Increase In Electromyographic Amplitude Research Articles

Stochastic electrical stimulation of the thoracic or cervical regions with surface electrodes facilitates swallow in rats.

Aspiration pneumonia, a leading cause of mortality, poses an urgent challenge in contemporary society. Neuromuscular electrical stimulation (NMES) has been commonly used in dysphagia rehabilitation. However, given that NMES at motor threshold targets only specific muscles, it carries a potential risk of further compromising functions related to swallowing, respiration, and airway protection. Considering that the swallow motor pattern is orchestrated by the entire swallow pattern generator (the neural mechanism governing a sequence of swallow actions), a rehabilitation approach that centrally facilitates the entire circuit through sensory nerve stimulation is desirable. In this context, we propose a novel stimulation method using surface electrodes placed on the back to promote swallowing. The efficacy of the proposed method in promoting swallowing was evaluated by electrically stimulating sensory nerves in the back or neck. Probabilistic stimulus was applied to either the back or neck of male and female rats. Swallows were evoked by an oral water stimulus, and electromyographic (EMG) activity of the mylohyoid, thyroarytenoid, and thyropharyngeus muscles served as the primary outcome measure. Gaussian frequency stimulation applied to the skin surface of the thoracic back elicited significant increases in EMG amplitude of all three swallow-related muscles. Neck stimulation elicited a significant increase in EMG amplitude of the thyroarytenoid during swallow, but not the mylohyoid or thyropharyngeus muscles. While the targeted thoracic spinal segments T9-T10 have been investigated for enhancing respiration, the promotion of swallowing through back stimulation has not been previously studied. Furthermore, this study introduces a new probabilistic stimulus based on Gaussian distribution. Probabilistic stimuli have been reported to excel in nerve stimulation in previous research. The results demonstrate that back stimulation effectively facilitated swallow more than neck stimulation and suggest potential applications for swallowing rehabilitation.

Optimal Blood Flow Restriction Occlusion Pressure for Shoulder Muscle Recruitment With Upper Extremity Exercise

Background: As blood flow restriction (BFR) utilization continues to rise, it is crucial to define optimal parameters for use. Currently unknown are the effects of occlusion level during BFR on muscle activity in the proximal shoulder. Purpose/Hypothesis: The purpose of this study was to compare electromyographic amplitude (EMGa) of shoulder musculature during exercise using limb occlusion percentages (LOPs). The authors hypothesized that EMGa would increase concurrently with occlusion. Study Design: Controlled laboratory study. Methods: α Fifteen healthy adults were recruited and underwent 4 experimental sessions, performing 3 common rotator cuff exercises at low intensity (20% maximal strength) to failure in the following order: cable external rotation (ER), cable internal rotation (IR), and dumbbell scaption. Exercises were completed at a different occlusion pressure (0%, 25%, 50%, and 75% LOP— order randomized) applied at the proximal arm. EMGa was recorded from shoulder musculature proximal to the occlusion site and averaged across 5-repetition intervals and overall for the first 30 repetitions. An analysis of variance repeated on occlusion pressure followed by a Bonferroni post hoc test was used to compare EMGa, repetitions to fatigue, and ratings of discomfort (visual analog scale [VAS], 0-10) between occlusion pressures. The type 1 error was set at α = .05 for all analyses. Results: Significant effects of the occlusion level on shoulder muscle EMGa were observed for all exercises (P < .05) with diminishing returns above 50% LOP (overall). For ER, elevations in EMGa were observed at ≥50% LOP for the anterior deltoid, middle deltoid, infraspinatus, and trapezius compared with 0% LOP (P < .05). For IR, elevations in EMGa were observed at ≥25% LOP for the anterior deltoid and trapezius compared with 0% LOP (P < .05). For the teres minor, a significant elevation in EMGa occurred at 75% LOP compared with 0%, 25%, and 50% LOP (P < .05). A decrease in EMGa was observed at ≥50% LOP compared with 0% LOP for the posterior deltoid (P < .05). For scaption, an increase in EMGa was observed at ≥25% LOP for the infraspinatus and teres minor muscles, at 75% LOP for the posterior deltoid, and at ≥50% LOP for the trapezius compared with 0% LOP (P < .05). Decreases in repetitions to failure relative to 0% LOP were observed at 75% LOP for ER (0%: 47 ± 5; 75%: 40 ± 2; P = .034), IR (0%: 82 ± 10; 75%: 64 ± 5; P = .017), and scaption (0%: 85 ± 9; 75%: 64 ± 6; P < .001). A significant linear increase in discomfort was observed for all exercises with increasing occlusion pressures (VAS: 0-10, 0% → 75% LOP; ER: 2.2 ± 0.4 → 7.2 ± 0.3; IR: 1.3 ± 0.2 → 6.1 ± 0.6; scaption: 1.3 ± 0.4 → 6.1 ± 0.4; P < .01). Conclusion: There are several differences in muscle activation about the shoulder based on exercise and occlusion when utilizing BFR. Increasing the percentage of limb occlusion leads to heightened EMGa with diminished returns past 50% LOP when considering muscle activation, discomfort, and achievable exercise volume. Clinical Relevance: These findings may be used to refine upper extremity BFR guidelines.

The Influence of Motoric Maneuvers on Cervical Vestibular Evoked Myogenic Potentials (cVEMPs).

The cervical vestibular evoked myogenic potential (cVEMP) is a vestibular response that is produced by the saccule in response to intense, often low-frequency, short-duration auditory stimuli, and is typically recorded from a contracted sternocleidomastoid (SCM) muscle. Previous research has shown that the amplitude of the cVEMP is related to the amount of SCM electromyographic (EMG) activity. The aim of this study was to determine the influence of various remote motoric maneuvers on the amplitude of the cVEMP, as well as whether they influence the level of SCM EMG activity. The cVEMP was recorded from the left SCM muscle to left ear stimulation, in response to the SCM condition, as well as three different motoric maneuvers (jaw clench, eye closure, and the Jendrassik maneuver). EMG activity was also varied between 50, 75, and 100% of maximal EMG activity. Data from 14 healthy subjects, with a mean age of 25.57 years (standard deviation = 5.93 years), was included in the present study. Mean latency and amplitude of the cVEMP were compared across the four conditions and varying magnitudes of EMG contraction. SPSS 26 was used to statistically analyze the results. cVEMP latency did not vary across condition. cVEMP amplitude decreased with decreasing EMG magnitude. SCM contraction with jaw clench produced the largest increase in cVEMP amplitude; however, this condition was not significantly different from the SCM condition alone. SCM contraction with the Jendrassik maneuver produced a cVEMP amplitude that was similar and not statistically different from SCM contraction alone, and the addition of the eye closure maneuver to SCM contraction resulted in the lowest cVEMP amplitude, which was found to be statistically different from the standard SCM condition at 100 and 75% EMG activity. The amplitude relationship across the conditions was not found to vary with changes in EMG activity; however, a significant increase in EMG amplitude was found during the 50% muscle contraction condition when subjects performed the Jendrassik maneuver in addition to the standard SCM contraction. The addition of the eye closure maneuver to SCM contraction resulted in a significant decrease in cVEMP amplitude, while the addition of the Jendrassik maneuver resulted in a significant increase in EMG activity at the lowest level of SCM activation (i.e., 50%). Additional research is necessary to determine how motoric maneuvers influence the cVEMP amplitude, and whether the results are also dependent on how SCM contraction is being produced (e.g., while supine vs. sitting).

The ability of fentanyls and other opioids to increase EMG amplitude in respiratory muscles correlates with their agonist efficacy

Acute overdose deaths involving fentanyls have been dramatically increasing in the USA since 2013. These potent opioids depress respiratory drive and produce rigidity in the intercostal muscles and diaphragm (resulting in what is referred to as Wooden Chest Syndrome) as well as in glottic and supraglottic muscles which further reduces the ability to breathe. In this study we have sought to characterise the ability of various opioid agonists to induce respiratory muscle rigidity using electromyographic (EMG) recording. EMG amplitude was recorded simultaneously from diaphragm, external and internal intercostal muscles of P21 male Wistar rats, using an in situ decerebrated and arterially perfused preparation. First, the effects of fentanyl and morphine on respiratory muscle EMG were studied using a dose of each agonist that depressed respiratory rate by approximately 40%. Fentanyl produced a marked increase in EMG amplitude during expiration in all three respiratory muscles whereas the effect of morphine was very slight. In order to understand whether the difference between fentanyl and morphine related to differences in chemical structure, lipid solubility or agonist intrinsic efficacy we studied the effects of a range of opioids that differed in these characteristics – carfentanil and fentanyl (piperidine derivatives, high lipid solubility, high efficacy), alfentanil (piperidine derivative, moderate lipid solubility, high efficacy) norbuprenorphine (thebaine derivative, high lipid solubility, high efficacy), levorphanol (morphinan, high lipid solubility, low efficacy), morphine and hydromorphone (morphine derivatives, low lipid solubility, low efficacy). With doses of each that produced around 40% depression of respiratory rate we observed that the rank order of ability to increase internal and external intercostal muscle EMG amplitude was carfentanil = fentanyl = norbuprenorphine > alfentanil = hydromorphone > morphine = levorphanol but for the diaphragm the rank order was fentanyl > alfentanil = norbuprenorphine ≥ hydromorphone > carfentanil ≥ morphine = levorphanol. These results suggest that the ability of opioid agonists to increase respiratory muscle EMG amplitude and therefore respiratory muscle rigidity does not depend solely on either chemical structure or lipid solubility of the agonist. For the intercostal muscles there is a better correlation with agonist efficacy. Why the effect of carfentanil on the diaphragm is weak remains to be elucidated.

Greater Neural Adaptations following High- vs. Low-Load Resistance Training.

We examined the neuromuscular adaptations following 3 and 6 weeks of 80 vs. 30% one repetition maximum (1RM) resistance training to failure in the leg extensors. Twenty-six men (age = 23.1 ± 4.7 years) were randomly assigned to a high- (80% 1RM; n = 13) or low-load (30% 1RM; n = 13) resistance training group and completed leg extension resistance training to failure 3 times per week for 6 weeks. Testing was completed at baseline, 3, and 6 weeks of training. During each testing session, ultrasound muscle thickness and echo intensity, 1RM strength, maximal voluntary isometric contraction (MVIC) strength, and contractile properties of the quadriceps femoris were measured. Percent voluntary activation (VA) and electromyographic (EMG) amplitude were measured during MVIC, and during randomly ordered isometric step muscle actions at 10–100% of baseline MVIC. There were similar increases in muscle thickness from Baseline to Week 3 and 6 in the 80 and 30% 1RM groups. However, both 1RM and MVIC strength increased from Baseline to Week 3 and 6 to a greater degree in the 80% than 30% 1RM group. VA during MVIC was also greater in the 80 vs. 30% 1RM group at Week 6, and only training at 80% 1RM elicited a significant increase in EMG amplitude during MVIC. The peak twitch torque to MVIC ratio was also significantly reduced in the 80%, but not 30% 1RM group, at Week 3 and 6. Finally, VA and EMG amplitude were reduced during submaximal torque production as a result of training at 80% 1RM, but not 30% 1RM. Despite eliciting similar hypertrophy, 80% 1RM improved muscle strength more than 30% 1RM, and was accompanied by increases in VA and EMG amplitude during maximal force production. Furthermore, training at 80% 1RM resulted in a decreased neural cost to produce the same relative submaximal torques after training, whereas training at 30% 1RM did not. Therefore, our data suggest that high-load training results in greater neural adaptations that may explain the disparate increases in muscle strength despite similar hypertrophy following high- and low-load training programs.

Facial nerve regeneration after facial allotransplantation: A longitudinal clinical and electromyographic follow-up of lip movements during speech

Facial allotransplantation constitutes a reconstructive option after extensive damage to facial structures. Functional recovery has been reported but remains an issue. A patient underwent facial allotransplantation after a ballistic injury with extensive facial tissue damage. Speech motor function was sequentially assessed clinically, along with repeated electromyography of lip movements during a follow-up of 3 years. Facial nerve recovery could be demonstrated within the first month, followed by a gradual increase in electromyographic amplitude and decrease in reaction times. These were accompanied by gradual improvement of clinical assessments. Axonal recovery starts early after transplantation. Electromyographic testing is sensitive in demonstrating this early recovery, which ultimately results in clinical improvements.

Effects of Work-to-Rest Ratios on Peak Torque and Neuromuscular Responses during Submaximal, Isometric Muscle Actions.

PURPOSE: The purpose of the present study was to examine the effects of work-to-rest ratios on the maximal voluntary isometric contraction (MVIC) torque and neuromuscular responses to intermittent, submaximal, isometric muscle actions. METHODS: Twenty resistance-trained men and women (mean age ± SD = 23 ± 2 years; resistance training = 15 ± 5 days per month) visited the lab on two occasions (separated by ≥ 48 hours) and performed two MVICs before (pretest) and after (posttest) randomly performing two protocols (4-s on, 4-s off vs. 4-s on, alternating 6- and 2-s off) that consisted of 50 intermittent, submaximal (65% of MVIC), isometric muscle actions of the dominant forearm flexors on a calibrated isokinetic dynamometer. In addition, bipolar surface electromyographic (EMG) and mechanomyographic (MMG) signals were simultaneously recorded from the biceps brachii muscle. Separate 2 X 2 (Time [pretest, posttest]) X (Protocol) repeated measures ANOVAs were used to analyze the MVIC torque, EMG amplitude (AMP), EMG mean power frequency (MPF), MMG AMP, and MMG MPF data. RESULTS: There were no significant (p > 0.05) interactions for any of the variables. There were, however, significant main effects for time (marginal means collapsed across protocol). Specifically, as a result of the 50 repetitions MVIC torque, EMG MPF, and MMG MPF decreased 22, 20, and 16%, respectively, while MMG AMP increased 21% from pretest to posttest. CONCLUSIONS: Work-to-rest ratios had no effects on MVIC torque or any of the neuromuscular parameters. As a result of the 50 submaximal muscle actions, however, there were decreases in MVIC torque, possibly due to a decrease in global motor unit firing rate (MMG MPF). The decrease in MMG MPF may also have resulted in decreased muscle stiffness and, therefore, allowed greater oscillations of the activated motor units which increased MMG AMP. The non-significant increase in EMG AMP suggested that muscle activation was unaffected by the submaximal muscle actions, while the decreases in action potential conduction velocity (EMG MPF) may reflect a fatigue-induced buildup of metabolic byproducts.

The effects of velocity on peak torque and neuromuscular responses during eccentric muscle actions

BACKGROUND: Previous investigations have examined the torque and neuromuscular responses to maximal concentric and isometric muscle actions. The literature, however, has paid less attention to the effects of performing maximal eccentric muscle actions. Furthermore, the available information in this regard is contradictory. OBJECTIVE: The purpose of the present investigation was to examine eccentric, isokinetic peak moment (PMe), electromyographic (EMG) amplitude (AMP), EMG mean power frequency (MPF), mechanomyographic (MMG) AMP, and MMG MPF patterns of responses to repeated, maximal, eccentric muscle actions at 60, 120, and 180°/s. METHODS: Twelve resistance-trained men visited the laboratory on three occasions (separated by ≥ 72 h) and performed 30 repeated, maximal, eccentric muscle actions of the dominant leg extensors on an isokinetic dynamometer at randomly ordered velocities of 60, 120, and 180°/s. RESULTS: There were no changes (p > 0.05) across the 30 repeated, eccentric muscle actions for PMe, MMG AMP, and EMG MPF for any of the velocities. There were, however, increases in EMG AMP and decreases in MMG MPF for each velocity. CONCLUSIONS: The decrease in MMG MPF, which reflects the global firing rate of the activated motor units, in conjunction with the lack of change in MMG AMP, which reflects motor unit recruitment, suggested that the increase in EMG AMP was due to motor unit synchronization.

Electromyographic Amplitude Changes in the Laryngeal Adductors during Thyroidectomy with Vagal Nerve Stimulation: A Marker of Tensile Stress in the Recurrent Laryngeal Nerve?

Background: Most Recurrent Laryngeal Nerve Palsies (RLNP) occurs with visually intact nerves, indicating neurapraxia. However the mechanism of RLNP neurapraxia in intact nerves is not well understood. During thyroid surgery, Recurrent Laryngeal Nerve (RLN) palsy has occasionally been observed immediately following anteromedial rotation of the thyroid lobe (AMRT), upon identification but prior to dissection of the RLN. We postulated that traction placed on RLN during AMRT may lead to neurapraxia. This study aimed to describe these cases, and to measure Electromyographic (EMG) changes in the vocal cord adductors (VCA) with Vagus Nerve (VN) stimulation, before and after AMRT, and to correlate the EMG findings to prediction of RLN palsy. Methods: Firstly, the cases of RLN palsy following AMRT are described. Secondly, in a prospective study, the EMG amplitudes of 138 VCA muscles following VN stimulation were measured using the Intraoperative Nerve Integrity Monitor (IONM) during thyroidectomy in 90 patients. The EMG amplitudes of VCA with VN stimulation were measured before and after AMRT. All data was collected during a 16-month period, between 2012 and 2013. Standard statistical methods were used to analyse the data. Results: A retrospective series of 7 cases is described where EMG activity with VN stimulation was lost following AMRT upon identification but prior to dissection of the RLN. In the prospective study of 90 patients, anteromedial rotation of the thyroid caused a significant increase in EMG amplitude on the right side (p=0.02) but not on the left (p=0.44). Multivariate analysis identified only extralaryngeal branching of the RLN to be associated with the EMG change. Conclusion: The increase in EMG amplitude of the VCA with right VN stimulation is likely to represent hyper excitability of the RLN after AMRT. Further studies are required to explore the underlying mechanism of this finding, and correlate it to the development of nerve palsy.

Reduced task-induced variations in the distribution of activity across back muscle regions in individuals with low back pain

This study investigated change in the distribution of lumbar erector spinae muscle activity and pressure pain sensitivity across the low back in individuals with low back pain (LBP) and healthy controls. Surface electromyographic (EMG) signals were recorded from multiple locations over the lumbar erector spinae muscle with a 13×5 grid of electrodes from 19 people with chronic nonspecific LBP and 17 control subjects as they performed a repetitive lifting task. The EMG root mean square (RMS) was computed for each location of the grid to form a map of the EMG amplitude distribution. Pressure pain thresholds (PPT) were recorded before and after the lifting task over a similar area of the back. For the control subjects, the EMG RMS progressively increased more in the caudal region of the lumbar erector spinae during the repetitive task, resulting in a shift in the distribution of muscle activity. In contrast, the distribution of muscle activity remained unaltered in the LBP group despite an overall increase in EMG amplitude. PPT was lower in the LBP group after completion of the repetitive task compared to baseline (average across all locations: pre: 268.0±165.9kPa; post: 242.0±166.7kPa), whereas no change in PPT over time was observed for the control group (320.1±162.1kPa; post: 322.0±179.5kPa). The results demonstrate that LBP alters the normal adaptation of lumbar erector spinae muscle activity to exercise, which occurs in the presence of exercise-induced hyperalgesia. Reduced variability of muscle activity may have important implications for the provocation and recurrence of LBP due to repetitive tasks.

PET/CT imaging of age- and task-associated differences in muscle activity during fatiguing contractions

The study compared positron emission tomography/computed tomography (PET/CT) of [(18)F]-2-fluoro-2-deoxy-D-glucose ([(18)F]-FDG) uptake by skeletal muscles and the amount of muscle activity as indicated by surface electromyographic (EMG) recordings when young and old men performed fatiguing isometric contractions that required either force or position control. EMG signals were recorded from thigh muscles of six young men (26 ± 6 yr) and six old men (77 ± 6 yr) during fatiguing contractions with the knee extensors. PET/CT scans were performed immediately after task failure. Glucose uptake in 24 leg muscles, quantified as standardized uptake values, was greater for the old men after the force task and differed across tasks for the young men (force, 0.64 ± 0.3 g/ml; position, 0.73 ± 0.3 g/ml), but not the old men (force, 0.84 ± 0.3 g/ml; position, 0.79 ± 0.26 g/ml) (age × task interaction; P < 0.001). In contrast, the rate of increase in EMG amplitude for the agonist muscles was greater for the young men during the two contractions and there was no difference for either group of subjects in the rate of increase in EMG amplitude across the two tasks. The imaging estimates of glucose uptake indicated age- and task-dependent differences in the spatial distribution of [(18)F]-FDG uptake by skeletal muscles during fatiguing contractions. The findings demonstrate that PET/CT imaging of [(18)F]-FDG uptake, but not surface EMG recordings, detected the modulation of muscle activity across the fatiguing tasks by the young men but not the old men.

Limited difference in time to failure between sustained force and position control contractions with the knee extensors

Different types of contractile fatiguing tasks ("force/position tasks") have shown that the rate of neuromuscular impairment is task dependent. Whether fatigue resistance is uniform across different types of limb joints is poorly understood because the force-position paradigm has mainly been applied to upper extremity joints under unstable conditions. Therefore, the purpose of the present study was to investigate task dependency in the more stable knee joint. Fourteen subjects performed two sustained isometric knee extensor contractions to failure. In the force task, 20% of maximal voluntary contraction force was maintained for as long as possible with visual feedback of the force, while in the position task, the load was similar, but subjects received visual joint angle feedback. No significant difference was observed in time to failure (force task: 423±61 s, position task: 379±48 s), increase in electromyographic amplitude or perceived exertion between tasks. The force-position paradigm has not been applied previously to the quadriceps, and the difference between the present and the previous results may partly be attributed to joint stability and the volume of co-contracting muscles, such that in addition to the previously noted mechanisms of muscle fatigue, the mechanical design of the relevant joint and muscle actuators may influence task dependency during sustained submaximal contractions.

Biofeedback and the electromyographic activity of pelvic floor muscles in pregnant women

Maintaining continence is among the functions of the pelvic floor muscles (PFM) and their dysfunction can cause urinary incontinence (UI), which is a common occurrence during pregnancy and the puerperal period. Pelvic floor muscle training (PFMT), therefore, is important during pregnancy, although most women perform the muscle contractions unsatisfactorily. This study is an exploratory analysis of the results of three electromyographic (EMG) activity biofeedback sessions in pregnant women. The study sample included 19 nulliparous women with low risk pregnancies. The participants performed three sessions of EMG biofeedback consisting of slow and fast contractions. The average value of the normalized amplitudes of surface electromyography was used to evaluate the results. The linear regression model with mixed effects was used for statistical analysis, with the EMG data normalized by maximum voluntary contraction (MVC). A steady increase in EMG amplitude was observed during each contraction and by the end of the biofeedback sessions, although this difference was only significant when comparing the first tonic contraction of each session (p=0.03). The results indicate that three sessions of training with biofeedback improved PFM EMG activity during the second trimester in women with low-risk pregnancies. The effectiveness of this protocol should be further investigated in randomized controlled trials.

Peak Torque, Mechanomyographic, And Electromyographic Responses Of The Vastus Medialis To Isometric Strength Training

2335 PURPOSE: The present investigation examined the peak torque (PT), mechanomyographic (MMG), and electromyographic (EMG) responses of the vastus medialis (VM) to eight weeks of isometric leg extension strength training. METHODS: Thirteen adult male volunteers (age19-29) were randomly assigned to a training (TRN) group (n = 6) or a control (CTL) group (n = 7). Maximal isometric PT for leg extension was measured along with EMG and MMG amplitude at leg flexion angles of 30°, 60°, and 90°. Measurements were collected three times during the study (weeks 0, 4, and 8). The TRN subjects performed unilateral isometric muscle actions with the non-dominant (ND) limb at 60° of leg flexion. The first two weeks, subjects performed two sets of muscle actions at 80% of their maximal isometric PT at 60°. For the remaining six weeks, subjects performed three sets of muscle actions at 80% of their maximal isometric PT. Maximal PT at 60° was reassessed at the end of the fourth week of training to adjust the training torque values. Each set consisted of ten repetitions lasting six seconds each. The subjects trained three times a week. RESULTS: The results indicated significant (p<0.05) increases in PT for the ND limb of the TRN group between week 0 and week 4 and between week 0 and week 8 of 9.8% and 14.8% respectively, at 60°. There was also a significant (p<0.05) increase in EMG amplitude for the ND limb of the TRN group between week 0 and week 8 of 46% at 60°. There was no training effect on MMG amplitude. CONCLUSION: These findings indicated that changes in muscle activation of the vastus medialis might be responsible for the training-induced increase in PT. The findings also indicated that there was no cross-training effect in the untrained limb of the TRN group for PT, MMG amplitude, and EMG amplitude.

Peak Torque, Mechanomyographic, And Electromyographic Responses Of The Vastus Medialis To Isometric Strength Training

2335 PURPOSE: The present investigation examined the peak torque (PT), mechanomyographic (MMG), and electromyographic (EMG) responses of the vastus medialis (VM) to eight weeks of isometric leg extension strength training. METHODS: Thirteen adult male volunteers (age19-29) were randomly assigned to a training (TRN) group (n = 6) or a control (CTL) group (n = 7). Maximal isometric PT for leg extension was measured along with EMG and MMG amplitude at leg flexion angles of 30°, 60°, and 90°. Measurements were collected three times during the study (weeks 0, 4, and 8). The TRN subjects performed unilateral isometric muscle actions with the non-dominant (ND) limb at 60° of leg flexion. The first two weeks, subjects performed two sets of muscle actions at 80% of their maximal isometric PT at 60°. For the remaining six weeks, subjects performed three sets of muscle actions at 80% of their maximal isometric PT. Maximal PT at 60° was reassessed at the end of the fourth week of training to adjust the training torque values. Each set consisted of ten repetitions lasting six seconds each. The subjects trained three times a week. RESULTS: The results indicated significant (p<0.05) increases in PT for the ND limb of the TRN group between week 0 and week 4 and between week 0 and week 8 of 9.8% and 14.8% respectively, at 60°. There was also a significant (p<0.05) increase in EMG amplitude for the ND limb of the TRN group between week 0 and week 8 of 46% at 60°. There was no training effect on MMG amplitude. CONCLUSION: These findings indicated that changes in muscle activation of the vastus medialis might be responsible for the training-induced increase in PT. The findings also indicated that there was no cross-training effect in the untrained limb of the TRN group for PT, MMG amplitude, and EMG amplitude.

Effect of fatigue on torque output and electromyographic measures of trunk muscles during isometric axial rotation

Ng JK-F, Parnianpour M, Richardson CA, Kippers V. Effect of fatigue on torque output and electromyographic measures of trunk muscles during isometric axial rotation. Arch Phys Med Rehabil 2003;84:374-81. Objectives: To examine the changes in torque output resulting from fatigue, as well as changes in electromyographic measures of trunk muscles during isometric axial rotation and to compare these changes between directions of axial rotation. Design: Subjects performed fatiguing right and left isometric axial rotation of the trunk at 80% of maximum voluntary contraction while standing upright. Setting: A rehabilitation center. Participants: Twenty-three men with no history of back pain. Interventions: Not applicable. Main Outcome Measures: Surface electromyographic signals were recorded from 6 trunk muscles bilaterally. The primary torque in the transverse plane and the coupling torques in sagittal and coronal planes were also measured. Results: During the fatiguing axial rotation contraction, coupling torques of both sagittal and coronal planes were slightly decreased and no difference was found between directions of axial rotation. Decreasing median frequency and an increase in electromyographic amplitude were also found in trunk muscles with different degrees of changes in individual muscles. There were significant differences ( P[lt ].05) between right and left axial rotation exertions in median frequency slope of external oblique, internal oblique, latissimus dorsi, and iliocostalis lumborum muscles, but no such difference was found in median frequency slope of rectus abdominis and multifidus muscles. This could be attributed to different functional roles among the muscles. Similar differences ( P[lt ].05) between right and left axial rotation in median frequency slope were also detected in the electromyographic amplitude slope of the trunk muscles. Coefficient of variation of the torque output and electromyographic activation in most of the trunk muscles increased during the fatigue process. Conclusion: The changing coupling torque, different fatigue rate, and activation changes of trunk muscles, as well as the increase in variability during fatiguing axial rotation exertion, could affect the internal loading and stability of the spine; this needs to be further quantified in future studies. [copy ] 2003 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Neuromuscular monitoring in intensive care patients: milliamperage requirements for supramaximal stimulation

We investigated the effects of peripheral oedema on the supramaximal current required for neuromuscular monitoring of critically ill patients. We studied 32 sedated patients who had not needed a neuromuscular blocking drug. The presence of oedema over the volar aspect of both wrists was assessed by a blinded observer and graded (grade 0, no oedema; grade 1, mild oedema; grade 2, gross oedema). The supramaximal current was derived by applying an incrementally increasing current over the ulnar nerve and measuring the amplitude of the electromyographic (EMG) response of the first dorsal interosseous muscle. The supramaximal current was that current above which there was no significant increase in EMG amplitude. It was 40 mA in the absence of oedema. This current was significantly increased in the presence of grade 1 oedema (60 mA, Mann-Whitney test, P<0.01) and grade 2 oedema (82.5 mA, Mann-Whitney test, P<0.01). In the presence of oedema, the required supramaximal current decreased significantly after the application of pressure over the stimulating electrodes (Wilcoxon signed rank test, P<0.05). Supramaximal current in critically ill patients is increased in the presence of peripheral oedema. We recommend that nerve stimulators used for neuromuscular monitoring in the ICU are capable of delivering a stimulus current of at least 100 mA.

Functional subdivision of the upper trapezius muscle during maximal isometric contractions

The electromyographic (EMG) activity pattern across the upper trapezius of 22 healthy subjects was investigated during maximal isometric contractions. Eight bipolar surface electrodes with 10 mm distance between adjacent electrode pairs were placed on a line from the clavicle to the scapula. At the region near the clavicle the highest EMG amplitudes were recorded during 90 ° arm abduction. At the more posterior parts the highest amplitudes were found both during arm abduction and shoulder elevation. A double differential recording technique which reduced the EMG cross-talk contribution supported the finding that the upper trapezius was differently activated when the arm posture was changed. The normalized EMG amplitude-force relationship during the shoulder elevation showed a curvilinear relationship on the anterior part of the upper trapezius with a slower increase in EMG amplitude than force at low force. The slope of the curve, at low force, increased gradually in the posterior direction on the upper trapezius. The EMG activity patterns across the upper trapezius indicate a flexibility in motor activation which maybe reflects a functional optimization of the contractions performed by this muscle.

The effects of parallel bars, body weight support and speed on the modulation of the locomotor pattern of spastic paretic gait. A preliminary communication

The effects of walking with and without parallel bars, providing 40% body weight support (BWS) and increasing speed on the gait pattern of spastic paretic subjects during treadmill locomotion were investigated. In asymmetrically involved subjects, walking without parallel bars led to a more symmetrical gait pattern with decreased compensation of the less involved side. This was accompanied by changes in electromyographic (EMG) and sagittal angular displacement profiles which favoured a more normal swing phase of the more involved limb. When symmetrically involved subjects walked without parallel bars, increases in EMG activity, with prolonged activation during the stance phase were noted, especially in the distal muscles. Providing 40% BWS facilitated gait when walking without parallel bars especially in the asymmetrically or severely involved subjects who showed marked difficulty at 0% BWS. Forty percent BWS led to a decrease in clonus associated with walking without parallel bars. Higher treadmill speeds increased clonus in some subjects while in others it only caused a small increase in EMG amplitude. Implications for gait training are discussed.