Gait analysis to assess the effects of botulinum toxin type A treatment in cerebral palsy: an open-label study in 10 children with equinus gait pattern

Botulinum toxin type A (BTX-A) injections induce a dose-related decrease in muscle tone and increased joint mobility in adults with spasticity and children with cerebral palsy. The aim of this study was to address the question of whether BTX-A-related improvements in joint mobility and muscle tone are associated with changes in instrumental gait analysis in children with cerebral palsy. Ten children with cerebral palsy and equinus gait were given a single dose of BTX-A (5 U BOTOX®/kg body weight per leg) into the gastrocnemius muscles. At follow-up (mean, 32.6 days post-injection), a significant ( P < 0.05) increase in both passive and active ankle range of motion was observed, together with a decrease in the modified Ashworth score. Instrumental gait analysis showed improvements in ankle and knee kinematics as well as in time-distance parameters, with a significant increase in step length observed ( P < 0.05). Semi-quantitative analysis of rectified electromyographic (EMG) recordings of the tibialis anterior muscle during gait showed a reduction in EMG activity during the stance phase and an increase in EMG activity during the swing phase. This study demonstrated the benefits of BTX-A treatment in improving joint mobility and ambulatory function in children with cerebral palsy, and showed that changes in tibial anterior muscle activity as a result of BTX-A injections into the gastrocnemius muscle can be measured by instrumental gait analysis.     

Altered phase-transitions in tibialis anterior and medial gastrocnemius during walking after limbsaving surgery

OBJECTIVE: In normal gait onset activity in tibialis anterior at end stance is closely linked to reduction in activity in medial gastrocnemius. Is a similar transition also present in patients undergoing limb-saving surgery? METHODS: Nineteen subjects after limb-saving surgery of the lower extremity and ten age-matched controls were compared. Patients walked on a treadmill at their preferred speed. Bipolar surface EMG activity was recorded from the tibialis anterior and the medial gastrocnemius. RESULTS: Patients showed asymmetry in gait. In controls a close tibialis anterior and medial gastrocnemius connection was seen. The close link between ipsilateral tibialis anterior and medial gastrocnemius was absent in patients. Instead, a link was found between tibialis anterior onset in the affected and medial gastrocnemius onset in the non-affected leg. CONCLUSIONS: This finding suggests that two control mechanisms can be seen: a contralateral connection between tibialis and gastrocnemius and a less important ipsilateral connection. This means that automated phase switching in patients does not rely primarily on ipsilateral mechanisms but that instead the onset of the ipsilateral swing is linked to the moment of load acceptance by the contralateral leg These results are strikingly similar to those obtained in simulated limping by normal subjects. SIGNIFICANCE: Patients after limbsaving surgery have a clinically significant problem that creates aberrant gait patterns. This study provides new information about linking of ankle dorsiflexors and plantarflexors, as well as reporting the uncoupling of this mechanism in these patients after major surgery.     

Posture in Parkinson's disease: impairment of reflexes and programming

The leg muscle electromyographic responses induced during stance by impulsive displacements of a treadmill belt (directed forward or backward and at different rates) were studied in a group of patients with Parkinson's disease and a group of age-matched healthy subjects. Young normal subjects were also studied both before and after intake of a dopamine antagonist (haloperidol). Compensatory gastrocnemius electromyographic responses resulting from backward-directed displacements were significantly smaller in both the patients and the young normal subjects following intake of haloperidol. The reduced sensitivity of the gastrocnemius muscle to stretch correlated with an inability to compensate for the perturbations. In the patients, the gastrocnemius response was followed by enhanced activation of the tibialis anterior muscle. This was not the case in the normal subjects after intake of dopamine antagonist and is probably not, therefore, the consequence of acute dopamine deficiency. In the patients the angular rotation at the ankle joint induced during faster backward-directed displacements was slower than that in normal subjects, despite identical amounts of gastrocnemius electromyographic activity. This supports earlier findings of changes in intrinsic muscle stiffness in Parkinson's disease. None of these differences were seen when the tibialis anterior muscle was stretched. This differential behavior of the antagonist leg muscles can best be explained by the different function fulfilled by these muscles in regulation of stance and gait.     

Gait pattern in two rare genetic conditions characterized by muscular hypotonia: Ehlers-Danlos and Prader-Willi syndrome

This study aimed to quantify and compare the gait pattern in Ehlers-Danlos (EDS) and Prader-Willi syndrome (PWS) patients to provide data for developing evidence-based rehabilitation strategies. Twenty EDS and 19 PWS adult patients were evaluated with an optoelectronic system and force platforms for measuring kinematic and kinetic parameters during walking. The results were compared with those obtained in a group of 20 normal-weight controls (CG). The results showed that PWS patients walked with longer stance duration and reduced velocity than EDS, close to CG. Both EDS and PWS showed reduced anterior step length than CG. EDS kinematics evidenced a physiological position at proximal joints (pelvis and hip joint) while some deficits were displayed at knee (reduced flexion in swing phase) and ankle level (plantar flexed position in stance and reduced dorsal flexion in swing). PWS showed a forward tilted pelvis in the sagittal plane, excessive hip flexion during the whole gait cycle and an increased hip movement in the frontal plane. Their knees were flexed at initial contact with reduced range of motion while ankle joints showed a plantar flexed position during stance. No differences were found in terms of ankle kinetics and joint stiffness. Our data showed that EDS and PWS patients were characterized by a different gait strategy: PWS showed functional limitations at every level of the lower limb joints, whereas in EDS limitations, greater than PWS, were reported mainly at the distal joints. PWS patients should be encouraged to walk for its positive impact on muscle mass and strength and energy balance. For EDS patients the rehabilitation program should be focused on ankle strategy improvement.     

Gait strategy in patients with Ehlers-Danlos syndrome hypermobility type: a kinematic and kinetic evaluation using 3D gait analysis

The aim of this study was to quantify the gait patterns of adults with joint hypermobility syndrome/Ehlers-Danlos syndrome (JHS/EDS-HT) hypermobility type, using Gait Analysis. We quantified the gait strategy in 12 JHS/EDS-HT adults individuals (age: 43.08 + 6.78 years) compared to 20 healthy controls (age: 37.23 ± 8.91 years), in terms of kinematics and kinetics. JHS/EDS-HT individuals were characterized by a non-physiological gait pattern. In particular, spatio-temporal parameters evidenced lower anterior step length and higher stance phase duration in JHS/EDS-HT than controls. In term of kinematics, in JHS/EDS-HT patients the main gait limitations involved pelvis, distal joints and ankle joint. Conversely, hip and knee joint showed physiological values. Ankle moment and power revealed reduced peak values during terminal stance. Differences in stiffness at hip and ankle joints were found between JHS/EDS-HT and controls. JHS/EDS-HT patients showed significant decreased of Kh and Ka parameters very probably due to congenital hypotonia and ligament laxity. These findings help to elucidate the complex biomechanical changes in JHS/EDS-HT and may have a major role in the multidimensional evaluation and tailored management of these patients.     

Subclinical abnormal EMG activation of the gastrocnemii during gait analysis in restless legs syndrome: a preliminary report in 13 patients

OBJECTIVE: The purpose of this study was to detect the eventual presence of a minor voluntary motor involvement in restless legs syndrome (RLS), not detectable clinically, which might be observed by means of a sophisticated instrumental analysis of movement, such as gait analysis. SUBJECTS AND METHODS: Gait analysis was performed and surface EMG activity was recorded in 13 RLS patients and 8 normal controls from 8 muscles: tibialis anterior, gastrocnemius lateralis, gastrocnemius medialis, and soleus in both legs. RESULTS: Ten out of the 13 RLS patients and none of the normal control group showed a mild abnormality of the EMG activation of the gastrocnemius muscles during gait which, however, had no detectable effects on its kinematics. CONCLUSIONS: These preliminary results might be interpreted as the effect of an impaired supraspinal dopaminergic control with possible action on spinal structures involved in the control of gait. If confirmed in future studies, this mild EMG abnormality might constitute an additional supportive feature for the diagnosis of RLS in difficult cases.     

Characteristics of parkinsonian and ataxic gaits: a study using surface electromyograms, angular displacements and floor reaction forces

To clarify the characteristics of parkinsonian and ataxic gaits, we analyzed electromyograms (EMGs) of the thigh and leg muscles, angular displacements of the hip and leg joints, and floor reaction forces during free walking for each gait phase in 16 patients with Parkinson's disease (PD) and 14 ataxic patients with cerebellar degenerations. We studied 17 healthy elderly subjects whose walking speed was similar to that of patients with moderate disease. Free walking by PD patients was characterized by low maximum activity of the gastrocnemius/soleus (GC) and tibialis anterior (TA) muscles. Ataxic patients showed high activity of GC and TA during the period when these muscles were not active in normal walking. The ratio of changes of EMG of the distal muscles to changes in angular displacement of the ankle (DeltaEMG/Deltaangle) was reduced in GC of PD patients in ankle dorsiflexion, whereas it was high in GC and TA of ataxic patients in ankle dorsiflexion and plantarflexion, respectively. Changes in DeltaEMG/Deltaangle coincided with those in proprioceptive reflexes reported previously. Our results showed that measurement of EMG for each phase revealed disease-specific factors, and that of DeltaEMG/Deltaangle might be a conventional clue for estimation of reflexes for these gait disorders.     

Lower limb muscle activity in ambulatory children with cerebral palsy before and after the treatment with Botulinum toxin A

Purpose: The study investigated the effect of Botulinum toxin A on the gait and lower limb muscle activity of ambulatory CP children. Methods: 19 spastic diplegic and 4 left hemiparetic CP children were injected with a mean dose of 23.5 units of Botulinum toxin A/kg body weight into the gastrocnemius and hamstring muscles. Muscle tone and gait analysis including the kinesiological electromyogram of the shank and thigh muscles were assessed before and four weeks after injection and compared with the help of a multivariate analysis (p < 0.05). Results: Botulinum toxin A caused a definite reduction of plantarflexor, knee and hip hypertonia in 21 children, resulting in a more plantar grade and erect gait in 17 children four weeks after injection. Gait analysis showed a statistically significant improvement in peak ankle dorsi-flexion and knee extension during stance, and the length of the force point of action under both feet increased. Electromyography revealed sig-nificantly less co-contraction of the lower leg muscles, due to a more phasic instead of a tonic activity of the tibialis anterior muscle, and an improved activation pattern of the left rectus and biceps femoris muscles. Conclusions: The present study demonstrated that the injection of Botulinum toxin A resulted in a more mature muscle activation pattern of CP children. Most of the children walked more plantigrade and erect, the functional gait parameters, however, did not change.     

Differences in the EMG pattern of leg muscle activation during locomotion in Parkinson's disease

In this pilot study, EMG patterns of leg muscle activation were studied in five parkinsonian patients with (B1) and five without (B2) freezing. Gastrocnemius medialis (GM) and tibialis anterior (TA) activity was analysed, by means of surface electromyography (EMG), during treadmill walking at two different belt speeds. Both groups showed reduced GM activity and an overactive TA at the lower speed compared with controls. Upon increasing the speed, the B2 patients showed a marked GM response (increment index 100%), while a moderate change was observed in the B1 group. Poor recruitment of the GM characterises parkinsonian gait in general; this pattern is much more marked in parkinsonian patients with freezing of gait, who show a loss of GM adaptation to variation of locomotion speed.     

Characteristics of the electromyographic patterns of lower limb muscles during gait in patients with Parkinson's disease when OFF and ON L-Dopa treatment

The purpose of this study was to compare the electromyographic (EMG) behavior of the triceps surae (TS), tibialis anterior (TA), quadriceps and hamstring muscles of the lower limbs during self-initiated free gait in a group of patients (n=15) with Parkinson's disease (PD), when OFF and ON L-Dopa, with that of normal controls. When OFF L-Dopa, we observed qualitative disturbances in muscle activation patterns, such as an absence or extreme reduction in TA activations in early stance or during the early and late swing phases. Other disturbances included flatter profiles of the TS activation burst at push off, and temporal alterations that included prolonged activation of the proximal muscles during the stance phase. Statistical analysis showed that the TA was the most affected muscle in most of the patients particularly during the activation burst in late swing (p<.0004). After medication (ON L-Dopa), the amplitude and timing of distal muscle activations became more similar to normal values, with the increase in EMG amplitude being dramatic in some patients. In the proximal muscles, the effects on EMG amplitude were less marked and prolonged activation often persisted even after the administration of L-Dopa.     

Characteristics of the electromyographic patterns of lower limb muscles during gait in patients with Parkinson''s disease when OFF and ON L-Dopa treatment

The purpose of this study was to compare the electromyographic (EMG) behavior of the triceps surae (TS), tibialis anterior (TA), quadriceps and hamstring muscles of the lower limbs during self-initiated free gait in a group of patients (n=15) with Parkinson's disease (PD), when OFF and ON L-Dopa, with that of normal controls. When OFF L-Dopa, we observed qualitative disturbances in muscle activation patterns, such as an absence or extreme reduction in TA activations in early stance or during the early and late swing phases. Other disturbances included flatter profiles of the TS activation burst at push off, and temporal alterations that included prolonged activation of the proximal muscles during the stance phase. Statistical analysis showed that the TA was the most affected muscle in most of the patients particularly during the activation burst in late swing (p<.0004). After medication (ON L-Dopa), the amplitude and timing of distal muscle activations became more similar to normal values, with the increase in EMG amplitude being dramatic in some patients. In the proximal muscles, the effects on EMG amplitude were less marked and prolonged activation often persisted even after the administration of L-Dopa.This work was supported by grants from Laval University.     

Normal and impaired regulation of muscle stiffness in gait: A new hypothesis about muscle hypertonia

The activation of leg muscles was analyzed in respect to ankle joint movement and the changes in tension produced by the triceps surae muscle during slow gait in spastic adults and children with cerebral palsy. In normal subjects the increase in tension of the triceps surae in the stance phase of gait is mainly due to an increase in gastrocnemius and sole EMG. In spastic patients the abnormally high tension development in triceps surae is due more to passive muscle stretch, for the reciprocally organized leg muscle EMG is reduced. It is concluded that the leg extensor muscles in spastic patients exhibit a pseudostretch-reflex behavior due to their mechanical properties, and that this is mainly responsible for muscle hypertonia. The coactivation of the leg muscles seen in children with cerebral palsy, which also is seen in the stepping of the newborn, suggests impaired maturation of the neuronal locomotor pattern.     

EMG activity and kinematics of human cycling movements at different constant velocities

Surface electromyographic (EMG) activity was recorded from the rectus femoris, vastus medialis, biceps femoris, gastrocnemius and tibialis anterior in the human lower extremity while subjects performed bicycling movements over a range of constant pedalling velocities. Kinematics of knee and hip cyclical movements were analyzed from 16 mm film. The reciprocal pattern of activation in agonist and antagonist muscles and timing of EMG initiation relative to knee joint were studied.

Reciprocal activation of rectus femoris and biceps femoris muscles was generally observed to occur during the mid-extension or mid-flexion phase of knee movements. This timing of activation pattern coincided well the period of peak angular velocity and zero angular acceleration.

As pedalling speeds approached maximum, activation times of the bifunctional, biarticular rectus femoris, biceps and gastrocnemius muscles were considerably advanced in phase relative to knee joint angles, whereas, EMG initiation of monofunctional, single joint, tibalis anterior and vastus medialis muscles maintained a relatively stable knee position-activation time relationship. At higher velocities, biceps femoris EMG activity was characterized as having a double burst pattern of activation. A less distinctive double burst pattern was seen in the rectus femoris EMG at higher cycling speeds.

EMG pattern analysis of the rectus femoris and biceps femoris muscles revealed an earlier onset of activity for both muscles during maximum cycling velocities, relative to cyclical phases of the knee joint angle. Considerable overlapping of the EMG bursts was seen beyond pedalling rates of 1 Hz. Co-contraction between rectus femoris and biceps femoris muscles could be observed during the acceleration period involving an abrupt switch to maximum pedalling performance. When co-contraction was observed, the joint angular acceleration curves observed during the knee flexion period accounted for a larger portion of a single cycle, and were more irregular than the angular accelerations observed during knee extension.     

Neuronal coordination of arm and leg movements during human locomotion

We aimed to study the neuronal coordination of lower and upper limb muscles. We therefore evaluated the effect of small leg displacements during gait on leg and arm muscle electromyographic (EMG) activity in walking humans. During walking on a split-belt treadmill (velocity 3.5 km/h), short accelerations or decelerations were randomly applied to the right belt during the mid or end stance phase. Alternatively, trains of electrical stimuli were delivered to the right distal tibial nerve. The EMG activity of the tibialis anterior (TA), gastrocnemius medialis (GM), deltoideus (Delt), triceps (Tric) and biceps brachii (Bic) of both sides was analysed. For comparison, impulses were also applied during standing and sitting. The displacements were followed by specific patterns of right leg and bilateral arm muscle EMG responses. Most arm muscle responses appeared with a short latency (65-80 ms) and were larger in Delt and Tric than in Bic. They were strongest when deceleration impulses were released during mid stance, associated with a right compensatory TA response. A similar response pattern in arm muscles was obtained following tibial nerve stimulation. The arm muscle responses were small or absent when stimuli were applied during standing or sitting. The arm muscle responses correlated more closely with the compensatory TA than with the compensatory GM responses. The amplitude of the responses in most arm muscles correlated closely with the background EMG activity of the respective arm muscle. The observations suggest the existence of a task-dependent, flexible neuronal coupling between lower and upper limb muscles. The stronger impact of leg flexors in this interlimb coordination indicates that the neuronal control of leg flexor and extensor muscles is differentially interconnected during locomotion. The results are compatible with the assumption that the proximal arm muscle responses are associated with the swinging of the arms during gait, as a residual function of quadrupedal locomotion.     

The association between premature plantarflexor muscle activity,muscle strength,and equinus gait in patients with various pathologies

This study provides an overview on the association between premature plantarflexor muscle activity (PPF), muscle strength, and equinus gait in patients with various pathologies. The purpose was to evaluate whether muscular weakness and biomechanical alterations are aetiological factors for PPF during walking, independent of the underlying pathology. In a retrospective design, 716 patients from our clinical database with 46 different pathologies (orthopaedic and neurologic) were evaluated. Gait analysis data of the patients included kinematics, kinetics, electromyographic activity (EMG) data, and manual muscle strength testing. All patients were clustered three times. First, patients were grouped according to their primary pathology. Second, all patients were again clustered, this time according to their impaired joints. Third, groups of patients with normal EMG or PPF, and equinus or normal foot contact were formed to evaluate the association between PPF and equinus gait. The patient groups derived by the first two cluster methods were further subdivided into patients with normal or reduced muscle strength. Additionally, the phi correlation coefficient was calculated between PPF and equinus gait. Independent of the clustering, PPF was present in all patient groups. Weak patients revealed PPF more frequently. The correlations of PPF and equinus gait were lower than expected, due to patients with normal EMG during loading response and equinus. These patients, however, showed higher gastrocnemius activity prior to foot strike together with lower peak tibialis anterior muscle activity in loading response. Patients with PPF and a normal foot contact possibly apply the plantarflexion–knee extension couple during loading response. While increased gastrocnemius activity around foot strike seems essential for equinus gait, premature gastrocnemius activity does not necessarily produce an equinus gait. We conclude that premature gastrocnemius activity is strongly associated with muscle weakness. It helps to control the knee joint under load independent from the underlying disease, and it is therefore a secondary deviation. If treated as primary target, caution should be exercised.     

Components of EMG symmetry and variability in parkinsonian and healthy elderly gait

Variability and bilateral symmetry of EMG gait-cycle profiles were studied in parkinsonian and healthy elderly subjects in the gastrocnemius, tibialis anterior, and vastus lateralis muscles. Components reflecting shape and timing were defined by the magnitude and phase of the cross-correlation function between individual stride profiles and the latency corrected ensemble average (LCEA) (variability), and between bilateral LCEAs (symmetry). Statistical significance was set at a confidence level of 0.01 reflecting a Bonferroni adjustment due to multiple measures. Parkinsonian gait was significantly different from the healthy elderly in several measures: increased shape variability and asymmetry in the gastrocnemius and tibialis anterior muscles, and reduced timing variability in the gastrocnemius. A portion of the parkinsonian group participated in a 3 week therapy program where they walked to rhythmic auditory stimulation. Gait parameters shifted toward healthy elderly values in each measure where population differences were found. Significant changes were observed in decreased tibialis anterior shape variability and asymmetry, and gastrocnemius shape variability. Strong trends were also observed in increased gastrocnemius timing variability and reduced bilateral asymmetry. In addition to the expected decrease in variability and asymmetry of healthy elderly, increased timing variability in the gastrocnemius was associated with a more normal gait, possibly reflecting feedback adaptability of muscle activity which may be useful in generating stable locomotion.     

The effects of external cues on ankle control during gait initiation in Parkinson's disease

The present study investigated the effects of external cues on motor control of the ankle joint during gait initiation in patients with Parkinson's disease (PD) and in age-matched healthy subjects. The soleus H-reflexes were recorded during self-generated and cue-triggered gait initiation. The tibialis anterior muscle burst during cue-triggered gait initiation was found to be significantly larger than that during self-generated gait initiation in both groups. External cues significantly increased soleus H-reflex depression during gait initiation in PD patients, although this significant increase was not present in healthy subjects. These findings indicate that external cues affect motor control of the extensor muscle of the ankle joint during gait initiation in PD patients.     

The coordination of posture and voluntary movement in patients with hemiparesis

Postural adjustments associated with the task of raising oneself on tiptoes were investigated in a reaction time paradigm in six normal subjects and six patients with hemiparesis due to stroke. Body and ankle position in space were measured by means of a movement analysis system (ELITE). The findings indicate that the task of going up on tiptoes is performed in two steps. First, the centre of gravity is shifted forward to a position per pendicular to the forefoot. This movement is initiated by a phasic burst of EMG activity in the tibialis anterior (TA). The activity of the quadriceps femoris (QUA) aids the forward shift and together with the biceps femoris (BF) stabilizes the knee. Following these postural adjustments, the action of going up on tip-toes is performed mainly by the gastrocnemius medialis (MG). The basic pattern of preparatory (TA, QUA, BF) and focal (MG) activity was disturbed in its temporal sequence in patients with hemiparesis. The analysis of the biomechanical data showed smaller movement velocities for leaning forward and going up on tiptoes in patients, with increased duration of going up on tiptoes and decreased movement amplitude on the paretic side. In addition, the correlation between the start of horizontal (leaning forward) and vertical (going up on tiptoes) hip movement was lost in patients. The preserved correlation between the latency of MG activity and the onset of the vertical hip movement on the paretic side in patients and the loss of correlation on the non-paretic side indicates that the EMG activity on the healthy side is adapted to the functional requirements of the affected side. The findings demonstrate that preparatory and executional activity are not programmed as a unit, but are more likely to be generated by a hierachically organized structure using proprioceptive and exteroceptive feedback.     

Adaptation and vision change the relationship between muscle activity of the lower limbs and body movement during human balance perturbations

ObjectiveInvestigate the relationship between changes in lower limb EMG root mean square (RMS) activity and changes in body movement during perturbed standing. Specifically, linear movement variance, torque variance and body posture were correlated against tibialis anterior and gastrocnemius RMS EMG activity during perturbed standing by vibration of the calf muscles.MethodsEighteen healthy participants (mean age 29.1 years) stood quietly for 30 s before vibration pulses were randomly applied to the calf muscles over a period of 200 s with eyes open or closed. Movement variance, torque variance and RMS EMG activity were separated into five periods, thereby allowing us to explore any time-varying changes of the relationships.ResultsChanges of tibialis anterior muscles EMG activity were positively correlated with changes in linear movement variance and torque variance throughout most of the trials, and negatively correlated with some mean angular position changes during the last 2 min of the trials. Moreover, the initial changes in Gastrocnemius EMG activity were associated with initial changes of mean angular position. Additionally, both tibialis anterior and gastrocnemius muscle activities were more involved in the initial control of stability with eyes closed than with eyes open.ConclusionsVisual information and adaptation change the association between muscle activity and movement when standing is perturbed by calf muscle vibration.SignificanceAccess to visual information changes the standing strategy to calf muscle vibrations. Training evoking adaptation could benefit those susceptible to falls by optimising the association between muscle activities and stabilising body movement.     

Motor unit involvement in spastic paresis. Relationship between leg muscle activation and histochemistry

In 4 patients with spastic hemiparesis the electromyograms (EMG) of leg muscles were recorded during walking and the gastrocnemius medialis on both sides was investigated by histochemistry and morphometry. During walking a reciprocal mode of muscle activation was preserved on the spastic side, but the EMG amplitude was reduced. In one patient the discharge behaviour of single motor units was investigated during stance. The mean discharge rate on both the spastic and the unaffected side amounted to about 5.5 Hz. Modification of this rate over a wider range by manoeuvres of the trunk was only observed on the unaffected side. Histochemistry and morphometry of the spastic muscle revealed: Increased levels of muscle fibre atrophy (especially type II); A predominance of type I fibres during later stages, when spasticity was established; Structural changes, such as the appearance of target fibres, mainly in type I fibres. These results suggest that the low level of tonic activation in spastic muscle develops tension enough during the stance phase of gait to support the body. The histopathological profile of the spastic gastrocnemius muscle is considered to be indicative of denervation, due to the combined effects of an impaired supraspinal control of the lower motoneurone and a concurrent transsynaptic muscle membrane dysfunction, muscle cell atrophy and fibre type transformation.