scholarly journals Electrically and hybrid-induced muscle activations: effects of muscle size and fiber type

2016 ◽  
Vol 26 (3) ◽  
Author(s):  
Kelly Stratton ◽  
Pouran D. Faghri
Keyword(s):  
Electrical Activity ◽  
Muscle Activation ◽  
Fiber Type ◽  
Vastus Lateralis ◽  
Maximum Voluntary Contraction ◽  
Voluntary Activation ◽  
Muscle Size ◽  
Muscle Coordination ◽  
Abductor Pollicis Brevis ◽  
Informed Consent Form

The effect of three electrical stimulation (ES) frequencies (10, 35, and 50 Hz) on two muscle groups with different proportions of fast and slow twitch fibers (abductor pollicis brevis (APB) and vastus lateralis (VL)) was explored. We evaluated the acute muscles’ responses individually and during hybrid activations (ES superimposed by voluntary activations). Surface electromyography (sEMG) and force measurements were evaluated as outcomes. Ten healthy adults (mean age: 24.4 ± 2.5 years) participated after signing an informed consent form approved by the university Institutional Review Board. Protocols were developed to: 1) compare EMG activities during each frequency for each muscle when generating 25% Maximum Voluntary Contraction (MVC) force, and 2) compare EMG activities during each frequency when additional voluntary activation was superimposed over ES-induced 25% MVC to reach 50% and 75% MVC. Empirical mode decomposition (EMD) was utilized to separate ES artifacts from voluntary muscle activation. For both muscles, higher stimulation frequency (35 and 50Hz) induced higher electrical output detected at 25% of MVC, suggesting more recruitment with higher frequencies. Hybrid activation generated proportionally less electrical activity than ES alone. ES and voluntary activations appear to generate two different modes of muscle recruitment. ES may provoke muscle strength by activating more fatiguing fast acting fibers, but voluntary activation elicits more muscle coordination. Therefore, during the hybrid activation, less electrical activity may be detected due to recruitment of more fatigue-resistant deeper muscle fibers, not reachable by surface EMG.

scholarly journals Central excitability does not limit postfatigue voluntary activation of quadriceps femoris

2006 ◽  
Vol 100 (6) ◽  
pp. 1757-1764 ◽  
Author(s):  
J. M. Kalmar ◽  
E. Cafarelli
Keyword(s):  
Evoked Potentials ◽  
Repeated Measures ◽  
Muscle Activation ◽  
Motor Evoked Potentials ◽  
Vastus Lateralis ◽  
Central Fatigue ◽  
Knee Extension ◽  
Voluntary Activation ◽  
Fatigue Protocol ◽  
Central Excitability

After fatigue, motor evoked potentials (MEP) elicited by transcranial magnetic stimulation and cervicomedullary evoked potentials elicited by stimulation of the corticospinal tract are depressed. These reductions in corticomotor excitability and corticospinal transmission are accompanied by voluntary activation failure, but this may not reflect a causal relationship. Our purpose was to determine whether a decline in central excitability contributes to central fatigue. We hypothesized that, if central excitability limits voluntary activation, then a caffeine-induced increase in central excitability should offset voluntary activation failure. In this repeated-measures study, eight men each attended two sessions. Baseline measures of knee extension torque, maximal voluntary activation, peripheral transmission, contractile properties, and central excitability were made before administration of caffeine (6 mg/kg) or placebo. The amplitude of vastus lateralis MEPs elicited during minimal muscle activation provided a measure of central excitability. After a 1-h rest, baseline measures were repeated before, during, and after a fatigue protocol that ended when maximal voluntary torque declined by 35% (Tlim). Increased prefatigue MEP amplitude ( P = 0.055) and cortically evoked twitch ( P < 0.05) in the caffeine trial indicate that the drug increased central excitability. In the caffeine trial, increased MEP amplitude was correlated with time to task failure ( r = 0.74, P < 0.05). Caffeine potentiated the MEP early in the fatigue protocol ( P < 0.05) and offset the 40% decline in placebo MEP ( P < 0.05) at Tlim. However, this was not associated with enhanced maximal voluntary activation during fatigue or recovery, demonstrating that voluntary activation is not limited by central excitability.

scholarly journals Electrical Stimulation Frequency and Skeletal Muscle Characteristics: Effects on Force and Fatigue

2017 ◽  
Vol 27 (4) ◽  
Author(s):  
Maria Vromans ◽  
Pouran Faghri
Keyword(s):  
Electrical Stimulation ◽  
Vastus Lateralis ◽  
Voluntary Contraction ◽  
Current Intensity ◽  
Muscle Size ◽  
Emg Activity ◽  
Abductor Pollicis Brevis ◽  
Fiber Composition ◽  
Initial Drop ◽  
Initial Force

This investigation aimed to determine the force and muscle surface electromyography (EMG) responses to different frequencies of electrical stimulation (ES) in two groups of muscles with different size and fiber composition (fast- and slow-twitch fiber proportions) during a fatigue-inducing protocol. Progression towards fatigue was evaluated in the abductor pollicis brevis (APB) and vastus lateralis (VL) when activated by ES at three frequencies (10, 35, and 50Hz). Ten healthy adults (mean age: 23.2 ± 3.0 years) were recruited; participants signed an IRB approved consent form prior to participation. Protocols were developed to 1) identify initial ES current intensity required to generate the 25% maximal voluntary contraction (MVC) at each ES frequency and 2) evaluate changes in force and EMG activity during ES-induced contraction at each frequency while progressing towards fatigue. For both muscles, stimulation at 10Hz required higher current intensity of ES to generate the initial force. There was a significant decline in force in response to ES-induced fatigue for all frequencies and for both muscles (p<0.05). However, the EMG response was not consistent between muscles. During the progression towards fatigue, the APB displayed an initial drop in force followed by an increase in EMG activity and the VL displayed a decrease in EMG activity for all frequencies. Overall, it appeared that there were some significant interactions between muscle size and fiber composition during progression towards fatigue for different ES frequencies. It could be postulated that muscle characteristics (size and fiber composition) should be considered when evaluating progression towards fatigue as EMG and force responses are not consistent between muscles.

THE EFFECT OF LEG PREFERENCE ON MECHANICAL EFFICIENCY DURING SINGLE-LEG EXTENSION EXERCISE

2021 ◽  
Author(s):  
Massimo Venturelli ◽  
Cantor Tarperi ◽  
Chiara Milanese ◽  
Luca Festa ◽  
Luana Toniolo ◽  
...  
Keyword(s):  
Muscle Activation ◽  
Near Infrared ◽  
Isometric Force ◽  
Fiber Type ◽  
Vastus Lateralis ◽  
Critical Role ◽  
Inverse Correlation ◽  
Mechanical Efficiency ◽  
Peak Power Output ◽  
Leg Extension

To investigate how leg preference affects net efficiency (ηnet), we examined central and peripheral hemodynamics, muscle fiber type, activation and force of preferred (PL) and non-preferred (NPL) leg. Our hypothesis was that PL greater efficiency could be explained by adaptations and interactions between central, peripheral factors and force. Fifteen young participants performed single-leg extension exercise at absolute (35W) and relative (50%peak power-output (Wpeak)) workloads with PL and NPL. Oxygen uptake, photoplethysmography, Doppler ultrasound, near-infrared-spectroscopy deoxy-hemoglobin [HHb], integrated electromyography (iEMG), maximal isometric force (MVC), rate of force development (RFD50-100) and muscle biopsies of both vastus lateralis, were studied to assess central and peripheral determinants of ηnet. During exercise executed at 35W, ηnet was 17.5±5.1% and 11.9±2.1% (p<0.01) in NP and NPL respectively, while during exercise at the 50% of Wpeak, was in PL = 18.1±5.1% and in NPL = 12.5±1.9 (p<0.01). The only parameter correlated with ηnet was iEMG which showed an inverse correlation for absolute (r=-0.83 and -0.69 for PL and NPL) and relative workloads (r=-0.92 and -0.79 for PL and NPL). MVC and RFD50-100 were higher in PL than in NPL but not correlated to ηnet. This study identified a critical role of leg preference in the efficiency during single-leg extension exercise. The whole spectrum of the central and peripheral, circulatory and muscular determinants of ηnet did not explain the difference between PL and NPL efficiency. Therefore, the lower muscle activation exhibited by the PL is likely the primary determinant of this physiological phenomenon.

scholarly journals Motor planning perturbation: muscle activation and reaction time

2018 ◽  
Vol 120 (4) ◽  
pp. 2059-2065
Author(s):  
Stefan Delmas ◽  
Agostina Casamento-Moran ◽  
Seoung Hoon Park ◽  
Basma Yacoubi ◽  
Evangelos A. Christou
Keyword(s):  
Reaction Time ◽  
Muscle Activity ◽  
Muscle Activation ◽  
Maximum Voluntary Contraction ◽  
Motor Planning ◽  
Reaction Time Task ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Time Interval ◽  
Voluntary Activity

Reaction time (RT) is the time interval between the appearance of a stimulus and initiation of a motor response. Within RT, two processes occur, selection of motor goals and motor planning. An unresolved question is whether perturbation to the motor planning component of RT slows the response and alters the voluntary activation of muscle. The purpose of this study was to determine how the modulation of muscle activity during an RT response changes with motor plan perturbation. Twenty-four young adults (20.5 ±1.1 yr, 13 women) performed 15 trials of an isometric RT task with ankle dorsiflexion using a sinusoidal anticipatory strategy (10–20% maximum voluntary contraction). We compared the processing part of the RT and modulation of muscle activity from 10 to 60 Hz of the tibialis anterior (primary agonist) when the stimulus appeared at the trough or at the peak of the sinusoidal task. We found that RT ( P = 0.003) was longer when the stimulus occurred at the peak compared with the trough. During the time of the reaction, the electromyography (EMG) power from 10 to 35 Hz was less at the peak than the trough ( P = 0.019), whereas the EMG power from 35 to 60 Hz was similar between the peak and trough ( P = 0.92). These results suggest that perturbation to motor planning lengthens the processing part of RT and alters the voluntary activation of the muscle by decreasing the relative amount of power from 10 to 35 Hz. NEW & NOTEWORTHY We aimed to determine whether perturbation to motor planning would alter the speed and muscle activity of the response. We compared trials when a stimulus appeared at the peak or trough of an oscillatory reaction time task. When the stimulus occurred at the trough, participants responded faster, with greater force, and less EMG power from 10-35 Hz. We provide evidence that motor planning perturbation slows the response and alters the voluntary activity of the muscle.

scholarly journals The Neuromuscular Determinants of Unilateral Jump Performance in Soccer Players Are Direction-Specific

2018 ◽  
Vol 13 (5) ◽  
pp. 604-611 ◽  
Author(s):  
Conall F. Murtagh ◽  
Christopher Nulty ◽  
Jos Vanrenterghem ◽  
Andrew O’Boyle ◽  
Ryland Morgans ◽  
...  
Keyword(s):  
Body Mass Index ◽  
Body Mass ◽  
Vastus Lateralis ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Soccer Players ◽  
Muscle Size ◽  
Fascicle Length ◽  
Jump Performance ◽  
Isometric Maximum Voluntary Contraction

Purpose: To investigate differences in neuromuscular factors between elite and nonelite players and to establish which factors underpin direction-specific unilateral jump performance. Methods: Elite (n = 23; age, 18.1 [1.0] y; body mass index, 23.1 [1.8] kg·m−2) and nonelite (n = 20; age, 22.3 [2.7] y; body mass index, 23.8 [1.8] kg·m−2) soccer players performed 3 unilateral countermovement jumps (CMJs) on a force platform in the vertical, horizontal-forward, and medial directions. Knee extension isometric maximum voluntary contraction torque was assessed using isokinetic dynamometry. Vastus lateralis fascicle length, angle of pennation, quadriceps femoris muscle volume (Mvol), and physiological cross-sectional area (PCSA) were assessed using ultrasonography. Vastus lateralis activation was assessed using electromyography. Results: Elite soccer players presented greater knee extensor isometric maximum voluntary contraction torque (365.7 [66.6] vs 320.1 [62.6] N·m; P = .045), Mvol (2853 [508] vs 2429 [232] cm3; P = .001), and PCSA (227 [42] vs 193 [25] cm2; P = .003) than nonelite. In both cohorts, unilateral vertical and unilateral medial CMJ performance correlated with Mvol and PCSA (r ≥ .310, P ≤ .043). In elite soccer players, unilateral vertical and unilateral medial CMJ performance correlated with upward phase vastus lateralis activation and angle of pennation (r ≥ .478, P ≤ .028). Unilateral horizontal-forward CMJ peak vertical power did not correlate with any measure of muscle size or activation but correlated inversely with angle of pennation (r = −.413, P = .037). Conclusions: While larger and stronger quadriceps differentiated elite from nonelite players, relationships between neuromuscular factors and unilateral jump performance were shown to be direction-specific. These findings support a notion that improving direction-specific muscular power in soccer requires improving a distinct neuromuscular profile.

scholarly journals Passive stretching decreases muscle efficiency in balance tasks

PLoS ONE ◽  
2021 ◽  
Vol 16 (9) ◽  
pp. e0256656
Author(s):  
Giuseppe Coratella ◽  
Stefano Longo ◽  
Susanna Rampichini ◽  
Christian Doria ◽  
Marta Borrelli ◽  
...  
Keyword(s):  
Muscle Activation ◽  
Balance Control ◽  
Vastus Lateralis ◽  
Maximum Voluntary Contraction ◽  
Knee Extensor ◽  
Biceps Femoris ◽  
Voluntary Contraction ◽  
Static Stretching ◽  
Balance Tests ◽  
Flexion Extension

The current study aimed to verify whether or not passive static stretching affects balance control capacity. Thirty-eight participants (19 women and 19 men) underwent a passive static stretching session, involving the knee extensor/flexor and dorsi/plantarflexor muscles, and a control session (no stretching, CTRL). Before (PRE), immediately after (POST), after 15 (POST15) and 30 min (POST30) from stretching (or rest in CTRL), balance control was evaluated under static and dynamic conditions, with open/closed eyes, and with/without somatosensory perturbation (foam under the feet). During tests, centre of pressure (CoP) sway area and perimeter and antero-posterior and medio-lateral sway mean speed were computed. Surface electromyography root mean square (sEMG RMS) was calculated from the vastus lateralis, biceps femoris, gastrocnemius medialis, and tibialis anterior muscles during MVC and during the balance tests. Hip flexion/extension and dorsi/plantarflexion range of motion (ROM), maximum voluntary contraction (MVC) and sEMG RMS during MVC were measured at the same time points. After stretching, ROM increased (≈6.5%; P<0.05), while MVC and sEMG RMS decreased (≈9% and ≈7.5%, respectively; P<0.05). Regardless of the testing condition, CoP sway area and the perimeter remained similar, while antero-posterior and medio-lateral sway mean speed decreased by ≈8% and ≈12%, respectively (P<0.05). sEMG RMS during the balance tests increased in all muscles in POST (≈7%, P<0.05). All variables recovered in POST30. No changes occurred in CTRL. Passive static stretching did not affect the overall balance control ability. However, greater muscle activation was required to maintain similar CoP sway, thus suggesting a decrease in muscle efficiency.

Recovery of Gait After Stroke: What Changes?

2008 ◽  
Vol 22 (6) ◽  
pp. 676-683 ◽  
Author(s):  
Jaap H. Buurke ◽  
Anand V. Nene ◽  
Gert Kwakkel ◽  
Victorien Erren-Wolters ◽  
Maarten J. IJzerman ◽  
...  
Keyword(s):  
Functional Recovery ◽  
Muscle Activation ◽  
Vastus Lateralis ◽  
Erector Spinae ◽  
Walking Ability ◽  
Muscle Coordination ◽  
Control Test ◽  
Trunk Control ◽  
Coordination Patterns ◽  
Over Time

Background. Little is known about whether changes in coordination patterns of muscle activation after stroke are related to functional recovery of walking. Objective . The present study investigated the longitudinal relationship between changes in neuromuscular activation patterns of paretic muscles in hemiplegic gait and improvement in walking ability after stroke. Methods. Thirteen patients diagnosed with a first unilateral ischemic stroke had their recovery of walking measured by the Rivermead Mobility Index, Functional Ambulation Categories, Barthel Index, Trunk Control Test, Motricity Index, and comfortable walking speed. Surface electromyography (SEMG) of the erector spinae, gluteus maximus, gluteus medius, rectus femoris, vastus lateralis, semitendinosus, gastrocnemius, and tibialis anterior muscles of both legs was used to quantify coordination patterns in comfortable walking mode. All clinical and electromyography-related measurements were taken at 3, 6, 9, 12, and 24 weeks poststroke. Timing parameters of the SEMG patterns were calculated, using an objective burst detection algorithm, and analyzed with the measures of functional recovery. Results . All functional measures, except Trunk Control Test, showed statistically significant improvement over time, whereas SEMG patterns did not change significantly over time. Conclusion. The lack of significant change in SEMG patterns over time suggests that functional gait improvements may be more related to compensatory strategies in muscle activation of the unaffected leg and biomechanical changes than by restitution of muscle coordination patterns in the affected leg.

Physiological basis of muscle functional MRI: predictions using a computer model

2005 ◽  
Vol 98 (1) ◽  
pp. 264-273 ◽  
Author(s):  
Bruce M. Damon ◽  
John C. Gore
Keyword(s):  
Functional Mri ◽  
Computer Model ◽  
Signal Intensity ◽  
Time Course ◽  
Muscle Activation ◽  
Fiber Type ◽  
Maximum Voluntary Contraction ◽  
Isometric Contractions ◽  
Physiological Basis ◽  
Tibialis Muscle

Muscle functional MRI (mfMRI) has been proposed as a tool for noninvasively measuring the metabolic and hemodynamic responses to muscle activation, but its theoretical basis remains unclear. One challenge is that it is difficult to isolate individually those variables affecting the magnitude and temporal pattern of the mfMRI response. Therefore, the purpose of this study was to develop a computer model of how physiological factors altered during exercise affect the mfMRI signal intensity time course and then predict the contributions made by individual factors. A model muscle containing 39,204 fibers was defined. The fiber-type composition and neural activation strategies were designed to represent isometric contractions of the human anterior tibialis muscle, for which published mfMRI data exist. Sustained isometric contractions at 25 and 40% maximum voluntary contraction were modeled, as were the vascular (capillary recruitment, blood oxygen extraction) and metabolic (lactate accumulation, phosphocreatine hydrolysis, pH) responses. The effects on the transverse relaxation of MRI signal were estimated, and the mfMRI signal intensity time course was measured from simulated images. The model data agreed well qualitatively with published experimental data, and at long exercise durations the quantitative agreement was also good. The model was then used to predict that NMR relaxation effects secondary to blood volume and oxygenation changes, plus the creatine kinase reaction, dominate the mfMRI time course at short exercise durations (up to ∼45 s) and that effects secondary to glycolysis are the main contributors at later times.

scholarly journals The Relationship Between Neuromuscular Function and the W′ in Elite Cyclists

2021 ◽  
pp. 1-7
Author(s):  
Mehdi Kordi ◽  
Len Parker Simpson ◽  
Kevin Thomas ◽  
Stuart Goodall ◽  
Tom Maden-Wilkinson ◽  
...  
Keyword(s):  
Goodness Of Fit ◽  
Critical Power ◽  
Pearson Correlation ◽  
Maximum Voluntary Contraction ◽  
Neuromuscular Function ◽  
Voluntary Activation ◽  
Muscle Size ◽  
Peak Power Output ◽  
Training Methods ◽  
Elite Cyclists

Purpose: To assess the association between the W′ and measures of neuromuscular function relating to the capacity of skeletal muscle to produce force in a group of elite cyclists. Methods: Twenty-two athletes specializing in a range of disciplines and competing internationally volunteered to participate. Athletes completed assessments of maximum voluntary torque (MVT), voluntary activation, and isometric maximum voluntary contraction to measure rate of torque development (RTD). This was followed by assessment of peak power output (PPO) and 3-, 5-, and 12-minute time trials to determine critical power. Pearson correlation was used to examine associations with critical power and W′. Goodness of fit was calculated, and significant relationships were included in a linear stepwise regression model. Results: Significant positive relationships were evident between W′ and MVT (r = .82), PPO (r = .70), and RTD at 200 milliseconds (r = .59) but not with RTD at 50 milliseconds and voluntary activation. Correlations were also observed between critical power and RTD at 200 milliseconds and MVT (r = .54 and r = .51, respectively) but not with PPO, voluntary activation, or RTD at 50 milliseconds. The regression analysis found that 87% of the variability in W′ (F1,18 = 68.75; P < .001) was explained by 2 variables: MVT (81%) and PPO (6%). Conclusions: It is likely that muscle size and strength, as opposed to neural factors, contribute meaningfully to W′. These data can be used to establish training methods to enhance W′ to improve cycling performance in well-trained athletes.

scholarly journals Neck muscle biomechanics and neural control

2018 ◽  
Vol 120 (1) ◽  
pp. 361-371 ◽  
Author(s):  
Jason B. Fice ◽  
Gunter P. Siegmund ◽  
Jean-Sébastien Blouin
Keyword(s):  
Neural Control ◽  
Muscle Activation ◽  
Maximum Voluntary Contraction ◽  
Neck Muscles ◽  
Voluntary Activation ◽  
Neck Muscle ◽  
Intrasubject Variability ◽  
Spatial Tuning ◽  
Muscle Biomechanics ◽  
The Moment

The mechanics, morphometry, and geometry of our joints, segments, and muscles are fundamental biomechanical properties intrinsic to human neural control. The goal of our study was to investigate whether the biomechanical actions of individual neck muscles predict their neural control. Specifically, we compared the moment direction and variability produced by electrical stimulation of a neck muscle (biomechanics) to the preferred activation direction and variability (neural control). Subjects sat upright with their head fixed to a six-axis load cell and their torso restrained. Indwelling wire electrodes were placed into the sternocleidomastoid (SCM), splenius capitis (SPL), and semispinalis capitis (SSC) muscles. The electrically stimulated direction was defined as the moment direction produced when a current (2–19 mA) was passed through each muscle’s electrodes. Preferred activation direction was defined as the vector sum of the spatial tuning curve built from root mean squared electromyogram when subjects produced isometric moments at 7.5% and 15% of their maximum voluntary contraction (MVC) in 26 three-dimensional directions. The spatial tuning curves at 15% MVC were well defined (unimodal, P < 0.05), and their preferred directions were 23°, 39°, and 21° different from their electrically stimulated directions for the SCM, SPL, and SSC, respectively ( P < 0.05). Intrasubject variability was smaller in electrically stimulated moment directions compared with voluntary preferred directions, and intrasubject variability decreased with increased activation levels. Our findings show that the neural control of neck muscles is not based solely on optimizing individual muscle biomechanics but, as activation increases, biomechanical constraints in part dictate the activation of synergistic neck muscles. NEW & NOTEWORTHY Biomechanics are an intrinsic part of human neural control. In this study, we found that the biomechanics of individual neck muscles cannot fully predict their neural control. Consequently, physiologically based computational neck muscle controllers cannot calculate muscle activation schemes based on the isolated biomechanics of muscles. Furthermore, by measuring biomechanics we showed that the intrasubject variability of the neural control was lower for electrical vs. voluntary activation of the neck muscles.

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