Different types of disturbed motor control in gait of hemiparetic patients

Forward propulsion asymmetry is indicative of changes in plantarflexor coordination during walking in individuals with post-stroke hemiparesis

BACKGROUND

A common measure of rehabilitation effectiveness post-stroke is self-selected walking speed, yet individuals may achieve the same speed using different coordination strategies. Asymmetry in the propulsion generated by each leg can provide insight into paretic leg coordination due to its relatively strong correlation with hemiparetic severity. Subjects walking at the same speed can exhibit different propulsion asymmetries, with some subjects relying more on the paretic leg and others on the nonparetic leg. The goal of this study was to assess whether analyzing propulsion asymmetry can help distinguish between improved paretic leg coordination versus nonparetic leg compensation.

METHODS

Three-dimensional forward dynamics simulations were developed for two post-stroke hemiparetic subjects walking at identical speeds before/after rehabilitation with opposite changes in propulsion asymmetry. Changes in the individual muscle contributions to forward propulsion were examined.

FINDINGS

The major source of increased forward propulsion in both subjects was from the ankle plantarflexors. How they were utilized differed and appears related to changes in propulsion asymmetry. Subject A increased propulsion generated from the paretic plantarflexors, while Subject B increased propulsion generated from the nonparetic plantarflexors. Each subject's strategy to increase speed also included differences in other muscle groups (e.g., hamstrings) that did not appear to be related to propulsion asymmetry.

INTERPRETATION

The results of this study highlight how speed cannot be used to elucidate underlying muscle coordination changes following rehabilitation. In contrast, propulsion asymmetry appears to provide insight into changes in plantarflexor output affecting propulsion generation and may be useful in monitoring rehabilitation outcomes.

Changes in predicted muscle coordination with subject-specific muscle parameters for individuals after stroke

Muscle weakness is commonly seen in individuals after stroke, characterized by lower forces during a maximal volitional contraction. Accurate quantification of muscle weakness is paramount when evaluating individual performance and response to after stroke rehabilitation. The objective of this study was to examine the effect of subject-specific muscle force and activation deficits on predicted muscle coordination when using musculoskeletal models for individuals after stroke. Maximum force generating ability and central activation ratio of the paretic plantar flexors, dorsiflexors, and quadriceps muscle groups were obtained using burst superimposition for four individuals after stroke with a range of walking speeds. Two models were created per subject: one with generic and one with subject-specific activation and maximum isometric force parameters. The inclusion of subject-specific muscle data resulted in changes in the model-predicted muscle forces and activations which agree with previously reported compensation patterns and match more closely the timing of electromyography for the plantar flexor and hamstring muscles. This was the first study to create musculoskeletal simulations of individuals after stroke with subject-specific muscle force and activation data. The results of this study suggest that subject-specific muscle force and activation data enhance the ability of musculoskeletal simulations to accurately predict muscle coordination in individuals after stroke.

Correlations between ankle-foot impairments and dropped foot gait deviations among stroke survivors

BACKGROUND

The purpose of this paper is to 1) evaluate the relationship between ankle kinematics during gait and standardized measures of ankle impairments among sub-acute stroke survivors, and 2) compare the degree of stroke-related ankle impairment between individuals with and without dropped foot gait deviations.

METHODS

Fifty-five independently ambulating stroke survivors participated in this study. Dropped foot was defined as decreased peak dorsiflexion during the swing phase and reduced ankle joint motion in stance. Standardized outcome measures included the Chedoke-McMaster Stroke Assessment (motor impairment), Modified Ashworth Scale (spasticity), Medical Research Council (muscle strength), passive and active range of motion, and isometric muscle force.

FINDINGS

Foot impairment was not related to peak dorsiflexion during swing (r=-0.17, P=0.247) and joint motion during stance (r=0.05, P=0.735). Active (r=0.45, P<0.001) and passive (r=0.48, P<0.001) range of motion was associated with stance phase joint motion. Peak dorsiflexion during swing was related to isometric dorsiflexor muscle force (r=-0.32, P=0.039). Individuals with dropped foot demonstrated greater motor impairment, plantarflexor spasticity and ankle muscle weakness compared to those without dropped foot.

INTERPRETATION

Our investigation suggests that ankle-foot impairments are related to ankle deviations during gait, as indicated by greater impairment among individuals with dropped foot. These findings contribute to a better understanding of gait-specific ankle deviations, and may lead to the development of a more effective clinical assessment of dropped foot impairment.

Effect of Intrathecal Baclofen Bolus Injection on Ankle Muscle Activation During Gait in Patients With Acquired Brain Injury

Background. Intrathecal baclofen (ITB) bolus injection effectively decreases spinal excitability but the impact on lower limb muscle activation during gait has not been thoroughly investigated. Objective. Examine activation of medial gastrocnemius (MG) and tibialis anterior (TA) muscles during gait before and after ITB bolus injection in patients with resting hypertonia after acquired brain injury. Methods. Lower extremity Ashworth score, temporospatial gait parameters, characteristics of the linear relationship between electromyogram (EMG) and lengthening velocity (LV) in MG during stance, and the duration and magnitude of TA-MG coactivation were assessed before and at 2, 4, and 6 hours after a 50-µg ITB injection via lumbar puncture in 8 hemorrhagic stroke and 11 traumatic brain injury subjects. Results. Temporospatial gait parameters did not significantly differ across the evaluation points ( P ≥ .170). However, Ashworth score ( P < .001), frequency and gain of significant positive EMG-LV slope ( P ≤ .020), and duration of TA-MG coactivation ( P ≤ .013) significantly decreased in the more-affected leg after ITB bolus. EMG changes were not significantly different between patients who did (n = 10) and did not (n = 9) increase gait speed after the injection. The timing of the largest decrease in Ashworth score and the largest decrease in EMG parameters coincided in 36% of cases, on average. Conclusions. ITB bolus injection alters the activation of MG and TA during gait. However, the changes in muscle activation are not closely related to the changes in gait speed or resting muscle hypertonia. The analysis of ankle muscle activation during gait better characterizes the response to ITB bolus injection than gait kinematics.

The influence of solid ankle-foot-orthoses on forward propulsion and dynamic balance in healthy adults during walking

BACKGROUND

In post-stroke hemiparetic subjects, solid polypropylene ankle-foot-orthoses are commonly prescribed to assist in foot clearance during swing while bracing the ankle during stance. Mobility demands, such as changing walking speed and direction, are accomplished by accelerating or decelerating the body and maintaining dynamic balance. Previous studies have shown that the ankle plantarflexors are primary contributors to these essential biomechanical functions. Thus, with ankle-foot-orthoses limiting ankle motion and plantarflexor output during stance, execution of these walking subtasks may be compromised. This study examined the influence of a solid polypropylene ankle-foot-orthosis on forward propulsion and dynamic balance in healthy adults.

METHODS

Kinematic and kinetic data were recorded from 10 healthy adults walking with and without a unilateral ankle-foot-orthosis at steady-state slow (0.6m/s) and moderate (1.2m/s) speeds, and during accelerated (0-1.8m/s at 0.06m/s(2)) and decelerated (1.8-0m/s at -0.06m/s(2)) walking. Propulsion was quantified by propulsive and braking impulses (i.e., time integral of the anterior-posterior ground reaction force) while dynamic balance was quantified by the peak-to-peak range of whole-body angular momentum.

FINDINGS

The propulsive impulses decreased in the leg with ankle-foot-orthosis compared to the contralateral leg and no ankle-foot-orthosis condition. Further, the ankle-foot-orthosis resulted in a greater range of angular momentum in both the frontal and sagittal planes, which were correlated with the reduced peak hip abduction and reduced ankle plantarflexor moments, respectively.

INTERPRETATION

Solid ankle-foot-orthoses limit the successful execution of important mobility subtasks in healthy adults and that the prescription of ankle-foot-orthosis should be carefully considered.

Altering length and velocity feedback during a neuro-musculoskeletal simulation of normal gait contributes to hemiparetic gait characteristics

Background

Spasticity is an important complication after stroke, especially in the anti-gravity muscles, i.e. lower limb extensors. However the contribution of hyperexcitable muscle spindle reflex loops to gait impairments after stroke is often disputed. In this study a neuro-musculoskeletal model was developed to investigate the contribution of an increased length and velocity feedback and altered reflex modulation patterns to hemiparetic gait deficits.

Methods

A musculoskeletal model was extended with a muscle spindle model providing real-time length and velocity feedback of gastrocnemius, soleus, vasti and rectus femoris during a forward dynamic simulation (neural control model). By using a healthy subject’s base muscle excitations, in combination with increased feedback gains and altered reflex modulation patterns, the effect on kinematics was simulated. A foot-ground contact model was added to account for the interaction effect between the changed kinematics and the ground. The qualitative effect i.e. the directional effect and the specific gait phases where the effect is present, on the joint kinematics was then compared with hemiparetic gait deviations reported in the literature.

Results

Our results show that increased feedback in combination with altered reflex modulation patterns of soleus, vasti and rectus femoris muscle can contribute to excessive ankle plantarflexion/inadequate dorsiflexion, knee hyperextension/inadequate flexion and increased hip extension/inadequate flexion during dedicated gait cycle phases. Increased feedback of gastrocnemius can also contribute to excessive plantarflexion/inadequate dorsiflexion, however in combination with excessive knee and hip flexion. Increased length/velocity feedback can therefore contribute to two types of gait deviations, which are both in accordance with previously reported gait deviations in hemiparetic patients. Furthermore altered modulation patterns, in particular the reduced suppression of the muscle spindle feedback during swing, can contribute largely to an increased plantarflexion and knee extension during the swing phase and consequently to hampered toe clearance.

Conclusions

Our results support the idea that hyperexcitability of length and velocity feedback pathways, especially in combination with altered reflex modulation patterns, can contribute to deviations in hemiparetic gait. Surprisingly, our results showed only subtle temporal differences between length and velocity feedback. Therefore, we cannot attribute the effects seen in kinematics to one specific type of feedback.

Foot force direction control during a pedaling task in individuals post-stroke

Background

Appropriate magnitude and directional control of foot-forces is required for successful execution of locomotor tasks. Earlier evidence suggested, following stroke, there is a potential impairment in foot-force control capabilities both during stationary force generation and locomotion. The purpose of this study was to investigate the foot-pedal surface interaction force components, in non-neurologically-impaired and stroke-impaired individuals, in order to determine how fore/aft shear-directed foot/pedal forces are controlled.

Methods

Sixteen individuals with chronic post-stroke hemiplegia and 10 age-similar non-neurologically-impaired controls performed a foot placement maintenance task under a stationary and a pedaling condition, achieving a target normal pedal force. Electromyography and force profiles were recorded. We expected generation of unduly large magnitude shear pedal forces and reduced participation of multiple muscles that can contribute forces in appropriate directions in individuals post-stroke.

Results

We found lower force output, inconsistent modulation of muscle activity and reduced ability to change foot force direction in the paretic limbs, but we did not observe unduly large magnitude shear pedal surface forces by the paretic limbs as we hypothesized.

Conclusion

These findings suggested the preservation of foot-force control capabilities post-stroke under minimal upright postural control requirements. Further research must be conducted to determine whether inappropriate shear force generation will be revealed under non-seated, postural demanding conditions, where subjects have to actively control for upright body suspension.

The impact of simulated ankle plantarflexion contracture on the knee joint during stance phase of gait: a within-subject study

BACKGROUND

Ankle plantarflexion contractures are common in adults with neurological disorders and known to cause secondary gait deviations. However, their impact on the knee joint is not fully understood. The aims of this study are to describe the effect of simulated plantarflexion contractures on knee biomechanics during the stance phase and on the spatiotemporal characteristics of gait.

METHODS

Mild (10-degree plantarflexion) and severe (20-degree plantarflexion) ankle contractures were simulated in thirteen able-bodied adults using an ankle-foot-orthosis. A no contracture condition was compared with two simulated contracture conditions.

FINDINGS

There was an increase in knee extension, sometimes resulting in hyperextension, throughout stance for the two contracture conditions compared to the no contracture condition (mean increase in knee extension ranged from 5° to 9°; 95% CI 0° to 17°). At the same time, there were reductions in extension moment and power generation at the knee. Simulated plantarflexion contractures also reduced gait velocity, bilateral step length and cadence. All these changes were more pronounced in the severe contracture condition than mild contracture condition. While the majority of participants adopted a foot-flat pattern on landing and exhibited an increase in knee extension during stance, two participants used a toe-walking pattern and exhibited an increase in knee flexion.

INTERPRETATION

Ankle plantarflexion contractures are associated with an increase in knee extension during stance phase. However, some people with simulated ankle contractures may walk with an increase in knee flexion instead. Ankle plantarflexion contractures also adversely affect gait velocity, step length and cadence.

The effect of stroke on foot kinematics and the functional consequences

BACKGROUND

Although approximately one-third of stroke survivors suffer abnormal foot posture and this can influence mobility, there is very little objective information regarding the foot and ankle after stroke.

OBJECTIVE

As part of a programme of research examining foot and ankle biomechanics after stroke, we investigated multi-planar kinematics and the relationship with function.

METHODS

In a single assessment session, static foot posture (Foot Posture Index); mobility limitations (Walking Handicap Scale) and multi-segment foot and ankle kinematics during stance phase of walking were measured in 20 mobile chronic stroke survivors and 15 sex and age-matched healthy volunteers.

RESULTS

Compared to the healthy volunteers, the stroke survivors demonstrated consistently reduced range of motion across most segments and planes, increased pronation and reduced supination, disruption of the rocker and the timing of joint motion. Changes in pronation/supination were associated with limited walking ability.

CONCLUSIONS

This study provides evidence of structural and movement deficiencies in the intrinsic foot segments affected by stroke. These would not have been detectable using a single segment foot model. Data do not support common clinical practices that focus on correction of sagittal ankle deformity and assumed excessive foot supination. Some of these abnormalities were associated with limitation in functional ability. Biomechanical abnormalities of foot and ankle are modifiable and there is potential for clinical studies and future developments of interventions to help prevent or treat these abnormalities which may improve functional ability post stroke.

Effects of walking with loads above the ankle on gait parameters of persons with hemiparesis after stroke

BACKGROUND

Walking with a load at the ankle during gait training is a simple way to resist lower limb movements to induce functional muscle strengthening. This study investigated the effects of walking with different loads attached above the paretic ankle on biomechanical gait parameters during over ground walking in post-stroke participants.

METHODS

Ten participants with moderate chronic hemiparesis were evaluated while walking over ground with three different loads (0.5, 1.0, and 1.5kg) attached above the paretic ankle. Gait speed, cadence, step lengths as well as hip and knee angular displacements, joint moments and power of the paretic limb were compared while walking with and without loads.

FINDINGS

Walking with a load led to an increased in gait speed (+0.03-0.05m/s), and in step length of the paretic leg (+5.6 to 9.4% step length, effect size=0.49-0.63), but not of the non-paretic leg. The proportion of the stance and swing phases did not change. Maximal joint moments (+20 to 48%, effect size=0.26-0.55) and power (+20 to 114%, effect size=0.30-0.57) increases varied across participants but were mostly affected in early stance at the hip and during the late swing phase at the knee. Mean angular displacement changes were less than 4°.

INTERPRETATION

Post-stroke participants are able to increase hip and knee power bursts to meet the increased mechanical demand of added loads attached to the paretic ankle, while preserving the basic pattern of walking. Further study is needed before using loading to functionally strengthen paretic muscles.

Does the rectus femoris nerve block improve knee recurvatum in adult stroke patients? A kinematic and electromyographic study

Knee recurvatum (KR) during gait is common in hemiplegic patients. Quadriceps spasticity has been postulated as a cause of KR in this population. The aim of this study was to assess the role of rectus femoris spasticity in KR by using selective motor nerve blocks of the rectus femoris nerve in hemiparetic stroke patients. The data from six adult, post-stroke hemiplegic patients who underwent a rectus femoris nerve block for a stiff-knee gait were retrospectively analyzed. An extensive clinical and functional evaluation was performed and gait was assessed by motion analysis (kinematic, kinetic and electromyographic parameters) before and during the block realized using 2% lidocaine injected under a neurostimulation and ultrasonographic targeting procedure. The main outcome measures were the peak knee extension in stance and peak knee extensor moment obtained during gait analysis. No serious adverse effect of the nerve block was observed. The block allowed a reduction of rectus femoris overactivity in all patients. Peak knee extension and extensor moment in stance did not improve in any patient, but peak knee flexion during the swing phase was significantly higher after block (mean: 31.2° post, 26.4 pre, p < 0.05). Our results provide arguments against the hypothesis that the spasticity of the rectus femoris contributes to KR.

Spinal plasticity in stroke patients after botulinum neurotoxin A injection in ankle plantar flexors

The effect of botulinum neurotoxin A (BoNT-A) in stroke patients' upper limbs has been attributed to its peripheral action only. However, BoNT-A depressed recurrent inhibition of lumbar motoneurons, likely due to its retrograde transportation along motor axons affecting synapses to Renshaw cells. Because Renshaw cells control group Ia interneurons mediating reciprocal inhibition between antagonists, we tested whether this inhibition, particularly affected after stroke, could recover after BoNT-A. The effect of posterior tibial nerve (PTN) stimulation on tibialis anterior (TA) electromyogram (EMG) was investigated in 13 stroke patients during treadmill walking before and 1 month after BoNT-A injection in ankle plantar flexors. Before BoNT-A, PTN stimuli enhanced TA EMG all during the swing phase. After BoNT-A, the PTN-induced reciprocal facilitation in TA motoneurons was depressed at the beginning of swing and reversed into inhibition in midswing, but at the end of swing, the reciprocal facilitation was enhanced. This suggests that BoNT-A induced spinal plasticity leading to the recovery of reciprocal inhibition likely due to the withdrawal of inhibitory control from Renshaw cells directly blocked by the toxin. At the end of swing, the enhanced reciprocal facilitation might be due to BoNT-induced modification of peripheral afferent inputs. Therefore, both central and peripheral actions of BoNT-A can modify muscle synergies during walking: (1) limiting ankle muscle co-contraction in the transition phase from stance to swing, to assist dorsiflexion, and (2) favoring it from swing to stance, which blocks the ankle joint and thus assists the balance during the single support phase on the paretic limb.

Comparison of foot pedal reaction time among patients with right or left hemiplegia and able-bodied controls

BACKGROUND

Although inpatient stroke rehabilitation provides clinicians with the opportunity to prepare patients for continuation of prestroke activities, little is known about the patients' ability to safely resume driving at the point of discharge to the community.

OBJECTIVE

To compare foot pedal response times of 20 stroke patients with right hemiplegia (RH) or left hemiplegia (LH) and 10 controls.

METHODS

A cross-sectional design was used. Response times were measured using 3 foot pedal operation techniques: (1) right-sided accelerator with right leg operating accelerator and brake, (2) right-sided accelerator with left leg operating accelerator and brake, and (3) left-sided accelerator with left leg operating accelerator and brake. Outcomes included reaction time (RT), movement time (MT), and total response time (TRT).

RESULTS

Controls demonstrated faster RT than patients with RH (263 vs 348 ms; P < .001) or LH (316 ms; P < .05) for all conditions, as well as faster MT than patients with RH (P < .05 for all) but not LH when using the right leg (258 vs 251 ms; P = .82). Controls demonstrated faster TRT than patients with RH (P < .001 for all) but not LH when using the right leg (515 vs 553 ms; P = .44).

CONCLUSIONS

When using the nonparetic leg, patients with LH had braking response times comparable to controls, but patients with RH demonstrated significant impairment of both the paretic and nonparetic legs.

Relative changes in ankle and hip control during bilateral joint movements in persons with multiple sclerosis

OBJECTIVE

The purpose of this study was to quantify hip and ankle impairments contributing to movement dysfunction in multiple sclerosis (MS).

METHODS

Volitional phasing of bilateral hip and ankle torques was assessed using a load-cell-instrumented servomotor drive system in ten participants with MS and 10 age-matched healthy participants. The hips and ankles were separately bilaterally oscillated 180° out of phase (40° range of motion) at a frequency of 0.75 Hz while the other joints were held stationary. Participants were instructed to assist in the same direction as the robot-imposed movement. The hip and ankle torques were measured and work was calculated for each movement.

RESULTS

Total negative work at the ankle was significantly different between groups (p=0.040). The participants with MS produced larger negative work during hip flexion (p=0.042) and ankle flexion (p=0.037). Negative work at the hip was significantly correlated with the Berg Balance Scores and Timed 25 Feet Walk Test, and trends demonstrated increasing negative work with increasing clinical impairment in MS.

CONCLUSIONS

These results suggest an increased importance of the hip in functional balance and gait in MS.

SIGNIFICANCE

Rehabilitation strategies targeting ankle recovery or compensation using the hip might improve movement function in MS.

Plasticity and modular control of locomotor patterns in neurological disorders with motor deficits

Human locomotor movements exhibit considerable variability and are highly complex in terms of both neural activation and biomechanical output. The building blocks with which the central nervous system constructs these motor patterns can be preserved in patients with various sensory-motor disorders. In particular, several studies highlighted a modular burst-like organization of the muscle activity. Here we review and discuss this issue with a particular emphasis on the various examples of adaptation of locomotor patterns in patients (with large fiber neuropathy, amputees, stroke and spinal cord injury). The results highlight plasticity and different solutions to reorganize muscle patterns in both peripheral and central nervous system lesions. The findings are discussed in a general context of compensatory gait mechanisms, spatiotemporal architecture and modularity of the locomotor program.

Spasticity

Antispastic medications that are directed to reduce clinical signs of spasticity, such as exaggerated reflexes and muscle tone, do not improve the movement disorder. Medication can even increase weakness which might interfere with functional movements, such as walking. In this chapter we address how spasticity affects mobility and how this should be taken into account in the treatment of spasticity. In clinical practice, signs of exaggerated tendon tap reflexes associated with muscle hypertonia are the consequence of spinal cord injury (SCI). They are generally thought to be responsible for spastic movement disorders. Most antispastic treatments are, therefore, directed at the reduction of reflex activity. In recent years, a discrepancy between spasticity as measured in the clinic and functional spastic movement disorder was noticed, which is primarily due to the different roles of reflexes in passive and active states, respectively. We now know that central motor lesions are associated with loss of supraspinal drive and defective use of afferent input with impaired behavior of short-latency and long-latency reflexes. These changes lead to paresis and maladaptation of the movement pattern. Secondary changes in mechanical muscle fiber, collagen tissue, and tendon properties (e.g., loss of sarcomeres, subclinical contractures) result in spastic muscle tone, which in part compensates for paresis and allows functional movements on a simpler level of organization. Antispastic drugs should primarily be applied in complete SCI. In mobile patients they can accentuate paresis and therefore should be applied with caution.

Comparison of the Amplitudes of the H-reflex of Post-stroke Hemiplegia Patients and Normal Adults during Walking

[Purpose] The purpose of this study was to compare H-reflex characteristics during gait of hemiplegic stroke patients. [Subjects] Twenty-five patients and age-matched twenty-five volunteers in good health were studied. All the subjects could walk independently. [Methods] An MP150 (BIOPAC Systems, Inc., Goleta, CA, USA) was used to record the electromyography (EMG) data collected with Ag-Ag/Cl measurement electrodes (BIOPAC, diameter of 2 cm). [Results] The comparison showed significant differences of H_max/M_max ratio (%) in all gait cycles between the stroke group and the control group. [Conclusion] In conclusion, this study furnished basic reference data for gait strategies and functional training programs for hemiplegic stroke patients.

The influence of merged muscle excitation modules on post-stroke hemiparetic walking performance

BACKGROUND

Post-stroke subjects with hemiparesis typically utilize a reduced number of modules or co-excited muscles compared to non-impaired controls, with at least one module resembling the merging of two or more non-impaired modules. In non-impaired walking, each module has distinct contributions to important biomechanical functions, and thus different merged module combinations post-stroke may result in different functional consequences.

METHODS

Three-dimensional forward dynamics simulations were developed for non-impaired controls and two groups of post-stroke hemiparetic subjects with different merged module combinations to analyze how paretic leg muscle contributions to body support, forward propulsion, mediolateral control and leg swing are altered.

FINDINGS

The potential of the plantarflexors to generate propulsion was impaired in both hemiparetic groups while the remaining functional consequences differed depending on which modules were merged. Paretic leg swing was impaired during pre-swing when Modules 1 (hip abductors and knee extensors during early stance), and 2 (plantarflexors during late stance) were merged and during late swing when Modules 1 and 4 (hamstrings during late swing into early stance) were merged. When Modules 1 and 4 were merged, body support during early stance was also impaired.

INTERPRETATION

These results suggest that improving plantarflexor ability to generate propulsion is critical during rehabilitation regardless of module composition. If Modules 1 and 2 are merged, then rehabilitation should also focus on improving paretic leg pre-swing whereas if Modules 1 and 4 are merged, then rehabilitation should also focus on improving early stance body support and late paretic leg swing.

Spatio-temporal parameters and intralimb coordination patterns describing hemiparetic locomotion at controlled speed

Background

Comparison between healthy and hemiparetic gait is usually carried out while subjects walk overground at preferred speed. This generates bias due to the lack of uniformity across selected speeds because they reflect the great variability of the functional level of post-stroke patients. This study aimed at examining coordinative adaptations during walking in response to unilateral brain damage, while homologous participants walked at two fixed speeds.

Methods

Five patients with left and five with right chronic hemiparesis, characterized by similar level of motor functioning, were enrolled. Ten non-disabled volunteers were recruited as matched control group. Spatio-temporal parameters, and intralimb thigh-leg and leg-foot coordination patterns were used to compare groups while walking on a treadmill at 0.4 and 0.6 m/s. The likelihood of Continuous Relative Phase patterns between healthy and hemiparetic subjects was evaluated by means of the root mean square of the difference and the cross correlation coefficient. The effects of the group (i.e., healthy vs. hemiparetics), side (i.e., affected vs.unaffected), and speed (e.g., slow vs. fast) were analyzed on all metrics using the Analysis of Variance.

Results

Spatio-temporal parameters of all hemiparetic subjects did not significantly differ from those of healthy subjects nor showed any asymmetry between affected and unaffected limbs. Conversely, both thigh-leg and foot-leg coordination patterns appeared to account for pathology related modifications.

Conclusion

Comparisons between hemiparetic and healthy gait should be carried out when all participants are asked to seek the same suitable dynamic equilibrium led by the same external (i.e., the speed) and internal (i.e., severity of the pathology) conditions. In this respect, biomechanical adaptations reflecting the pathology can be better highlighted by coordinative patterns of coupled segments within each limb than by the spatio-temporal parameters. Accordingly, a deep analysis of the intralimb coordination may be helpful for clinicians while designing therapeutic treatments.

Use of segmental coordination analysis of nonparetic and paretic limbs during obstacle clearance in community-dwelling persons after stroke

OBJECTIVE

To use a segment coordination analysis to identify coordination differences between the paretic and nonparetic limbs for obstacle clearance in community-dwelling persons after stroke.

DESIGN

Within-participant design.

SETTING

Gait analysis laboratory.

PARTICIPANTS

Six community-dwelling persons with a stroke (excluding cerebellar stroke).

METHODS

Participants stepped over obstacles of 2 different heights (7.5% and 15% of leg length), leading alternately with their paretic and nonparetic limbs.

MAIN OUTCOME MEASUREMENTS

Kinematic data were collected, and segment elevation angles (absolute segment angular position with respect to vertical) were calculated for the thigh, shank, and foot segments. Established mathematical techniques related to the planar law of intersegmental coordination (principal component analysis to quantify covariance and temporal phase relationships among elevation angles) were then applied to compare and contrast the coordination of these segment elevation angle trajectories between paretic and nonparetic limbs.

RESULTS

Segment covariance in elevation angles followed the planar law of intersegmental coordination during level walking (ie, 3 elevation angles that form a plane and the variance explained by 2 principal components) for both paretic and nonparetic limbs. During obstacle clearance, however, relationships between covariance plane characteristics and phase differences for elevation angles of adjacent segments differed in the nonparetic limb, likely related to a need for greater limb elevation for obstacle clearance during paretic limb support or an altered foot trajectory, which resulted from preobstacle foot placement.

CONCLUSIONS

The present coordination analysis suggests the preservation of basic control mechanisms in the paretic limb during obstacle clearance after stroke and also reveals its specific motor control compensations. However, a larger study with differing levels of stroke severity must be conducted to understand how the evaluation of intersegmental coordination during walking could guide treatment of specific locomotor control deficits in stroke rehabilitation.

A study of various normalization procedures for within day electromyographic data

Normalization of electromyographic (EMG) data has been described in the scientific literature as crucial for comparisons between subjects and between muscles. The reference value used in the normalization equation has, however, varied across reports. Comparison between studies could be facilitated by use of a common value. We propose the best way to select the common value is through a reliability approach. Accordingly, the purpose of this study was to identify which of three EMG normalization values provided the most reproducible data set. The gastrocnemius EMG results from 20 normal persons and 20 individuals with anterior cruciate deficiency who were participating in a larger study were normalized to a maximum voluntary isometric contraction (MVIC) EMG, peak dynamic EMG, and mean dynamic EMG. Values were then subjected to evaluation using four statistical measures: inter and intrasubject coefficients of variation (CV), variance ratio (VR), and intraclass correlation coefficient (ICC). The CV measures, while not being reflective of reliability were included for comprehensive consideration in view of other literature. The intersubject CV which measures group variability and the intrasubject CV which measures precision were lower for the dynamic conditions, however, the VR and ICC suggested reproducibility was best with EMG from the MVIC. Given that other studies have advocated normalizing EMG by taking data from the dynamic event, reconsideration may be warranted if high reproducibility is desired. Interpretations of the findings given the population, muscle and condition studied are discussed.

EMG patterns during running: Intra- and inter-individual variability

Rectified surface electromyographic (EMG) patterns of five healthy, young, physically-fit subjects running at 4.2 m s(-1) on a treadmill were recorded with the objective of defining a normal profile of EMG activity for running gait. This knowledge is important in understanding how the central nervous system (CNS) controls simple running tasks under normal conditions. The EMG signals from seven muscles (erector spinae, rectus femoris, vastus medialis, vastus lateralis, biceps femoris, tibialis anterior and gastrocnemius) were recorded, together with footswitch signals. The intra- and inter-individual variability of each muscle's EMG profile and peak times were analysed. Interindividual EMG peak time values were analysed to define the timing of the activity of the muscles studied relative to the stride cycle and its subphases. For each muscle, little variation was found within individuals in EMG profile and peak time across trials, but differences between subjects were significant (P < 0.01). EMG peak time analysis showed two distinct activation sequences of different muscles: the first at stance phase and the second at terminal swing. In conclusion, in spite of a significant variability among subjects in EMG profile and peak time values for each muscle, the EMG peak timing analysis showed a sequence of activation at stance phase, no EMG peak activity during the first double swing and another sequence of activation during terminal swing. These findings are evidence of a neuromuscular control strategy common to all subjects.

EEG during pedaling: evidence for cortical control of locomotor tasks

OBJECTIVE

This study characterized the brain electrical activity during pedaling, a locomotor-like task, in humans. We postulated that phasic brain activity would be associated with active pedaling, consistent with a cortical role in locomotor tasks.

METHODS

Sixty four channels of electroencephalogram (EEG) and 10 channels of electromyogram (EMG) data were recorded from 10 neurologically-intact volunteers while they performed active and passive (no effort) pedaling on a custom-designed stationary bicycle. Ensemble averaged waveforms, 2 dimensional topographic maps and amplitude of the β (13-35 Hz) frequency band were analyzed and compared between active and passive trials.

RESULTS

The peak-to-peak amplitude (peak positive-peak negative) of the EEG waveform recorded at the Cz electrode was higher in the passive than the active trials (p < 0.01). β-band oscillations in electrodes overlying the leg representation area of the cortex were significantly desynchronized during active compared to the passive pedaling (p < 0.01). A significant negative correlation was observed between the average EEG waveform for active trials and the composite EMG (summated EMG from both limbs for each muscle) of the rectus femoris (r = -0.77, p < 0.01) the medial hamstrings (r = -0.85, p < 0.01) and the tibialis anterior (r = -0.70, p < 0.01) muscles.

CONCLUSIONS

These results demonstrated that substantial sensorimotor processing occurs in the brain during pedaling in humans. Further, cortical activity seemed to be greatest during recruitment of the muscles critical for transitioning the legs from flexion to extension and vice versa.

SIGNIFICANCE

This is the first study demonstrating the feasibility of EEG recording during pedaling, and owing to similarities between pedaling and bipedal walking, may provide valuable insight into brain activity during locomotion in humans.

Walking velocity and lower limb coordination in hemiparesis

BACKGROUND/OBJECTIVE

Gait training at fast speed has been suggested as an efficient rehabilitation method in hemiparesis. We investigated whether maximal speed walking might positively impact inter-segmental coordination in hemiparetic subjects.

METHODS

We measured thigh-shank and shank-foot coordination in the sagittal plane during gait at preferred (P) and maximal (M) speed using the continuous relative phase (CRP), in 20 healthy and 27 hemiparetic subjects. We calculated the root-mean square (CRP(RMS)) and its variability (CRP(SD)) over each phase of the gait cycle. A small CRP(RMS) indicates in-phasing, i.e. high level of synchronization between two segments along the gait cycle. A small CRP(SD) indicates high stability of the inter-segmental coordination across gait cycles.

RESULTS

Increase from preferred to maximal speed was 57% in healthy and 49% in hemiparetic subjects (difference NS). In healthy subjects, the main change was shank-foot in-phasing at stance (CRP(Shank-Foot/RMS), P, 98±10; M, 67±12, p<0.001). In hemiparetic subjects, we also found shank-foot in-phasing at late stance bilaterally (non-paretic CRP(Shank-Foot/RMS), P, 37±9; M, 29±8, p<0.001; paretic CRP(Shank-Foot/RMS), P, 38±13; M, 32±12, p<0.001), and thigh-shank in-phasing at mid-stance in the non-paretic limb (CRP(Thigh-Shank/RMS), P, 57±9; M, 49±9, p<0.001). CRP(Thigh-Shank) variability diminished in the paretic limb (CRP(Thigh-Shank/SD), P, 18.3±6.3; M, 16.1±5.2, p<0.001).

CONCLUSION

During gait velocity increase in hemiparesis, there is improvement of thigh-shank coordination stability in the paretic limb and of shank-foot synchronization at late stance bilaterally, which optimizes the propulsive phase similarly to healthy subjects. These findings may add incentive for rehabilitation clinicians to explore maximal velocity gait training in hemiparesis.

Design of Human-Machine Interface and altering of pelvic obliquity with RGR Trainer

The Robotic Gait Rehabilitation (RGR) Trainer targets secondary gait deviations in stroke survivors undergoing rehabilitation. Using an impedance control strategy and a linear electromagnetic actuator, the device generates a force field to control pelvic obliquity through a Human-Machine Interface (i.e. a lower body exoskeleton). Herein we describe the design of the RGR Trainer Human-Machine Interface (HMI) and we demonstrate the system's ability to alter the pattern of movement of the pelvis during gait in a healthy subject. Results are shown for experiments during which we induced hip-hiking - in healthy subjects. Our findings indicate that the RGR Trainer has the ability of affecting pelvic obliquity during gait. Furthermore, we provide preliminary evidence of short-term retention of the modified pelvic obliquity pattern induced by the RGR Trainer.

Rehabilitation of gait after stroke: a review towards a top-down approach

This document provides a review of the techniques and therapies used in gait rehabilitation after stroke. It also examines the possible benefits of including assistive robotic devices and brain-computer interfaces in this field, according to a top-down approach, in which rehabilitation is driven by neural plasticity.The methods reviewed comprise classical gait rehabilitation techniques (neurophysiological and motor learning approaches), functional electrical stimulation (FES), robotic devices, and brain-computer interfaces (BCI).From the analysis of these approaches, we can draw the following conclusions. Regarding classical rehabilitation techniques, there is insufficient evidence to state that a particular approach is more effective in promoting gait recovery than other. Combination of different rehabilitation strategies seems to be more effective than over-ground gait training alone. Robotic devices need further research to show their suitability for walking training and their effects on over-ground gait. The use of FES combined with different walking retraining strategies has shown to result in improvements in hemiplegic gait. Reports on non-invasive BCIs for stroke recovery are limited to the rehabilitation of upper limbs; however, some works suggest that there might be a common mechanism which influences upper and lower limb recovery simultaneously, independently of the limb chosen for the rehabilitation therapy. Functional near infrared spectroscopy (fNIRS) enables researchers to detect signals from specific regions of the cortex during performance of motor activities for the development of future BCIs. Future research would make possible to analyze the impact of rehabilitation on brain plasticity, in order to adapt treatment resources to meet the needs of each patient and to optimize the recovery process.

Short-latency stretch reflexes do not contribute to premature calf muscle activity during the stance phase of gait in spastic patients

OBJECTIVE

To identify whether a relationship exists between stretch and activity of the calf muscles during the stance phase of gait in patients with upper motor neuron syndrome (UMNS), while taking into account the physiologic phase shift between these entities.

DESIGN

Survey.

SETTING

Ambulatory care and general community.

PARTICIPANTS

Patients with UMNS (n=15; 9 patients with stroke, 6 patients with hereditary spastic paraparesis) with premature calf muscle activity during the stance phase of gait and healthy controls (n=13).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

Timing of optimal association (phase shift) between the lengthening velocity of the gastrocnemius muscle and its electromyographic activity as revealed by cross-correlation analyses.

RESULTS

Although premature calf muscle activity was evident in the patient groups, the phase shift between calf muscle stretch and its activity did not correspond with the monosynaptic stretch reflex latency (40- to 80-ms time window). However, there was a main effect of group on the phase shifts (F(3,33)=3.23, P=.035). Post hoc analysis revealed that in the paretic leg of stroke patients, the electromyographic activity preceded the lengthening velocity by 9 ± 54ms, whereas in the control group, the electromyographic activity followed the pattern of the muscle-lengthening velocity with a delay of 61 ± 54ms (P=.029).

CONCLUSIONS

Short-latency stretch reflexes do not significantly contribute to premature calf muscle activity in the stance phase of (spastic) gait. This notion questions the validity of the clinical assessment of hyperreflexia and clonus of the calf as a predictor of calf muscle spasticity during gait.

The relationship of lower limb muscle strength and knee joint hyperextension during the stance phase of gait in hemiparetic stroke patients

BACKGROUND AND PURPOSE

Despite the finding that 40% to 60% of stroke patients suffer from knee joint hyperextension during gait, there is a lack of agreement of the possible causes of this problem. The aim of this study was to determine whether there is a relationship between lower limb muscle weakness and knee joint hyperextension in hemiparetic stroke patients.

METHODS

This is a cross-sectional observational comparison study. Twenty patients (mean age 66 years) who had suffered a single hemiparetic stroke and were ambulant with no major lower limb joint pathology participated. Muscle strength of the hip extensors, hip flexors, hip abductors, knee extensors, knee flexors, ankle plantarflexors and ankle dorsiflexors of both limbs was measured using a hand-held dynamometer. Computerized and visual gait analysis identified subjects with and without knee hyperextension in loading response and midstance. Subjects were categorized as having weakness of a particular muscle group if the difference in strength between the paretic and non-paretic muscle was greater than 50%. The Pearson's chi-squared test was used to evaluate the association between weakness and knee hyperextension.

RESULTS

A strong relationship was found between ankle plantarflexor weakness and knee hyperextension during midstance (p = 0.044). No relationship was found between lower limb muscle weakness and knee hyperextension during loading response (p > 0.05). No relationship was found between any other lower limb muscle groups and knee hyperextension in midstance (p > 0.05).

CONCLUSIONS

Weak ankle plantarflexors, in particular gastrocnemius, may have an important role in the presence of knee hyperextension. The results of this study did not support a role for weak hamstrings or quadriceps in knee hyperextension during gait. Further research is needed to clarify the role of gastrocnemius during the stance phase and to determine if strengthening weak gastrocnemius reduces knee hyperextension.

Guiding task-oriented gait training after stroke or spinal cord injury by means of a biomechanical gait analysis

To recover the ability to walk is one of the most important goals of persons recovering from a stroke or spinal cord injury (SCI). While a task-oriented approach to gait training is recommended, randomized controlled trials or meta-analyses comparing different methods of delivering training have failed in general to demonstrate the superiority of one approach over the other. The large variations in the mean outcome gait measures reported in these studies reflect, at least in part, the heterogeneity of the sensorimotor impairments underlying the gait disability as well as variations in the therapeutic response. The purpose of this chapter is to demonstrate that biomechanical gait analysis can reveal information pertinent to the selection of a task-oriented approach to enhance gait training as well as the therapeutic response that clinical evaluations alone cannot provide. We first briefly review locomotor impairments underlying the gait disability after stroke and SCI as well as the effects of selected technological task-oriented gait training interventions. We then give examples that demonstrate the use of gait analysis to pinpoint underlying impairments that can guide the choice of sensorimotor therapy and then immediately identify responders to the intervention. Such an individualized approach should promote therapeutic efficacy while leading over time to the identification of clinical indices to guide therapy when gait analysis is not feasible. Given the requirements of a gait analysis laboratory and the qualified personnel to capture and interpret the data, future studies will need to demonstrate the feasibility of the technological proposed approach and assess the costs and benefits for the health care system.

Force control of quadriceps muscle is bilaterally impaired in subacute stroke

We tested the hypothesis that force variability and error during maintenance of submaximal isometric knee extension are greater in subacute stroke patients than in controls and are related to motor impairments. Contralesional (more-affected) and ipsilesional (less-affected) legs of 33 stroke patients with sufficiently high motor abilities (62 ± 13 yr, 16 ± 2 days postinjury) and the dominant leg of 20 controls (62 ± 10 yr) were tested in sitting position. After peak knee extension torque [maximum voluntary contraction (MVC)] was established, subjects maintained 10, 20, 30, and 50% of MVC as steady and accurate as possible for 10 s by matching voluntary force to the target level displayed on a monitor. Coefficient of variation (CV) and root-mean-square error (RMSE) were used to quantify force variability and error, respectively. The MVC was significantly smaller in the more-affected than less-affected leg, and both were significantly lower than in controls. The CV was significantly larger in the more-affected than less-affected leg at 20 and 50% MVC, whereas both were significantly larger compared with controls across all force levels. Both more-affected and less-affected legs of patients showed significantly greater RMSE than controls at 30 and 50% MVC. The CV and RMSE were not related to the Fugl-Meyer motor score or to the Rivermead Mobility Index. The CV negatively correlated with MVC in controls but only in the less-affected leg of patients. It is concluded that isometric knee extension strength and force control are bilaterally impaired soon after stroke but more so in the more-affected leg. Future studies should examine possible mechanisms and the evolution of these changes.

Muscle work is increased in pre-swing during hemiparetic walking

BACKGROUND

Muscle mechanical work is likely affected by gait abnormalities in hemiparetic walking during the paretic pre-swing phase (i.e., double support phase preceding paretic toe-off). Previous experimental studies suggest that muscle work may be decreased in the paretic leg, but paretic work may have been underestimated since experimental approaches based on net joint moments do not account for co-contraction of antagonist muscles. Also, whether the non-paretic leg does more work compared to control subjects at matched speeds and how work generation may differ between hemiparetic subjects walking with different self-selected speeds remains unknown.

METHODS

Three-dimensional forward dynamics simulations of two representative hemiparetic subjects walking with different self-selected speeds (i.e., limited community=0.45 m/s and community walkers=0.9 m/s) and a speed and age-matched control subject were generated to quantify musculotendon (fiber and in-series tendon) work during paretic pre-swing.

FINDINGS

Total paretic and non-paretic fiber work were increased in both the limited community and community hemiparetic walkers compared to the control. Increased fiber work in the limited community walker was primarily related to decreased fiber and tendon work by the paretic plantar flexors requiring compensatory work by other muscles. Increased fiber work in the community walker was primarily related to increased work by the hip abductors and adductors.

INTERPRETATION

The hemiparetic walkers would expend more metabolic energy during pre-swing if the hemiparetic and control subjects were to perform work with the same mechanical efficiency. These results may partly explain the increased metabolic cost of hemiparetic walkers compared to nondisabled walkers at matched speeds.

Improving poststroke recovery: neuroplasticity and task-oriented training

Neurorehabilitation is a critical part of the overall process to achieve optimal outcome after stroke. Presently, the field of neurorehabilitation is in transition. New research suggesting novel approaches to optimize functional recovery after stroke is on the horizon, but clear knowledge of the underlying mechanisms of this recovery is still being unraveled. In practice, many rehabilitation centers continue to provide traditional compensatory rehabilitation training while many others are practicing newer, "task-oriented" approaches. A few centers are incorporating new technology, such as computer-based training devices or robotics, into rehabilitation care. This transition is happening because neuroscientific research has shown that neuroplastic changes in the cerebral cortex and in other parts of the central nervous system (CNS) are necessarily linked to motor skill retraining in the affected limbs. Task-oriented training that focuses on the practice of skilled motor performance is the critical link to facilitating neural reorganization and "rewiring" in the CNS. Therefore, whenever possible, task-oriented training at an intense level should be incorporated into the rehabilitation program of any patient with stroke-related motor deficits. Two such task-oriented therapies that should be available at all neurorehabilitation centers are constraint-induced movement therapy and body weight-supported treadmill training. The optimal intensity of training (frequency and duration) is still not clear but is certainly greater than that available in clinical programs. Therefore, the incorporation of automated training devices will be necessary in the future. However, the engineering necessary to make these devices effective, easy to use, affordable, and portable remains a challenge for the next decade of neurologic bioengineering research.

Neuromuscular strategies in the paretic leg during curved walking in individuals post-stroke

Reduced flexibility over the neuromotor control of paretic leg muscles may impact the extent to which individuals post-stroke modulate their muscle activity patterns to walk along curved paths. The purpose of this study was to compare lower-limb movements and neuromuscular strategies in the paretic leg of individuals with stroke with age-matched controls during curved walking. Participants walked at their preferred walking velocity along four different paths of increasing curvature, while lower-limb kinematics and muscle activity were recorded. A second group of able-bodied individuals walked along the four paths, matching the walking speed of the stroke group. The stroke group showed reduced lower-limb joint excursion and disordered modulation of foot pressure during curved walking, accompanied by reduced modulation of muscle activity patterns. In the inner leg of the curve in control subjects, the posteromedial muscles (medial gastrocnemius and medial hamstrings) showed decreased electromyographic amplitude as path curviture increased. Conversely, activity of the posterolateral musculature of the outer leg was decreased with increasing path curvature. Activity in the tibialis anterior and gluteus medius was also modulated with path curvature. However, in the stroke group, we found reduced modulation of muscle activity in the paretic leg during curved walking. The extent of modulation was also associated with the level of physical impairment due to stroke. The results of this study provide further knowledge about neuromuscular control of locomotor adaptations post-stroke.

The ACT-4D: a novel rehabilitation robot for the quantification of upper limb motor impairments following brain injury

Rehabilitation robots and other controlled diagnostic devices are useful tools to objectively quantify debilitating, post-stroke impairments. The goal of this paper is to describe the design of the ACT-4D rehabilitation robot which can quantify arm impairments during functional movement. The robot can instantly switch between a compliant mode that minimizes impedance of voluntary movement, and a stiff mode that applies controlled position/speed perturbations to the elbow (up to 75 Nm or 450 deg/s at 4500 deg/s(2)). It has a limited range of movement of the shoulder and elbow, which is further reduced when a damper is needed to enhance the positional stiffness of the base robot. In recent experiments, the ACT-4D has been used successfully for the quantification of elbow impairments.

Voluntary activation failure contributes more to plantar flexor weakness than antagonist coactivation and muscle atrophy in chronic stroke survivors

The contributions of nervous system muscle activation and muscle atrophy to poststroke weakness have not been evaluated together in the same subject. Maximal voluntary contraction (MVC) torque, voluntary activation (twitch interpolation), and electromyographic (EMG) amplitude were determined bilaterally in the plantar flexors of seven chronic stroke survivors (40-63 yr, 24-51 mo poststroke). Volumes of the plantar flexor muscles were determined bilaterally with magnetic resonance imaging (MRI). The mean (±SD) contralesional (paretic) MVC torque was less than one-half of the ipsilesional leg: 56.7 ± 57.4 vs. 147 ± 35.7 Nm (P = 0.006). Contralesional voluntary activation was only 48 ± 36.9%, but was near complete in the ipsilesional leg, 97 ± 1.9% (P = 0.01). The contralesional MVC EMG amplitude (normalized to the maximum M-wave peak-to-peak amplitude) of the gastrocnemii and soleus were 36.0 ± 28.5 and 36.0 ± 31.0% of the ipsilesional leg. Tibialis anterior (TA) EMG coactivation was not different between the contralesional (23.2 ± 24.0% of TA MVC EMG) and ipsilesional side (12.3 ± 5.7%) (P = 0.24). However, TA EMG coactivation was excessive (71%) in one subject and accounted for ~8% of her weakness based on the estimated antagonist torque. Relative (%ipsilesional leg) plantar flexor and gastrocnemii volumes were 88 ± 6% (P = 0.004) and 76 ± 15% (P = 0.01), respectively. Interlimb volume differences of the soleus, deep plantar flexors, and peronei were not significant. Preferred walking speed (0.83 ± 0.33 m/s) was related to the contralesional MVC torque (r(2) = 0.57, P = 0.05, N = 7), but the two subjects with the greatest weakness walked faster than three others. Our findings suggest that plantar flexor weakness in mobile chronic stroke survivors reflects mostly voluntary activation failure, with smaller contributions from antagonist activity and atrophy.

Quantitative Analysis of Human Movement Synergies: Constructive Pattern Analysis for Gait

To record three-dimensional coordinates of the joints from normal human subjects during locomotion, we used a digital motion analysis system (ELITE). Recordings were obtained under several different conditions, which included normal walking and stepping over obstacles. Principal component analysis was used to analyze coordinate data after conversion of the data to segmental angles. This technique gave a stable summary of the redundancy in gait kinematic data in the form of reduced variables (principal components). By modeling the shapes of the phase plots of reduced variables (distortion analysis) and using a limited number of model parameters, good resolution was obtained between subtly different conditions. Hence, it was possible to accurately resolve small distributed changes in gait patterns within subjects. These methods seem particularly suited to longitudinal studies in which relevant movement features are not known a priori. Assumptions and neurophysiological applications are discussed.

Genu recurvatum in cerebral palsy--part B: hamstrings are abnormally long in children with cerebral palsy showing knee recurvatum

Hyperextension of the knee in stance (knee recurvatum) is a common disorder in patients with spastic cerebral palsy (CP). A group 35 children with CP (47 lower limbs) was divided into two subgroups according to the timing of maximum knee extension during the stance phase of gait. Gait analysis and musculoskeletal modelling data were compared with a control group of 12 normally developing children. We observed no difference in kinematics between the CP groups who showed an equinus position of the foot at initial contact. Both groups showed increased external extensor moments across the knee. The muscle-tendon lengths of the hamstrings were abnormally long at initial contact, and in both recurvatum groups, contracted faster compared with the control group. Surface electromyography revealed prolonged activity of the hamstrings in stance and early activation in swing. Abnormally long hamstrings at initial contact together with equinus position of the foot are the main causes of genu recurvatum in children with CP.

Genu recurvatum in cerebral palsy--part A: influence of dynamic and fixed equinus deformity on the timing of knee recurvatum in children with cerebral palsy

The aim of the study was to confirm the hypothesis of the influence of the dynamic and fixed equinus deformity on the timing of knee recurvation (hyperextension). According to our hypothesis, dynamic equinus is linked to early and fixed equinus and to late knee hyperextension. A group 35 children with cerebral palsy (47 lower limbs) was divided into two subgroups according to the timing of maximum knee hyperextension. Clinical examination confirmed our hypothesis. Gait analysis and musculoskeletal modelling results were compared with 12 normally developing children. Both recurvatum groups had forefoot landing and neither achieved normal ankle dorsiflexion. Electromyographic examination revealed an abnormally high soleus activity in a single stance. Muscle length changes of medial gastrocnemius and soleus were in agreement with our hypothesis. Such a finding might simplify the decision as to which treatment to select for equinus deformity, present in patients with genu recurvatum.