Corticomuscular and intermuscular coherence as a function of age and walking balance difficulty.

We determined beta-band intermuscular (IMC) and corticomuscular coherence (CMC) as a function of age and walking balance difficulty. Younger (n=14, 23y) and older individuals (n=19, 71y) walked 13 m overground, on a 6-cm-wide ribbon overground, and on a 6-cm-wide (5-cm-high) beam. Walking distance as a proxy for walking balance and speed were computed. CMC was estimated between electroencephalographic signal at Cz electrode and surface electromyographic signals of seven leg muscles, while IMC was calculated in four pairs of leg muscles, during stance and swing gait phases. With increasing difficulty, walking balance decreased in old individuals and speed decreased gradually independent of age. Beam walking increased IMC, while age increased IMC in proximal muscle pairs, and decreased IMC in distal muscle pairs. Age and difficulty increased CMC independent of gait phases. Concluding, CMC and IMC increased with walking balance difficulty and age, except for distal muscle pairs, which had lower IMC with age. These findings suggest an age-related increase in corticospinal involvement in the neural control of walking balance. DATA AVAILABILITY: The datasets used in this study are available from the corresponding author upon reasonable request.

Age, Cognitive Task, and Arm Position Differently Affect Muscle Synergy Recruitment but have Similar Effects on Walking Balance.

Age modifies walking balance and neuromuscular control. Cognitive and postural constraints can increase walking balance difficulty and magnify age-related differences. However, how such challenges affect neuromuscular control remains unknown. We determined the effects of age, cognitive task, and arm position on neuromuscular control of walking balance. Young (YA) and older adults (OA) walked on a 6-cm wide beam with and without arm crossing and a cognitive task. Walking balance was quantified by the distance walked on the beam. We also computed step speed, margin of stability, and cognitive errors. Neuromuscular control was determined through muscle synergies extracted from 13 right leg and trunk muscles. We analyzed neuromuscular complexity by the number of synergies and the variance accounted for by the first synergy, coactivity by the number of significantly active muscles in each synergy, and efficiency by the sum of the activation of each significantly active muscle in each synergy. OA vs. YA walked a 14% shorter distance, made 12 times more cognitive errors, and showed less complex and efficient neuromuscular control. Cognitive task reduced walking balance mainly in OA. Decreases in step speed and margin of stability, along with increased muscle synergy coactivity and reduced efficiency were observed in both age groups. Arm-crossing also reduced walking balance mostly in OA, but step speed decreased mainly in YA, in whom the margin of stability increased. Arm-crossing reduced the complexity of synergies. Age, cognitive task, and arm position affect differently muscle synergy recruitment but have similar effects on walking balance.

Comparison of ground reaction force and marker-based methods to estimate mediolateral center of mass displacement and margins of stability during walking.

Dynamic balance control during human walking can be described by the distance between the mediolateral (ML) extrapolated center of mass (XCoM) position and the base of support, the margin of stability (MoS). The ML center of mass (CoM) position during treadmill walking can be estimated based on kinematic data (marker-based method) and a combination of ground reaction forces and center of pressure positions (GRF-based method). Here, we compare a GRF-based method with a full-body marker-based method for estimating the ML CoM, ML XCoM and ML MoS. Fifteen healthy adults walked on a dual-belt treadmill at comfortable walking speed for three minutes. Kinetic and kinematic data were collected and analyzed using a GRF-based and marker-based method to compare the ML CoM, ML XCoM and ML MoS. High correlation coefficients (r > 0.98) and small differences (Root Mean Square Difference < 0.0072 m) in ML CoM and ML XCoM were found between the GRF-based and marker-based methods. The GRF-based method resulted in larger ML XCoM excursion (0.0118 ± 0.0074 m) and smaller ML MoS values (0.0062 ± 0.0028 m) than the marker-based method, but these differences were consistent across participants. In conclusion, the GRF-based method is a valid method to determine the ML CoM, XCoM and MoS. One should be aware of higher ML XCoM and smaller ML MoS values in the GRF-based method when comparing absolute values between studies. The GRF-based method strongly reduces measurement times and can be used to provide real-time CoM-CoP feedback during treadmill gait training.

Effects of asymmetrical support on lower limb muscle activity during Lokomat guided gait in persons with a chronic stroke: an explorative study.

BACKGROUND: The Lokomat, one of the most popular robotic exoskeletons, can take the asymmetry in the gait pattern of unilaterally affected patients into account with its opportunity to provide unequal levels of movement support (or 'guidance') to each of the legs. This asymmetrical guidance may be used to selectively unburden limbs with impaired voluntary control and/or to exploit the interlimb couplings for training purposes. However, there is a need to explore and understand these specific device opportunities more broadly before implementing them in training. AIM: The aim of this study was to explore the effects of (a)symmetrical guidance settings on lower limb muscle activity in persons with post stroke hemiparesis, during Lokomat guided gait. DESIGN: A single group, dependent factorial design. SETTING: Rehabilitation center; a single session of Lokomat guided walking. POPULATION: A group of ten persons with post stroke hemiparesis. METHODS: Participants walked in the Lokomat in eight conditions, consisting of symmetrical and asymmetrical guidance situations, at both 0.28 m/s and 0.56 m/s. During symmetrical conditions, both legs received 30% or 100% guidance, while during asymmetrical conditions one leg received 30% and the other leg 100% guidance. Surface electromyography was bilaterally measured from: Biceps Femoris, Rectus Femoris, Vastus Medialis, Medial Gastrocnemius and Tibialis Anterior. Statistical effects were assessed using Statistical Parametric Mapping. RESULTS: The provision of assymetrical guidance did not affect the level of lower limb muscle activity. In addition, no effect (except for Vastus Medialis in the affected leg during 1.5-2.4% of the gait cycle) of symmetrical guidance on muscle amplitude could be observed. CONCLUSIONS: The results show no evidence that either symmetrical or asymmetrical guidance settings provided by the Lokomat can be used to manipulate activity of lower limb musculature in persons with post stroke hemiparesis. CLINICAL REHABILITATION IMPACT: This study provides insights for the use of specific opportunities provided by the Lokomat for training purposes post stroke.

Split-belt walking: An experience that is hard to forget.

BACKGROUND: The common paradigm to study the adaptability of human gait is split-belt walking. Short-term savings (minutes to days) of split-belt adaptation have been widely studied to gain knowledge in locomotor learning but reports on long-term savings are limited. Here, we studied whether after a prolonged inter-exposure interval (three weeks), the newly acquired locomotor pattern is subject to forgetting or that the pattern is saved in long-term locomotor memory. RESEARCH QUESTION: Can savings of adaptation to split-belt walking remain after a prolonged inter-exposure interval of three weeks? METHODS: Fourteen healthy adults participated in a single ten-minute adaptation session to split-belt walking and five-minute washout to tied-belt walking. They received no training after the first exposure and returned to the laboratory exactly three weeks later for the second exposure. To identify the adaptation trends and quantify saving parameters we used Singular Spectrum Analysis, a non-parametric, data-driven approach. We identified trends in step length asymmetry and double support asymmetry, and calculated the adaptation volume (reduction in asymmetry over the course of adaptation), and the plateau time (time required for the trend to level off). RESULTS: At the second exposure after three weeks, we found substantial savings in adaptation for step length asymmetry volume (61.6-67.6% decrease) and plateau time (76.3 % decrease). No differences were found during washout or in double support asymmetry. SIGNIFICANCE: This study shows that able-bodied individuals retain savings of split-belt adaptation over a three-week period, which indicates that only naïve split-belt walkers should be included in split-belt adaptation studies, as previous experience to split-belt walking will not be washed out, even after a prolonged period. In future research, these results can be compared with long-term savings in patient groups, to gain insight into factors underlying (un)successful gait training in rehabilitation.

The relationship between the anteroposterior and mediolateral margins of stability in able-bodied human walking.

BACKGROUND: Control of dynamic balance in human walking is essential to remain stable and can be parameterized by the margins of stability. While frontal and sagittal plane margins of stability are often studied in parallel, they may covary, where increased stability in one plane could lead to decreased stability in the other. Hypothetically, this negative covariation may lead to critically low lateral stability during step lengthening. RESEARCH QUESTION: Is there a relationship between frontal and sagittal plane margins of stability in able-bodied humans, during normal walking and imposed step lengthening? METHODS: Fifteen able-bodied adults walked on an instrumented treadmill in a normal walking and a step lengthening condition. During step lengthening, stepping targets were projected onto the treadmill in front of the participant to impose longer step lengths. Covariation between frontal and sagittal plane margins of stability was assessed with linear mixed-effects models for normal walking and step lengthening separately. RESULTS: We found a negative covariation between frontal and sagittal plane margins of stability during normal walking, but not during step lengthening. SIGNIFICANCE: These results indicate that while a decrease in anterior instability may lead to a decrease in lateral stability during normal walking, able-bodied humans can prevent lateral instability due to this covariation in critical situations, such as step lengthening. These findings improve our understanding of adaptive dynamic balance control during walking in able-bodied humans and may be utilized in further research on gait stability in pathological and aging populations.

Amplitude and stride-to-stride variability of muscle activity during Lokomat guided walking and treadmill walking in children with cerebral palsy.

BACKGROUND: The Lokomat is a commercially available exoskeleton for gait training in persons with cerebral palsy (CP). Because active contributions and variability over movement repetitions are determinants of training effectiveness, we studied muscle activity in children with CP, and determined (i) differences between treadmill and Lokomat walking, and (ii) the effects of Lokomat training parameters, on the amplitude and the stride-to-stride variability. METHODS: Ten children with CP (age 13.2 ± 2.9, GMFCS level II(n = 6)/III(n = 4)) walked on a treadmill (±1 km/h; 0% bodyweight support(BWS)), and in the Lokomat (50% and 100% guidance; ±1 km/h and ±2 km/h; 0% and 50% BWS). Activity was recorded from Gluteus Medius (GM), Vastus Lateralis (VL), Biceps Femoris (BF), Medial Gastrocnemius (MG) and Tibialis Anterior (TA) of the most affected side. The averaged amplitude per gait phase, and the second order coefficient of variation was used to determine the active contribution and stride-to-stride variability, respectively. RESULTS: Generally, the amplitude of activity was lower in the Lokomat than on the treadmill. During Lokomat walking, providing guidance and BWS resulted in slightly lower amplitudes whereas increased speed was associated with higher amplitudes. No significant differences in stride-to-stride variability were observed between Lokomat and treadmill walking, and in the Lokomat only speed (MG) and guidance (BF) affected variability. CONCLUSIONS: Lokomat walking reduces muscle activity in children with CP, whereas altering guidance or BWS generally does not affect amplitude. This urges additional measures to encourage active patient contributions, e.g. by increasing speed or through instruction.

Maintaining sagittal plane balance compromises frontal plane balance during reactive stepping in people post-stroke.

BACKGROUND: Maintaining balance in response to perturbations during walking often requires the use of corrective responses to keep the center of mass within the base of support. The relationship between the center of mass and base of support is often quantified using the margin of stability. Although people post-stroke increase the margin of stability following perturbations, control deficits may lead to asymmetries in regulation of margins of stability, which may also cause maladaptive coupling between the sagittal and frontal planes during balance-correcting responses. METHODS: We assessed how paretic and non-paretic margins of stability are controlled during recovery from forward perturbations and determined how stroke-related impairments influence the coupling between the anteroposterior and mediolateral margins of stability. Twenty-one participants with post-stroke hemiparesis walked on a treadmill while receiving slip-like perturbations on both limbs at foot-strike. We assessed anteroposterior and mediolateral margins of stability before perturbations and during perturbation recovery. FINDINGS: Participants walked with smaller anteroposterior and larger mediolateral margins of stability on the paretic versus non-paretic sides. When responding to perturbations, participants increased the anteroposterior margin of stability bilaterally by extending the base of support and reducing the excursion of the extrapolated center of mass. The anteroposterior and mediolateral margins of stability in the paretic limb negatively covaried during reactive steps such that increases in anteroposterior were associated with reductions in mediolateral margins of stability. INTERPRETATION: Balance training interventions to reduce fall risk post-stroke may benefit from incorporating strategies to reduce maladaptive coupling of frontal and sagittal plane stability.

Anticipatory control of human gait following simulated slip exposure.

A cautious gait (CG), marked by wider and shorter steps, is typically employed to mitigate expected perturbations proactively. However, it is not well understood if and how CG is informed by the task requirements. Therefore, we assessed how CG is adjusted to these requirements. Three groups of ten healthy young adults were exposed to a single uninterrupted protocol of treadmill walking that consisted of three distinct phases. Spatiotemporal step characteristics and margins of stability of the unperturbed strides were compared when participants were (i) only warned of a perturbation, (ii) exposed to fifty unilateral (right) slip-like perturbations and (iii) kept unaware of perturbation removal. Only the perturbation intensity predictability differed between groups. This was either kept consistent or pseudo-randomly or randomly varied. Participants walked with wider and shorter steps following the perturbation warning. However, this extinguished in continuing perturbation absence. Next, during perturbation exposure, participants shortened the step of the perturbed but increased the step of the unperturbed leg. This did not differ between groups. Finally, participants persisted in displaying CG on perturbation removal, but this extinguished over time. Collectively, we show that CG is functionally adjusted to the task requirements. These findings may have practical implications for fall-prevention training.

Adaptive Control of Dynamic Balance across the Adult Lifespan.

INTRODUCTION: The ability to adapt dynamic balance to perturbations during gait deteriorates with age. To prevent age-related decline in adaptive control of dynamic balance, we must first understand how adaptive control of dynamic balance changes across the adult lifespan. We examined how adaptive control of the margin of stability (MoS) changes across the lifespan during perturbed and unperturbed walking on the split-belt treadmill. METHODS: Seventy-five healthy adults (age range, 18-80 yr) walked on an instrumented split-belt treadmill with and without split-belts. Linear regression analyses were performed for the mediolateral (ML) and anteroposterior (AP) MoS, step length, single support time, step width, double support time, and cadence during unperturbed and perturbed walking (split-belt perturbation), with age as predictor. RESULTS: Age did not significantly affect dynamic balance during unperturbed walking. However, during perturbed walking, the ML MoS of the leg on the slow belt increased across the lifespan due to a decrease in bilateral single support time. The AP MoS did not change with aging despite a decrease in step length. Double support time decreased and cadence increased across the lifespan when adapting to split-belt walking. Age did not affect step width. CONCLUSIONS: Aging affects the adaptive control of dynamic balance during perturbed but not unperturbed treadmill walking with controlled walking speed. The ML MoS increased across the lifespan, whereas bilateral single support times decreased. The lack of aging effects on unperturbed walking suggests that participants' balance should be challenged to assess aging effects during gait. The decrease in double support time and increase in cadence suggests that older adults use the increased cadence as a balance control strategy during challenging locomotor tasks.

Lokomat guided gait in hemiparetic stroke patients: the effects of training parameters on muscle activity and temporal symmetry.

Purpose: The Lokomat is a commercially available robotic gait trainer, applied for gait rehabilitation in post-stroke hemiparetic patients. Selective and well-dosed clinical use of the Lokomat training parameters, i.e. guidance, speed and bodyweight support, requires a good understanding of how these parameters affect the neuromuscular control of post-stroke hemiparetic gait.Materials and methods: Ten stroke patients (unilateral paresis, 7 females, 64.5 ± 6.4 years, >3months post-stroke, FAC scores 2-4)) walked in the Lokomat under varying parameter settings: 50% or 100% guidance, 0.28 or 0.56m/s, 0% or 50% bodyweight support. Electromyography was recorded bilaterally from Gluteus Medius, Biceps Femoris, Vastus Lateralis, Medial Gastrocnemius, and Tibialis Anterior. Pressure sensors placed under the feet were used to determine the level of temporal gait symmetry.Results: Varying guidance and bodyweight support had little effect on muscle activity, but increasing treadmill speed led to increased activity in both the affected (Biceps Femoris, Medial Gastrocnemius, Tibialis Anterior) and unaffected leg (all muscles). The level of temporal symmetry was unaffected by the parameter settings.Conclusions: The Lokomat training parameters are generally ineffective in shaping short term muscle activity and step symmetry patients with hemiparetic stroke, as speed is the only parameter that significantly affects muscular amplitude.Trial Registration: d.n.a.IMPLICATIONS FOR REHABILITATIONThe Lokomat is a commercially available gait trainer that can be used for gait rehabilitation in post-stroke hemiparetic patients.This study shows that muscle amplitude is generally low during Lokomat guided walking, and that treadmill Speed is the main training parameter to influence muscular output in stroke patients during Lokomat walking.Varying Guidance and Bodyweight Support within a clinical relevant range barely affected muscle activity, and temporal step symmetry was unaffected by variation in any of the training parameters.Based on the findings it is advised to increase speed as early as possible during Lokomat therapy, or use other means (e.g. feedback or instructions) to stimulate active involvement of patients during training.

Bilateral temporal control determines mediolateral margins of stability in symmetric and asymmetric human walking.

Human bipedal gait requires active control of mediolateral dynamic balance to stay upright. The margin of stability is considered a measure of dynamic balance, and larger margins are by many authors assumed to reflect better balance control. The inverted pendulum model of gait indicates that changes in the mediolateral margin of stability are related to changes in bilateral single support times. We propose updated equations for the mediolateral margin of stability in temporally symmetric and asymmetric gait, which now include the single support times of both legs. Based on these equations, we study the relation between bilateral single support times and the mediolateral margin of stability in symmetric, asymmetric, and adaptive human gait. In all conditions, the mediolateral margin of stability during walking followed predictably from bilateral single support times, whereas foot placement co-varied less with the mediolateral margin of stability. Overall, these results demonstrate that the bilateral temporal regulation of gait profoundly affects the mediolateral margin of stability. By exploiting the passive dynamics of bipedal gait, bilateral temporal control may be an efficient mechanism to safeguard dynamic stability during walking, and keep an inherently unstable moving human body upright.

Handrail Holding During Treadmill Walking Reduces Locomotor Learning in Able-Bodied Persons.

Treadmills used for gait training in clinical rehabilitation and experimental settings are commonly fitted with handrails to assist or support persons in locomotor tasks. However, the effects of balance support through handrail holding on locomotor learning are unknown. Locomotor learning can be studied on split-belt treadmills, where participants walk on two parallel belts with asymmetric left and right belt speeds, to which they adapt their stepping pattern within a few minutes. The aim of this study was to determine how handrail holding affects the walking pattern during split-belt adaptation and after-effects in able-bodied persons. Fifty healthy young participants in five experimental groups were instructed to hold handrails, swing arms freely throughout the experiment or hold handrails during adaptation and swing arms freely during after-effects. Step length asymmetry and double support asymmetry were measured to assess the spatiotemporal walking pattern. The results showed that holding handrails during split-belt adaptation reduces magnitude of initial perturbation of step length asymmetry and reduces after-effects in step length asymmetry upon return to symmetric belt speeds. The findings of this study imply that balance support during gait training reduces locomotor learning, which should be considered in daily clinical gait practice and future research on locomotor learning.

The effect of asymmetric movement support on muscle activity during Lokomat guided gait in able-bodied individuals.

BACKGROUND: To accommodate training for unilaterally affected patients (e.g. stroke), the Lokomat (a popular robotic exoskeleton-based gait trainer) provides the possibility to set the amount of movement guidance for each leg independently. Given the interlimb couplings, such asymmetrical settings may result in complex effects, in which ipsilateral activity co-depends on the amount of guidance offered to the contralateral leg. To test this idea, the effect of asymmetrical guidance on muscle activity was explored. METHODS: 15 healthy participants walked in the Lokomat at two speeds (1 and 2 km/h) and guidance levels (30% and 100%), during symmetrical (both legs receiving 30% or 100% guidance) and asymmetrical conditions (one leg receiving 30% and the other 100% guidance) resulting in eight unique conditions. Activity of the right leg was recorded from Erector Spinae, Gluteus Medius, Biceps Femoris, Semitendinosus, Vastus Medialis, Rectus Femoris, Medial Gastrocnemius and Tibialis Anterior. Statistical Parametric Mapping was used to assess whether ipsilateral muscle activity depended on guidance settings for the contralateral leg. RESULTS: Muscle output amplitude not only depended on ipsilateral guidance settings, but also on the amount of guidance provided to the contralateral leg. More specifically, when the contralateral leg received less guidance, ipsilateral activity of Gluteus Medius and Medial Gastrocnemius increased during stance. Conversely, when the contralateral leg received more guidance, ipsilateral muscle activity for these muscles decreased. These effects were specifically observed at 1 km/h, but not at 2 km/h. CONCLUSIONS: This is the first study of asymmetrical guidance on muscle activity in the Lokomat, which shows that ipsilateral activity co-depends on the amount of contralateral guidance. In therapy, these properties may be exploited e.g. to promote active contributions by the more affected leg. Therefore, the present results urge further research on the use of asymmetrical guidance in patient groups targeted by Lokomat training.

Adaptive control of dynamic balance in human gait on a split-belt treadmill.

Human bipedal gait is inherently unstable, and staying upright requires adaptive control of dynamic balance. Little is known about adaptive control of dynamic balance in reaction to long-term, continuous perturbations. We examined how dynamic balance control adapts to a continuous perturbation in gait, by letting people walk faster with one leg than the other on a treadmill with two belts (i.e. split-belt walking). In addition, we assessed whether changes in mediolateral dynamic balance control coincide with changes in energy use during split-belt adaptation. In 9 min of split-belt gait, mediolateral margins of stability and mediolateral foot roll-off changed during adaptation to the imposed gait asymmetry, especially on the fast side, and returned to baseline during washout. Interestingly, no changes in mediolateral foot placement (i.e. step width) were found during split-belt adaptation. Furthermore, the initial margin of stability and subsequent mediolateral foot roll-off were strongly coupled to maintain mediolateral dynamic balance throughout the gait cycle. Consistent with previous results, net metabolic power was reduced during split-belt adaptation, but changes in mediolateral dynamic balance control were not correlated with the reduction of net metabolic power during split-belt adaptation. Overall, this study has shown that a complementary mechanism of relative foot positioning and mediolateral foot roll-off adapts to continuously imposed gait asymmetry to maintain dynamic balance in human bipedal gait.

Differences in muscle activity and temporal step parameters between Lokomat guided walking and treadmill walking in post-stroke hemiparetic patients and healthy walkers.

BACKGROUND: The Lokomat is a robotic exoskeleton that can be used to train gait function in hemiparetic stroke. To purposefully employ the Lokomat for training, it is important to understand (1) how Lokomat guided walking affects muscle activity following stroke and how these effects differ between patients and healthy walkers, (2) how abnormalities in the muscle activity of patients are modulated through Lokomat guided gait, and (3) how temporal step characteristics of patients were modulated during Lokomat guided walking. METHODS: Ten hemiparetic stroke patients (>3 months post-stroke) and ten healthy age-matched controls walked on the treadmill and in the Lokomat (guidance force 50%, no bodyweight support) at matched speeds (0.56 m/s). Electromyography was used to record the activity of Gluteus Medius, Biceps Femoris, Vastus Lateralis, Medial Gastrocnemius and Tibialis Anterior, bilaterally in patients and of the dominant leg in healthy walkers. Pressure sensors placed in the footwear were used to determine relative durations of the first double support and the single support phases. RESULTS: Overall, Lokomat guided walking was associated with a general lowering of muscle activity compared to treadmill walking, in patients as well as healthy walkers. The nature of these effects differed between groups for specific muscles, in that reductions in patients were larger if muscles were overly active during treadmill walking (unaffected Biceps Femoris and Gluteus Medius, affected Biceps Femoris and Vastus Lateralis), and smaller if activity was already abnormally low (affected Medial Gastrocnemius). Also, Lokomat guided walking was associated with a decrease in asymmetry in the relative duration of the single support phase. CONCLUSIONS: In stroke patients, Lokomat guided walking results in a general reduction of muscle activity, that affects epochs of overactivity and epochs of reduced activity in a similar fashion. These findings should be taken into account when considering the clinical potential of the Lokomat training environment in stroke, and may inform further developments in the design of robotic gait trainers.

The combined effects of guidance force, bodyweight support and gait speed on muscle activity during able-bodied walking in the Lokomat.

BACKGROUND: The ability to provide automated movement guidance is unique for robot assisted gait trainers such as the Lokomat. For the design of training protocols for the Lokomat it is crucial to understand how movement guidance affects the patterning of muscle activity that underlies walking, and how these effects interact with settings for bodyweight support and gait speed. METHODS: Ten healthy participants walked in the Lokomat, with varying levels of guidance (0, 50 and 100%), bodyweight support (0 or 50% of participants' body weight) and gait speed (0.22, 0.5 or 0.78m/s). Surface electromyography of Erector Spinae, Gluteus Medius, Vastus Lateralis, Biceps Femoris, Medial Gastrocnemius and Tibialis Anterior were recorded. Group averaged levels of muscle activity were compared between conditions, within specific phases of the gait cycle. FINDINGS: The provision of guidance reduced the amplitude of activity in muscles associated with stability and propulsion (i.e. Erector Spinae, Gluteus Medius, Biceps Femoris and Medial Gastrocnemius) and normalized abnormally high levels of activity observed in a number of muscles (i.e. Gluteus Medius, Biceps Femoris, and Tibialis anterior). The magnitude of guidance effects depended on both speed and bodyweight support, as reductions in activity were most prominent at low speeds and high levels of bodyweight support. INTERPRETATION: The Lokomat can be effective in eliciting normal patterns of muscle activity, but only under specific settings of its training parameters.

The combined effects of body weight support and gait speed on gait related muscle activity: a comparison between walking in the Lokomat exoskeleton and regular treadmill walking.

BACKGROUND: For the development of specialized training protocols for robot assisted gait training, it is important to understand how the use of exoskeletons alters locomotor task demands, and how the nature and magnitude of these changes depend on training parameters. Therefore, the present study assessed the combined effects of gait speed and body weight support (BWS) on muscle activity, and compared these between treadmill walking and walking in the Lokomat exoskeleton. METHODS: Ten healthy participants walked on a treadmill and in the Lokomat, with varying levels of BWS (0% and 50% of the participants' body weight) and gait speed (0.8, 1.8, and 2.8 km/h), while temporal step characteristics and muscle activity from Erector Spinae, Gluteus Medius, Vastus Lateralis, Biceps Femoris, Gastrocnemius Medialis, and Tibialis Anterior muscles were recorded. RESULTS: The temporal structure of the stepping pattern was altered when participants walked in the Lokomat or when BWS was provided (i.e. the relative duration of the double support phase was reduced, and the single support phase prolonged), but these differences normalized as gait speed increased. Alternations in muscle activity were characterized by complex interactions between walking conditions and training parameters: Differences between treadmill walking and walking in the exoskeleton were most prominent at low gait speeds, and speed effects were attenuated when BWS was provided. CONCLUSION: Walking in the Lokomat exoskeleton without movement guidance alters the temporal step regulation and the neuromuscular control of walking, although the nature and magnitude of these effects depend on complex interactions with gait speed and BWS. If normative neuromuscular control of gait is targeted during training, it is recommended that very low speeds and high levels of BWS should be avoided when possible.

Cognitive recovery after stroke: a 2-year follow-up.

OBJECTIVES: To determine (1) whether long-term improvement of cognitive function takes place after stroke and (2) which clinical factors influence cognitive recovery. DESIGN: Cohort study with patients who were assessed at 2.3 and 27.7 months after stroke. SETTING: Home-based stroke patients. PARTICIPANTS: From a group of 229 stroke patients, 92 were approached to participate. Sixty-five (43 men, 22 women; mean age, 56.4y) agreed, and they were neuropsychologically assessed at 72.2 days after stroke. A group of 33 controls (12 men, 21 women; mean age, 52.4y) was used as a reference sample. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Orientation, memory, attention, visuospatial, visuoconstructive, language, and arithmetic abilities were assessed with an extensive neuropsychologic test battery. RESULTS: Significant improvements across time were noted for all cognitive domains. The biggest improvement was found in the attentional domain; the least, in the memory domain. In addition, a small subset of patients accounted for the significant improvement in all cognitive domains; most patients showed no improvement or declined. Factors influencing recovery were side of the stroke and incidence of lowered consciousness on admission. Patients with right-side brain damage performed better than those with left-side brain damage and showed more improvement over time. Patients with lowered consciousness on admission performed worse than patients without lowered consciousness. No significant effect was found for gender, type of stroke, cortical versus subcortical lesions, having 1 stroke or multiple strokes, or the interval between the stroke and the neuropsychologic assessment. CONCLUSION: There was room for improvement in all cognitive domains, although this improvement was gained by only a small number of patients. Hence, most patients must cope with serious permanent cognitive decline after stroke.

Reflex sympathetic dystrophy of the left hand and motor impairments of the unaffected right hand: impaired central motor processing?

OBJECTIVE: To test whether central motor processing can be impaired in chronic reflex sympathetic dystrophy (RSD). DESIGN: Experimental 2-group analysis. SETTING: Tertiary care center in the Netherlands. PARTICIPANTS: Five patients with stage 3 RSD of the left forearm, free of symptoms and complaints in the right forearm; and 10 healthy control subjects. INTERVENTION: On a digitizer, RSD patients and controls had to draw 3 sequences of graphemes of different complexity with their (unaffected) dominant right hand. The drawing tracks were segmented in time periods between points of velocity minima of the pen tip. MAIN OUTCOME MEASURES: Mean velocity, coefficients of variation of both length and movement time per segment, and mean intersegmental pausing time were calculated for each sequence. RESULTS: A repeated-measures analysis of variance by using the multivariate method yielded a 35% lower mean velocity (F(1,13) = 5.83, P =.031), a 110% larger segment length variability (F(1,13) = 9.72, P =.008) and a 60% larger variability of movement time per segment (F(1,13) = 5.78, P =.032) in RSD patients. No group difference was found for intersegmental pausing time or any interaction effect with the type of task. CONCLUSION: Patients with chronic RSD have a normal ability to preprogram sequential movements of their unaffected hand; but with impaired temporospatial coding and movement execution. We concluded that cortical mechanisms may be involved in motor impairments in patients with chronic RSD.