possible age-related deficits at the neuromuscular control level have not been studied yet. METHODS: In the present study, obstacle avoidance reactions were investigated in 15 young and 9 older adults. While the participants walked on a treadmill, an obstacle was dropped in front of the left foot either in late stance, early swing, or mid-swing. Muscle activity in response to the obstacle was measured from the left biceps femoris (BF), rectus femoris (RF), tibialis anterior (TA), and medial head of gastrocnemius (GM). Avoidance success rates, as well as initial response latencies and response amplitudes over the first 50 ms of the response, were determined. RESULTS: In both young and older adults, a large initial response was consistently observed in BF at very short latencies (104-111 ms in the young group), especially for mid-swing obstacle presentations (yielding the highest time pressure). Onset latencies in the elderly group were delayed by 10 ms on average. Response amplitudes were larger in young than in older adults, most prominently in BF and RF, but with a similar tendency in TA. Both onset latency and response amplitude were significantly associated with avoidance success rates. CONCLUSIONS: The results of the present study suggest that age-related deficits in the neuromuscular control of obstacle avoidance could play a role in the large numbers of obstacle-related falls in the elderly population.

High failure rates when avoiding obstacles during treadmill walking in patients with a transtibial amputation.

OBJECTIVE: To investigate if and to what extent patients with a transtibial amputation are less successful in avoiding unexpected obstacles while walking than healthy adults. DESIGN: Experimental 2-group design. SETTING: Dutch rehabilitation center. PARTICIPANTS: Eleven patients with a transtibial amputation and 14 healthy controls. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Subjects walked on a treadmill at .56m/s. In 2 series of 12 trials each, an obstacle was dropped in front of the prosthetic or the nonprosthetic leg of the amputation group and the left leg of the control group at different phases during the step cycle. It was noted which avoidance strategy was used (a long step strategy [LSS] or a short step strategy [SSS]) and whether the obstacle was avoided successfully or not. These data were expressed as a percentage of the total number of trials completed by each subject. RESULTS: With either leg, the amputation group made significantly more errors than the control subjects (prosthetic leg, 24%+/-17%; nonprosthetic leg, 21%+/-17% vs 2%+/-2% for the control group). Highest failure rates were in the amputation group when time pressure was high, requiring an SSS, especially on the prosthetic side. An LSS under time pressure, however, nearly always resulted in failure for both the prosthetic and nonprosthetic legs. Subjects with the longest time since amputation were most successful in avoiding unexpected obstacles. CONCLUSIONS: Under time pressure, patients with a lower-leg prosthesis perform best when they use their nonprosthetic leg as the lead limb in an SSS. The fact that some subjects with the longest time since amputation made no errors suggests that over many years it is possible to relearn the appropriate avoidance reactions sufficiently fast.

Advancing age progressively affects obstacle avoidance skills in the elderly.

The ability to adequately avoid obstacles while walking is an important skill that allows safe locomotion over uneven terrain. The high proportion of falls in the elderly that is associated to tripping over obstacles potentially illustrates an age-related deterioration of this locomotor skill. Some studies have compared young and old adults, but very little is known about the changes occurring within different age groups of elderly. In the present study, obstacle avoidance performance was studied in 25 young (20-37 years) and 99 older adults (65-88 years). The participants walked on a treadmill at a speed of 3 km/h. An obstacle was dropped 30 times in front of the left foot at various phases in the step cycle. Success rates (successful avoidance) were calculated and related to the time available between obstacle appearance and the estimated instant of foot contact with the obstacle (available response times or ARTs ranging from 200 to more than 350 ms). In addition, latencies of avoidance reactions, the choice of avoidance strategies (long or short step strategy, LSS or SSS), and three spatial parameters related to obstacle avoidance (toe distance, foot clearance, and heel distance) were determined for each participant. Compared to the young, the older adults had lower success rates, especially at short ARTs. Furthermore, they had longer reaction times, more LSS reactions, smaller toe and heel distances, and larger foot clearances. Within the group of elderly, only the 65-69 year olds were not different from young adults with respect to success rate, despite marked changes in the other parameters measured. In particular, even this younger group of elderly showed a dramatic reduction in the amount of SSS trials compared to young adults. Overall, age was a significant predictor of success rates, reaction times, and toe distances. These parameters deteriorated with advancing age. Finally, avoidance success rates at short ARTs were considerably worse in elderly participants who sustained recurrent falls in the six-month period prior to the assessment compared to those who sustained no or only one fall. An exercise program has been shown to improve avoidance success rates, especially at short ARTs, but the training effects on the determinants of success still need to be assessed.

Restoration of weight-shifting capacity in patients with postacute stroke: a rehabilitation cohort study.

OBJECTIVES: To identify and interrelate recovery characteristics of voluntary weight shifting after stroke and to examine whether the assessment of weight shifting adds information about balance recovery compared with the assessment of quiet standing. DESIGN: Exploratory study using an inception cohort with findings related to reference values from healthy elderly persons. SETTING: Dutch rehabilitation center. PARTICIPANTS: Thirty-six inpatients (mean age, 61.8 y; mean time poststroke, 10 wk) with a first hemispheric intracerebral infarction or hematoma who were admitted to retrain standing balance and walking. INTERVENTION: Individualized therapy. MAIN OUTCOME MEASURES: Center of pressure (COP) displacements were registered during voluntary frontal-plane weight shifting guided by visual COP feedback using a dual-plate force platform. Besides the speed (number of weight shifts) and imprecision (normalized average lateral COP displacement per weight shift), the weight-transfer time asymmetry and the spatiotemporal distribution were determined. Assessments took place as soon as patients could stand unassisted for at least 30 seconds and at 2, 4, 8, and 12 weeks later. RESULTS: During the 12-week training period, the stroke patients increased both their speed (2.3 hits/30 s; 95% confidence interval [CI], 1.1-3.4) and precision (37.7 mm/hit; 95% CI, 10.4-65.0) of weight shifting. Although the speed appeared to stabilize at a suboptimal level after 8 weeks, precision reached normal reference values after 12 weeks. Both older age (>/=65 y) and the presence of visuospatial hemineglect negatively affected weight-shifting speed but not its relative improvement in time. During the training period, a small degree of weight-transfer time asymmetry persisted (mean change, .07; 95% CI, -.21 to .36), with an average of 23% slower weight shifts toward the paretic leg, but the spatiotemporal distribution remained symmetrical. The correlations between weight-shifting and quiet-standing control at the end of training were moderate (Spearman rho range, .50-.77). CONCLUSIONS: Even subjects with severe stroke who are selected for inpatient rehabilitation are able to improve their speed and precision of weight shifting by reducing the weight-transfer time toward both legs in a proportionate manner. The observed correlations between weight shifting and quiet standing indicate that the assessment of weight-shifting capacity provides unique information about balance recovery after stroke.

Effects of visual center of pressure feedback on postural control in young and elderly healthy adults and in stroke patients.

The goal of this study was to compare young and elderly healthy individuals and elderly stroke patients in their capacity to use visual CP feedback (VF) in controlling both quiet standing and weight shifting and to assess their sensory re-weighing when this VF is withdrawn. A total of 40 participants were involved in this study. Participants were asked to either quietly stand on a force platform for a period of 45 s with eyes open (EO), using visual feedback (VF) or without visual feedback (No VF) or to perform a dynamic weight shifting task while using VF or No VF. During the quiet standing trials with VF, only the young (YO) were able to decrease the amplitude and increase the frequency of their sway in either plane. Removal of the VF resulted in a 'destabilizing' effect in both healthy elderly (EL) and stroke patients (ST) in the sagittal plane. With regard to the dynamic task, both the YO and EL were generally more successful at weight shifting in terms of speed and control when compared to the ST. Yet, when VF was removed, only the YO were able to largely maintain speed and precision of control. Hence, providing or removing visual CP feedback during quiet standing or removing VF during visually controlled weight shifting can discriminate healthy young participants from healthy elderly, but does not clearly discriminate healthy elderly from stroke patients in the same age group. Results revealed that sagittal plane imbalance in healthy elderly and stroke patients may be largely due to the effects of aging, whereas frontal plane imbalance is much more specific for the postural problems associated with stroke.