Spatial EMG potential distribution of biceps brachii muscle during resistance training and detraining

Acute neuromuscular and perceptual responses to blood flow restriction exercise in adults with severe haemophilia: A pilot study

INTRODUCTION

No previous studies have implemented a standard blood flow restriction (BFR) training session in people with severe haemophilia (PwH), where this type of training has been contraindicated.

AIMS

The purpose of this study was to evaluate the tolerability, adverse events, and neuromuscular and perceptual responses to an acute session of low load (LL) knee extensions with BFR in PwH under prophylaxis.

METHODS

Eight PwH performed one LL-BFR session with 40% arterial occlusion pressure (AOP). Perceptual responses and adverse effects were assessed, together with high-density surface electromyography of vastus medialis (VM) and lateralis (VL).

RESULTS

Significant normalized root mean square differences were found within each set, but not between sets. Spatial distribution (centroid displacement (p > .05), modified entropy (VM, set two, cycles three and five, p = .032) and coefficient of variation (VM, set two, cycles four and five lower than cycle three (p = .049; p = .036)) showed changes within each set. Median frequency showed a slight increase during cycle four of set four (p = .030). Rate of perceived exertion slightly increased with each set while tolerability slightly decreased in the last set and fear of training with BFR generally decreased after the session.

CONCLUSIONS

In PwH, a LL-BFR session at 40% AOP is safe and feasible. Our results suggest that potential muscle impairments may blunt neuromuscular adaptations induced by BFR.

Analysis of the suprahyoid muscles during tongue elevation: High-density surface electromyography as a novel tool for swallowing-related muscle assessment

BACKGROUND

High-density surface electromyography (HD-sEMG) has enabled non-invasive analysis of motor unit (MU) activity and recruitment, but its application to swallowing-related muscles is limited.

OBJECTIVE

We aimed to investigate the utility of HD-sEMG for quantitatively evaluating the MU recruitment characteristics of the suprahyoid muscles during tongue elevation.

METHODS

We measured the sEMG activity of the suprahyoid muscles of healthy participants during tongue elevation using HD-sEMG. Maximum voluntary contraction (MVC) was measured, followed by data collection during sustained and ramp-up tasks to capture suprahyoid muscle activity. Changes in the temporal/spatial MU recruitment patterns within individual suprahyoid muscles were analysed.

RESULTS

This study enrolled 16 healthy young adults (mean age: 27.8 ± 5.3 years; eight males and eight females). Increasing muscle force corresponded to a decrease in modified entropy and correlation coefficient and an increase in the coefficient of variation. No significant differences were observed between male and female participants.

CONCLUSION

The results of this study, consistent with those observed in other muscles, such as the vastus lateralis muscle, suggest that HD-sEMG is a valuable and reliable tool for quantitatively evaluating MU recruitment in the suprahyoid muscles. This measurement technique holds promise for novel assessments of swallowing function.

Neuromuscular Responses and Perceptions of Health Status and Pain-Related Constructs in End-Stage Knee Osteoarthritis During Resistance Training With Blood Flow Restriction

ABSTRACT

Ogrezeanu, DC, López-Bueno, L, Sanchís-Sánchez, E, Carrasco, JJ, Cuenca-Martínez, F, Suso-Martí, L, López-Bueno, R, Cruz-Montecinos, C, Martinez-Valdes, E, Casaña, J, and Calatayud, J. Neuromuscular responses and perceptions of health status and pain-related constructs in end-stage knee osteoarthritis during resistance training with blood flow restriction. J Strength Cond Res 38(4): 762-772, 2024-We aimed to evaluate the neuromuscular responses and their relationship with health status, kinesiophobia, pain catastrophizing, and chronic pain self-efficacy in patients with end-stage knee osteoarthritis during acute resistance training with different levels of blood flow restriction (BFR). Seventeen patients with end-stage knee osteoarthritis participated in 3 experimental sessions separated by 3 days, performing 4 sets of knee extensions with low load and 3 levels of concurrent BFR performed in a random order: control (no BFR), BFR at 40% arterial occlusion pressure (AOP), and BFR at 80% AOP. Normalized root-mean-square (nRMS), nRMS spatial distribution (centroid displacement, modified entropy, and coefficient of variation), and normalized median frequency (nFmed) were calculated from the vastus medialis (VM) and lateralis (VL) using high-density surface electromyography. Subjects were asked to report adverse effects after the sessions. In the VM, nRMS was higher with 80% AOP than with 40% AOP ( p = 0.008) and control ( p < 0.001), whereas there were no differences between conditions in the VL. Normalized root-mean-square also showed an association with pain catastrophizing, chronic pain self-efficacy, and health status (VM: -0.50, 0.49, -0.42; VL: -0.39, 0.27, -0.33). Spatial distribution varied between conditions but mostly in the VL. Overall, nFmed did not vary, with only a slight increase in the VL with 40% AOP, between set 3 and 4. BFR during knee extensions at 80% AOP increases VM activity and VL amplitude distribution more than 40% AOP and control. Importantly, muscle activity increases are modulated by pain catastrophizing, chronic pain self-efficacy, and health status in these patients, and kinesiophobia seems to especially modulate entropy.

Effects of 7-day quercetin intervention on motor unit activity and muscle contractile properties before and after resistance exercise in young adults randomized controlled trials

We investigated whether the alteration of the motor unit recruitment threshold (MURT) caused by quercetin ingestion intervention for 7 days modifies motor unit activation patterns before and after a single session of resistance exercise. Twenty young male and female adults were divided into two groups: ingestion of placebo (PLA) or quercetin glycosides at 200 mg/day (QUE). High-density surface electromyography during submaximal contractions was measured to assess the motor unit firing rate (MUFR) and MURT of the vastus lateralis muscle before (PRE) and after (POST) resistance exercise (DAY1). The same measurements were repeated after 7 days of placebo or quercetin glycoside ingestion (DAY8). In QUE, MURT decreased more from DAY1-PRE to DAY8-PRE (29.1 ± 9.1 to 27.1 ± 9.5% MVC, p < 0.001) but not in PLA (29.8 ± 10.4 to 28.9 ± 9.7% MVC, p < 0.167). For percentage change in MUFR following resistance exercise, there was a significant interaction (day × group, p < 0.001). The degree of changes in MURT from DAY1-PRE to DAY8-PRE was significantly correlated with the percentage change of MUFR from DAY8-PRE to DAY8-POST in QUE (p = 0.014, r = -0.363) but not in PLA (p = 0.518). The study suggests that 7-day quercetin ingestion alters the motor unit recruitment pattern, and this may induce changes in motor unit firing patterns during a single session of resistance training (Trial registration: UMIN000052255, R000059650).

Advances in EMG measurement techniques, analysis procedures, and the impact of muscle mechanics on future requirements for the methodology

Muscular coordination enables locomotion and interaction with the environment. For more than 50 years electromyography (EMG) has provided insights into the central nervous system control of individual muscles or muscle groups, enabling both fine and gross motor functions. This information is available either at individual motor units (Mus) level or on a more global level from the coordination of different muscles or muscle groups. In particular, non-invasive EMG methods such as surface EMG (sEMG) or, more recently, spatial mapping methods (High-Density EMG - HDsEMG) have found their place in research into biomechanics, sport and exercise, ergonomics, rehabilitation, diagnostics, and increasingly for the control of technical devices. With further technical advances and a growing understanding of the relationship between EMG and movement task execution, it is expected that with time, especially non-invasive EMG methods will become increasingly important in movement sciences. However, while the total number of publications per year on non-invasive EMG methods is growing exponentially, the number of publications on this topic in journals with a scope in movement sciences has stagnated in the last decade. This review paper contextualizes non-invasive EMG development over the last 50 years, highlighting methodological progress. Changes in research topics related to non-invasive EMG were identified. Today non-invasive EMG procedures are increasingly used to control technical devices, where muscle mechanics have a minor influence. In movement science, however, the effect of muscle mechanics on the EMG signal cannot be neglected. This explains why non-invasive EMG's relevance in movement sciences has not developed as expected.

Heavier Load Alters Upper Limb Muscle Synergy with Correlated fNIRS Responses in BA4 and BA6

In neurorehabilitation, motor performances may improve if patients could accomplish the training by overcoming mechanical loads. When the load inertia is increased, it has been found to trigger linear responses in motor-related cortices. The cortical responses, however, are unclear whether they also correlate to changes in muscular patterns. Therefore, it remains difficult to justify the magnitude of load during rehabilitation because of the gap between cortical and muscular activation. Here, we test the hypothesis that increases in load inertia may alter the muscle synergies, and the change in synergy may correlate with cortical activation. Twelve healthy subjects participated in the study. Each subject lifted dumbbells (either 0, 3, or 15 pounds) from the resting position to the armpit repetitively at 1 Hz. Surface electromyographic signals were collected from 8 muscles around the shoulder and the elbow, and hemodynamic signals were collected using functional near-infrared spectroscopy from motor-related regions Brodmann Area 4 (BA4) and BA6. Results showed that, given higher inertia, the synergy vectors differed farther from the baseline. Moreover, synergy similarity on the vector decreased linearly with cortical responses in BA4 and BA6, which associated with increases in inertia. Despite studies in literature that movements with similar kinematics tend not to differ in synergy vectors, we show a different possibility that the synergy vectors may deviate from a baseline. At least 2 consequences of adding inertia have been identified: to decrease synergy similarity and to increase motor cortical activity. The dual effects potentially provide a new benchmark for therapeutic goal setting.

Effect of postural differences on the activation of intrinsic foot muscles during ramp-up toe flexion in young men

BACKGROUND

Intrinsic foot muscle exercises are used in clinical and sports practice to improve performance. Force generation during toe flexion is greater in the standing posture than in the sitting posture; nonetheless, the mechanism underlying the activation of intrinsic foot muscles during force generation and whether there exists a difference between these two postures still remain unclear.

RESEARCH QUESTION

Are the activities of intrinsic foot muscles affected by standing and sitting postures during gradual force generation?

METHODS

Seventeen men participated in the laboratory based cross-sectional study. Each participant performed a force ramp-up toe flexion task from 0% to 80% of the maximal toe flexor strength (MTFS) in sitting and standing postures. High-density surface electromyography signals obtained during the task were determined by calculating the root mean square (RMS). Additionally, modified entropy and coefficient of variation (CoV) were calculated at 20-80 % MTFS for each 10 % MTFS.

RESULTS

The RMS between the two postures indicated an interaction effect (p < 0.01). Post-hoc analyses revealed that intrinsic foot muscle activity during the ramp-up task was significantly higher in the standing posture than in the sitting posture at 60 % MTFS (67.53 ± 15.91 vs 54.64 ± 19.28 % maximal voluntary contraction [MVC], p = 0.03), 70 % MTFS (78.11 ± 12.93 vs 63.28 ± 18.65 % MVC, p = 0.01), and 80 % MTFS (81.78 ± 14.07 vs 66.90 ± 20.32 % MVC, p = 0.02). In the standing posture, the modified entropy at 80 % MTFS was lower than that at 20 % MTFS (p = 0.03), and the CoV at 80 % MTFS was higher than that at 20 % MTFS (p = 0.03).

SIGNIFICANCE

These results indicated that posture selection is important for high-intensity exercises of the intrinsic foot muscles, such as resistance training. Thus, improving performance related to toe flexor strength might be more effective when conducted under adequate weight-bearing situations, such as in the standing posture.

SPATIAL DISTRIBUTION PATTERN OF THE ELECTROMYOGRAPHIC POTENTIAL IN THE VASTUS MEDIALIS AND LATERALIS MUSCLES FOR THREE KNEE FLEXION ANGLES DURING ISOMETRIC KNEE EXTENSION

Understanding the function of the vastus lateralis (VL) and vastus medialis (VM) muscles is important since these muscles are essential for daily and sport activities. The association between the knee flexion angle and spatial muscle activation is controversial. This study compares the distribution patterns of multi-channel electromyographic activities of the VL and VM muscles at three knee flexion angles for three intensities of isometric contraction. Sixteen men performed isometric knee extensions at 30%, 50% and 70% maximal voluntary contraction (MVC), at [Formula: see text], [Formula: see text] and [Formula: see text] knee flexion. Alterations in the spatial electromyographic potential distribution were determined by the root mean square (RMS), modified entropy, and coefficient of variation in the spatial electromyographic potential. Modified entropy and the coefficient of variation showed differences in the VM muscle between [Formula: see text] and [Formula: see text] knee flexion. The RMS at the three angles was similar between the VL and VM muscles, with no differences in contraction intensities at 30%, 50%, or 70% MVC. The VL and VM muscle function differed among knee flexion angles, as did activity in the distal and proximal VM muscles. These findings suggest the need for functional evaluation of the VL and VM muscles at each knee flexion angle.

Physical and electrophysiological motor unit characteristics are revealed with simultaneous high-density electromyography and ultrafast ultrasound imaging

Electromyography and ultrasonography provide complementary information about electrophysiological and physical (i.e. anatomical and mechanical) muscle properties. In this study, we propose a method to assess the electrical and physical properties of single motor units (MUs) by combining High-Density surface Electromyography (HDsEMG) and ultrafast ultrasonography (US). Individual MU firings extracted from HDsEMG were used to identify the corresponding region of muscle tissue displacement in US videos. The time evolution of the tissue velocity in the identified region was regarded as the MU tissue displacement velocity. The method was tested in simulated conditions and applied to experimental signals to study the local association between the amplitude distribution of single MU action potentials and the identified displacement area. We were able to identify the location of simulated MUs in the muscle cross-section within a 2 mm error and to reconstruct the simulated MU displacement velocity (cc > 0.85). Multiple regression analysis of 180 experimental MUs detected during isometric contractions of the biceps brachii revealed a significant association between the identified location of MU displacement areas and the centroid of the EMG amplitude distribution. The proposed approach has the potential to enable non-invasive assessment of the electrical, anatomical, and mechanical properties of single MUs in voluntary contractions.

High-Density Electromyography Provides Improved Understanding of Muscle Function for Those With Amputation

Transtibial amputation can significantly impact an individual's quality of life including the completion of activities of daily living. Those with lower limb amputations can harness the electrical activity from their amputated limb muscles for myoelectric control of a powered prosthesis. While these devices use residual muscles from transtibial-amputated limb as an input to the controller, there is little research characterizing the changes in surface electromyography (sEMG) signal generated by the upper leg muscles. Traditional surface EMG is limited in the number of electrode sites while high-density surface EMG (HDsEMG) uses multiple electrode sites to gather more information from the muscle. This technique is promising for not only the development of myoelectric-controlled prostheses but also advancing our knowledge of muscle behavior with clinical populations, including post-amputation. The HDsEMG signal can be used to develop spatial activation maps and features of these maps can be used to gain valuable insight into muscle behavior. Spatial features of HDsEMG can provide information regarding muscle activation, muscle fiber heterogeneity, and changes in muscle distribution and can be used to estimate properties of both the amputated limb and intact limb. While there are a few studies that have examined HDsEMG in amputated lower limbs they have been limited to movements such as gait. The purpose of this study was to examine the quadriceps muscle during a slow, moderate and fast isokinetic knee extensions from a control group as well as a clinical patient with a transtibial amputation. HDsEMG was collected from the quadriceps of the dominant leg of 14 young, healthy males (mean age = 25.5 ± 7 years old). Signals were collected from both the intact and amputated limb muscle of a 23 year old clinical participant to examine differences between the affected and unaffected leg. It was found that there were differences between the intact and amputated limb limb of the clinical participant with respect to muscle activation and muscle heterogeneity. While this study was limited to one clinical participant, it is important to note the differences in muscle behavior between the intact and amputated limb limb. Understanding these differences will help to improve training protocols for those with amputation.

Alterations of tibialis anterior muscle activation pattern in subjects with type 2 diabetes and diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is associated with loss of motor units (MUs), which can cause changes in the activation pattern of muscle fibres. This study investigated the pattern of muscle activation using high-density surface electromyography (HD-sEMG) signals from subjects with type 2 diabetes mellitus (T2DM) and DPN. Thirty-five adults participated in the study: 12 healthy subjects (HV), 12 patients with T2DM without DPN (No-DPN) and 11 patients with T2DM with DPN (DPN). HD-sEMG signals were recorded in the tibialis anterior muscle during an isometric contraction of ankle dorsiflexion at 50% of the maximum voluntary isometric contraction (MVIC) during 30-s. The calculated HD-sEMG signals parameters were the normalised root mean square (RMS), normalised median frequency (MDF), coefficient of variation (CoV) and modified entropy (ME). The RMS increased significantly (p = 0.001) with time only for the DPN group, while the MDF decreased significantly (p < 0.01) with time for the three groups. Moreover, the ME was significantly lower (p = 0.005), and CoV was significantly higher (p = 0.003) for the DPN group than the HV group. Using HD-sEMG, we have demonstrated a reduction in the number of MU recruited by individuals with DPN. This study provides proof of concept for the clinical utility of this technique for identifying neuromuscular impairment caused by DPN.

Effect of Acute Static Stretching on the Activation Patterns Using High-Density Surface Electromyography of the Gastrocnemius Muscle during Ramp-Up Task

This study aimed to evaluate motor unit recruitment during submaximal voluntary ramp contraction in the medial head of the gastrocnemius muscle (MG) by high-density spatial electromyography (SEMG) before and after static stretching (SS) in healthy young adults. SS for gastrocnemius was performed in 15 healthy participants for 2 min. Normalized peak torque by bodyweight of the plantar flexor, muscle activity at peak torque, and muscle activation patterns during ramp-up task were evaluated before and after SS. Motor unit recruitment during the submaximal voluntary contraction of the MG was measured using SEMG when performing submaximal ramp contractions during isometric ankle plantar flexion from 30 to 80% of the maximum voluntary contraction (MVC). To evaluate the changes in the potential distribution of SEMG, the root mean square (RMS), modified entropy, and coefficient of variation (CV) were calculated from the dense surface EMG data when 10% of the MVC force was applied. Muscle activation patterns during the 30 to 80% of MVC submaximal voluntary contraction tasks were significantly changed from 50 to 70% of MVC after SS when compared to before. The variations in motor unit recruitment after SS indicate diverse motor unit recruitments and inhomogeneous muscle activities, which may adversely affect the performance of sports activities.

Influence of hybrid assistive limb gait training on spatial muscle activation patterns in spinal muscular atrophy type III

Background: Despite the potential benefits, the effects of Hybrid Assistive Limb (HAL) gait training on changes in neuromuscular activation that accompany functional gains in individuals with spinal muscular atrophy (SMA) type III is not well known. In this article, we quantify the effects of HAL gait training on spatial muscle activity patterns in a patient with SMA type III using multi-channel surface electromyography (SEMG). Methods: A 21-years old male (168 cm, 47.8 kg) with spinal muscular atrophy type III, when diagnosed at 18-years old by genetic screening, participated in this case study. Although he presented with forearm distal muscle weakness, atrophy of the intrinsic muscles of the hand, and neuromuscular fatigue, his activities of daily living is independent. The patient underwent a separate, single 33-minute session of both HAL and treadmill gait training. To evaluate the coefficient of variation (CoV) of force and alterations in the SEMG spatial distribution patterns, modified entropy and CoV of root mean square (RMS) were calculated from the vastus lateralis (VL) muscle before and after the intervention of HAL and treadmill gait training. Each training session was separated by a period of one month to avoid cross-over effects. Results: There was a greater decrease in the ΔCoV of force and an increase in the magnitude of whole VL muscle activation from pre-intervention to post-intervention with the HAL gait training as compared to the treadmill gait training. In response to only HAL gait training, the CoV of RMS was higher, and the modified entropy was lower post-intervention than pre-intervention. Conclusions: Our results support the notion that HAL gait training has a positive benefit on motor output not only in the magnitude of SEMG generated but also the patterns of neural activation.

The effect of electrical muscle stimulation on quadriceps muscle strength and activation patterns in healthy young adults

AbstractThe aim of the present study was to clarify the effect of electrical muscle stimulation (EMS) on the spatial distribution pattern of electromyographic activity in healthy young adults using multi-channel surface electromyography (SEMG). A total of 32 men (age = 21-26 years) were randomly assigned to the intervention group (n = 18) and control group (n = 14). Participants in the intervention group performed EMS to stimulate the bilateral lower limb muscle for four weeks (20 min/3 days/week). The control group received no EMS intervention. To understand the effects of EMS, the following measurements were made at baseline and four weeks: knee extension torque, muscle mass, and spatial distribution of neuromuscular activation during a target torques [10%, 30%, 50%, and 70% of the maximal voluntary contraction (MVC)] using multi-channel SEMG. The knee extension torque was significantly increased in intervention group compared with control group (p < 0.0001). However, the muscle mass did not show a significant difference between pre and post intervention in each group. The muscle activation patterns of 50% and 70% MVC task showed significant enhancement between baseline and four weeks in the intervention group. Furthermore, a moderate correlation between Δ knee extension torque and Δ spatial distribution pattern of electromyographic activity of 50% and 70% MVC in the intervention group was observed. These results suggested EMS intervention induced different distribution of muscle activity at high-intensity muscle contraction compared with low-intensity muscle contraction.

Effect of inspiratory resistive training on diaphragm shear modulus and accessory inspiratory muscle activation

This study aimed to elucidate changes in diaphragm and accessory inspiratory muscle (sternocleidomastoid (SCM) muscle and intercostal muscle (IC)) function after a 6-week training program. Nineteen male elite collegiate swimmers were assigned to either a control group (n = 9) or training group (n = 10). The subjects in the training group performed 30 maximum inspirations at a load resistance of 50% of maximum inspiratory mouth pressure (PImax) using an inspiratory muscle training device. These were conducted twice per day and 6 days per week. At baseline and after 6 weeks, PImax, shear modulus of the diaphragm, and electromyograms (EMG) of the SCM and IC during a maximal inspiratory maneuver were evaluated. Relative change in PImax was greater in the training group than in controls. The shear modulus during a PImax maneuver had increased significantly in both groups after 6 weeks. EMG amplitudes of the SCM increased in the training group after 6 weeks, but not in the control group. EMG amplitudes of the IC did not change after 6 weeks in either group. These results suggest that 6-week inspiratory resistive training significantly improves the activation of the SCM, which could be one of the major mechanisms behind increases in inspiratory muscle strength after resistive training. Novelty Six-week inspiratory resistive training increased diaphragm stiffness during maximal inspiration maneuver. Six-week inspiratory resistive training increased electromyogram amplitudes of the sternocleidomastoid during maximal inspiration maneuver.

Effect of the Combination of Whole-Body Neuromuscular Electrical Stimulation and Voluntary Exercise on Metabolic Responses in Human

Purpose

Since neuromuscular electrical stimulation (NMES) can recruit high-threshold motor units and enhance glucose metabolism, the combination of NMES and voluntary low-intensity exercise would induce both anerobic and aerobic energy consumptions and this type of exercise could be more efficient and effective than conventional exercise regimens. We aimed to investigate metabolic responses and muscle fatigue during whole body NMES (WB-NMES), voluntary exercise, and their combination.

Methods

The blood lactate concentration and maximal voluntary contraction were measured before and after specified exercises: WB-NMES (E), voluntary exercise (V), and their combination (VE), and expired gas was sampled during the exercises in thirteen healthy young men. Each exercise was conducted for 15 min and interval between exercise was > 48h.

Results

Energy expenditure and V˙O2 relative to the body mass during VE were significantly higher than during V and E (p < 0.05). The Respiratory gas exchange ratio (RER) during both E and VE was higher than during V (p < 0.05), and the blood lactate concentration after VE was significantly higher than after V and E (p < 0.05). Although V˙O2 relative to the body mass was 18.6 ± 3.1 ml/min/kg and the metabolic equivalent was 5.31 ± 0.89 Mets, the blood lactate concentration reached 7.5 ± 2.7 mmol/L after VE.

Conclusion

These results suggest that the combination of WB-NMES and voluntary exercise can enhance the metabolic response to a level equivalent to high intensity exercise under the net physiological burden of low-middle intensity exercises.

The effect of a portable electrical muscle stimulation device at home on muscle strength and activation patterns in locomotive syndrome patients: A randomized control trial

The aim of the present study was to quantify the effect of electrical muscle stimulation (EMS) intervention using a portable device on muscle strength and activation patterns in locomotive syndrome. Nineteen women were randomly assigned to the intervention group (n = 10; age = 71-82 years) and control group (n = 9; age = 70-84 years). Participants in the intervention group used a portable EMS device to stimulate the bilateral quadriceps muscles for 8 weeks (23 min/5 days/week). To understand the effects of EMS, the following measurements were made at baseline, 8 weeks, and 12 weeks: locomotive syndrome assessment score, knee extensor strength, vastus lateralis muscle activation patterns during a maximal isometric knee extension contraction using multi-channel surface electromyography, and muscle thickness. The locomotive syndrome assessment, muscle strength, muscle thickness, and muscle activity patterns in the intervention group were significantly different to control after 8 weeks (p < 0.05). However, these results were not sustained at 12 weeks. EMS increased locomotor assessment scores, which were accompanied by enhanced muscle strength, increased muscle thickness, and changes in muscle activation patterns in locomotive syndrome patients. These results suggest that EMS is potentially useful for improving muscle neural activation and force output in locomotive syndrome.

The effect of medication on vastus lateralis muscle activation patterns in Parkinson's disease patients

The effect of levodopa on muscle activity patterns in Parkinson's disease (PD) patients is currently unclear. The aim of the present study was to compare the spatial distribution pattern of electromyographic activity during sustained isometric contraction in PD patients during on- and off-medication periods using multi-channel surface electromyography (SEMG). Ten female PD patients were recruited for the present study. All patients performed a sustained isometric knee extension at 10% maximum voluntary contraction task for 60 s. To evaluate alterations in the spatial SEMG potential distribution, the coefficient of variation (CV) of force, normalized root mean square (RMS), modified entropy, CV of the RMS, and correlation coefficients were calculated at during contraction task. The off-medication period exhibited more fluctuation during the contraction task than those in the on-medication period. The off-medication period exhibited less change in modified entropy, the CV of RMS, the correlation coefficient and patterns of spatial SEMG distribution. These data demonstrated that the heterogeneity and changes in the activation pattern are smaller in the off-medication period than in those in the on-medication period. These findings might indicate that levodopa enhanced the activation of muscle action potentials during force production.

Relationships between muscle strength and multi-channel surface EMG parameters in eighty-eight elderly

Background

Since age-related muscle strength loss cannot be explained solely by muscle atrophy, other determinants would also contribute to muscle strength in elderly. The present study aimed to clarify contribution of neuromuscular activation pattern to muscle strength in elderly group. From 88 elderlies (age: 61~ 83 years), multi-channel surface electromyography (EMG) of the vastus lateralis muscle was recorded with two-dimensional 64 electrodes during isometric submaximal ramp-up knee extension to assess neuromuscular activation pattern. Correlation analysis and stepwise regression analysis were performed between muscle strength and the parameters for signal amplitude and spatial distribution pattern, i.e., root mean square (RMS), correlation coefficient, and modified entropy of multi-channel surface EMG.

Results

There was a significant correlation between muscle strength and RMS (r = 0.361, p = 0.001) in the elderly. Muscle thickness (r = 0.519, p < 0.001), RMS (r = 0.288, p = 0.001), and normalized RMS (r = 0.177, p = 0.047) were selected as major determinants of muscle strength in stepwise regression analysis (r = 0.664 in the selected model).

Conclusion

These results suggest that inter-individual difference in muscle strength in elderly can be partly explained by surface EMG amplitude. We concluded that neuromuscular activation pattern is also major determinants of muscle strength on elderly in addition to indicator of muscle volume.

Spatial electromyography distribution pattern of the vastus lateralis muscle during ramp up contractions in Parkinson's disease patients

Parkinson's disease (PD) related decreases in muscle strength may result from both central and peripheral factors. However, the effect of PD on the neuromuscular system, such as motor unit activation properties, remains unclear. The purpose of the present study was to compare the spatial distribution pattern of electromyographic activity during sustained contractions in healthy subjects and PD patients. Twenty-five female PD patients and 25 healthy age-matched female control subjects performed ramp submaximal contractions during an isometric knee extension from 20% to 80% of the maximal voluntary contraction (MVC). To evaluate alterations in the spatial electromyography (EMG) potential distribution, normalized root mean square (RMS), modified entropy, coefficient of variation, and correlation coefficients were calculated from multi-channel surface electromyography at 10% force increments. The comparison between PD and healthy subjects revealed that, during increased force exertions, PD patients exhibited less change in normalized RMS, modified entropy, coefficient of variation, and pattern of spatial EMG distribution. These data showed that the heterogeneity and the changes in the activation pattern are smaller in the PD patients than in healthy subjects. This finding may be associated with central adaptation and/or peripheral changes in PD patients.

Sex differences in variances of multi-channel surface electromyography distribution of the vastus lateralis muscle during isometric knee extension in young adults

PURPOSE

The aim of the present study was to compare spatial electromyographic potential distribution during force production between healthy young female and male using multi-channel surface electromyography (multi-SEMG).

METHODS

Thirty healthy subjects (15 females) performed sustained isometric knee extension at 10% maximal voluntary contraction (MVC) task for 120 s. Multi-SEMG signals from the vastus lateralis muscle were detected and the modified entropy, coefficient of variation (CV), and correlation coefficient determined.

RESULTS

The modified entropy and CV showed significant interaction and difference between females and males at all time points during the 10% MVC task. The correlation coefficient in females was significantly lower at 90 and 120 s than that of males.

CONCLUSIONS

The multi-SEMG potential distribution pattern in females showed more varied motor unit recruitment during sustained low-intensity isometric contraction than that of males. Variations in motor unit recruitment may result from recruitment and/or de-recruitment of motor units.