Stretch reflexes of triceps surae in patients with upper motor neuron syndromes

Applying Stretch to Evoke Hyperreflexia in Spasticity Testing: Velocity vs. Acceleration

In neurological diseases, muscles often become hyper-resistant to stretch due to hyperreflexia, an exaggerated stretch reflex response that is considered to primarily depend on the muscle's stretch velocity. However, there is still limited understanding of how different biomechanical triggers applied during clinical tests evoke these reflex responses. We examined the effect of imposing a rotation with increasing velocity vs. increasing acceleration on triceps surae muscle repsonse in children with spastic paresis (SP) and compared the responses to those measured in typically developing (TD) children. A motor-operated ankle manipulator was used to apply different bell-shaped movement profiles, with three levels of maximum velocity (70, 110, and 150°/s) and three levels of maximum acceleration (500, 750, and 1,000°/s²). For each profile and both groups, we evaluated the amount of evoked triceps surae muscle activation. In SP, we evaluated two additional characteristics: the intensity of the response (peak EMG burst) and the time from movement initiation to onset of the EMG burst. As expected, the amount of evoked muscle activation was larger in SP compared to TD (all muscles: p < 0.001) and only sensitive to biomechanical triggers in SP. Further investigation of the responses in SP showed that peak EMG bursts increased in profiles with higher peak velocity (lateral gastrocnemius: p = 0.04), which was emphasized by fair correlations with increased velocity at EMG burst onset (all muscles: r > 0.33-0.36, p ≤ 0.008), but showed no significant effect for acceleration. However, the EMG burst was evoked faster with higher peak acceleration (all muscles p < 0.001) whereas it was delayed in profiles with higher peak velocity (medial gastrocnemius and soleus: p < 0.006). We conclude that while exaggerated response intensity (peak EMG burst) seems linked to stretch velocity, higher accelerations seem to evoke faster responses (time to EMG burst onset) in triceps surae muscles in SP. Understanding and controlling for the distinct effects of different biological triggers, including velocity, acceleration but also length and force of the applied movement, will contribute to the development of more precise clinical measurement tools. This is especially important when aiming to understand the role of hyperreflexia during functional movements where the biomechanical inputs are multiple and changing.

Motorized versus manual instrumented spasticity assessment in children with cerebral palsy

AIM

We compared the outcomes of manual and motorized instrumented ankle spasticity assessments in children with cerebral palsy (CP).

METHOD

Ten children with spastic CP (three males, seven females; mean age 11y [standard deviation 3y], range 6-14y; Gross Motor Function Classification System levels I-III) were included. During motorized assessments, fast (100°/s) rotations were imposed around the ankle joint by a motor-driven footplate; during manual assessments, rotations of comparable speed were applied by a therapist using a foot orthotic. Angular range of motion, maximum velocity, acceleration, work, and muscle activity (electromyography [EMG]) of the triceps surae and tibialis anterior were compared during passive muscle stretch between motorized and manual assessments. Both movement profiles were also compared to CP gait ankle movement profile.

RESULTS

The imposed movement profile differed between methods, with the motorized assessment reaching higher maximum acceleration. Despite equal maximum velocity, the triceps surae were more often activated in motorized assessments, with low agreement of 44% to 72% (κ≤0) for EMG onset occurrence between methods. The manually applied ankle velocity profile matched more closely with the gait profile.

INTERPRETATION

The differences in acceleration possibly account for the different muscle responses, which may suggest acceleration, rather than velocity-dependency of the stretch reflex. Future prototypes of instrumented spasticity assessments should standardize movement profiles, preferably by developing profiles that mimic functional tasks such as walking.

Biceps femoris late latency responses and the "notching sign" in spasticity

Background

Spasticity is a motor impairment due to lesions in the brain and spinal cord. Despite being a well-known problem, difficulties remain in the assessment of the condition. The electrophysiological and kinesiological characteristics of the patellar pendulum changes during the movement triggered by the patellar T reflex could be used to assess spasticity.

Methods

Features of the patellar pendulum during the patellar T reflex were considered using a goniometric approach in spastic patients evaluated with the Ashworth scale. Medium and late latency responses in the rectus and biceps femoris muscles were examined electrophysiologically. For each pendulum, the maximum angle extension during an oscillation of the knee joint, maximal extension time, angular velocities of extensions of the knee joint and frequency of motion due to the patellar reflex were calculated. The damping of the amplitude in the pendulum was calculated.

Results

The spasticity group consisted of 65 patients (38 males and 27 females) with a mean age of 47.6 ± 14.0 years. The normal control group consisted of 25 individuals (19 males and six females) with a mean age of 32.1 ± 10 years. The biceps and rectus femoris long latency late responses were not observed in the normal cases. The biceps femoris medium latency response was observed only in 24 % of healthy individuals; conversely, late responses were observed in 84 % of patients. Activation of the antagonist muscles at a certain level of spasticity created a notching phenomenon. Amplitude of the reflex response and mean angular velocity of the first oscillation present in a dichotomic nature in the spasticity groups. Frequency of the first pendular oscillation increased with the increase of the Ashworth scale, while the damping ratio decreased with increasing scale. The Ashworth scale showed a correlation with the damping ratio. The damping ratio strongly distinguished the spastic subgroups and showed a strong negative correlation with the Ashworth scale.

Conclusions

The Ashworth scale presents a good correlation with kinesiological parameters, but it is only possible to differentiate normal and spastic cases with electrophysiologic parameters. Furthermore, the notching phenomenon could be evaluated as a determinant of spasticity.

Electromyographic analysis of upper limb muscles during standardized isotonic and isokinetic robotic exercise of spastic elbow in patients with stroke

Although it has been reported that strengthening exercise in stroke patients is beneficial for their motor recovery, there is little evidence about which exercise method is the better option. The purpose of this study was to compare isotonic and isokinetic exercise by surface electromyography (EMG) analysis using standardized methods. Nine stroke patients performed three sets of isotonic elbow extensions at 30% of their maximal voluntary isometric torque followed by three sets of maximal isokinetic elbow extensions with standardization of mean angular velocity and the total amount of work for each matched set in two strengthening modes. All exercises were done by using 1-DoF planner robot to regulate exact resistive torque and speed. Surface electromyographic activity of eight muscles in the hemiplegic shoulder and elbow was recorded. Normalized root mean square (RMS) values and co-contraction index (CCI) were used for the analysis. The isokinetic mode was shown to activate the agonists of elbow extension more efficiently than the isotonic mode (normalized RMS for pooled triceps: 96.0±17.0 (2nd), 87.8±14.4 (3rd) in isokinetic, 80.9±11.0 (2nd), 81.6±12.4 (3rd) in isotonic contraction, F[1,8]=11.168; P=0.010) without increasing the co-contraction of muscle pairs, implicating spasticity or synergy.

Stretch reflex spatial threshold measure discriminates between spasticity and rigidity

OBJECTIVE

Muscle spasticity following stroke has been shown to result from limitations in the range of regulation of the tonic reflex spatial threshold (ST), i.e., the joint angle at which the stretch reflex begins to act due to descending and segmental influences on motoneurons. The purpose of this study was to determine whether spasticity due to stroke and rigidity due to parkinsonism can be discriminated based on the ST measure.

METHODS

Elbow muscles were stretched at different velocities in healthy, stroke (spasticity) and parkinsonism (rigidity) subjects. The elbow angle at which muscle activation began for each stretch velocity (dynamic ST) and the velocity sensitivity of the ST were measured. Dynamic ST values extrapolated to zero velocity defined the tonic ST.

RESULTS

Compared to healthy subjects, spasticity and rigidity were associated with a decrease in the range of central regulation of tonic STs. STs were hypersensitive in spastic muscles and either hypo- or inversely sensitive to stretch velocity in rigid muscles.

CONCLUSIONS

ST characteristics discriminate between neurological deficits of muscle tone.

SIGNIFICANCE

Results suggest that spasticity and rigidity result from deficits in descending facilitatory control combined with deficits in dynamic fusimotor or/and presynaptic control of Ia inputs to motoneurons.

The Correlation between Modified Ashworth Scale and Biceps T-reflex and Inter-rater and Intra-rater Reliability of Biceps T-reflex

Objective

To establish a correlation between the modified Ashworth scale (MAS) and amplitude and latency of T-reflex and to demonstrate inter-rater and intra-rater reliability of the T-reflex of the biceps muscle for assessing spasticity after stroke.

Method

A total of 21 patients with hemiplegia and spasticity after ischemic stroke were enrolled for this study. The spasticity of biceps muscle was evaluated by an occupational therapist using the MAS. The mean value of manual muscle test of biceps muscles was 2.3±0.79. Latency and amplitude of T-reflex were recorded from biceps muscles by two physicians. The onset latency and peak to peak amplitude of the mean of 5 big T-reflex were measured. The examinations were carried out by two physicians at the same time to evaluate the inter-rater reliability. Further, one of the physicians performed the examination again after one week to evaluate the intra-rater reliability. The correlations between MAS and T-reflex, and the intra- and inter-rater reliability of biceps T-reflex were established by calculating the Spearman correlation coefficients and the intra-class correlation coefficients (ICCs).

Results

Amplitude of the biceps T-reflex increased with increasing level of MAS (r_s=0.464 and 0.573, respectively, p<0.01). ICCs of latency and amplitude of biceps T-reflex were 0.914 and 0.822. The Spearman correlation coefficients of latency and amplitude of biceps T-reflex were 0.937 and 0.635, respectively (p<0.01).

Conclusion

Biceps T-reflex demonstrates a good quantitative measurement and correlation tool with MAS for spasticity, and also shows acceptable inter- and intra-rater reliability, which can be used for patients with spasticity after stroke.

“Abnormal” movements: What are they reflections of?

We agree with Latash & Anson that therapeutic approaches should be directed toward solving the underlying problem, not toward adapting the abnormal to normal behaviour. The fundamental obstacle, however, is that doing so requires a solution of the “equivalence problem” in movement control.

Defective preprogramming does not account for the clinical deficits of Parkinson's disease

Latash & Anson argue that changed motor patterns should not be viewed as pathological. Instead, they should be viewed as adaptations to a primary deficit. We argue that the evidence shows: (1) bradykinesia is not an adaptation to a different primary deficit, and (2) bradykinetic movements are not “normal” slowed movements but, to the contrary, bradykinesia is part of the pathophysiology of Parkinson's disease.

Generic mechanisms of coordination in special populations

We show that left-handers can be considered as a “special” population. We indicate that the asymmetries in performance exhibited by left-handers are due to a basic asymmetry in the underlying coordination dynamics that constrains bimanual coordination. In contrast to the claims of Latash & Anson, we argue that considerable knowledge has been gained regarding the essential equations of motion that govern biological coordination.

“Normal” is not the issue: It is “effective” goal attainment that counts

Adaptive motor patterns that emerge after a neuromusculoskeletal lesion reflect not only the primary lesion, but also the dynamic characteristics of the musculoskeletal linkage and environment in which the action is performed. Although these patterns may be optimal, they may also be ineffective as goal-directed actions; effectiveness may only be regained if training addresses primary deficits and ensures practice without gross biomechanical adaptations.

The goal of treatment for motor impairment is not to “normalize” but to “functionalize” through facilitative modulation and enabling context

Adaptations occurring in the central nervous system (CNS) in the presence of pathology are not uniformly “good” for the organism when viewed in a functional context. A functional reordering of CNS priorities can be produced by allowing restructuring of the external context or through modification of neuromuscular physiology or anatomy designed to reduce the inherent restriction of functional movement in upper motor neuron syndrome. In fact, volitional control can often be “unmasked” through such interventions. Therapeutic interventions should not be directed toward “normalization” of motor patterns but should permit a functional reordering of CNS priorities that would otherwise not be possible.

What are “normal movements” in atypical populations?

Redundancy of the motor control system is an important feature that gives the central control structures options for solving everyday motor problems. The choice of particular control patterns is based on priorities (coordinative rules) that are presently unknown. Motor patterns observed in unimpaired young adults reflect these priorities. We hypothesize that under certain atypical conditions, which may include disorders in perception of the environment and in decision making, structural or biochemical changes within the central nervous system (CNS), and/or structural changes of the effectors, the central nervous system may reconsider its priorities. A new set of priorities will reflect the current state of the system and may lead to different patterns of voluntary movement. Under such conditions, changed motor patterns should be considered not pathological but rather adaptive to a primary disorder and may even be viewed as optimal for a given state of the system of movement production. Therapeutic approaches should not be directed toward restoring the motor patterns to as close to “normal” as possible but rather toward resolving the original underlying problem. We illustrate this approach using, as examples, movements in amputees, in patients with Parkinson's disease, in patients with dystonia, and in persons with Down syndrome.

What are “normal movements” inanypopulation?

It is the contention of Latash & Anson (L&A) that in atypical populations, such as those with cognitive, central neurological, or peripheral disorders, the central nervous system (CNS) is capable of producing more effective, though often less “normal,” movement patterns ifleft to its own devices. It is the aim of this commentary to extend their argument to other populations by pointing out the many parallels with development of movement patterns in sport.

Should stereotypic movement synergies in hemiparetic patients be considered adaptive?

The motor deficits observed in patients following some lesions of the central nervous system may be viewed as falling at one extreme of the continuum of possible motor behaviours. They are usually associated with an impaired ability to select and control specific movements from the available repertoire. Such movements may not be viewed as abnormal. However, it is unlikely that the primary motor deficits can all be considered adaptive.

“Constraint” versus “choice” in preferred movement patterns

Movement patterns in impaired gait are not selected by a smart central nervous system (CNS), but arise by virtue of mutual constraints of task, limitations in personal dynamics available for the task, and optimality criteria. An oscillatory model of gait cycle is presented that exemplifies this control and coordination scheme. Preferred gait patterns may be based on physical principles rather than CNS “coordinative rules.”

Developmental “movement disorders” and problem solving

Normal infants show a wide range of “atypical” movements. These, like the movements of atypical and normal adults, are best characterized as solutions to motor problems. Motor patterns alone may not be precise indicators of neurological status.

Is motor pathology associated with setting new CNS priorities or with increased difficulty in overcoming or suppressing preexisting CNS priorities?

Whereas Latash & Anson (L&A) have underscored the rearrangement or setting of new priorities, our primary focus is on preexisting central nervous system (CNS) priorities that become even more prevalent and intrusive under pathological conditions. The adaptations observed in the disordered motor system can often be understood against the backdrop of these primary CNS constraints. Even though this perspective has not been specifically addressed in the target article, we consider it complementary and not necessarily in opposition to L&A's primary thesis.

Clinometric properties of a clinical spasticity measurement tool

PURPOSE

To investigate clinometric properties of an Anglo-Dutch spasticity measurement tool (ADSMT), an objective tool providing information about both neurophysiological and biomechanical aspects of spasticity about the wrist joint in the clinical setting.

METHOD

ADSMT measurements were performed with 12 healthy and 11 participants with post-stroke spasticity, and consisted of assessing the maximum range of passive wrist movement (pROM) and passive wrist extension at different cycle rates. Outcome measures were wrist angle, flexor and extensor activation, and resistance to movement. Intra-class Correlation Coefficients (ICCs) were calculated for inter-rater and test-retest reliability. Validity was investigated by calculating Spearman's rho between ADSMT outcome measures and the Modified Ashworth Scale (n=12), the Action Research Arm Test (n=6), and a validated wrist rig (n=6).

RESULTS

Impaired participants had higher flexor activity and higher resistance to movement during passive wrist extension compared to unimpaired participants. For all outcome measures inter-rater and test-retest reliability were satisfactory to good and concurrent validity was sufficient.

CONCLUSIONS

Outcome measures related to wrist flexor activity and resistance to movement during extension are promising for spasticity assessment using the ADSMT. Further knowledge on reference values and practicality is necessary for this tool to become incorporated in the clinical setting.

Immunohistochemical, Histochemical and Radioassay Analysis of Nitric Oxide Synthase Immunoreactivity in the Lumbar and Sacral Dorsal Root Ganglia of the Dog

In this study, immunohistochemistry for neuronal nitric oxide synthase (bNOS-IR), nicotinamide adenine dinucleotide phosphate diaphorase histochemistry (NADPHd) and nitric oxide synthase radioassay were used to study the occurrence, number and distribution pattern of nitric oxide synthesizing neurons in the lumbar (L1-L7) and sacral (S1-S3) dorsal root ganglia of the dog. Nitric oxide synthase immunolabelling was present in a large number of small- (area <1,000 microm(2)) and medium-sized (area 1,000-2,000 microm(2)) as well as in a limited number of large-sized (area >2000 microm(2)) neurons. Although neuronal nitric oxide synthase immunolabelling and histochemical staining provided intense staining of multiple small- and medium-sized neurons in all lumbar and sacral dorsal root ganglia, immuno-labelled or histochemically stained somata exhibited little topographic distribution in individual dorsal root ganglia. Great heterogeneity was noticed in the immunolabelling of medium-sized nitric oxide synthase immunopositive neurons ranging from lightly immuno-labelled somata to heavily immunoreactive ones with completely obscured nuclei. Both staining procedures proved to be highly effective in visualizing intraganglionic fibers of various diameters. In general, the largest fibers revealed at the peripheral end of lumbar and sacral dorsal root ganglia were larger, 6.49-9.35 mum in diameter, while those running centrally and proceeding into the dorsal roots were about 30% reduced, ranging between 5.32 and 8.67 microm in diameter. Peripherally, the occurrence of nitric oxide synthase detected in axonal profiles, and confirmed histochemically, in the specimens of the femoral and sciatic nerves, is the first indication of the presence of nitric oxide synthase in the peripheral processes of somata located in L4-S2 dorsal root ganglia. Large and thin central nitric oxide synthase immunoreactive processes of L1-S3 dorsal root ganglion neurons segregate shortly before entering the spinal cord, the former making a massive medial bundle in the dorsal root accompanied by a slim lateral bundle penetrating Lissauer's tract. Quantitative assessment of the distribution of bNOS-IR and/or NADPHd-stained neurons showed a peculiar pattern in relation to spinal levels. Apparent incongruity was found in the total number of NADPHd-stained versus bNOS-IR neurons, demonstrating a clear prevalence of small bNOS-IR somata in all lumbar ganglia, while medium-sized NADPHd-stained somata clearly prevailed all along the rostrocaudal axis with a peak in L5 ganglion. While the number of small bNOS-IR neurons clearly outnumbered NADPHd-stained and NADPHd-unstained somata in S1-S3 ganglia, an inverse relation appeared comparing the total number of medium-sized NADPHd-stained and NADPHd-unstained somata compared with the number of moderate and intense bNOS-IR neurons. Densitometry of bNOS-IR and NADPHd-stained neurons in lumbar and sacral ganglia revealed two distinct subsets of densitometric profiles, one relating to more often found medium-sized bNOS immuno-labelled and the other, characteristic for moderately bNOS immunoreactive somata of the same cell size. Considerable differences in catalytic nitric oxide synthase activity, determined by conversion of [(3)H]arginine to [(3)H]citrulline were obtained in lumbosacral dorsal root ganglia all along the lumbosacral intumescence, the lowest (0.898+/- 0.2 dpm/min/microg protein) being in the L4 dorsal root ganglion and the highest (4.194+/-0.2 dpm/min/microg protein) in the S2 dorsal root ganglion.

Reflex contribution of spindle group Ia and II afferent input to leg muscle spasticity as revealed by tendon vibration in hemiparesis

OBJECTIVE

Foot dorsiflexion evokes a short- (SLR) and a medium-latency EMG response (MLR) in the soleus of standing subjects. SLR is mediated by spindle group Ia, while group II fibres contribute to MLR through an oligosynaptic circuit. We studied the effects of Achilles' tendon vibration on both responses in spastic patients to disclose any abnormal excitability of these pathways.

METHODS

SLR and MLR were evoked in 11 hemiparetics and 11 normals. The vibration-induced changes in both responses were correlated to the Ashworth score of the affected leg.

RESULTS

There were no differences between normals and patients in the size of control SLR or MLR. Vibration decreased SLR to 70% in normal subjects, but increased it to 110% in patients, in both affected and unaffected leg. Vibration did not affect MLR in normals, but increased it to 165% on the affected and 120% on the unaffected side of patients. Ashworth score was solely correlated with the degree of vibration-induced increase of MLR.

CONCLUSIONS

While the lack of inhibitory effect of vibration on SLR confirms a reduced inhibitibility of the monosynaptic reflex, the increased MLR indicates a disinhibition of group II pathway in patients, connected to the loss of descending control on group II interneurones. Spastic hypertonia depends on release of group II rather than group Ia reflex pathways.

SIGNIFICANCE

These findings give a neurophysiological support for the pharmacological treatment of spastic hypertonia and suggest a method for the assessment of its effects.

Evaluation of upper-limb spasticity after stroke: A clinical and neurophysiologic study

OBJECTIVES

To assess upper-limb spasticity after stroke by means of clinical and instrumental tools and to identify possible variables influencing the clinical pattern.

DESIGN

Descriptive measurement study of a consecutive sample of patients with upper-limb spasticity after stroke.

SETTING

Neurorehabilitation hospital.

PARTICIPANTS

Sixty-five poststroke hemiplegic patients.

INTERVENTIONS

Not applicable. Main outcome measures Upper-limb spasticity, as assessed clinically (Modified Ashworth Scale [MAS], articular goniometry) and neurophysiologically (maximum H-reflex [Hmax], maximum M response [Mmax], Hmax/Mmax ratio).

RESULTS

Poorer MAS scores were associated with lower passive range of motion (PROM) values at the wrist ( P =.01) and elbow ( P =.002). The flexor carpi radialis Hmax/Mmax ratio correlated directly with MAS scores at the wrist ( P =.005) and correlated inversely with PROM. The presence of pain in the fingers, wrist, and elbow was significantly associated only with lower PROM values at the wrist.

CONCLUSIONS

Upper-limb spasticity is involved in the development of articular PROM limitation after a stroke. Pain appears to be related to PROM reduction as well, but the exact causal relationship between these 2 factors is still unclear. The MAS and the Hmax/Mmax ratio correlated when evaluating poststroke spasticity; they characterize 2 different aspects of spasticity, clinical and neurophysiologic, respectively, and they could be used as an integrated approach to study and follow poststroke patients.

Differences in kinematic parameters and plantarflexor reflex responses between manual (Ashworth) and isokinetic mobilisations in spasticity assessment

OBJECTIVE

The purpose of this study was first to compare the kinematic parameters of imposed ankle mobilizations measured during Ashworth or isokinetic tests and, second, to better understand why the stretch reflex was more or less easily elicited by one method or the other.

METHODS

Passive dorsiflexions were applied on eight adult patients with plantarflexor spasticity in two conditions: (i) manually, using the Ashworth test where passive dorsiflexions were performed freely by seven rehabilitation clinicians, and (ii) instrumentally, using an isokinetic device (Cybex Norm) and a dorsiflexion velocity at 300 degrees /s. Mean values of initial ankle position, maximal angular velocity (theta;'(max)), maximal angular acceleration (theta;''(max)) and plantarflexor reflex responses obtained with each method were compared.

RESULTS

During the Ashworth test, all the patients presented reflex activities in the triceps surae while, during the isokinetic mobilization, only three out of the eight patients tested shown reflex responses. theta;'(max) values were significantly higher (P<0.05) in the manual test (308+/-80 degrees /s vs 216+/-5.5 degrees /s for the isokinetic test). The most marked difference concerned the theta;''(max) values (5046+/-2181 degrees /s(2) for the Ashworth test vs 819+/-18 degrees /s(2) for the isokinetic test, P<0.001). This parameter was significantly correlated with the mean rms-EMG values of the gastrocnemius lateralis (GL) and the soleus (SOL).

CONCLUSIONS

This study indicates that passive dorsiflexions imposed during Ashworth and isokinetic tests largely differ in velocity and acceleration, and the higher dynamic parameters evaluated during the Ashworth test could mainly explain that the stretch reflex was more easily elicited during this manual testing.

SIGNIFICANCE

If isokinetic devices offer numerous advantages in the assessment of passive resistance to spastic muscle stretch, they cannot be used to simulate the manual test.

Disruption of Coordination between Arm, Trunk, and Center of Pressure Displacement in Patients with Hemiparesis

To determine how arm movements influence postural sway in the upright position after stroke, interactions between arm, trunk, and center of pressure (CoP) displacements in the sagittal direction were investigated in participants with hemiparesis and healthy subjects. Participants swung both arms sagittally in either of 2 directions (in-phase, anti-phase) and at 2 speeds (preferred, fast) while standing on separate force plates. Variables measured included amplitude and frequency of arm swinging, shoulder and trunk range of motion, CoP displacements under each foot and of the whole body, and the relationships between the arm, trunk, and CoP displacements. CoP displacements under the non-paretic leg were greater than those under the paretic leg, which may in part be related to the larger amplitude of swinging of the non-paretic arm. CoP displacements under each foot were not related to arm swinging during in-phase swinging at the preferred speed in healthy subjects. When speed of arm swinging was increased, however, the CoP moved in a direction opposite to the arm movement. In contrast, in individuals with hemiparesis, CoPs and arms moved in the same direction for both speeds. During anti-phase swinging in healthy subjects, the trunk counterbalanced the arm movements, while in participants with hemiparesis, the trunk moved with the affected arm. Results show that stroke resulted in abnormal patterns of arm-trunk-CoP interactions that may be related to a greater involvement of the trunk in arm transport, an altered pattern of coordination between arm and CoP displacements, and an impaired ability of the damaged nervous system to adapt postural synergies to changes in movement velocity.

Evidence for transcortical reflex pathways in the lower limb of man

The existence of transcortical reflex pathways in the control of distal arm and hand muscles in man is now widely accepted. Much more controversy exists regarding a possible contribution of such reflexes to the control of leg muscles. It is often assumed that transcortical reflex pathways play no, or only a minor, role in the control of leg muscles. Transcortical reflex pathways according to this view are reserved for the control of the distal upper limb and are seen in close relation to the evolution of the primate hand. Here we review data, which provide evidence that transcortical reflexes do exist for lower limb muscles and may play a significant role in the control of at least some of these muscles. This evidence is based on animal research, recent experiments combining transcranial magnetic stimulation with peripheral electrical and mechanical stimulation in healthy subjects and neurological patients. We propose that afferent activity from muscle and skin may play a role in the regulation of bipedal gait through transcortical pathways.

Pathophysiology of chorea and bradykinesia in Huntington's disease

This article reviews the neurophysiological abnormalities described in Huntington's disease. Among the typical features of choreic movements are variable and random patterns of electromyographic (EMG) activity, including cocontraction of agonist and antagonist muscles. Studies of premotor potentials show that choreic movements are not preceded by a Bereitschaftspotential, therefore demonstrating that choreic movement is involuntary. Early cortical median-nerve somatosensory-evoked potentials have reduced amplitudes and the reduction correlates with reduced glucose consumption in the caudate nucleus. Long-latency stretch reflexes evoked in the small hand muscles are depressed. These findings may reflect failed thalamocortical relay of sensory information. In Huntington's disease, the R2 response of the blink reflex has prolonged latencies, diminished amplitudes, and greater habituation than normal. These abnormalities correlate with the severity of chorea in the face. Patients with Huntington's disease perform simple voluntary movements more slowly than normal subjects and with an abnormal triphasic EMG pattern. Bradykinesia is also present during their performance of simultaneous and sequential movements. Eye movements show abnormalities similar to those seen in arm movements. In Huntington's disease, arm movement execution is associated with reduced PET activation of cortical frontal areas. Studies using transcranial magnetic stimulation show that patients with Huntington's disease have normal corticospinal conduction but some patients have a prolonged cortical silent period. Bradykinesia results from degeneration of the basal ganglia output to the supplementary motor areas concerned with the initiation and maintenance of sequential movements. The coexisting hyperkinetic and hypokinetic movement disorders in patients with Huntington's disease probably reflect the involvement of direct and indirect pathways in the basal ganglia-thalamus-cortical motor circuit.

Antispastic effects of L-dopa

Antispastic effects of the noradrenaline and dopamine precursor l-3,4-dihydroxyphelanine (L-dopa) were investigated in 11 subjects in which exaggerated stretch reflexes developed after spinal cord injuries. The effects were evaluated from changes in the electromyographic (EMG) response of the quadriceps muscle during tendon jerks evoked by standardized taps over the patellar tendon, in clonus and in resistance to passive movements of the limb. After administration of L-dopa, EMG responses occurring 30-150 ms after the tendon tap decreased to about 50% of control, and clinical tests revealed a marked decrease in the resistance to muscle stretches and in the degree of clonus. The effects were maximal within about 1 h. The depressive actions of L-dopa are interpreted as being exerted primarily at the spinal level, since they were evoked in paraplegics and tetraplegics. The results support the previous hypothesis that group II muscle afferents contribute to.the exaggerated stretch reflex in spastic patients because L-dopa depresses transmission from group II but not from group I muscle afferents. They also indicate the possibility of using L-dopa in the treatment of spastic patients.

Impaired stretch reflex and joint torque modulation during spastic gait in multiple sclerosis patients

The modulation of the short latency stretch reflex of the soleus muscle during walking was investigated in seven spastic multiple sclerosis (MS) patients and nine healthy control subjects. Ankle joint stretches were applied by a system which can rotate that ankle joint in any phase of the step cycle during treadmill walking. The torque related to the muscle fibres contracting prior to the stretch and the passive tissues around the ankle joint were measured as the "non-reflex torque". At the same time the short latency stretch reflex-mediated EMG response was measured. The findings show that the stretch reflex modulation was impaired in spastic patients during walking. The stretch reflex modulation was quantified by a modulation index of an average 50% (range -5 to 100%) in the patients and 93% (78-100%) in the control subjects (P < 0.05). The passive stiffness of the ankle joint was at the same time increased in the patients (P < 0.05). It is proposed that the impaired modulation of the stretch reflex along with increased ankle joint stiffness contribute to the impaired walking ability in spastic MS patients.

Thought is action

It is difficult to chart “normal movements” in atypical populations, such as those with Parkinson's disease, because there is great variability in the pattern of motor changes, both within and between patients. However, the potential clinical implications of Latash & Anson's theme are positive and powerful.

When are adaptive motor patterns nonadaptive?

The assumption that adaptive changes in motor patterns are optimal is questioned. Instances are cited where alteration of the adaptive motor patterns may be warranted. Other issues discussed are: (1) the relationship between central nervous system (CNS) priorities and the individual's priorities, (2) the use of cognitive bypass strategies by impaired individuals, and (3) conceiving CNS priorities as coordinative rules.

Dynamic similarities in action systems

Latash & Anson's contention that movement patterns that are different from those typically observed in persons without impairments should not be considered abnormal and usually should not be corrected is consistent with Davis & Burton's Ecological Task Analysis (ETA). Extending from the ETA concept of performer-scaled performance measures, the use of Froude numbers may offer insight into the global dynamics of a person's action system.

On optimality and movement disorders: A dynamic systems perspective

The argument that disordered or changed motor patterns can be adaptive or optimal given the constraints imposed is supported. Two major points of criticism are made, concerning the perceived superstates of the primary disorder and the absence of a systematic approach to identifying this adaptivity and optimality. We have tried to give the general outlines of such an approach to disordered movements from a dynamic systems perspective.

Bradykinesia in Parkinson's disease and cocontraction activity in dystonia are unlikely to be due to adaptive changes in the CNS

Latash & Anson's explanation of bradykinesia in patients with Parkinson's disease and cocontraction in dystonic patients is intriguing. However, the proposed adaptive changes in the central nervous system do not fit well with both clinical and experimental evidence of motor impairment in these patients. In particular, we question the explanation of: (1) the role of postural reactions and spatial accuracy in bradykinesia, (2) certain abnormalities during the execution of sequential and simultaneous movements, (3) the sudden changes in mobility (ON and OFF) of Parkinsonian patients, and (4) the meaning of reflex circuitry changes in dystonia.

Evaluation of central commands: Toward a theoretical basis for rehabilitation

The commentary focuses on the need for motor control modeling as a rationale for rehabilitation. We give examples in a bimanual unloading task and examine the potential consequences for recovery in patients with cerebral lesions. Hierarchical models of motor control lead to a distinction between “task optimization” and “motor optimization” and to a qualifier on Latash & Anson's “hands-off” position.

Toward peaceful coexistence of adaptive central strategies and medical professionals

We start with a number of philosophical and theoretical issues related to motor control, proceed through a spectrum of problems related to the role of adaptive changes in the central nervous system (CNS) in response to a primary disorder, and end with tentative practical recommendations. We consider the hierarchical and dynamic approaches to motor control not as incompatible alternatives but as ways of approaching two equally important issues, those of control and coordination. Professionals working in the area of physical therapy and rehabilitation should make use of the adaptive abilities of the CNS, identify goals, provide tools, and allow the CNS to develop optimal strategies. Therapists should intervene if they suspect that the CNS settles down in a local rather than a global optimum because of such factors as pain or the lack of a long-term predictive ability. Adaptive changes within the CNS may be important not only in pathologies but also in cases of specialized training, normal growth, and normal ageing.

Rehabilitation promotes functional movement in atypical populations

The suggestion that movement disorders exhibited by people with central nervous system (CNS) dysfunction should be considered normal and therefore not rehabilitated is rejected from three standpoints: (1) the CNS does not always select the best movement patterns for optimal long term outcome, (2) there is literature demonstrating that rehabilitation enhances motor function and independence, and (3) there exists a capacity for motor recovery and motor skill learning following brain damage.

Posturo-kinetic capacity in the disabled

“Normal movements” in atypical populations address the question of postural control: Voluntary movement is a perturbation of body balance and cannot be executed without a convenient counterperturbation. Despite a change in the postural program in relation to the impairment (Parkinson's disease, paraplegia), the performance level is decreased. Movements are not “normal,” owing to a reduction in posturokinetic capacity.

What is the appropriate criterion for therapeutic intervention in the motor domain?

Observations are made on Latash & Anson's theme that changed motor patterns should not be viewed as pathological. Normality in motor control might be characterised in terms of qualitative differences in control mechanisms rather than differences in movement patterns. Understanding of the concepts implicit in instructions to subjects should be confirmed. Principles of energy expenditure in atypical movements are outlined. If restoration of normality is not adopted as a criterion for therapeutic intervention, what might be proposed as an alternative?

Altered bilateral muscle synergies after stroke

Using movement disorders to understand the central nervous system's goals for motor behaviour may be easier in neurological models with a focal lesion of sudden onset, because the distinction between primary and adaptive changes may be clearer than in slowly progressive and/or diffuse neurological disease.

What makes a population atypical–priorities or constraints?

Priorities for movement reflect constraints deriving from the motor system, task goals, and physical environment. Atypical and typical populations alike set and reset priorities in response to constraints, and they do so at many processing loci and time scales. Efforts to understand what is atypical about a population should focus first on the constraints it encounters.

Anticipatory postural mechanisms: Some evidence and methodological implications

To understand the basic priorities of the central nervous system in human motor control, neurophysiological parameters are important. Certain H-reflex methods related to anticipatory postural control are particularly useful and may have therapeutic implications.

The concept of “normal” movement and its consequences for therapy

The guideline for therapy should be the improvement of the individual's functionality, not the acquisition of the ill-defined “goldstandard” of normal movement. However, Latash & Anson's suggestion that only primary causes of dysfunction should be treated is problematic for two reasons: First, the distinction between genuine and adaptive changes in motor performance is not always possible, and second, adaptive changes do not necessarily improve motor function, but may actually be detrimental to the system's performance.

Towards functional movement: Implications for research and therapy

Researchers and clinicians have different goals and constraints in trying to understand and treat movement disorders. Research on primary and secondary aspects of disorders may lead to effective treatment aimed at restoring functional movements even if the primary disorder cannot be cured. Similarly, movement patterns may be maladaptive and hence need therapeutic intervention to restore functional movement skills.

Frames of reference and normal movement

Latash & Anson propose that so-called abnormal movements may be stable and adaptive coordination and control solutions to task goals in action. Their interpretation of this established viewpoint is confused throughout in the persistent crossing of frames of reference, both in the description of movement and action and the proposed theory for motor control.

Adaptive changes in postural reactions after unilateral leg amputation

Changes in anticipatory postural adjustment following below-the-knee amputation may be considered as adaptive for reacquiring balance control.

How functional are atypical motor patterns?

Latash & Anson are commended for pointing out that investigators of atypical motor performance have too often failed to recognize the adaptive nature of many atypical movement characteristics. However, the authors' assumption that atypical motor patterns can be considered “normal” and, by implication, that it is futile to attempt to teach different patterns to patients that may be more functional, is criticized.