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1.
J Vis Exp ; (169)2021 03 04.
Artigo em Inglês | MEDLINE | ID: mdl-33749677

RESUMO

Skeletal muscle plasticity in response to countless conditions and stimuli mediates concurrent functional adaptation, both negative and positive. In the clinic and the research laboratory, maximal muscular strength is widely measured longitudinally in humans, with knee extensor musculature the most reported functional outcome. Pathology of the knee extensor muscle complex is well documented in aging, orthopedic injury, disease, and disuse; knee extensor strength is closely related to functional capacity and injury risk, underscoring the importance of reliable measurement of knee extensor strength. Repeatable, in vivo assessment of knee extensor strength in pre-clinical rodent studies offers valuable functional endpoints for studies exploring osteoarthritis or knee injury. We report an in vivo and non-invasive protocol to repeatedly measure isometric peak tetanic torque of the knee extensors in mice across time. We demonstrate consistency using this novel method to measure knee extensor strength with repeated assessment in multiple mice producing similar results.


Assuntos
Articulação do Joelho/fisiologia , Músculo Esquelético/fisiologia , Animais , Área Sob a Curva , Calibragem , Análise de Dados , Eletrodos , Humanos , Contração Isométrica/fisiologia , Camundongos Endogâmicos C57BL , Força Muscular/fisiologia , Software , Torque
2.
Am J Phys Med Rehabil ; 100(3): 235-242, 2021 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-33595935

RESUMO

OBJECTIVE: The aims of this study were to (1) evaluate the relationships between stationary and dynamic associated reaction (AR) tests in people with acquired brain injury using surface electromyography (sEMG) muscle activity and three-dimensional motion analysis kinematic measures and (2) assess the test-retest reliability of sEMG and seated tests of ARs. DESIGN: Forty-two adults with acquired brain injury underwent AR testing with seated contralateral maximal voluntary isometric contraction tests and walking (self-selected and fast speeds). Associated reaction measurements included biceps brachii sEMG, elbow goniometry, and three-dimensional motion analysis kinematics during walking. Pearson correlations evaluated the relationships between seated and dynamic walking AR tests and between muscle activity and kinematic measures. Chronic participants were reassessed 1 wk later for reliability. RESULTS: A strong (r = 0.65) and moderate (r = 0.53) relationship existed for biceps brachii sEMG during seated and walking tests at self-selected and fast walk, respectively. A weak to moderate relationship existed between biceps brachii sEMG and kinematics during walking and between seated and walking measures of ARs (r = 0.23-0.53). All tests had strong to very strong test-retest reliability (intraclass correlation coefficients, >0.78). CONCLUSION: Seated contralateral maximal voluntary isometric contraction tests correlate only weakly to moderately with AR walking kinematics and moderately to strongly with biceps brachii activation during walking. Moderate relationships exist between sEMG and kinematics, indicating that they may provide different information for ARs.


Assuntos
Lesões Encefálicas/fisiopatologia , Transtornos Neurológicos da Marcha/fisiopatologia , Contração Isométrica/fisiologia , Movimento/fisiologia , Músculo Esquelético/fisiopatologia , Postura Sentada , Extremidade Superior/fisiopatologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Fenômenos Biomecânicos , Eletromiografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Amplitude de Movimento Articular , Reprodutibilidade dos Testes , Adulto Jovem
3.
Artigo em Inglês | MEDLINE | ID: mdl-33525530

RESUMO

Residual force enhancement (rFE) is observed when isometric force following an active stretch is elevated compared to an isometric contraction at corresponding muscle lengths. Acute rFE has been confirmed in vivo in upper and lower limb muscles. However, it is uncertain whether rFE persists using multiple, consecutive contractions as per a training simulation. Using the knee flexors, 10 recreationally active participants (seven males, three females; age 31.00 years ± 8.43 years) performed baseline isometric contractions at 150° knee flexion (180° representing terminal knee extension) of 50% maximal voluntary activation of semitendinosus. Participants performed post-stretch isometric (PS-ISO) contractions (three sets of 10 repetitions) starting at 90° knee extension with a joint rotation of 60° at 60°·s-1 at 50% maximal voluntary activation of semitendinosus. Baseline isometric torque and muscle activation were compared to PS-ISO torque and muscle activation across all 30 repetitions. Significant rFE was noted in all repetitions (37.8-77.74%), with no difference in torque between repetitions or sets. There was no difference in activation of semitendinosus or biceps femoris long-head between baseline and PS-ISO contractions in all repetitions (ST; baseline ISO = 0.095-1.000 ± 0.036-0.039 Mv, PS-ISO = 0.094-0.098 ± 0.033-0.038 and BFlh; baseline ISO = 0.068-0.075 ± 0.031-0.038 Mv). This is the first investigation to observe rFE during multiple, consecutive submaximal PS-ISO contractions. PS-ISO contractions have the potential to be used as a training stimulus.


Assuntos
Músculos Isquiossurais , Contração Isométrica , Adulto , Eletromiografia , Feminino , Humanos , Masculino , Músculo Esquelético , Torque
4.
Sci Data ; 8(1): 63, 2021 02 18.
Artigo em Inglês | MEDLINE | ID: mdl-33602931

RESUMO

Control of contemporary, multi-joint prosthetic hands is commonly realized by using electromyographic signals from the muscles remaining after amputation at the forearm level. Although this principle is trying to imitate the natural control structure where muscles control the joints of the hand, in practice, myoelectric control provides only basic hand functions to an amputee using a dexterous prosthesis. This study aims to provide an annotated database of high-density surface electromyographic signals to aid the efforts of designing robust and versatile electromyographic control interfaces for prosthetic hands. The electromyographic signals were recorded using 128 channels within two electrode grids positioned on the forearms of 20 able-bodied volunteers. The participants performed 65 different hand gestures in an isometric manner. The hand movements were strictly timed using an automated recording protocol which also synchronously recorded the electromyographic signals and hand joint forces. To assess the quality of the recorded signals several quantitative assessments were performed, such as frequency content analysis, channel crosstalk, and the detection of poor skin-electrode contacts.


Assuntos
Eletromiografia , Gestos , Mãos/fisiologia , Adulto , Membros Artificiais , Eletrodos , Feminino , Antebraço/fisiologia , Humanos , Contração Isométrica , Masculino , Pessoa de Meia-Idade , Movimento/fisiologia , Músculo Esquelético/fisiologia , Desenho de Prótese
5.
J Physiol ; 599(5): 1551-1566, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-33481277

RESUMO

KEY POINTS: Changes in corticospinal excitability prior to a contraction may depend on its characteristics, including the rate of torque development. This study compared the specific modulation of cortical and spinal excitability during the preparation phase (last 500 ms before contraction) of fast (ballistic) and ramp contractions of ankle dorsiflexors, using transcranial magnetic stimulation and peripheral nerve stimulation. The results indicate earlier changes at the cortical than at the spinal level during the preparation phase of both contraction types. However, these adjustments are delayed prior to ballistic relative to ramp contractions. This study suggests that the time course of change in cortical and spinal excitability during the preparation phase of a voluntary action is specific to the intended rate of torque development of the upcoming contraction. ABSTRACT: The present study investigated cortical and spinal excitability during the preparation phase of ballistic (BAL) and ramp (RAMP) isometric contractions. To this end, young adults performed BAL and RAMP (1500 ms torque rise time) contractions, reaching a similar torque level, with the ankle dorsiflexor muscles. Transcranial magnetic stimulation of the motor cortex was randomly applied to record motor evoked potentials (MEP) in the tibialis anterior during the last 500 ms preceding the contraction (n = 16). Short-interval intracortical inhibition (SICI; n = 10) and spinal motor neurone excitability (F-wave occurrence; n = 8) were also assessed during this period. Data were averaged over 100 ms time windows beginning 500 ms prior to the onset of contractions. An increase in MEP amplitude and a decrease in SICI were observed from the 200-100 ms and 300-200 ms time windows prior to BAL and RAMP contractions (P < 0.05), respectively, with greater changes prior to RAMP than to BAL within the 300-200 ms time window (P < 0.05). F-wave occurrence, used to assess spinal motor neurone excitability, increased prior to RAMP (200-100 ms, P < 0.05) but not BAL contractions. Data obtained in a few participants during the last 100 ms confirmed a delayed and steeper rise in corticospinal excitability prior to BAL contractions. These results indicate earlier changes at the cortical than at the spinal level, with delayed changes prior to BAL contractions. This study suggests that the time course of change in cortical and spinal excitability during the preparation phase of a voluntary action is specific to the intended rate of torque development of the upcoming contraction.


Assuntos
Potencial Evocado Motor , Córtex Motor , Eletromiografia , Humanos , Contração Isométrica , Contração Muscular , Músculo Esquelético , Tratos Piramidais , Estimulação Magnética Transcraniana , Adulto Jovem
6.
Sports Health ; 13(1): 85-90, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-32940548

RESUMO

BACKGROUND: Suspension training systems, which use body weight resistance under unstable conditions, may be effective for muscle strengthening in persons with scapular dyskinesis or subacromial impingement syndrome. HYPOTHESIS: Greater arm, scapular, and trunk muscle recruitment will occur during horizontal abduction row exercises. STUDY DESIGN: Descriptive laboratory study. LEVEL OF EVIDENCE: Level 5. METHODS: Surface electromyography data were collected from 28 participants (14 men, 14 women). A total of 13 right-sided muscles were studied at a sampling frequency of 1000 Hz. Maximal voluntary isometric contractions (MVICs) were established. Participants completed 3 repetitions per exercise in random order. We compared muscle recruitment during 3 rowing exercises: low row, high row, and horizontal abduction row. Data were compared with repeated-measures analyses of variance and post hoc Bonferroni corrections. RESULTS: For high row and horizontal abduction row conditions, the upper, middle, and lower trapezius and posterior deltoid demonstrated >60% MVIC magnitudes of recruitment, and the upper erector spinae demonstrated 40% to 60% MVIC magnitudes of recruitment, respectively. In contrast, in the low row exercise, 40% to 60% MVIC magnitudes of recruitment were observed only in the middle trapezius, latissimus dorsi, and posterior deltoid. CONCLUSION: With the suspension system, high row and horizontal abduction row exercises promote muscle strengthening (>50% MVIC) in the upper, middle, and lower fibers of the trapezius, posterior deltoid, and upper erector spinae. CLINICAL RELEVANCE: Rowing exercises performed with suspension straps may be recommended for muscle strengthening in patients with scapular dyskinesis and subacromial impingement syndrome as well as for healthy persons in need of enhanced scapular muscle performance.


Assuntos
Músculo Esquelético/fisiologia , Treinamento de Resistência/métodos , Ombro/fisiologia , Esportes Aquáticos/fisiologia , Braço/fisiologia , Cotovelo/fisiologia , Eletromiografia , Feminino , Humanos , Contração Isométrica , Masculino , Treinamento de Resistência/instrumentação , Escápula/fisiologia , Escápula/fisiopatologia , Síndrome de Colisão do Ombro/fisiopatologia , Tronco/fisiologia , Adulto Jovem
7.
Phys Ther Sport ; 48: 1-11, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33341516

RESUMO

OBJECTIVE: To determine the validity, intra- and inter-rater, and absolute reliability of a return to sport testing battery for the shoulder in a healthy cohort. DESIGN: Cross-sectional design. All participants completed a battery of strength (isokinetic, isometric, and repetition to failure) and functional assessments on two occasions. Concurrent validity to isokinetic testing was assessed, and intra-rater, inter-rater, and absolute reliability were established for all assessments. SETTING: Controlled clinical environment. PARTICIPANTS: Thirty healthy adults active in recreational sports participated, mean age 24.0 ± 1.6 years; MAIN OUTCOME MEASURES: Correlations (Pearson's r), reliability (Intraclass Correlation Coefficient), Standard error of the measurement, Minimal detectable change. RESULTS: Correlations to isokinetic assessments at 60° & 180°/second were moderate to strong for isometric (r: 0.68-0.80) and functional testing (r: 0.55-0.83) and weak for repetition to failure testing (r: 0.37-0.74). All isokinetic (ICC: 0.88-0.94), isometric (ICC: 0.83-0.94), and functional assessments (ICC: 0.80-0.92) had good to excellent intra-rater reliability, while repetition to failure testing had poor to moderate reliability (ICC: 0.48-0.57). The inter-rater reliability of the isometric assessments was moderate to excellent (ICC: 0.71-0.92) across movements. Expressed as a percentage of the mean, the standard error of the measurement ranged from 7% to 25% and the minimal detectable change ranged from 20% to 69% across all assessment methods. CONCLUSION: The isokinetic, isometric, and functional assessments used in this return to sports testing battery demonstrates acceptable validity and reliability. Further refinement to the methods used to assess muscular endurance is needed to improve reliability. This study offers clinicians information that can be utilized in clinical decision-making as it relates the testing battery's psychometric properties.


Assuntos
Teste de Esforço/métodos , Força Muscular , Volta ao Esporte , Ombro/fisiologia , Adulto , Fenômenos Biomecânicos , Estudos Transversais , Feminino , Voluntários Saudáveis , Humanos , Contração Isométrica , Masculino , Dinamômetro de Força Muscular , Psicometria , Reprodutibilidade dos Testes , Esportes , Adulto Jovem
8.
J Electromyogr Kinesiol ; 56: 102491, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33310413

RESUMO

The aims of this study were to explore muscle activity levels during different violin repertoires, quantify the general levels bilaterally in upper extremity muscles, and evaluate associations between muscle activity and anthropometrics characteristics. In 18 skilled violin players surface EMG was recorded bilaterally from trapezius (UT), flexor digitorum superficialis (FDS), extensor carpi ulnaris (ECU), extensor digitorum cummunis (EDC), and extensor carpi radialis (ECR) during A and E major scales played in three octaves and Mozart's Violin Concerto no. 5. To compare side differences the static, median and peak levels of muscle activity were calculated from an amplitude probability distribution function (APDF). This study demonstrated that scales played as standardized tasks can be used to estimate the average muscle activity during violin playing. Comparing results from scales and the music piece revealed a similar muscle activity across all muscles in the music piece and E major scales. The static, median and peak EMG levels were higher in left than in right forearm muscles with left ECU presenting the highest peak load of 30 %MVE. Females demonstrated a higher muscle activity than males, but this was in accordance with differences in anthropometric measures.


Assuntos
Antropometria/métodos , Eletromiografia/métodos , Antebraço/fisiologia , Músculo Esquelético/fisiologia , Música , Ombro/fisiologia , Adulto , Feminino , Humanos , Contração Isométrica/fisiologia , Masculino , Pessoa de Meia-Idade , Músculos Superficiais do Dorso/fisiologia , Adulto Jovem
9.
J Electromyogr Kinesiol ; 56: 102509, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33310606

RESUMO

The pectoralis major assists in several shoulder movements, such as humeral vertical and horizontal adduction, flexion, extension, and internal rotation. Despite its involvement in numerous functional activities, its role in typical shoulder function is ambiguous. Due to this, its purpose in arm movement is largely diminished. However, mounting evidence associates pectoralis major injuries to long-term debilitating arm disability. Therefore, a more deliberate investigation of its role in typical shoulder function is paramount. The purpose of this paper is to outline the current limitations in the acquisition and characterization of pectoralis major activation using standard bipolar surface electromyography. Macroscopic level analyses are used to investigate pectoralis major activation in eight tasks at low (15-25% of maximal voluntary effort (MVE) and moderate (50% MVE) efforts in healthy males. Virtually derived bipolar EMG amplitudes are quantified for the clavicular and the upper sternocostal regions based on the common locations used to acquire EMG signals from classic EMG. HD-sEMG amplitudes from three pectoralis major regions (i.e. clavicular, upper, and lower sternocostal) were compared to virtually derived bipolar EMG amplitudes (i.e. clavicular and upper sternocostal) to determine if current EMG methods misestimate pectoralis major activity. Current findings indicate that classic EMG recordings mischaracterize pectoralis major activation in several tasks and effort levels, highlighting the importance of acquiring signals from multiple pectoralis major regions.


Assuntos
Eletromiografia/métodos , Contração Isométrica/fisiologia , Músculos Peitorais/fisiologia , Desempenho Psicomotor/fisiologia , Articulação do Ombro/fisiologia , Adulto , Humanos , Masculino , Rotação , Ombro/fisiologia , Adulto Jovem
10.
J Strength Cond Res ; 35(1): 16-24, 2021 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-33332802

RESUMO

ABSTRACT: Williams, MJ, Gibson, N, Sorbie, GG, Ugbolue, UC, Brouner, J, and Easton, C. Activation of the gluteus maximus during performance of the back squat, split squat, and barbell hip thrust and the relationship with maximal sprinting. J Strength Cond Res 35(1): 16-24, 2021-The purpose of this research was to compare muscle activation of the gluteus maximus and ground reaction force between the barbell hip thrust, back squat, and split squat and to determine the relationship between these outcomes and vertical and horizontal forces during maximal sprinting. Twelve, male, team sport athletes (age, 25.0 ± 4.0 years; stature, 184.1 ± 6.0 cm; body mass, 82.2 ± 7.9 kg) performed separate movements of the 3 strength exercises at a load equivalent to their individual 3 repetition maximum. The ground reaction force was measured using force plates and the electromyography (EMG) activity of the upper and lower gluteus maximus and was recorded in each leg and expressed as percentage of the maximum voluntary isometric contraction (MVIC). Subjects then completed a single sprint on a nonmotorized treadmill for the assessment of maximal velocity and horizontal and vertical forces. Although ground reaction force was lower, peak EMG activity in the gluteus maximus was higher in the hip thrust than in the back squat (p = 0.024; 95% confidence interval [CI] = 4-56% MVIC) and split squat (p = 0.016; 95% CI = 6-58% MVIC). Peak sprint velocity correlated with both anterior-posterior horizontal force (r = 0.72) and peak ground reaction force during the barbell hip thrust (r = 0.69) but no other variables. The increased activation of gluteus maximus during the barbell hip thrust and the relationship with maximal running speed suggests that this movement may be optimal for training this muscle group in comparison to the back squat and split squat.


Assuntos
Contração Isométrica , Músculo Esquelético , Adulto , Nádegas , Eletromiografia , Humanos , Masculino , Coxa da Perna , Adulto Jovem
11.
J Strength Cond Res ; 35(1): 33-40, 2021 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-33332803

RESUMO

ABSTRACT: Hill, EC, Housh, TJ, Smith, CM, Keller, JL, Schmidt, RJ, and Johnson, GO. High- vs. low-intensity fatiguing eccentric exercise on muscle thickness, strength, and blood flow. J Strength Cond Res 35(1): 33-40, 2021-The purpose of this investigation was to examine the acute effects of equal volumes of fatiguing high- vs. low-intensity eccentric muscle actions on changes in muscle thickness, echo intensity, muscle blood flow, and adipose thickness. Eighteen men (mean ± SD = 23.2 ± 3.0 years) performed eccentric peak torque (PT) and maximal voluntary isometric contraction (MVIC) trials before (pretest), immediately after (posttest), and 5 minutes after (recovery) performing randomly ordered fatiguing eccentric, isokinetic (180°·s-1) muscle actions of the elbow flexors at 40% (72 repetitions) or 80% (36 repetitions) of eccentric PT. Muscle thickness, exercise-induced edema, muscle blood flow, and adipose thickness were also assessed via ultrasound at pretest, posttest, and recovery. There were no intensity-specific effects on the patterns of responses for eccentric PT, MVIC, muscle thickness, echo intensity, muscle blood flow, or adipose thickness. There were, however, effects across time that decreased from pretest to posttest and from pretest to recovery for eccentric PT (21.5 and 13.0%), MVIC (14.6 and 5.8%), and adipose thickness (10.0 and 6.0%), but increased for muscle thickness (7.6 and 5.9%), echo intensity (13.7 and 9.9%), and muscle blood flow (129.6 and 90.1%) (collapsed across 40 and 80%). These findings indicated that when matched for exercise volume, there were no intensity-related effects on the increases in muscle thickness, echo intensity, muscle blood flow, or the decreases in eccentric PT, MVIC, and adipose thickness after fatiguing eccentric muscle actions. Therefore, exercise volume, independent of exercise intensity and number of repetitions, may be a mediating factor of muscle fatigue and performance during eccentric muscle actions.


Assuntos
Fadiga Muscular , Músculo Esquelético , Exercício Físico , Humanos , Contração Isométrica , Masculino , Contração Muscular , Força Muscular , Músculo Esquelético/diagnóstico por imagem , Torque
12.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 690-693, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018081

RESUMO

The nonstationarity measure of surface Electromyography (sEMG) signals provide an index for muscle fatigue conditions. In this paper, a new framework has been proposed for the analysis of sEMG signal using Instantaneous Spectral Centroid (ISC). The novelty of the proposed work is use of topological signal processing method to quantify the nonstationarity of sEMG signal. For this, the signals are recorded from the biceps brachii muscles of 25 healthy subjects in isometric contraction. The analytical signals corresponding to nonfatigue and fatigue segments are computed using Hilbert Transform. Further, topological features such as center of gravity (CoG), triangular area function (TAF) and ISC are calculated from the geometrical representation of a transformed signal. The result indicates the increase of TAF in fatigue condition and the significant right shift of CoG in x-axis for 80% of subjects. Importantly, the ISC estimate is decreased by 17% upon fatiguing for 84% of subjects. The obtained results show statistical significance with p < 0.05. It is observed that the shape parameters are varied in accordance with the changes observed in global characteristics of sEMG signals during muscle fatigue. The preliminary results show that the topological features are able to quantify the nonstationarity in sEMG signal. Therefore, the proposed method can be used as a fatigue index for diagnosing various neuromuscular disorders.Clinical Relevance-This method can be used to establish metrics of muscle fatigue for the benefit of physicians especially in the field of fitness, sports, pre and post-surgery surveillance and rehabilitation.


Assuntos
Contração Isométrica , Fadiga Muscular , Animais , Braço , Eletromiografia , Músculo Esquelético
13.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 728-731, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018090

RESUMO

Surface electromyogram (sEMG) has been widely applied in neurorehabilitation techniques such as human-machine interface (HMI). The individual difference of sEMG characteristics has long been a challenge for multi-user HMI. However, the individually unique sEMG property indicates its high potential as a biometrics modality. In this work, we propose a novel application of high-density sEMG (HD-sEMG) for personal identification. HD-sEMG can decode the high-resolution spatial patterns of muscle activations, besides the widely studied temporal features, thus providing more sufficient information. We acquired 64-channel HD-sEMG signals on the dorsum of the right hand from 22 subjects during finger muscle isometric contractions. We achieved an accuracy of 99.5% to recognize the identity of each subject, demonstrating the excellent performance of HD-sEMG for personal identification. To the best of our knowledge, this is the first study to employ HD-sEMG for personal identification.Clinical relevance-Our work has proved the huge individual difference of HD-sEMG, which may result from the individually unique bioelectrophysiological activity of human body, deriving from both neural and biomechanical factors. The investigation of subject-specific HD-sEMG pattern may contribute to a better design of subject-specific clinical rehabilitation robots and a deeper understanding of human movement mechanism.


Assuntos
Contração Isométrica , Músculo Esquelético , Eletromiografia , Dedos , Humanos , Movimento
14.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 732-735, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018091

RESUMO

In this study, an attempt has been made to distinguish between nonfatigue and fatigue conditions in surface Electromyography (sEMG) signal using the time frequency distribution obtained from analytic Bump Continuous Wavelet Transform. For the analysis, sEMG signals from biceps brachii muscle of 22 healthy subjects are acquired during isometric contraction protocol. The signals acquired is preprocessed and partitioned into ten equal segments followed by the decomposition of selected segments using analytic Bump wavelets. Further, Singular Value Decomposition is applied to the time frequency distribution matrix and the maximum singular value and entropy feature for each segment are obtained. The usefulness of both the features is estimated using the Wilcoxon sign rank test that gives higher significance with a p < .00001. It is observed that the proposed method is capable of analyzing the fatigue regions in sEMG signals.


Assuntos
Contração Isométrica , Análise de Ondaletas , Eletromiografia , Humanos , Fadiga Muscular , Músculo Esquelético
15.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3118-3121, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018665

RESUMO

In this paper, the validity of the stochastic model-based variance distribution of surface electromyogram (EMG) signals during isometric contraction is investigated. In the model, the EMG variance is considered as a random variable following an inverse gamma distribution, thereby allowing the representation of variations in the variance. This inverse gamma-based model for the EMG variance is experimentally validated through comparison with the empirical distribution of variances. The difference between the model distribution and the empirical distribution is quantified using the Kullback- Leibler divergence. Additionally, regression analysis is conducted between the model parameters and the statistics calculated from the empirical distribution of EMG variances. Experimental results showed that the inverse gamma-based model is potentially suitable and that its parameters can be used to evaluate the stochastic properties of the EMG variance.


Assuntos
Algoritmos , Contração Isométrica , Eletromiografia , Distribuições Estatísticas
16.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3220-3223, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018690

RESUMO

Localized muscle fatigue (LMF) decreases muscular strength, while affects the performance and potentially increases the risk of musculoskeletal disorders (MSD). An important mechanism in recovering from muscle fatigue is blood flow (BF). The BF response to muscle contraction and fatigue is highly dynamic and difficult to predict, as it depends on both metabolic demand and intramuscular pressure. The aim of this study was to measure both fatigue and BF during intermittent exertion of the first dorsal interosseous (FDI) muscle, in order to better characterize the relationship between BF and LMF during muscle contraction and rest. This study utilized Diffuse Correlation Spectroscopy (DCS) for BF measurement within the microvasculature of the FDI muscle. Exertion levels (EL) for intermittent fatiguing contraction were set to 20%, 30%, and 40% of an individual's maximum voluntary contraction (MVC). Our results showed that as an individual fatigued, relative BF rates increased, on average, by ~66% during exertion periods and ~330% during rest periods. Differences between exerting and resting BF increased over time for every EL (p<0.04), increasing by up to 11 times the baseline BF. At the same levels of muscle capacity (%MVC), resting BF was also found to increase with EL consistently. Our findings highlight BF dependence on both EL and history of muscle contraction. These results imply a variable recovery rate based on both the current state of contraction, (i.e., exertion vs. rest), and the muscle contraction history. The outcome of our study may facilitate the estimation of BF, thus, the muscle recovery rate, which can be implemented in the fatigue models to improve the prediction of muscle capacity to generate force/power.


Assuntos
Contração Isométrica , Músculos , Humanos , Microvasos , Contração Muscular , Fadiga Muscular
17.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3465-3468, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018749

RESUMO

We analyze the efficiency of motor unit (MU) filter prelearning from high-density surface electromyographic (HDEMG) recordings of voluntary muscle contractions in the identification of the motor unit firing patterns during elicited muscle contractions. Motor unit filters are assessed from 10 s long low level isometric voluntary contractions by gradient-based optimization of three different cost functions and then applied to synthetic HDEMG recordings of elicited muscle contractions with dispersion of motor unit firings ranging from 13 ms to 1 ms. We demonstrate that the number of identified MUs and the precision of MU identification depend significantly on the selected cost function. Regardless the selected cost function and MU synchronization level, the median precision of motor unit identification in elicited contraction is ≥ 95 % and is comparable to the precision in voluntary contractions. On the other hand, median miss rate increases significantly from < 1 % to ~ 3 % with the tested level of MU synchronization.Clinical Relevance-The identification of MU firings from HDEMG in elicited muscle contractions provides a new tool for in vivo investigation of motor excitability in humans.


Assuntos
Contração Isométrica , Neurônios Motores , Potenciais de Ação , Eletromiografia , Humanos , Contração Muscular
18.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 4803-4806, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33019065

RESUMO

Muscle synergy is the theory that movements are controlled by a module of coordinated combined muscles. This theory is thought to solve the degrees-of-freedom problem in the musculoskeletal system. Previous studies have investigated the robustness of muscle synergies under conditions such as varying speeds and required degrees of accuracy. One of the principles of human movement is that when movement becomes faster, spatial accuracy is reduced. This is called the "speed-accuracy trade-off" (SAT), and many models have been proposed to explain this phenomenon. Studies on muscle synergies have shown that muscle synergy modules are robust against changes in speed; however, the relationship between SAT and motor control by muscle synergies remains unclear. Therefore, we investigated the relationship between changes in spatial accuracy and changes in speed and muscle synergies from measured behavioral data and surface electromyography. This was achieved by performing an isometric contraction task in which subjects exerted a horizontal force with various movement speeds. The results showed that the module structures of muscle synergies were robust against speed changes, and that the neural commands to muscle synergies changed in response to speed changes. In addition, changes in spatial accuracy with variations in speed tended to increase when movement was performed with a single muscle synergy. These results suggest that the number of muscle synergies used for movement may affect movement accuracy.Clinical Relevance-The results of this study suggest that the number of muscle synergies used for movement affects spatial accuracy.


Assuntos
Contração Isométrica , Músculo Esquelético , Eletromiografia , Humanos , Movimento
19.
Arch. med. deporte ; 37(199): 291-297, sept.-oct. 2020. tab, graf
Artigo em Inglês | IBECS | ID: ibc-199342

RESUMO

AIM: The objective of the present study was to compare the amplitude of the electromyographic (EMG) signal of the quadriceps muscle portions vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF) and the activation ratio (VM/VL, VM/RF and VL/RF) in protocols with different durations of concentric and eccentric muscular actions. MATERIAL AND METHOD: Twelve female volunteers performed the knee extensor exercise with two different protocols [1s for concentric muscle action and 5s for eccentric muscle action (1:5); 5s of concentric muscle action and 1s of eccentric muscle action (5:1)] and 3 sets of 6 repetitions, 180s of pause between each sets and a intensity of 50% of 1RM. The root mean square of the amplitude of the normalized EMG signal was calculated for each repetition in each series. RESULTS: it was observed an increase in the activation of the VM and VL portions in equivalent repetitions of each series and for the VL portion, the 1: 5 protocol provided greater activation compared to the other protocol. No differences were found for muscles activation ratios VM/RF and VL/RF, being that for the VM/VL ratio there was only change at one repetition. CONCLUSION: The results suggest that the portions of the quadriceps muscle may present different EMG responses in similar protocols, but this fact may not interfere in the synergism between them. The reduced degrees of freedom of the knee extension exercise and the characteristics of the protocols adopted may be the elements that contributed to the limited alterations that occurred in the present study


OBJETIVO: El objetivo del presente estudio fue comparar la amplitud de la señal electromiográfica (EMG) de las porciones de músculo cuádriceps vasto medial (VM), vasto lateral (VL) y recto femoral (RF) y la relación de activación (VM/VL, VM/RF y VL/RF) en protocolos con diferentes duraciones de acciones musculares concéntricas y excéntricas. MATERIAL Y MÉTODO: Doce mujeres voluntarias realizaron el ejercicio extensor de rodilla con dos protocolos diferentes [1 s para la acción muscular concéntrica y 5 s para la acción muscular excéntrica (1: 5); 5s de acción muscular concéntrica y 1s de acción muscular excéntrica (5: 1)] y 3 series de 6 repeticiones, 180s de pausa entre cada serie y una intensidad del 50% de 1RM. La raíz media cuadrática de la amplitud de la señal electromiográfica normalizada se calculó para cada repetición en cada serie. RESULTADOS: se observó un aumento en la EMG de las porciones de VM y VL en repeticiones equivalentes de cada serie y para la porción de VL, el protocolo 1: 5 proporcionó una mayor activación en comparación con el otro protocolo. No se encontraron diferencias para las relaciones de activación de los músculos VM/RF y VL/RF, siendo que para la relación VM/VL solo hubo cambios en una repetición. CONCLUSIÓN: Los resultados sugieren que las partes del músculo del cuádriceps pueden presentar diferentes respuestas de EMG en protocolos similares, pero este hecho puede no interferir en el sinergismo entre ellos. Los grados reducidos de libertad del ejercicio de extensión de la rodilla y las características de los protocolos adoptados pueden ser los elementos que contribuyeron a las alteraciones limitadas que se produjeron en el presente estudio


Assuntos
Humanos , Feminino , Adolescente , Adulto Jovem , Adulto , Exercícios de Alongamento Muscular , Músculo Quadríceps/fisiologia , Contração Isométrica/fisiologia , Eletromiografia , Fatores de Tempo , Valores de Referência , Articulação do Joelho/fisiologia
20.
J Sports Med Phys Fitness ; 60(8): 1057-1064, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32955831

RESUMO

BACKGROUND: Rock climbers are characterized by enhanced forearm fatigue resistance. This study compared the forearm isometric force of rock climbers (RC), strength-matched power lifters (PL) and aerobically trained (AT) athletes to determine the contribution of muscle oxygen desaturation during ischemia. METHODS: Aerobically trained athletes (N.=6, 23±1 years, 77±1 kg), power lifters (N.=7, 24±1 years, 80±3 kg) and rock climbers (N.=8, 25±2 years, 74±2 kg) took part in a controlled forearm ischemic occlusion (5 min) assessment using near infrared spectroscopy. In addition, three fatigue protocols were completed: protocol 1, sustained maximal voluntary contraction (MVC) until exhaustion; protocol 2, sustained 40% MVC for 3 mins duration; protocol 3, an intermittent 40% MVC (5-s contraction, 5-s recovery) for a duration of 3 mins. Forearm contractile fatigue was quantified as the reduction in MVC. RESULTS: MVC was equivalent between groups (P>0.05). Sustained MVC force (time to decline 50% MVC) was longer in the RC versus AT (AT: 35±5, PL: 46±6, RC: 54±4 s, P<0.05) and both AT and PL for sustained 40% MVC (AT: 56±9, RT: 62±8, RC: 87±7 s, P<0.05). Reduction in MVC was less in RC post intermittent 40% contractions (P<0.05). Oxygen desaturation half-time was longer in the RC versus AT (AT: 65±9, RT: 86±7, RC: 99±7 s, P<0.05) and this was associated with time to 50% MVC (P<0.05, r2=0.53) and time to 40% MVC task failure (P<0.05, r2=0.32). CONCLUSIONS: Rock climbers' enhanced isometric fatigue-resistance and ability to maintain MVC was associated with a lower oxygen consumption of the forearm flexors during the ischemic state. This suggests a training adaptation involving intracellular oxygen consumption.


Assuntos
Antebraço/fisiologia , Montanhismo/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Adaptação Fisiológica , Adulto , Dedos/fisiologia , Antebraço/irrigação sanguínea , Antebraço/diagnóstico por imagem , Humanos , Contração Isométrica/fisiologia , Masculino , Músculo Esquelético/irrigação sanguínea , Músculo Esquelético/diagnóstico por imagem , Consumo de Oxigênio , Condicionamento Físico Humano/fisiologia , Espectroscopia de Luz Próxima ao Infravermelho , Levantamento de Peso/fisiologia , Adulto Jovem
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