Performance of a bimanual load-lifting task by parkinsonian patients.

Normal subjects and Parkinsonian patients performed a bimanual load lifting task. In this task, one "postural" forearm, held in a horizontal position while supporting a 1 kg weight, was unloaded either by the experimenter's hand (imposed unloading) or by the subject's other hand in response to a tone burst (voluntary unloading). The variables recorded were reaction time (RT: time interval between the tone and beginning of unloading) and movement time (MT: duration of the change in force measured by a force platform on the "postural" forearm). Elbow angle changes were also measured with a potentiometer. The EMG activity from brachioradialis of the "postural" arm and that from the biceps of the "active" arm were recorded. The Parkinsonian patients showed an increase in both RT and MT and an impairment of the co-ordination between movement and posture which was reflected in an increase in amplitude of the elbow rotation after voluntary unloading. Moreover, the decrease in EMG activity in the brachioradialis of the postural arm during unloading was less in Parkinsonian patients than in the normal group. This disorder of postural command was often accompanied by a lack of anticipatory EMG changes. Comparison between treated and non-treated patients showed that dopamine agonists brought about recovery of both RT and MT but did not improve postural co-ordination. The co-ordination was less impaired when the voluntary unloading was performed by the preferred hand. Several hypotheses are discussed concerning the mechanism underlying this impaired co-ordination.     

Flexors activity of affected upper extremity in stroke patients during different standing conditions and their relationships with clinical scales: a cross-sectional study

ABSTRACT

Purpose: To explore the flexors activity of affected upper extremity in stroke patients during different standing conditions and their relationships with clinical scales.

Materials and methods: Sixteen stroke patientswere recruited, all subjects stood on balance equipment with four different standing postures. The electromyogram (EMG) simultaneously recorded the muscle activity of bilateral biceps brachii, triceps brachii, flexor carpi radialis and extensor carpi radialis and their integrated electromyogram were figured out the contraction rate of elbow flexors(biceps brachii/triceps brachii) and wrist flexors(flexor carpi radialis/extensor carpi radialis). All subjects were assessed using Fugl-Meyer Assessment of the Upper Extremity (FMA-UE), Berg Balance Scale (BBS), Barthel Index (BI) and Modified Ashworth Scale (MAS).

Results: The contraction rate of affected elbow flexors in the condition of feet together on soft surface was significantly higher than that in the condition of feet separatedon hard surface (P < 0.05). The contraction rate of affected elbow flexors in four standing conditions tended to increase, all the values of which were greater than numerical value1. The difference in the contraction rate of elbow flexor between the affected side and the unaffected side was statistically significant (P < 0.05). No correlation was observed between the contraction rate of the elbow flexor and the results of MAS, FMA-UE, BBS and BI regardless of the standing conditions.

Conclusions: The contraction rates of elbowflexor in the affected side increase with the difficulty in different standing postures,and it may be a good index to reflect the changes of muscle tone in postural control.     

Feedforward postural adjustments in a simple two-joint synergy in patients with Parkinson's disease

Patients with Parkinson's disease, age-matched controls and young control subjects performed discrete elbow or wrist movements in a sagittal plane under the instruction to move one of the joints “as fast as possible.” Relative stability of the other, postural joint was comparable in all 3 groups, while movement time was the highest in the patients and the lowest in young controls. Typically, EMG patterns in both muscle pairs acting at the joints demonstrated a commonly observed “tri-phasic” pattern. A cross-correlation analysis of the EMGs confirmed virtually simultaneous bursts in the wrist and elbow flexors and in the wrist and elbow extensors. In all 3 groups, there were no signs of anticipatory activation of postural muscles in about 90% of movements. We consider postural anticipation not a separate process, but a separate peripheral pattern of a single control process that may involve a number of joints and muscles. We conclude that the postural deficits in Parkinson's disease are not related to a basic deficit in the ability to generate feedforward postural adjustments but to other factors that may include the specificity of maintaining the vertical posture in the field of gravity.     

Reflex responses of paraspinal muscles to tapping

Erector spinae reflex studies in healthy subjects revealed two responses: a 12·0±1·6 ms latency, oligosynaptic response, and a 30 to 50 ms latency response with polysynaptic reflex characteristics. There was a silent period after the first and second responses. The effect of limb position, trunk, neck, postural changes, Jendrassik manoeuvre and vibration on both responses were also evaluated.     

Modifiability of abnormal isometric elbow and shoulder joint torque coupling after stroke

Unlike individuals with mild stroke, individuals with severe stroke are constrained to stereotypical movement patterns attributed to abnormal coupling of shoulder abductors with elbow flexors, and shoulder adductors with elbow extensors. Whether abnormal muscle coactivation and associated joint torque patterns can be changed in this population is important to determine given that it bears on the development of effective rehabilitation interventions. Eight subjects participated in a protocol that was designed to reduce abnormal elbow/shoulder joint torque coupling by training them to generate combinations of isometric elbow and shoulder joint torques away from the constraining patterns. After training, subjects demonstrated a significant reduction in abnormal torque coupling and a subsequent significant increase in ability to generate torque patterns away from the abnormal pattern. We suggest the rapid time-course of these changes reflects a residual capacity of the central nervous system to adapt to a novel behavioral training environment.     

Electromyographic activity patterns of ankle flexor and extensor muscles during spontaneous and L-DOPA-induced locomotion in freely moving neonatal rats

In rats, hindlimb postural and locomotor functions mature during the first 3 postnatal weeks. Previous evidence indicates that maturation of descending monoaminergic pathways is important for the postnatal emergence of locomotion with adequate antigravity postural support. Here we have studied the effect of the monoamine precursor L-DOPA on locomotor activity in freely moving postnatal rats (7-9 days old) using electromyographic recordings from ankle extensor (soleus) and flexor (tibialis anterior or extensor digitorum longus) muscles. Before pharmacological treatment, both muscles were usually silent at rest, and during spontaneous movements there was a high degree of coactivation between the two antagonists. This was due to a longer electromyographic (EMG) burst duration in flexors, which partly overlapped with the extensor burst. L-DOPA administration (150 mg/kg) resulted in a marked increase in postural tonic EMG activity in extensors which appeared gradually within 10 min after injection and was sufficient for the pups to maintain a standing posture with the pelvis raised above ground. Thereafter, episodes of locomotion characterized by rhythmic reciprocal bursts of EMG activity in flexor and extensor muscles were seen. The L-DOPA-induced rhythmic EMG pattern was also seen in postnatal rats subjected to a midthoracic spinal cord transection, indicating that the effect of L-DOPA on motor coordination is exerted primarily at the level of the spinal pattern generator. Analysis of EMG burst characteristics showed that the pattern of L-DOPA-induced locomotion in both intact and spinalized postnatal rats resembled in some respects that observed in adults during spontaneous locomotion. The appearance of reciprocal activation during L-DOPA-induced locomotion in neonates was primarily due to a shortening of the EMG burst duration in flexors, which reduced the degree of antagonist coactivation. These results show that the spinal cord has the potential to produce coordinated overground locomotion several days before such movements are normally expressed in the freely moving animal.     

Functional organization of the motor process underlying the transition from movement to posture

In these experiments we studied the organization of the neural pattern of activity underlying the achievement and maintenance of final limb position.The examination of the alpha motoneuronal inputs to flexors and extensors acting on the elbow and writst joints revealed that a change from one posture to another required a modulation of both flexors and extensors. For a given position, the final EMG level of flexors and extensors is more variable than the ratio between the alpha neuronal activity of these two antagonistic muscles. Further, the ratio was not significantly affected by the direction, amplitude or velocity of the movement. These results indicate that the final positioncould be coded in the central nervous system (CNS) as the ratio of activity in antagonistic muscles acting on a joint.     

Coactivation of the elbow antagonist muscles is not affected by the speed of movement in isokinetic exercise

Since muscle coactivation increases the stiffness and stability of a joint, greater coactivation is likely during faster than slower movements. Very few studies, though, have been conducted to verify this hypothesis. Moreover, a large number of studies have examined coactivation of muscles surrounding the knee joint whereas there are few reports on the elbow joint. The aim of this study was therefore to compare the antagonist activation of the elbow flexors and extensors during isokinetic concentric exercises and to investigate the influence of angular velocity on their activation. Twelve men participated in the study. The surface electromyographic signals (sEMG) were recorded from the biceps brachii (BB) and triceps brachii (TB) muscles during three maximal voluntary isometric contractions (MVC) of elbow flexors and extensors and a set of three maximal elbow flexions and extensions each at 15 degrees, 30 degrees , 60 degrees, 120 degrees, 180 degrees, and 240 degrees.s(-1). Normalized root mean square (RMS) of sEMG was calculated during the isokinetic phase of movement as an index of sEMG amplitude. During elbow flexion, the antagonist activation of BB averaged 16.2% lower than TB, and this difference was statistically significant at all angular velocities. The normalized RMS values ranged from 26.0% +/- 19.0 at MVC to 37.8% +/- 13.9 at 240 degrees.s(-1) for antagonist TB activation, and from 5.7% +/- 5.2 at MVC to 18.9% +/- 8.6 at 240 degrees.s(-1) for antagonist BB activation. No influence of angular velocity on agonist and antagonist activity was found. Moreover, flexion and extension torques were both strongly affected by the amount of antagonist activation. The functional specialization of the two muscle groups could be responsible for the different levels of antagonist activation. The frequent use of BB, which is not assisted by gravity during daily activities, could lead to reduced coactivation due to a better functioning of the control system based upon reciprocal innervation. These findings may have significant implications in the design of rehabilitation programs directed to the elbow joint.     

A comparison of the effects of concentric versus eccentric exercise on force and position sense at the human elbow joint

It is generally accepted that our sense of limb position and movement is provided, in part, by signals from muscle spindles, while the sense of muscle force derives from signals in tendon organs. Experiments are described here, using human subjects, in which the effects of eccentric and concentric exercise of elbow flexor muscles are compared on the sense of forearm position and the sense of tension in elbow flexors. Subjects were required to compress a preloaded spring with one arm, carrying out a concentric contraction in elbow flexors, then flexors of the other arm released the spring from compression and thereby carried out an eccentric contraction. The force of the spring was adjusted to be 20% maximum voluntary contraction (MVC), and each subject carried out a minimum of 120 contractions. Position sense was measured in blindfolded subjects by placing one forearm at a set angle and asking subjects to match it by positioning the other arm. Over 4 days postexercise, subjects placed the eccentrically exercised arms in a more extended position than the concentrically exercised arm suggesting that they thought the muscle was shorter than it actually was. In a force-matching task, subjects systematically undershot the target 10% MVC with their eccentrically exercised arm. Since it is known that eccentric exercise is associated with damage to muscle fibres, it is postulated that this leads to a disturbance of muscle receptors, the muscle spindles and tendon organs.     

The effects of muscle conditioning on movement detection thresholds at the human forearm

We have used the muscle history dependence of the sensitivity of muscle spindles to stretch, to provide evidence for their contribution to kinaesthesia, the sense of position and movement. Stretch sensitivity is altered depending on whether or not slack has been introduced in intrafusal fibres [13]. At the human elbow joint detection threshold was measured to passive movements applied at different speeds to the forearm after a conditioning co-contraction of muscles of the upper arm, with the arm held either flexed (‘hold short’) or extended (‘hold long’). Test measurements were made with the elbow joint at 90°. For the three speeds of movement, 2°s⁻¹, 0.2°s^{− 1} and 0.02°s⁻¹, after ‘hold short’ conditioning thresholds were lower for movements into extension, after ‘hold long’ conditioning they were lower for movements into flexion. It is concluded that when muscle conditioning introduces slack in the intrafusal fibres of muscle spindles, this must be taken up by the test movements before they can be detected by the subject. It means that whenever detection thresholds to passive movements are measured at a joint, the contraction history of the muscles acting at that joint must be taken into account.     

Widespread short-latency stretch reflexes and their modulation during stumbling over obstacles

The present study investigated whether short-latency stretch reflexes are present during human stumbling reactions. While subjects walked on a treadmill, the forward sway of the foot was unexpectedly obstructed with an obstacle. All subjects showed reflex responses with average latencies of 34–42 ms in both the upper and the lower leg flexors and extensors of the obstructed leg. The amplitudes of these responses depended on the phase in the step cycle and were not strictly related to either the background activity of the corresponding muscles or variations in the perturbation. Hence, mechanisms at a premotoneuronal level might play a role in the active phase-dependent control of these responses. The coactivation of antagonists as well as the lack of obvious kinesiologic consequences following the responses suggest that the short-latency responses may generate joint stiffness. This may be a first line of defense in preparing for the functional reaction, which is generated by longer latency responses, in order to take appropriate action concerning the obstacle.     

Initial center of pressure position prior to anticipatory postural adjustments during gait initiation in people with Parkinson's disease with freezing of gait

IntroductionFreezing of gait (FOG) in Parkinson's disease (PD) is associated with an altered posture during quiet stance as well as an impaired preparation and execution of the gait initiation process. We aimed to investigate whether an altered initial posture impacts anticipatory postural adjustments (APAs) and first-step execution during gait initiation in people with PD with FOG (PD + FOG).MethodsTwenty-seven PD+FOG, 30 PD patients without FOG and 27 age-matched healthy controls performed self-generated gait initiation. Initial mean center of pressure (COP) position prior to APA onset, characteristics of APAs and features of first-step execution were investigated.ResultsContrarily to controls, PD patients showed a COP that was initially positioned more towards the stance leg (p = 0.007). Moreover, significantly smaller backward COP shift, longer duration of swing-foot unloading phase, and lower first-step length and velocity characterized PD+FOG compared to controls. While size and duration of backward COP shift during APA and lateral COP shift during the unloading phase were main predictors of first-step length and velocity in all groups, the medio-lateral shift of the initial COP position in PD+FOG was a main predictor of first-step execution (β = −0.191, p = 0.001 for velocity).ConclusionIn PD+FOG, the more the COP was initially positioned towards the stance foot, the slower and shorter the first step. The initial medio-lateral COP position may be a compensatory strategy to address postural instability of PD+FOG. A specific training regarding postural control prior to gait preparation and execution could improve functional mobility in PD+FOG.     

Intra-rater reliability of the modified Tardieu scale to quantify spasticity in elbow flexors and ankle plantar flexors in adult stroke subjects

Objectives:

The purpose of this study was to investigate Iintra-rater reliability of the Modified Tardieu Scale (MTS) in elbow flexors and ankle plantar flexors in adult subjects with stroke.

Materials and Methods:

A total of 91 subjects with stroke participated in this test-retest study. Intra-rater reliability of the MTS was investigated by a qualified and trained physiotherapist for elbow flexors and ankle plantar flexors in two sessions. A rater was one who performed the procedure and an observer only records the angles so that the rater was blinded to findings. Outcome measures in this study were measurable components of MTS, which are angle of muscle reaction (R1), passive range of motion (R2), dynamic component (R2-R1), and quality of muscle reaction (grade 0 – 4) termed as MTS score.

Results:

Intra-rater reliability of MTS was very good for R1, R2, R2-R1, and MTS score (ICC > 0.85, P<0.0001) across two sessions in elbow flexors and ankle plantar flexors.

Conclusion:

MTS is a reliable clinical tool for measurement of spasticity in the elbow flexors and ankle plantar flexors in adult subjects with stroke.     

Changes in short and long latency stretch responses during the transition from posture to movement

Experiments were performed in 18 normal subjects to estimate the time course of changes in the gains of pathways mediating short- and long-latency responses to muscle stretch during the transition from a maintained posture against a steady load to a rapid ballistic movement. Subjects were instructed to rapidly flex or extend their forearm in response to a tone from an initial position of 90° of elbow flexion. Torque pulses stretching the biceps muscle were applied to the forearm at 8 different times before and after the signal to initiate the movement, and the gains of short- and long-latency pathways were estimated from averages of rectified biceps EMG activity for 20 trials at each time interval between the onsets of the tone and torque pulse.The findings demonstrate that changes in the magnitude of long-latency responses (M2, M3) occur during the period between the onset of the auditory signal and the voluntary motor response. However, the magnitude of the short-latency response (M1) remains unchanged until after the onset of voluntary motor activity. The differences in the timing of short- and long-latency stretch responses suggests that activity in long-latency pathways may play an important preparatory role in facilitating the transition from posture to movement.     

Ontogeny of altered synaptic function in a rat model of chronic temporal lobe epilepsy

In the limbic status model of chronic temporal lobe epilepsy, hippocampal stimulation induces acute status epilepticus in rats; recurrent, spontaneous seizures develop following an asymptomatic silent period lasting several weeks. Previous work has shown increased excitability and decreased inhibition in CA1 pyramidal neurons in chronically epileptic animals. To determine the relationship of altered cellular responses to seizure onset, in vitro intracellular recording was used to follow the evolution of changes in synaptic physiology occurring during the seizure-free silent period. Pyramidal cells displayed increasing epileptiform activity throughout the period investigated, 3–14 days following status; the mean number of evoked action potentials from 1.1±0.05 in control cells to 2.4±0.4 early (3 days after status) and 4.3±0.7 late (14 days) in the silent period. Monosynaptic inhibitory postsynaptic potentials mediated by γ-aminobutyric acid-A receptors in silent period cells differed markedly from controls. Area, rise time, and duration of these potentials decreased by 40–60% within 3 days following status and to values commensurate with chronically epileptic animals in 7 to 10 days. γ-Aminobutyric acid-B receptor-mediated IPSPs diminished more gradually in the silent period, reaching a minimum at day 14. In contrast, presynaptic γ-aminobutyric acid-B receptor function showed maximum impairment 3 days after status. The benzodiazepine type 1 receptor agonist zolpidem reduced hyperexcitability in both silent period and chronically epileptic cells, but was more effective at unmasking the underlying IPSP in silent period neurons. The results indicate that changes in different components of pyramidal cell inhibitory synaptic physiology associated with chronic epilepsy in this model evolve individually at different rates, but are all complete before seizure onset. Although the results do not imply causality, they do suggest that the development of physiological changes in CA1 pyramidal cells may contribute to the lag period preceding the onset of chronic seizures.     

Changes in corticomotor excitation and inhibition during prolonged submaximal muscle contractions

Changes in motor evoked potential (MEP) amplitude, post-MEP silent period duration, and interpolated twitch torque were measured using transcranial magnetic (TMS) and electrical (TES) stimulation during a 20% maximum voluntary contraction of the elbow flexors sustained to exhaustion. TMS- and TES-induced MEP amplitude increased progressively over the contraction period up until the point of exhaustion. The TMS-induced silent period was prolonged only during the second half of the contraction period, the time course being different from that of the MEP responses, whereas the TES-induced silent period did not change. The findings indicate that corticomotor excitability increases during a sustained submaximal voluntary contraction and that, as fatigue develops, there is a progressive buildup of intracortical inhibition. This may represent a mechanism whereby corticomotor output is maintained at an appropriate level to preserve optimal motor unit firing frequencies during a fatiguing contraction. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20:1158–1166, 1997     

Deficits in corticospinal control of stretch reflex thresholds in stroke: Implications for motor impairment

ObjectivesThe corticospinal system (CS) regulates muscle activation through shifts in muscle-level tonic stretch-reflex thresholds (TSRT). This ability is impaired in stroke and contributes to sensorimotor impairments such as spasticity. We determined the role of CS in elbow flexor activity regulation in healthy and post-stroke subjects. We also determined whether CS modulation deficits were related to sensorimotor impairment intensity in post-stroke individuals.MethodsSeventeen healthy (59.8 ± 12.2 yr) and 27 stroke subjects (58.7 ± 10.1 yr) had transcranial magnetic stimulation (TMS) applied over the primary motor cortex (M1) flexor representation to elicit motor-evoked potentials (MEPs) in elbow flexors in different angular positions. In a subset of post-stroke subjects (n = 12), flexor TSRTs were measured in passive and active conditions, and TSRT modulation was determined.ResultsPosition-related MEP amplitude modulation was similar in healthy and mild stroke subjects, while subjects with more severe stroke exhibited less consistent modulation. MEP modulation in stroke was related to clinical upper limb motor impairment, spasticity, and the ability to modulate TSRTs between passive and active elbow movements.ConclusionsCS output was closely related to TSRT modulation. Impairments in TSRT regulation may underlie motor deficits in moderate-to-severe post-stroke individuals.SignificanceTranslation of these neurophysiological findings to clinical applications may enhance post-stroke motor recovery.     

Independent control of voluntary movements and associated anticipatory postural responses in a bimanual task.

OBJECTIVE: When one hand loads the other arm, EMG responses in the stationary arm anticipate the load. This study used transcranial magnetic stimulation over each hemisphere to clarify the relationship between a voluntary movement on one side and the anticipatory postural response on the other. METHODS: Subjects (n = 7) performed elbow flexion movements of one arm as a reaction-time task. Because subjects' arms were linked, flexion about one elbow resulted in extension force about the other, and an anticipatory response occurred in those elbow flexor muscles. After the 'go' signal and before the predicted onset of EMG, transcranial magnetic stimuli were delivered over one or other motor cortex. RESULTS: Stimulation contralateral to the reaction-time movement delayed the onset of voluntary EMG (46 ms in right biceps, 77 ms left) but did not alter the onset of EMG in the postural arm. Stimulation contralateral to the anticipatory postural response delayed only the postural EMG (left 96 ms, right 52 ms). CONCLUSIONS: Thus, the associated voluntary and postural responses were delayed independently by stimuli over their respective contralateral motor cortex. SIGNIFICANCE: This suggests that, although timing of responses may be linked by an initial signal, the response from each motor cortex develops independently.     

Anticipatory postural adjustments in a bimanual load‐lifting task in children with developmental coordination disorder

Aim Postural control is a fundamental component of action in which deficits have been shown to contribute to motor difficulties in children with developmental coordination disorder (DCD). The purpose of this study was to examine anticipatory postural adjustments (APAs) in children with DCD in a bimanual load‐lifting task. Method Sixteen children with reported motor problems (two females, 14 males; mean age 9y; SD 2y) and 16 typically developing, age‐matched children (six females, 10 males; mean age 9y; SD 2y) took part in the study. The task required the children to maintain a stable elbow angle, despite imposed or voluntary unloading of the forearm. APAs were assessed using electromyography and kinematics analysis. Results Although children with DCD could compensate for the consequences of unloading, the results demonstrated that APAs were less efficient in children with DCD than in typically developing children. A positive and significant coefficient of regression between the flexor inhibition latency and the postural stabilization was only found in typically developing children. Interpretation The impaired fine‐tuning of the muscle contribution and the poor stabilization performances demonstrate poor predictive modelling in DCD.     

Electromyogram coactivation patterns of the elbow antagonist muscles during slow isokinetic movement

Electromyograms from the flexor and extensor muscles of normal human elbows were simultaneously recorded during maximal-effort isokinetic movement at 15 degrees/s over the joint's full range of motion. The antagonist electromyogram was normalized with respect to its electromyogram when acting as agonist at maximal effort and plotted as a function of joint angle. The coactivation patterns were nearly inversely related to each muscle's moment arm variations with joint angle, suggesting that the antagonist may have generated constant opposing torque throughout the movement. Female subjects had a statistically significant higher coactivation level of the flexors and extensors compared with that of males, reflecting the increase in joint efficiency associated with daily muscular activity which is manifested by reduction in antagonist activity. The functional role of antagonist coactivation in augmenting ligament stabilizing functions, equalizing the pressure distribution over the articular surface, and regulating the joint's mechanical impedance are discussed. The source of such coactivation appears to be due to proprioceptive and joint kinesthetic afferent input in addition to possible direct common drive.