Changes In Electromyographic Activity Research Articles

One hour jaw muscle training does not evoke plasticity in the corticomotor control of the masseter muscle

Transcranial magnetic stimulation (TMS) has been used to assess corticomotor control of jaw muscles, but few studies have examined cortical plasticity of the masticatory system and potential modification by jaw muscle training. ObjectivesTo determine if a 1-h jaw muscle training task would be sufficient to induce signs of neuroplastic changes in the corticomotor excitability of the masseter muscle. Materials and methodsCorticomotor excitability was assessed by changes in electromyographic activity evoked by TMS in 15 healthy participants. Motor evoked potentials (MEPs) recorded in the masseter and the first dorsal interosseos (FDI – as a control) muscle were assessed at four time points: at baseline, immediately after the 1-h training, 1h after training and 1 day follow-up (n=7). MEPs were assessed by stimulus–response curves and corticomotor mapping. ResultsAll participants successfully performed the task (mean success rate: 47.0±4.1%) which increased significantly during the 1-h training. However, no significant effect of jaw muscle training on masseter and FDI MEPs or corticomotor maps were observed. ConclusionThe present finding showed that 1-h jaw muscle training is insufficient to evoke neuroplastic changes in corticomotor excitability. The potential for training-induced neuroplasticity may vary among different cranial muscles which may have therapeutic consequences.

Electromyographic Evaluation of Abdominal-Muscle Function With and Without Concomitant Pelvic-Floor-Muscle Contraction

Coactivation of abdominal and pelvic-floor muscles (PFM) is an issue considered by researchers recently. Electromyography (EMG) studies have shown that the abdominal-muscle activity is a normal response to PFM activity, and increase in EMG activity of the PFM concomitant with abdominal-muscle contraction was also reported. The purpose of this study was to compare the changes in EMG activity of the deep abdominal muscles during abdominal-muscle contraction (abdominal hollowing and bracing) with and without concomitant PFM contraction in healthy and low-back-pain (LBP) subjects. A 2 × 2 repeated-measures design. Laboratory. 30 subjects (15 with LBP, 15 without LBP). Peak rectified EMG of abdominal muscles. No difference in EMG of abdominal muscles with and without concomitant PFM contraction in abdominal hollowing (P = .84) and abdominal bracing (P = .53). No difference in EMG signal of abdominal muscles with and without PFM contraction between LBP and healthy subjects in both abdominal hollowing (P = .88) and abdominal bracing (P = .98) maneuvers. Adding PFM contraction had no significant effect on abdominal-muscle contraction in subjects with and without LBP.

Changes in electromyographic activity of trunk muscles within the sub-acute phase for individuals deemed recovered from a low back injury

Evidence indicates that previous low back injury (LBI) is a strong predictor for re-injury. The purpose of this study was to examine whether neuromuscular patterns remain altered in a LBI group who were deemed recovered. Surface electromyograms from 12-abdominal and 12-back extensors sites and motion variables were recorded from 33 LBI individuals (sub-acute phase) and 54 asymptomatic controls. Pain-related variables were recorded and a clinical assessment performed for LBI participants. Subjects performed a symmetrical lift and replace task in two reaches. Pattern recognition techniques were applied to normalized activation amplitude patterns to extract key recruitment strategies. Mixed model ANOVAs tested for effects (p<0.05). Despite similar task performance, significantly (p<0.05) different recruitment strategies were observed for the LBI group. There were higher activation amplitudes for LBI subjects in all muscles (except posterior external oblique) and greater co-activation between abdominal and back extensor sites compared to controls. Local abdominal and back extensor sites showed altered responses to increased physical demands in the LBI group. Despite outcomes indicating recovery, the LBI group had altered neuromuscular patterns compared to asymptomatic controls supporting that residual alterations remain following recovery.

Change in Electromyographic Activity of Wrist Extensor by Cylindrical Brace

PurposeTo verify the effect of a newly-developed cylindrical type forearm brace, which was designed to give focal counterforce perpendicularly on the muscle belly of the wrist extensor.Materials and MethodsThe dominant hands of 24 (12 males, 12 females) healthy subjects were tested. Two types of forearm braces (focal cylindrical type and broad pneumatic type) were examined. The braces were applied at the extensor carpi radialis brevis, 5 to 7 cm distal to the lateral epicondyle. Two surface electrodes were attached to the proximal and distal parts of the brace. By quantitative electromyography, the mean amplitudes of voluntary extensor carpi radialis brevis contraction before and after applying each brace were recorded and analyzed.ResultsThe mean amplitudes of the focal cylindrical brace and broad pneumatic brace were reduced significantly compared to no brace (p<0.05), with a larger reduction for the cylindrical brace than the pneumatic brace (p<0.05). There was no significant difference between the proximal and distal mean amplitudes with each brace.ConclusionA cylindrical type brace decreased electromyographic activity in the wrist extensor more effectively than did the pneumatic type brace.

Effectiveness of global postural reeducation in the treatment of temporomandibular disorder: Case report

The aim of the present study was to evaluate the effectiveness of global postural reeducation in the treatment of temporomandibular disorder through bilateral surface electromyographic (EMG) analysis of the masseter muscle in a 23-year-old volunteer. EMG values for the masseter were collected at rest (baseline) and during a maximal occlusion. There was a change in EMG activity both at rest and during maximal occlusion following the intervention, evidencing neuromuscular rebalancing between both sides after treatment as well as an increase in EMG activity during maximal occlusion, with direct improvement in the recruitment of motor units during contractile activity and a decrease in muscle tension between sides at rest. The improvement in postural patterns of the cervical spine provided an improvement in aspects of the EMG signal of the masseter muscle in this patient. However, a multidisciplinary study is needed in order to determine the effect of different forms of treatment on this condition and compare benefits between interventions. Therefore, this study can provide a direction regarding the application of this technique in patients with temporomandibular disorder.

Spring–mass behavior and electromyographic activity evolution during a cycle-run test to exhaustion in triathletes

PurposeTo evaluate spring–mass (SM) behavior and associated electromyographic (EMG) activity during a run to exhaustion following a cycle exercise in trained triathletes. MethodsTen triathletes completed four tests: a cycling test to determine V˙O2max; a running test to determine the lactate threshold (LT); a 5min control run at LT (C-Run) followed after a total recovery period by a cycle-to-run session to exhaustion [30min of cycling at ∼80% V˙O2max followed by a run until exhaustion at LT (T-Run)]. SM behavior and EMG signals in nine lower limb muscles were recorded throughout the running sessions. ResultsImmediately after cycling, leg stiffness was 12.1% higher than its C-Run value and a concomitant increase of EMG activity of knee extensors was observed during pre-contact. Throughout T-Run, leg stiffness decreased by 7.3%, while knee extensors and ankle flexors activities decreased during pre-contact and braking phases. No significant variations in SM parameters and no significant increase of muscle activity were reported between C-Run and the end of T-Run. ConclusionSM behavior during the cycle-run test was consistent with EMG activity changes. Cessation of exercise was not associated with significant alterations of stiffness values and EMG activity.

Unilateral eccentric exercise of the knee flexors affects muscle activation during gait

Uni-lateral muscle soreness is common yet the effects on gait or electromyographic (EMG) activity are unknown. The purpose of our study was to induce delayed onset muscle soreness (DOMS) in the knee flexor group and measure the resultant change in EMG activity and knee motion during gait. Nine healthy subjects participated in the study. Measures of function, evoked tenderness of the biceps femoris, as well as knee angle, and EMG activity during gait were assessed prior and 48h after an eccentric exercise protocol. DOMS was induced unilaterally in the knee flexors using an isokinetic dynamometer and subjects exercised until they could not generate 50% of their maximal voluntary isometric contraction (MVIC). There was a significant decrease in biceps femoris activity after DOMS during the last phase of gait. Moreover, there was a day×phase interaction for gastrocnemius activity with the last two phases displaying an increase in activity. There was no significant change in knee angle during gait. The decrease in biceps femoris activity as well as the increase in gastrocnemius activity could be evidence of a protective mechanism designed to decrease activity of the sore muscle while increasing the activity of a synergistic muscle.

Is Constant Current or Constant Voltage Spinal Cord Stimulation Superior for the Suppression of Nociceptive Visceral and Somatic Stimuli? A Rat Model

This study compares the effects of constant current (CC) and constant voltage (CV) spinal cord stimulation (SCS) at various frequencies and intensities on standard nociceptive measurements in rats, the visceromotor reflex (VMR) and neuronal activity, during noxious visceral and somatic stimuli. Abdominal muscle electromyographic activity changes were measured to indicate VMR, and extracellular activity of L6-S2 spinal neurons was recorded during somatic (pinching) and noxious visceral stimulation (colorectal distension [CRD], 60 mmHg) in anesthetized rats. A stimulating (unipolar ball) electrode at L2-L3 delivered CC- or CV-SCS at varied frequencies and intensities. CC-SCS reduced VMR evoked by CRD significantly more than CV-SCS (p < 0.05). For neuronal activity, high-frequency CC-SCS (40 and 100 Hz) and CV-SCS (100 Hz) effectively reduced intraspinal somatic nociceptive transmission more than low-frequency SCS (2 Hz). No significant differences were observed between the effects of CC- and CV-SCS on spontaneous activity and nociceptive responses of spinal neurons to noxious CRD following short- (five to ten minutes) or long-term (20-30 min) SCS. Although high-frequency CC- and CV-SCS may be more useful for the management of somatic pain, CC-SCS may be more effective for treating complex pain systems like visceral hypersensitivity.

Changes in Electromyographic Activity after Conditioning Contraction

[Purpose] Post-activation potentiation is the increase in muscle twitch force in response to electrical stimulation after a conditioning contraction (CC) of maximum or near-maximum intensity. It is controversial whether muscular force during low-level voluntary contractions increases after maximum contraction. This study investigated the changes in electromyographic activity after CC. [Subjects and Methods] Fifteen healthy adults participated in this study. In the first experiment, a supramaximal electrical pulse was applied to the tibial nerve, and the isometric twitch force of plantar flexion was measured. After maximum voluntary contraction (MVC), i.e., CC, the twitch force elicited by electrical stimulation was monitored. In the second experiment, the surface electromyogram were recorded at an intensity of 20% MVC before and after CC. [Results] Results indicated the twitch force significantly increased by 30% within 30 s after CC. In the second experiment, the electromyographic activity significantly decreased by 16% for the gastrocnemius muscle but did not change for the soleus. Correlation coefficients between changes in the twitch force and electromyographic activity at 20%MVC were -0.54 for the gastrocnemius muscle and 0.04 for the soleus muscle. [Conclusion] Post-activation potentiation might work for daily physical activities compensating for reduced force output of the fatigued muscle.

Blood Flow Restriction: How Does It Work?

Blood Flow Restriction: How Does It Work?

Laryngeal electromyographic responses to perturbations in voice pitch auditory feedback.

The present study was conducted to test the hypothesis that intrinsic laryngeal muscles are involved in producing voice fundamental frequency (F(0)) responses to perturbations in voice pitch auditory feedback. Electromyography (EMG) recordings of the cricothyroid and thyroarytenoid muscles were made with hooked-wire electrodes, while subjects sustained vowel phonations at three different voice F(0) levels (conversational, high pitch in head register, and falsetto register) and received randomized pitch shifts (±100 or ±300 cents) in their voice auditory feedback. The median latencies from stimulus onset to the peak in the EMG and voice F(0) responses were 167 and 224 ms, respectively. Among the three different F(0) levels, the falsetto register produced compensatory EMG responses that occurred prior to vocal responses and increased along with rising voice F(0) responses and decreased for falling F(0) responses. For the conversational and high voice levels, the EMG response timing was more variable than in the falsetto voice, and changes in EMG activity with relevance to the vocal responses did not follow the consistent trend observed in the falsetto condition. The data from the falsetto condition suggest that both the cricothyroid and thyroarytenoid muscles are involved in generating the compensatory vocal responses to pitch-shifted voice feedback.

Effects of Wearing the Wrong Glove Size on Shoulder and Forearm Muscle Activities during Simulated Assembly Work

This study was performed to determine the changes in electromyographic activities in the shoulder and forearm muscles when using the bare hands, well-fitting gloves, and gloves that are one size smaller or one size larger for simulated assembly operations. Sixteen asymptomatic seated workers with normal hands and no obvious deformities, skin diseases, or allergies were recruited. The subjects were asked to simulate assembly operations using their bare hands, well-fitting gloves, and one size smaller or one size larger. This study showed that wearing the wrong glove size led to a decrease in forceful activation of the forearm muscle and a compensatory increase in shoulder movement. In contrast, use of the bare hands or wearing well-fitting gloves led to effective forearm muscle activation, which decreased inefficient shoulder movement. These data indicate that wearing the wrong glove size will lead to continuous inefficient use of the forearm and shoulder muscles, and result in overuse of the shoulder.

Low Level Laser Effects On Pain to Palpation and Electromyographic Activity in TMD Patients: A Double-Blind, Randomized, Placebo-Controlled Study

The purpose of this study was to evaluate the effect of diode laser (GaAlAs – 780 nm) on pain to palpation and electromyographic (EMG) activity of the masseter and anterior temporalis muscles. The laser was applied on the temporalis and masseter muscles twice a week (four weeks). Forty-eight (48) patients with myofascial pain were randomly assigned between actual and placebo treatments and between the energetic doses of 25 J/cm2 and 60 J/cm2, and were evaluated using VAS before, immediately after the final application, and 30 days after the laser treatment. Surface electromyography was performed with maximum dental clenching before and after laser therapy. The results show there were no significant statistical differences in the EMG activity between the groups before and after laser treatment. With regard to the pain at palpation, although both groups presented a significant difference in the symptoms before and after the treatment, only the active doses showed statistically significant reductions in pain level in all the regions of the palpated muscles. However, there was no significant statistical difference between groups (experimental and placebo). In conclusion, low level laser did not promote any changes in EMG activity. The treatment did, however, lessen the pain symptoms in the experimental groups.

Effects of Wrist-extension Orthosis on Shoulder and Scapular Muscle Activities during Simulated Assembly Tasks

The purpose of this study was to observe changes in electromyographic activity appeared in shoulder and scapular muscles when one wears no wrist extension orthosis, short wrist extension orthosis and long wrist extension orthosis when performing two model assembling operations. The study subjects were 16 adults who use right hand and did not have any functional disorder on their wrist or the upper limbs without any orthopedic surgery. The study subjects were asked to do the two model assembling operations without wrist extension orthosis, with a short wrist extension orthosis and with a long wrist extension orthosis. As a result of repetitive assembling operation that requires shoulder movement, electromyographic activity in upper trapezius and serratus anterior increased significantly when the subjects wore the short and long wrist extension orthoses compared to none. When the subjects performed repetitive assembling operation that requires shoulder stability, electromyographic activity in upper trapezius, lower trapezius, serratus anterior, and anterior deltoid showed significant increase when they wore the short and long wrist extension orthoses compared to none. Especially, the upper trapezius showed significantly high electromyographic activity when they wore the long wrist extension orthosis compared to a short one.

Training-induced changes in the pattern of triceps to biceps activation during reaching tasks after chronic and severe stroke

This exploratory study was undertaken to investigate the mechanisms that contributed to improvements in upper limb function following a novel training program. Surface electromyography (EMG) was used to examine training-induced changes in the pattern of triceps and biceps activation during reaching tasks in stroke survivors with severe paresis in the chronic stage of recovery. The EMG data were obtained in the context of a single blind randomised clinical trial conducted with 42 stroke survivors with minimal upper limb muscle activity and who were more than 6 months post-stroke. Of the 33 participants who completed the study, 10 received training of reaching using a non-robotic upper limb training device, the SMART Arm, with EMG triggered functional electrical stimulation (EMG-stim), 13 received training of reaching using the SMART Arm alone, and 10 received no intervention. Each intervention group engaged in 12 1-h training sessions over a 4-week period. Clinical and laboratory measures of upper limb function were administered prior to training (0 weeks), at completion (4 weeks) and 2 months (12 weeks) after training. The primary outcome measure was 'upper arm function' which is Item 6 of the Motor Assessment Scale (MAS). Laboratory measures consisted of two multijoint reaching tasks to assess 'maximum isometric force' and 'maximum distance reached'. Surface EMG was used to monitor triceps brachii and biceps brachii during the two reaching tasks. To provide a comparison with normal values, seven healthy adults were tested on one of the reaching tasks according to the same procedure. Study findings demonstrated a statistically significant improvement in upper limb function for stroke participants in the two training groups compared to those who received no training however no difference was found between the two training groups. For the reaching tasks, all stroke participants, when compared to normal healthy adults, exhibited lower triceps and biceps activation and a lower ratio of triceps to biceps activation. Following training, stroke participants demonstrated increased triceps activation and an increased ratio of triceps to biceps activation for the task that was trained. Better performance was associated with greater triceps activation and a higher ratio of triceps to biceps activation. The findings suggest that increased activation of triceps as an agonist and an improved coordination between triceps and biceps could have mediated the observed changes in arm function. The changes in EMG activity were small relative to the changes in arm function indicating that factors, such as the contribution of other muscles of reaching, may also be implicated.

Changes in spinal reflex and locomotor activity after a complete spinal cord injury: a common mechanism?

Locomotor activity and spinal reflexes (SRs) show common features in different mammals, including humans. Here we report the time-course of the development of locomotor activity and SRs after a complete spinal cord injury in humans. SRs evoked by tibial nerve stimulation were studied, as was the leg muscle electromyography activity evoked by mechanically assisted locomotion (Lokomat) in biceps femoris, rectus femoris, tibialis anterior and gastrocenmius medialis. Around 8 weeks after the injury, an early SR component (latency 60-120 ms) appeared, as in healthy subjects, and a well-organized leg muscle activity was present during assisted locomotion. At around 6 months after injury an additional, late reflex component (latency 120-450 ms) appeared, which remained even 15 years after the spinal cord injury. In contrast, the early component had markedly decreased at 18 months after injury. These changes in SR were associated with a loss of electromyography activity and a successively stronger electromyography exhaustion (i.e. decline of electromyography amplitude), when comparing the level of electromyography activity at 2 and 10 min, respectively, during assisted locomotion. These changes in electromyography activity affected mainly the biceps femoris, gastrocenmius medialis and tibialis anterior but less so the rectus femoris. When the amplitude relationship of the early to late SR component was calculated, there was a temporal relationship between the decrease of the early component and an increase of the late component and the degree of exhaustion of locomotor activity. In chronic, severely affected but sensori-motor incomplete spinal cord injury subjects a late SR component, associated with an electromyography exhaustion, was present in subjects who did not regularly perform stepping movements. Our data are consistent with the proposal of a common mechanism underlying the changes in SR activity and locomotor activity after spinal cord injury. These findings should be taken into consideration in the development of novel rehabilitation schemes and programs to facilitate regeneration-inducing therapies in spinal cord injury subjects.

Changes in EMG activity during clenching in chronic pain patients with unilateral temporomandibular disorders

The study assessed the differences in electromyographic (EMG) activity recorded during clenching in women with chronic unilateral temporomandibular disorders (TMDs) as compared to control subjects. Seventy-five full dentate, normo-occlusion, right-handed, similarly aged female subjects were recruited. Twenty five subjects presented with right side TMD, 25 presented with left side TMD and 25 pain-free control subjects participated. Using integrated surface EMG over a 1 s contraction, the anterior temporalis and masseter muscles were evaluated bilaterally while subjects performed maximum voluntary clenching. Lower EMG activation was observed in patients with TMD as compared to control subjects (temporalis: 195.74 ± 18.57 vs. 275.74 ± 22.11, P = 0.011; masseters: 151.09 ± 17.37 vs. 283.29 ± 31.87, P < 0.001). An asymmetry index (SAI) was calculated to determine ratios of right to left sided activation. Patients with right-sided TMD demonstrated preferential use of their left-sided muscles (SAI −5.35 ± 4.02) whereas patients with left-sided TMD demonstrated preferential use of their right-sided muscles (SAI 6.95 ± 2.82), ( P = 0.016). This unilateral reduction in temporalis and masseter activity could be considered as a specific protective functional adaptation of the neuromuscular system due to nociceptive input. The asymmetry index (SAI) may be a useful measure in discriminating patients with right vs. left-sided TMD.

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.

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.

Activation of Extracellular Signal-Regulated Protein Kinase in Sensory Neurons After Noxious Gastric Distention and Its Involvement in Acute Visceral Pain in Rats

Changes in the properties of visceral sensory neurons contribute to the development of gastrointestinal pain. However, little is known about the molecules involved in mechanosensation from the gastrointestinal tract. We investigated the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), a member of the mitogen-activated protein kinase cascade, in dorsal root ganglion (DRG) and nodose ganglion (NG) neurons by noxious gastric distention (GD) and its involvement in acute visceral pain in rats. Electromyographic responses to gastric balloon distention through gastrostomy were recorded from the acromiotrapezius muscle in rats after splanchnic nerve resection or vagotomy and in control rats. We then examined the phosphorylated-ERK1/2 (p-ERK1/2) labeling in the DRG and NG after GD using immunohistochemistry. Gastric distention induced p-ERK1/2 in DRG and NG neurons with a peak at 2 minutes after stimulation. We found a stimulus intensity-dependent increase in the number of activated neurons, and this activation corresponded well with the incidence of the visceromotor response. Most of these p-ERK1/2-labeled neurons were small- and medium-sized neurons that coexpressed transient receptor potential vanilloid 1 ion channel and acid-sensing ion channel 3. Splanchnic nerve resection, but not vagotomy, affected the visceromotor response, and attenuated the ERK1/2 activation in DRG neurons produced by GD. Furthermore, intrathecal administration of the mitogen-activated protein kinase kinase 1/2 inhibitor, U0126, altered the response to noxious GD. The activation of ERK1/2 pathways in DRG neurons by noxious GD may be correlated with functional activity, and may be involved in acute visceral pain.