Reduction In Electromyographic Activity Research Articles

Effect of Botulinum Toxin Injection on EMG Activity and Bite Force in Masticatory Muscle Disorder: A Randomized Clinical Trial.

Botulinum toxin type A (BoNT-A) is increasingly used in treating masticatory muscle pain disorder; however, safe doses and reinjection intervals still need to be established. The purpose of this randomized clinical trial was to evaluate the degree and duration of the impairment of masticatory muscle performance. Fifty-seven subjects were randomly divided into two groups: one of which received BoNT-A first (n = 28) while the other received saline first (n = 29), with the cross-over being in week 16, and a total follow-up period of 32 weeks. A total dose of 50 U of BoNT-A was injected in the masseter and temporal muscles bilaterally. Electromyographic (EMG) activity and bite forces were assessed. A significant reduction in EMG activity was observed up to week 18 (p ≤ 001), with total recovery at week 33. A significant reduction in maximum bite force was observed up to week 11 (p ≤ 005), with total recovery at week 25. In conclusion, when treating masticatory muscle pain disorder with 50 U of BoNT-A, a reinjection interval of 33 weeks can be considered safe since the recovery of muscle function occurs by that time.

Longitudinal changes in electromyographic activity of masseter and anterior temporalis muscles before and after alloplastic total joint replacement in patients with temporomandibular ankylosis: a prospective study

The purpose of the study was to evaluate the longitudinal changes in electromyographic (EMG) activity of the masseter and temporalis muscles before and after temporomandibular joint (TMJ) total joint replacement (TJR) in ankylosis patients. A prospective longitudinal study was designed on patients undergoing unilateral or bilateral TMJ-TJR. EMG activity at rest and maximal voluntary contraction (MVC) was recorded for the muscles preoperatively (T0), and at one-week (T1) and six-month (T2) follow up. The study sample was composed of 10 (male: female 2.3:1) patients undergoing TMJ-TJR. The number of unilateral and bilateral cases was three and seven, respectively. In both unilateral and bilateral cases a statistically significant reduction in EMG activity of the masseter and anterior temporalis muscles was observed at T1. At T2, EMG activity of the muscles was found to be approaching the preoperative value. In unilateral cases, when the affected side at T0, T1, and T2 was compared with T0 for the unaffected side, statistically significant differences were seen for the masseter. In the case of the temporalis, similar results were seen except at T2 for the postural rest position. The results indicate that re-attachment of the masseter and temporalis muscles occurs progressively post TMJ-TJR.

Robust Torque Predictions From Electromyography Across Multiple Levels of Active Exoskeleton Assistance Despite Non-linear Reorganization of Locomotor Output.

Robotic exoskeletons can assist humans with walking by providing supplemental torque in proportion to the user's joint torque. Electromyographic (EMG) control algorithms can estimate a user's joint torque directly using real-time EMG recordings from the muscles that generate the torque. However, EMG signals change as a result of supplemental torque from an exoskeleton, resulting in unreliable estimates of the user's joint torque during active exoskeleton assistance. Here, we present an EMG control framework for robotic exoskeletons that provides consistent joint torque predictions across varying levels of assistance. Experiments with three healthy human participants showed that using diverse training data (from different levels of assistance) enables robust torque predictions, and that a convolutional neural network (CNN), but not a Kalman filter (KF), can capture the non-linear transformations in EMG due to exoskeleton assistance. With diverse training, the CNN could reliably predict joint torque from EMG during zero, low, medium, and high levels of exoskeleton assistance [root mean squared error (RMSE) below 0.096 N-m/kg]. In contrast, without diverse training, RMSE of the CNN ranged from 0.106 to 0.144 N-m/kg. RMSE of the KF ranged from 0.137 to 0.182 N-m/kg without diverse training, and did not improve with diverse training. When participant time is limited, training data should emphasize the highest levels of assistance first and utilize at least 35 full gait cycles for the CNN. The results presented here constitute an important step toward adaptive and robust human augmentation via robotic exoskeletons. This work also highlights the non-linear reorganization of locomotor output when using assistive exoskeletons; significant reductions in EMG activity were observed for the soleus and gastrocnemius, and a significant increase in EMG activity was observed for the erector spinae. Control algorithms that can accommodate spatiotemporal changes in muscle activity have broad implications for exoskeleton-based assistance and rehabilitation following neuromuscular injury.

Effects of Kinesio Taping on scapular kinematics and electromyographic activity in subjects with shoulder impingement syndrome

ObjectiveTo investigate the effects of Kinesio Taping® (KT) on scapular kinematics and electromyographic (EMG) activity in subjects with shoulder impingement syndrome (SIS). MethodsTwenty subjects with a diagnosis of SIS performed abduction, scaption, and flexion movements in two load conditions: (1) without load and (2) holding a dumbbell. The same movements were evaluated again with the use of KT over the deltoid muscle with a 20% tension. Scapular kinematics data of the shoulder complex were captured with BTS SMART-DX at a frequency rate of 100 Hz. EMG activity was evaluated for the upper trapezius, lower trapezius, middle deltoid, and serratus anterior muscles with BTS FREE EMG 1000 at a frequency rate of 1000 Hz. The root mean square values normalized by the maximal voluntary contraction and the peak values of upward rotation, internal rotation, and posterior tilt were compared with the KT conditions through repeated-measures ANOVA (α = 0.05) using SPSS software. ResultsNo significant differences between KT conditions were found for scapular kinematics (p > 0.05). For EMG activity, a reduction in the lower trapezius was found (p < 0.05) during abduction with load (p < 0.05) and elevation without load (p < 0.05). ConclusionsAccording to the results of this study, it was not possible to verify changes in scapular kinematics in subjects with SIS. However, a reduction in EMG activity was observed for the lower trapezius muscle. Therefore, caution should be taken in prescribing KT for SIS subjects, who already have a reduction in EMG activity in this muscle, as KT may have an adverse effect.

Acute changes in neuromuscular activity in vertical jump and flexibility after exposure to whole body vibration.

This study was aimed to investigate the neuromuscular activity after 10 minutes of exposure to a whole body vibration (WBV) session.Twenty male young adults (24.8 ± 2.5 year olds) were randomized and divided into 2 groups: the vibration group (VG) was exposed to 10 minutes of WBV at 35 Hz; performed 10 minutes of WBV at 35 Hz (displacement = 5 mm; magnitude = 5 g); the nonvibrated group (NVG) was the placebo group that maintained the same position on the plate but without exposure to any type of vibration. Subjects were evaluated with counter movement jump (CMJ) and muscular flexibility by means of electromyographic (EMG) analysis recorded on the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and gastrocnemius lateralis (LG).The 10 minutes of WBV showed an increase in muscular flexibility, associated with a decrease of EMG activity in BF (P < .01) and jump height. The latter was associated with a reduction of EMGs activity in BF (P < .01). The control group did not show any significant difference in all considered parameters.These results support the hypothesis that 10 minutes of WBV had effects on flexibility and explosive strength performance influencing neuromuscular behavior through inhibitor effects on antagonist muscles more than the stretch reflex activity on agonist muscles.

Electric line workers' ingress and egress to aerial buckets: design features to reduce risk of slip or fall

ABSTRACTThe objective was to investigate how different design features of an aerial bucket could reduce electric line workers' risk of a fall or slip when entering and exiting aerial buckets. Three design features were evaluated: a step inside the bucket, the number of external steps (one or two) and a handlebar. Heights of a worker's waist above the bucket's rim, force on the bucket rim and electromyographic (EMG) activity of upper and lower extremity muscles were measured. Sixteen line workers were tested. An inside step lowered the worker's waist above the rim, decreased body weight force on the bucket rim and reduced EMG activity of the triceps. One external step decreased the EMG activity of the rectus femoris. A handlebar allows for a more secure three points of contact. These design features in an aerial bucket may lower the risk of a worker falling out of an aerial bucket.

Walking with a four wheeled walker (rollator) significantly reduces EMG lower-limb muscle activity in healthy subjects

To investigate the immediate effect of four-wheeled- walker(rollator)walking on lower-limb muscle activity and trunk-sway in healthy subjects. In this cross-sectional design electromyographic (EMG) data was collected in six lower-limb muscle groups and trunk-sway was measured as peak-to-peak angular displacement of the centre-of-mass (level L2/3) in the sagittal and frontal-planes using the SwayStar balance system. 19 subjects walked at self-selected speed firstly without a rollator then in randomised order 1. with rollator 2. with rollator with increased weight-bearing. Rollator-walking caused statistically significant reductions in EMG activity in lower-limb muscle groups and effect-sizes were medium to large. Increased weight-bearing increased the effect. Trunk-sway in the sagittal and frontal-planes showed no statistically significant difference between conditions. Rollator-walking reduces lower-limb muscle activity but trunk-sway remains unchanged as stability is likely gained through forces generated by the upper-limbs. Short-term stability is gained but the long-term effect is unclear and requires investigation.

The Brighter Side of Music in Dystonia

To report a patient with genetically proven DYT1 dystonia who shows dramatic improvement in symptoms while playing the piano. Case study. Sobell Department for Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, England. A 49-year-old right-handed male civil servant. The patient was videotaped, and electromyographic activity was recorded from the splenius capitis, sternocleidomastoid, and orbicularis oculi muscles, while he was (1) at rest, (2) playing an electric piano with auditory feedback, and (3) playing an electric piano without auditory feedback (ie, when the sound of the piano is turned off). At baseline, the patient had generalized dystonia with prominent upper limb, neck, and facial involvement. While he was playing the piano, there was an instant and almost complete improvement in dystonia symptoms. The improvement was also noticeable when he played the piano without auditory feedback. There was a significant reduction in electromyographic activity for all recorded muscles when he played the piano, compared with his baseline electromyographic activity. This is a unique case of “paradoxical” improvement in dystonia symptoms with activity (ie, playing a piano), in contrast to the typical worsening of dystonia symptoms with activity. We discuss the possible mechanisms underlying this phenomenon. One of the most intriguing features of primary dystonia is the variability of abnormal muscle activity relative to the context in which movement is attempted (eg, the exquisite task specificity of focal hand dystonia or the phenomenon of the geste antagoniste). We present a unique case of an amateur pianist with genetically proven DYT1 dystonia who shows dramatic improvement in generalized dystonia symptoms while playing piano.

Change Mechanisms in EMG Biofeedback Training: Cognitive Changes Underlying Improvements in Tension Headache

Forty-three college students suffering from recurrent tension headache were randomly assigned to 1 of 4 electromyographic (EMG) biofeedback training conditions. Although all subjects were led to believe they were learning to decrease frontal EMG activity, actual feedback was contingent on decreased EMG activity for half of the subjects and increased EMG activity for the other half. Within these 2 groups, subjects also viewed bogus video displays designed to convince them they were achieving large (high success) or small (moderate success) reductions in EMG activity. Regardless of actual changes in EMG activity, subjects receiving high-success feedback showed substantially greater improvement in headache activity (53%) than subjects receiving moderate success feedback (26%). Performance feedback was also related to changes in locus of control and self-efficacy. Changes in these 2 cognitive variables during biofeedback training were also correlated with reductions in headache activity following treatment, whereas changes in EMG activity exhibited during training were uncorrelated with outcome. These results suggest that the effectiveness of EMG biofeedback training with tension headache may be mediated by cognitive changes induced by performance feedback and not primarily by reductions in EMG activity.

A Response: Change Mechanisms in EMG Biofeedback Training Revisited

Forty-three college students suffering from recurrenttension headache were randomly assigned to 1 of 4 elec-tromyographic (EMG) biofeedback training conditions.Although all subjects were led to believe they were learn-ing to decrease frontal EMG activity, actual feedback wascontingent on decreased EMG activity for half of the sub-jectsandincreasedEMGactivityfortheotherhalf.Withinthese 2 groups, subjects also viewed bogus video displaysdesignedtoconvincethemtheywereachievinglarge(highsuccess) or small (moderate success) reductions in EMGactivity. Regardless of actual changes in EMG activity,subjects receiving high-success feedback showed substan-tially greater improvement in headache activity (53%)than subjects receiving moderate success feedback (26%).Performance feedback was also related to changes inlocus of control and self-efficacy. Changes in these 2 cog-nitive variables during biofeedback training were alsocorrelated with reductions in headache activity followingtreatment, whereas changes in EMG activity exhibitedduring training were uncorrelated with outcome. Theseresults suggest that the effectiveness of EMG biofeedbacktraining with tension headache may be mediated by cog-nitive changes induced by performance feedback and notprimarily by reductions in EMG activity.

The Immediate Effect of Changing Mandibular Position on the EMG Activity of the Masseter, Temporalis, Sternocleidomastoid, and Trapezius Muscles

This study investigated the immediate effect of changing mandibular position on the electromyographic (EMG) activity of the masseter (MS), temporalis (TM), sternocleidomastoid (SCM) and trapezius (TR) muscles. Thirty-three (33) asymptomatic subjects (16 males and 17 females), ages 23 to 52 were selected. Surface EMG recordings were obtained for all muscles bilaterally with the mandible in a relaxed open position (relaxed) and during maximal voluntary clenching (fullbite) for the following: a non-repositioning appliance (NONREPOS) and repositioning appliance (REPOS). REPOS significantly reduced EMG activity of all muscles bilaterally during fullbite. During relaxation, reduction in EMG activity was only found for TR bilaterally. NONREPOS decreased the EMG activity bilaterally for TM and TR and unilaterally (left) for MS and SCM during fullbite. During relaxation, NONREPOS decreased muscle activity bilaterally for TR and SCM. A unilateral reduction was found for TM (right). These findings suggest that immediate alterations in mandibular position affect the cranio-cervical system. Both mandibular positions tested lowered the EMG activity of masticatory and cervical muscles in the relaxed and fullbite positions. The trapezius muscle was the most responsive to alterations in mandibular position.

Depression of involuntary activity in muscles paralyzed by spinal cord injury

Involuntary muscle contractions are common after spinal cord injury (SCI). Increased sensitivity to Ia muscle afferent input may contribute to the development of these spasms. Since tendon vibration results in a period of postactivation depression of the Ia synapse, we sought to determine whether Achilles tendon vibration (80 HZ for 2 s) altered involuntary contractions evoked by superficial peroneal nerve (SPN) stimulation (5 pulses at 300 HZ) in paralyzed leg muscles of subjects with chronic (>1 year) SCI. Responses to SPN stimulation that were conditioned by vibration were reduced in 66% of trials (by 33+/-12% in tibialis anterior and 40+/-16% in soleus). These reductions in electromyographic activity are unlikely to be mediated by changes at the Ia synapse or motoneuron because vibration did not alter the magnitude of the soleus H reflex. The electromyographic reductions may involve long-lasting neuromodulatory effects on spinal inhibitory interneurons or synapses involved in the flexor reflex pathway. Vibration-evoked depression of electromyographic activity may be clinically useful in controlling involuntary muscle contractions after SCI.

Effects of mental relaxation and slow breathing in essential hypertension

To compare mental relaxation and slow breathing as adjunctive treatment in patients of essential hypertension by observing their effects on blood pressure and other autonomic parameters like heart rate, respiratory rate, peripheral skin temperature, electromyographic activity of the frontalis muscle and skin conductance. One hundred patients of essential hypertension either receiving antihypertensive drugs or unmedicated were selected randomly. Various parameters were recorded during the resting state and then during mental relaxation and slow breathing for 10 min each, separated by a quiet period of 15 min. All parameters were recorded again after mental relaxation and slow breathing. Changes in various parameters observed after mental relaxation and slow breathing were analyzed and compared. Both mental relaxation and slow breathing resulted in a fall in systolic blood pressure, diastolic blood pressure, heart rate, respiratory rate and electromyographic activity with increase in peripheral skin temperature and skin conductance. Slow breathing caused a significantly higher fall in heart rate (p<0.05), respiratory rate (p<0.001), systolic blood pressure (p<0.05) and diastolic blood pressure (p<0.01). Increase in peripheral skin temperature (p<0.05) and reduction in electromyographic activity (p<0.05) occurred more with mental relaxation. No significant differences were seen between increases in skin conductance (p>0.2) observed with both the modalities. Even a single session of mental relaxation or slow breathing can result in a temporary fall in blood pressure. Both the modalities increase the parasympathetic tone but have effects of different intensity on different autonomic parameters.

Leg muscle activity during walking with assistive devices at varying levels of weight bearing

Clark BC, Manini TM, Ordway NR, Ploutz-Snyder LL. Leg muscle activity during walking with assistive devices at varying levels of weight bearing. Arch Phys Med Rehabil 2004;85:1555–60. Objective To evaluate the muscle activation patterns at varying levels of weight-bearing forces during assisted walking with an axillary crutch and a recently designed device that allows weight transfer through the pelvic girdle (ED Walker). Design Descriptive, repeated measures. Setting University-based research laboratory. Participants Twelve healthy volunteers (age, 39.6±13.6y). Interventions Not applicable. Main outcome measures Electromyographic activity was recorded from the anterior tibialis, soleus, biceps femoris, and vastus lateralis muscles on a test leg during assisted axillary crutch and ED Walker ambulation. Force platform readings measured weight-bearing load (non, light, heavy). These values were normalized to normal walking gait. Results In the vastus lateralis and soleus muscles, both devices allowed for approximately 50% and 65% reductions in electromyographic activity during the non-weight-bearing condition. During crutch ambulation, electromyographic activity of the soleus was significantly reduced compared with that required for normal walking at all levels of weight-bearing load. In the vastus lateralis for the weight-bearing conditions, the ED Walker required significantly higher electromyographic activity than crutch ambulation (light: 105.0%±12.3% vs 72.7%±10.1%; heavy: 144.8%±23.5% vs 100.0%±13.5%). Both devices required similar peak vertical ground reaction forces during the heavy weight-bearing conditions (crutch: 75%±1.6%; ED Walker: 73%±1.8%), whereas axillary crutch gait produced less force than the ED Walker in the light condition (32%±2.0% vs 48%±1.6%). Conclusions During walking with assistive devices, muscle activation patterns varied with weight-bearing load. The leg extensor muscles appeared to incur a greater reduction in muscle activity when compared with their flexor counterparts. Additionally, the ED Walker and axillary crutch differed with respect to their muscle activity levels and weight-bearing characteristics. Clinically, knowledge of these muscle activity and force characteristics may aid in the decision-making process of prescribing a device type and timeline to follow in restoring weight-bearing loads.

Characteristics of Sensory Trick Maneuvers in Idiopathic Oromandibular Jaw Opening Dystonia

Objective: We have attempted to evaluate the efficacy of different sensory trick manoeuvres in oromandibular dystonia (OMD). Background: Jaw opening OMD is a form of focal dystonia involving lower facial, labial, lingual as well as pterygoid and submental muscles resulting in unvoluntary muscle spasms especially during speaking. As in other forms of dystonia, symptoms may be alleviated by several sensory trick manoeuvres (e.g., biting on a toothpick) although hitherto only little is known about the underlying pathophysiological mechanisms. Methods: In this study we systematically examined a homogeneous group of seven patients with idiopathic jaw opening dystonia performing a standardized counting task with and without the use of a small wooden stick serving as a sensory trick. The following conditions were tested while counting: 1) no use of the stick, 2) stick placed in the mouth between teeth and cheek, 3) slight biting on the stick, and 4) voluntary jaw closure without use of the stick. For further analysis we assessed the following parameters: self-rating using a visual analogue scale, quality of speech using audio recordings for blinded evaluation and surface electromyographic (EMG) recordings from the temporal, perioral, and submental regions. Results: Self-assessment showed a significant reduction of symptoms for both conditions using the stick, while biting on it was most effective (–48%, p<0.015). Analysis of EMG data showed a significant reduction of perioral EMG activity during condition 2 (–28%, p<0.05) whereas biting on the stick (condition 3) had a significant effect mainly on submental muscles (–21%, p<0.01). Although voluntary jaw closure (condition 4) did neither improve speech nor self-assessment, it significantly reduced EMG activity of submental muscles to a similar degree as biting on the stick (–23%, p<0.015). Speech showed no significant changes although there was a trend for condition 3 (biting on the stick, –15.1%, p=0.114). Conclusions: Sensory tricks in jaw opening OMD are an effective and valuable tool to reduce dystonic muscle activity. Besides primary sensory stimulation of the oral region, slight voluntary jaw closure (with or without the use of a stick) decreases dystonic muscle activity indicating that muscle spindle afferents may play a role in the action of sensory trick manouevers. These findings may have therapeutic implications to be used in specific speech training programs for OMD patients. Supported by Dystonia Foundation, USA.

Hypnotically induced emotional numbing: A real-simulating analysis.

This study compared 20 real, hypnotized and 20 simulating, unhypnotized participants who were administered a hypnotic induction and then presented with emotionally distressing and neutral visual images. Half were administered a hypnotic suggestion for emotional numbing. Reals and simulators who received the emotional numbing suggestion reported comparably less responsivity to distressing stimuli than others. Whereas emotionally numb reals displayed little change in electromyographic (EMG) activity during the distressing stimuli, simulators displayed marked reduction in EMG activity. Reals (not simulators) displayed a dissociation between their affective response and awareness of the negative content of the stimuli following the numbing suggestion.

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 &lt; 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 &lt; 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.

Bilateral experimental muscle pain changes electromyographic activity of human jaw-closing muscles during mastication.

The effects of bilateral experimental muscle pain on human masticatory patterns were studied. Jaw movements and electromyographic (EMG) recordings of the jaw-closing muscles were divided into multiple single masticatory cycles and analyzed on a cycle-by-cycle basis. In ten men simultaneous bilateral injections of hypertonic saline (5%) into the masseter muscles caused strong pain (mean+/-SE: 7.5+/-0.4 on a 0-10 scale), significantly reduced EMG activity of jaw-closing muscles in the agonist phase, and significantly increased EMG activity in the antagonist phase. Nine of the subjects reported a sensation of less intense mastication during pain. Injections of isotonic saline (0.9%) did not cause pain or significant changes in masticatory patterns. The influence of higher brain centers on conscious human mastication can not be discarded but the observed phase-dependent modulation could be controlled by local neural circuits and/or a central pattern generator in the brain stem which are capable of integrating bilateral nociceptive afferent activity.

Respiratory muscle activity during rapid eye movement (REM) sleep in patients with chronic obstructive pulmonary disease.

In patients with chronic obstructive pulmonary disease (COPD) periods of hypopnoea occur during rapid eye movement (REM) sleep, but the mechanisms involved are not clear. Ten patients with stable COPD were studied during nocturnal sleep. Detailed measurements were made of surface electromyographic (EMG) activity of several respiratory muscle groups and the accompanying chest wall motion using magnetometers. Hypopnoea occurred in association with eye movements during phasic rapid eye movement (pREM) sleep. During pREM sleep there were reductions in EMG activity of the intercostal, diaphragm, and upper airway muscles compared with non-REM sleep. Episodic hypopnoea due to partial upper airway occlusion ("obstructive" hypopnoea) was seen consistently in four subjects while the others showed the pattern of "central" hypopnoea accompanied by an overall reduction in inspiratory muscle activity. Although activity of the intercostal muscles was reduced relatively more than that of the diaphragm, lateral rib cage paradox (Hoover's sign) was less obvious during pREM-related hypopnoea than during wakefulness or non-REM sleep. Hypopnoea during REM sleep in patients with COPD is associated with reduced inspiratory muscle activity. The pattern of hypopnoea may be either "obstructive" or "central" and is generally consistent within an individual. Relatively unopposed action of the diaphragm on the rib cage during REM sleep is not accompanied by greater lateral inspiratory paradox.

Stretch-induced electromyographic activity and torque in spastic elbow muscles. Differential modulation of reflex activity in passive and active motor tasks.

Stretch-evoked electromyographic (EMG) activity and torque signals have been studied in elbow joint muscles of both sides of patients with spastic hemiparesis and healthy subjects. In order to reveal differences in the generation of muscle tone between clinical assessment and functional movement, stretches of different velocities and amplitudes were applied during passive and quasi-functional active motor tasks. In spastic patients the strength and duration of the EMG responses following stretching of flexor and extensor muscles during both passive and active tasks were dependent on the stretch velocity and duration, respectively. This effect was seen on both the spastic and unaffected side. Under passive conditions EMG activity after stretching was negligible in the limb muscles of healthy subjects, of small amplitude in unaffected limbs of the patients, but was strong in affected muscles. Under active conditions, the amplitude of the early (M1) component of the EMG signal was larger, while the later components (M2 and M3) were smaller. These differences were due more to a change in reflex gain than to a change in reflex threshold when the stretch velocity signal was the basis for calculation. It is suggested that in spastic paresis, modulation of stretch-induced EMG activity in the spastic limb becomes restricted to a smaller range with a poor ability to switch off under passive conditions. Furthermore, the reflex EMG activity suffers a reduced facilitation under active conditions. In comparison with unaffected limbs the stretch-evoked torque on the affected side was increased under passive conditions (due to the extra EMG activity) and decreased under active conditions (due to a reduced EMG activity). An increased torque to EMG ratio was found in spastic flexor and extensor muscles during active tasks. This is thought to be due to changes in mechanical muscle fibre properties suffered as a consequence of defective muscle activation following cerebral lesions. The consequences for clinical assessment of muscle tone and therapy of spastic movement disorder are discussed.