Action observation with motor simulation improves reactive stepping responses following strong backward balance perturbations in healthy young individuals.

BACKGROUND AND OBJECTIVE: Adequate reactive steps are critical for preventing falls following balance perturbations. Perturbation-based balance training was shown to improve reactive stepping in various clinical populations, but its delivery is labor-intensive and generally uses expensive equipment. Action observation of reactive steps with either motor imagery (AOMI) or motor simulation (AOMS) are potential alternative training modalities. We here aimed to study their effects on reactive stepping performance. METHODS: Sixty healthy young subjects were subjected to forward platform translations that elicited backward reactive steps. The AOMI group (n = 20) was tested after AOMI of an actor's reactive steps, while the AOMS group (n = 20) additionally stepped along with the actor. The control group (n = 20) was tested without any prior observation. Our primary outcome was the step quality of the first trial response, as this best represents a real-life loss-of-balance. Step quality was quantified as the leg angle with respect to the vertical at stepping-foot contact. We also studied single step success rates and reactive step quality across repeated trials. RESULTS: Reactive step quality was significantly better in the AOMI and AOMS groups than in the control group, which differences coincided with a twofold higher single step success rate. Reactive step quality improved upon repeated trials in all groups, yet the AOMS group needed the fewest repetitions to reach plateau performance. SIGNIFICANCE: The present results demonstrate that both AOMI and AOMS improved first and repeated trial reactive stepping performance. These findings point at the potential applicability of these concepts for home-based reactive balance training, for instance in serious games, with overt movements (AOMS) possibly having some benefits over mental imaginations (AOMI). Whether similar beneficial effects also emerge in the target populations of balance-impaired individuals remains to be investigated.

Benefits of implanted peroneal functional electrical stimulation for continual gait adaptations in people with 'drop foot' due to chronic stroke.

BACKGROUND: Benefits of peroneal functional electrical stimulation in people with post-stroke drop foot may particularly emerge in environments that require continual gait adaptation. Such adaption is known to increase the attentional demands of gait. RESEARCH QUESTIONS: Is performance of a target stepping task more accurate and less attention demanding with electrical stimulation ON compared to OFF in people with post-stroke drop foot? METHODS: Thirteen people with an implanted electrical stimulation system participated in this observational study. Participants performed a walking task with irregularly spaced targets on a self-paced treadmill, both as a single task and combined with an auditory Stroop task. Participants performed each task with electrical stimulation ON and OFF. In the OFF condition participants were allowed to use their own ankle-foot orthosis. The effects of Device (ON, OFF) and interaction of Device*Task (single, dual) on stepping performance in mediolateral and anteroposterior direction were tested based on the total error of foot placement relative to the targets, using repeated measurements ANOVA. Differences between electrical stimulation ON and OFF on auditory Stroop task accuracy were assessed using a non-parametric Wilcoxon signed-rank test. Non-parametric correlations were calculated to associate changes in stepping performance with paretic leg motor function (Fugl-Meyer Assessment - leg score). RESULTS: Data of 12 participants were used for analysis. Mediolateral total error was smaller with peroneal functional electrical stimulation ON compared to OFF (Δ = 1.0 cm, p = 0.011). In the anteroposterior direction, no significant effects of Device were found. There were no significant interaction effects of Device*Task in either direction. Changes in total error (ON vs OFF) were not significantly associated with leg motor function. Stroop task accuracy was not statistically different between ON and OFF. SIGNIFICANCE: Implanted electrical stimulation may have benefits with regard to mediolateral accuracy of a continual target stepping task, although the effect size is relatively small. This benefit seems to be independent of the performance of a concurrent attention-demanding task and may reflect better gait stability in the mediolateral direction, which is known to be a problem in people with stroke.

Long-term use of implanted peroneal functional electrical stimulation for stroke-affected gait: the effects on muscle and motor nerve.

BACKGROUND: Peripheral changes to muscle and motor nerves occur following stroke, which may further impair functional capacity. We investigated whether a year-long use of an implanted peroneal FES system reverses stroke-related changes in muscles and motor nerves in people with foot drop in the chronic phase after supratentorial stroke. METHODS: Thirteen persons with a chronic stroke (mean age 56.1 years, median Fugl-Meyer Assessment leg score 71%) were included and received an implanted peroneal FES system (ActiGait®). Quantitative muscle ultrasound (QMUS) images were obtained bilaterally from three leg muscles (i.e. tibialis anterior, rectus femoris, gastrocnemius). Echogenicity (muscle ultrasound gray value) and muscle thickness were assessed over a one-year follow-up and compared to age-, sex-, height- and weight-corrected reference values. Compound motor action potentials (CMAPs) and motor evoked potentials (MEPs) were obtained from the tibialis anterior muscle. Generalized estimated equation modeling was used to assess changes in QMUS, CMAPs and MEPs outcomes over the follow-up period. RESULTS: Echogenicity of the tibialis anterior decreased significantly during the follow-up on the paretic side. Z-scores changed from 0.88 at baseline to - 0.15 after 52 weeks. This was accompanied by a significant increase in muscle thickness on the paretic side, where z-scores changed from - 0.32 at baseline to 0.48 after 52 weeks. Echogenicity of the rectus femoris normalized on both the paretic and non-paretic side (z-scores changed from - 1.09 and - 1.51 to 0.14 and - 0.49, respectively). Amplitudes of CMAP and MEP (normalized to CMAP) were reduced during follow-up, particularly on the paretic side (ΔCMAP = 20% and ΔMEP = 14%). CONCLUSIONS: We show that the structural changes to muscles following stroke are reversible with FES and that these changes might not be limited to electrically stimulated muscles. No evidence for improvement of the motor nerves was found.

Surplus value of implanted peroneal functional electrical stimulation over ankle-foot orthosis for gait adaptability in people with foot drop after stroke.

BACKGROUND: Implanted peroneal functional electrical stimulation (FES) is an effective alternative treatment to ankle-foot orthosis (AFO) in people with drop foot after stroke. With FES no constraints on ankle mobility are imposed which might particularly be exploited in challenging walking environments that require adaptations of the gait pattern to environmental disturbances. RESEARCH QUESTION: Is gait adaptability, by means of the capacity to avoid sudden obstacles while walking on a treadmill, superior with implanted FES compared to AFO in people with drop foot after stroke? METHODS: A 4-channel peroneal nerve stimulator (ActiGait®) was implanted in 22 persons with stroke (>6 months) who regularly used an AFO. Gait adaptability was tested with an obstacle avoidance task on an instrumented treadmill up to 26 weeks (n = 10) or 52 weeks (n = 12) after FES-system activation. At assessments, 30 trials, in which obstacles were suddenly dropped onto the treadmill in front of the paretic leg, were recorded with each device (FES / AFO). Trials were grouped by available response times (ART) and success rates were calculated. The effect of device, ART and follow up time on success rates was tested using generalized estimated equations. Nonparametric correlations were calculated to associate changes in success rates with clinimetrics. RESULTS: Success rates of obstacle avoidance were higher when participants used their FES system compared to AFO (Δ4.7%, p = 0.03), which effect was largest for longest ARTs (Δ15%, p = 0.03). Participants with greater motor impairment of the paretic leg showed greater benefit from FES (rs=-0.49, p = 0.04). SIGNIFICANCE: FES has been found equally effective as AFO in improving walking speed of people with drop foot after stroke. We now present superior walking performance in a complex walking environment for implanted peroneal FES compared to AFO. These findings underline the importance of using gait assessments that require interplay with the environment, besides assessment of stationary walking, in community ambulators.

StartReact during gait initiation reveals differential control of muscle activation and inhibition in patients with corticospinal degeneration.

Corticospinal lesions cause impairments in voluntary motor control. Recent findings suggest that some degree of voluntary control may be taken over by a compensatory pathway involving the reticulospinal tract. In humans, evidence for this notion mainly comes from StartReact studies. StartReact is the acceleration of reaction times by a startling acoustic stimulus (SAS) simultaneously presented with the imperative stimulus. As previous StartReact studies mainly focused on isolated single-joint movements, the question remains whether the reticulospinal tract can also be utilized for controlling whole-body movements. To investigate reticulospinal control, we applied the StartReact paradigm during gait initiation in 12 healthy controls and 12 patients with 'pure' hereditary spastic paraplegia (HSP; i.e., retrograde axonal degeneration of corticospinal tract). Participants performed three consecutive steps in response to an imperative visual stimulus. In 25% of 16 trials a SAS was applied. We determined reaction times of muscle (de)activation, anticipatory postural adjustments (APA) and steps. Without SAS, we observed an overall delay in HSP patients compared to controls. Administration of the SAS accelerated tibialis anterior and rectus femoris onsets in both groups, but more so in HSP patients, resulting in (near-)normal latencies. Soleus offsets were accelerated in controls, but not in HSP patients. The SAS also accelerated APA and step reaction times in both groups, yet these did not normalize in the HSP patients. The reticulospinal tract is able to play a compensatory role in voluntary control of whole-body movements, but seems to lack the capacity to inhibit task-inappropriate muscle activity in patients with corticospinal lesions.

Kinematic and kinetic benefits of implantable peroneal nerve stimulation in people with post-stroke drop foot using an ankle-foot orthosis.

BACKGROUND: Contralesional 'drop foot' after stroke is usually treated with an ankle-foot orthosis (AFO). However, AFOs may hamper ankle motion during stance. Peroneal functional electrical stimulation (FES) is an alternative treatment that provides active dorsiflexion and allows normal ankle motion. Despite this theoretical advantage of FES, the kinematic and kinetic differences between AFO and FES have been scarcely investigated. OBJECTIVE: To test whether walking with implanted FES leads to improvements in stance stability, propulsion, and swing initiation compared to AFO. METHODS: A 4-channel peroneal nerve stimulator (ActiGait ®) was implanted in 22 chronic patients after stroke. Instrumented gait analyses were performed during comfortable walking up to 26 weeks (n = 10) or 52 weeks (n = 12) after FES-system activation. Kinematics of knee and ankle (stance and swing phase) and kinetics (stance phase) of gait were determined, besides spatiotemporal parameters. Finally, we determined whether differences between devices regarding late stance kine(ma)tics correlated with those regarding the swing phase. RESULTS: In mid-stance, knee stability improved as the peak knee extension velocity was lower with FES (ß = 18.1°/s, p = 0.007), while peak ankle plantarflexion velocity (ß = -29.2°/s, p = 0.006) and peak ankle plantarflexion power (ß = -0.2 W/kg, p = 0.018) were higher with FES compared to AFO. With FES, the ground reaction force (GRF) vector at peak ankle power (i.e., 'propulsion') was oriented more anteriorly (ß = -1.1°, p = 0.001). Similarly, the horizontal GRF (ß = -0.8% body mass, p = 0.003) and gait speed (ß = 0.03 m/s, p = 0.015) were higher. An increase in peak ankle plantarflexion velocity and a more forward oriented GRF angle during late stance were moderately associated with an increase in hip flexion velocity during initial swing (rs = 0.502, p = 0.029 and rs = 0.504, p = 0.028, respectively). CONCLUSIONS: This study substantiates the evidence that implantable peroneal FES as a treatment for post-stroke drop foot may be superior over AFO in terms of knee stability, ankle plantarflexion power, and propulsion.

A startling acoustic stimulus facilitates voluntary lower extremity movements and automatic postural responses in people with chronic stroke.

A startling acoustic stimulus (SAS) involuntary releases prepared movements at accelerated latencies, known as the StartReact effect. Previous work has demonstrated intact StartReact in paretic upper extremity movements in people after stroke, suggesting preserved motor preparation. The question remains whether motor preparation of lower extremity movements is also unaffected after stroke. Here, we investigated StartReact effects on ballistic lower extremity movements and on automatic postural responses (APRs) following perturbations to standing balance. These APRs are particularly interesting as they are critical to prevent a fall following balance perturbations, but show substantial delays and poor muscle coordination after stroke. Twelve chronic stroke patients and 12 healthy controls performed voluntary ankle dorsiflexion movements in response to a visual stimulus, and responded to backward balance perturbations evoking APRs. Twenty-five percent of all trials contained a SAS (120 dB) simultaneously with the visual stimulus or balance perturbation. As expected, in the absence of a SAS muscle and movement onset latencies at the paretic side were delayed compared to the non-paretic leg and to controls. The SAS accelerated ankle dorsiflexion onsets in both the legs of the stroke subjects and in controls. Following perturbations, the SAS accelerated bilateral APR onsets not only in controls, but for the first time, we also demonstrated this effect in people after stroke. Moreover, APR inter- and intra-limb muscle coordination was rather weak in our stroke subjects, but substantially improved when the SAS was applied. These findings show preserved movement preparation, suggesting that there is residual (subcortical) capacity for motor recovery.

Does the StartReact Effect Apply to First-Trial Reactive Movements?

INTRODUCTION: StartReact is the acceleration of reaction time by a startling acoustic stimulus (SAS). The SAS is thought to release a pre-prepared motor program. Here, we investigated whether the StartReact effect is applicable to the very first trial in a series of repeated unpractised single-joint movements. METHODS: Twenty healthy young subjects were instructed to perform a rapid ankle dorsiflexion movement in response to an imperative stimulus. Participants were divided in two groups of ten. Both groups performed 17 trials. In one group a SAS (116 dB) was given in the first trial, whereas the other group received a non-startling sound (70 dB) as the first imperative stimulus. In the remaining 16 trials, the SAS was given as the imperative stimulus in 25% of the trials in both groups. The same measurement was repeated one week later, but with the first-trial stimuli counterbalanced between groups. RESULTS: When a SAS was given in the very first trial, participants had significantly shorter onset latencies compared to first-trial responses to a non-startling stimulus. Succeeding trials were significantly faster compared to the first trial, both for trials with and without a SAS. However, the difference between the first and succeeding trials was significantly larger for responses to a non-startling stimulus compared to responses triggered by a SAS. SAS-induced acceleration in the first trial of the second session was similar to that in succeeding trials of session 1. DISCUSSION: The present results confirm that the StartReact phenomenon also applies to movements that have not yet been practiced in the experimental context. The excessive SAS-induced acceleration in the very first trial may be due to the absence of integration of novel context-specific information with the existing motor memory for movement execution. Our findings demonstrate that StartReact enables a rapid release of motor programs in the very first trial also without previous practice, which might provide a behavioural advantage in situations that require a rapid response to a potentially threatening environmental stimulus.

Secondary task performance during challenging walking tasks and freezing episodes in Parkinson's disease.

Parkinson's disease (PD) patients likely use attentional strategies to compensate for their gait deficits, which increases the cognitive challenge of walking. The interplay between cognitive functions and gait can be investigated by evaluating the subject's attendance to a secondary task during walking. We hypothesized that the ability to attend to a secondary task decreases during challenging walking conditions in PD, particularly during freezing of gait (FOG)-episodes. Twenty-nine PD patients and 14 age-matched controls performed a simple reaction task that involved squeezing a ball as fast as possible in response to an auditory stimulus. Participants performed this reaction task during four conditions: (1) walking at preferred speed; (2) walking with short steps at preferred speed; (3) walking with short steps, as rapidly as possible; (4) making rapid full turns. We used surface electromyography to determine reaction times, and a pressure sensor located within the ball to determine movement onset. Reaction times of PD patients were slower (on average by 42 ms) compared to controls, regardless of the walking task. In both groups, reaction times were significantly longer during the turning condition compared to all other conditions. FOG-episodes were most often seen during the turning condition. In PD patients, reaction times were significantly longer during FOG-episodes compared to trials without FOG. Our results suggest that turning requires more attentional resources than other walking tasks. The observation of delayed reaction times during FOG-episodes compared to trials without FOG suggests that freezers use additional resources to overcome their FOG-episodes.

StartReact effects support different pathophysiological mechanisms underlying freezing of gait and postural instability in Parkinson's disease.

INTRODUCTION: The pathophysiology underlying postural instability in Parkinson's disease is poorly understood. The frequent co-existence with freezing of gait raises the possibility of shared pathophysiology. There is evidence that dysfunction of brainstem structures contribute to freezing of gait. Here, we evaluated whether dysfunction of these structures contributes to postural instability as well. Brainstem function was assessed by studying the StartReact effect (acceleration of latencies by a startling acoustic stimulus (SAS)). METHODS: We included 25 patients, divided in two different ways: 1) those with postural instability (HY = 3, n = 11) versus those without (HY<3, n = 14); and 2) those with freezing (n = 11) versus those without freezing (n = 14). We also tested 15 matched healthy controls. We tested postural responses by translating a balance platform in the forward direction, resulting in backward balance perturbations. In 25% of trials, the start of the balance perturbation was accompanied by a SAS. RESULTS: The amplitude of automatic postural responses and length of the first balance correcting step were smaller in patients with postural instability compared to patients without postural instability, but did not differ between freezers and non-freezers. In contrast, the StartReact effect was intact in patients with postural instability but was attenuated in freezers. DISCUSSION: We suggest that the mechanisms underlying freezing of gait and postural instability in Parkinson's disease are at least partly different. Underscaling of automatic postural responses and balance-correcting steps both contribute to postural instability. The attenuated StartReact effect was seen only in freezers and likely reflects inadequate representation of motor programs at upper brainstem level.

Subcortical structures in humans can be facilitated by transcranial direct current stimulation.

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that alters cortical excitability. Interestingly, in recent animal studies facilitatory effects of tDCS have also been observed on subcortical structures. Here, we sought to provide evidence for the potential of tDCS to facilitate subcortical structures in humans as well. Subjects received anodal-tDCS and sham-tDCS on two separate testing days in a counterbalanced order. After stimulation, we assessed the effect of tDCS on two responses that arise from subcortical structures; (1) wrist and ankle responses to an imperative stimulus combined with a startling acoustic stimulus (SAS), and (2) automatic postural responses to external balance perturbations with and without a concurrent SAS. During all tasks, response onsets were significantly faster following anodal-tDCS compared to sham-tDCS, both in trials with and without a SAS. The effect of tDCS was similar for the dominant and non-dominant leg. The SAS accelerated the onsets of ankle and wrist movements and the responses to backward, but not forward perturbations. The faster onsets of SAS-induced wrist and ankle movements and automatic postural responses following stimulation provide strong evidence that, in humans, subcortical structures--in particular the reticular formation--can be facilitated by tDCS. This effect may be explained by two mechanisms that are not mutually exclusive. First, subcortical facilitation may have resulted from enhanced cortico-reticular drive. Second, the applied current may have directly stimulated the reticular formation. Strengthening reticulospinal output by tDCS may be of interest to neurorehabilitation, as there is evidence for reticulospinal compensation after corticospinal lesions.

Reduced StartReact effect and freezing of gait in Parkinson's disease: two of a kind?

Freezing of gait (FOG) is a disabling feature of Parkinson's disease. Emerging evidence suggests that dysfunction of the pedunculopontine nucleus (PPN) and pontomedullary reticular formation (pmRF) plays a role in the causation of FOG. These brainstem structures can be examined by the StartReact paradigm, which utilizes a startling stimulus to accelerate reaction times (StartReact). Here, we examined gait initiation in PD patients with and without FOG using this paradigm. Twenty-six patients with Parkinson's disease (12 freezers and 14 non-freezers) and 15 controls performed two tasks: rapid gait initiation in response to an imperative 'go' signal; and a control condition, involving a simple reaction-time task involving ankle dorsiflexion. During both tasks, a startling acoustic stimulus was combined with the imperative signal in 25 % of trials. In controls, the startle accelerated gait initiation and shortened the onset latency of tibialis anterior responses during ankle dorsiflexion. This acceleration was intact in non-freezers, but was significantly attenuated in the freezers. Independent of the occurrence of a startle, freezers showed a reduced length of the first step compared to non-freezers and controls. The diminished StartReact effect in freezers probably reflects deficient representation or release of motor programs at the brainstem reticular level due to dysfunction of the PPN, the pmRF, or both. These brainstem structures are presumably involved in integrating anticipatory postural adjustments with subsequent stepping movements. We suggest that with time-varying demands, these structures may no longer be able to coordinate the integration of anticipatory postural adjustments with steps, leading to FOG episodes.

StartReact restores reaction time in HSP: evidence for subcortical release of a motor program.

Startling acoustic stimuli (SAS) can accelerate reaction times ("StartReact" effect), but the underlying mechanism remains unclear. Both direct release of a subcortically stored motor program and a subcortically mediated trigger for a cortically stored motor program have been hypothesized. To distinguish between these hypotheses, we examined the StartReact effect in humans with pure hereditary spastic paraplegia (HSP). Delayed reaction times in HSP patients in trials both with and without a SAS would argue in favor of a cortically stored response. We instructed 12 HSP patients and 12 matched controls to respond as rapidly as possible to a visual imperative stimulus, in two different conditions: dorsiflexion of the dominant ankle; or flexion of the dominant wrist. In 25% of trials, a SAS was delivered simultaneously with the imperative stimulus. Before these tests, subjects received five SAS while standing to verify normal function of the reticulospinal tract in HSP. Latencies of startle responses in sternocleidomastoid and tibialis anterior muscles were comparable between patients and controls. During the ankle dorsiflexion task, HSP patients had an average 19 ms delay in reaction times compared with controls. Administration of a SAS accelerated ankle dorsiflexion in both groups, but more so in the patients, which completely normalized their latencies. The wrist flexion task yielded no differences in onset latencies between HSP patients and controls. The reticulospinal tract seems unaffected in HSP patients, because startle reflex onsets were normal. The corticospinal tract was affected, as reflected by delayed ankle dorsiflexion reaction times. These delayed onsets in HSP were normalized when the imperative stimulus was combined with a SAS, presumably through release of a subcortically stored motor program conveyed by the preserved reticulospinal tract.

Mechanisms of postural instability in hereditary spastic paraplegia.

Hereditary spastic paraplegia (HSP) is characterized by progressive lower extremity spasticity and weakness, due to retrograde axonal degeneration of the corticospinal tract and posterior spinal columns. HSP patients fall frequently. We hypothesized that delayed postural responses contribute to their balance impairments. To distinguish between a delay in afferent and efferent signals, we combined postural responses with a startling acoustic stimulus (SAS). The SAS triggers a postural response directly, bypassing afferent proprioceptive input. We performed two experiments. First, 18 HSP patients and nine healthy controls stood on a balance platform and were instructed to counteract forward and backward balance perturbations, without taking a step or grabbing a handrail. Second, 12 HSP patients and nine controls received backward perturbations, while a SAS accompanied onset of platform motion in 25% of trials. HSP patients were less successful than controls in maintaining balance following backward and forward perturbations. Furthermore, latencies of postural responses were significantly delayed in HSP-patients, by 34 ms in gastrocnemius following forward, and by 38 ms in tibialis anterior following backward perturbations. A SAS accelerated postural responses in all participants, but more so in HSP patients whose latencies were normalized. Our results suggest that delayed postural responses in HSP patients contribute to their balance problems. Combining balance perturbations with a SAS restored normal latencies, suggesting that conduction of efferent signals (presumably by the reticulospinal tract) is normal. We therefore suggest that the delayed postural responses in HSP are caused by slowed conduction time via the posterior spinal columns.

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.

Community-dwelling people with chronic stroke need disproportionate attention while walking and negotiating obstacles.

The objective of the present study was to examine the attentional demands of gait adaptations required to walk over irregular terrain in community-dwelling people with chronic stroke. Eight community ambulators (>6 months post-stroke, aged 57 ± 15 years) and eight age-matched healthy controls participated in the study. As the primary motor task, participants walked on a treadmill while they quickly reacted to a sudden obstacle in front of the affected (in the stroke group) or left (in healthy controls) leg. The secondary, cognitive task was an auditory Stroop task. Outcomes were avoidance success rate and muscle reaction times of the biceps and rectus femoris (motor task), and a composite score of accuracy and verbal reaction time (cognitive task). Success rates did not differ between single- and dual-task conditions in either group, while muscle reaction times deteriorated equally during the dual task in both groups. However, compared with the Stroop scores just before and after obstacle crossing, the scores while crossing the obstacle deteriorated more in the stroke group than in the controls (p=0.012). The higher dual-task costs on the Stroop task reflect greater attentional demands during walking and crossing obstacles. The absence of dual-task effects on obstacle avoidance performance suggests that the people with stroke used a "posture-first strategy". The results imply that common daily life tasks such as obstacle crossing while walking require disproportionate attention even in well-recovered people with stroke.

The possible price of auditory cueing: influence on obstacle avoidance in Parkinson's disease.

BACKGROUND: Under carefully controlled conditions, rhythmic auditory cueing can improve gait in patients with Parkinson's disease (PD). In complex environments, attention paid to cueing might adversely affect gait, for example when a simultaneous task-such as avoiding obstacles-has to be executed. We primarily examined whether concurrent auditory cueing interferes with an obstacle avoidance task in patients with PD. The secondary aim was to study differences between patients with and without freezing of gait. METHODS: Nineteen patients with PD (8 with freezing) were examined on a treadmill in 4 conditions: normal walking; walking with auditory cueing; walking with an obstacle avoidance task; and walking with auditory cueing and obstacle avoidance. Outcome measures included kinematic gait parameters and obstacle crossing parameters. RESULTS: Auditory cueing improved gait in PD, without negative effects on concurrent obstacle avoidance. Additionally, freezers avoided obstacles less efficiently than non-freezers. CONCLUSIONS: PD patients are able to successfully execute an obstacle avoidance task, when auditory cueing is administered simultaneously. The different obstacle avoidance behavior in freezers may contribute to their higher fall risk.

Effect of peroneal electrical stimulation versus an ankle-foot orthosis on obstacle avoidance ability in people with stroke-related foot drop.

BACKGROUND: Walking ability of people with foot drop in the chronic phase after stroke is better with functional electrical stimulation (FES) of the peroneal nerve than without an orthotic device. However, the literature is not conclusive on whether peroneal FES also is better than an ankle-foot orthosis (AFO) in this regard. OBJECTIVE: This study aimed to identify potential benefits of peroneal FES over an AFO with respect to the ability to negotiate a sudden obstacle. DESIGN: The study design was a within-subject comparison between FES and AFO using repeated measures. METHODS: Twenty-four community-dwelling people with stroke (mean age=52.6 years, SD=12.7) who regularly used a polypropylene AFO were fitted with a transcutaneous FES device. The participants' obstacle avoidance ability was tested after 2 and 8 weeks. They had to avoid 30 obstacles that were suddenly dropped on a treadmill in front of the affected leg while walking with either FES or an AFO. The obstacle avoidance success rates were determined. RESULTS: Success rates were higher with FES than with an AFO, especially after adjustment for individual leg muscle strength. Participants with relatively low muscle strength (Motricity Index score <64) were most likely to benefit from FES regarding obstacle avoidance ability. LIMITATION: Further work is needed to determine whether the results may be generalized to other groups of people with stroke. CONCLUSIONS: Peroneal FES seems to be superior to an AFO with regard to obstacle avoidance ability in community-dwelling people with stroke. The observed gains in obstacle avoidance ability appear to be clinically most relevant in the people with relatively low leg muscle strength.

Near-normal gait pattern with peroneal electrical stimulation as a neuroprosthesis in the chronic phase of stroke: a case report.

In recent years, the use of functional electrical stimulation (FES) of the peroneal nerve has increased as an alternative for an ankle-foot orthosis (AFO) to treat stroke-related drop foot. We present a chronic stroke patient demonstrating an almost normal gait pattern with peroneal FES as a neuroprosthesis. A 60-year-old survivor of a right hemisphere infarction 21 months ago, who regularly used a polypropylene AFO, was provided with a surface-based peroneal FES device for severe drop foot. In a second instance, he received an implanted FES system because of skin problems with the surface stimulator. With both FES devices, the patient achieved an adequate foot elevation. Moreover, his hip and knee flexion angles during walking increased to normal values and his ankle push-off power increased. His gait pattern became almost symmetrical and less variable than with the AFO. Furthermore, his ability to avoid a sudden obstacle improved to normal values with FES. Our patient showed benefits from peroneal FES beyond what can be attributed to improved foot lift alone. With regard to the potential working mechanisms underlying this response to FES, biomechanical benefits related to improved ankle push-off are suggested as the main mechanism.

Is transcutaneous peroneal stimulation beneficial to patients with chronic stroke using an ankle-foot orthosis? A within-subjects study of patients' satisfaction, walking speed and physical activity level.

OBJECTIVE: The aim of this study was to evaluate whether community-dwelling chronic stroke patients wearing an ankle-foot orthosis would benefit from changing to functional electrical stimulation of the peroneal nerve. METHODS: In 26 community-dwelling chronic (> 6 months post-onset) patients after stroke, their ankle-foot orthosis was replaced by a surface-based functional electrical stimulation device (NESS L300). Comfortable walking speed over 10 m was measured at baseline with the ankle-foot orthosis and after 2 and 8 weeks with both ankle-foot orthosis and functional electrical stimulation. The level of physical activity was assessed with a pedometer, and patients' satisfaction was assessed with a questionnaire at baseline and at week 8 regarding ankle-foot orthosis and functional electrical stimulation, respectively. RESULTS: Ankle-foot orthosis and functional electrical stimulation were equally effective with regard to walking speed and activity level. The participants were more satisfied with functional electrical stimulation than with their ankle-foot orthosis regarding the effort and stability of walking, quality of the gait pattern, walking distance, comfort of wearing and appearance of the device. CONCLUSION: The patients judged functional electrical stimulation superior to their ankle-foot orthosis, but measurements of walking speed and physical activity could not objectify the experienced benefits of functional electrical stimulation. Other outcome measures focusing on the stability and effort of ambulation may objectify the perceived benefits of functional electrical stimulation in community-dwelling chronic stroke patients.