Are Voluntary Activation Determined By The Interpolated Twitch Technique And Mechanomyographic Amplitude Synonymous?

We demonstrate that reductions in voluntary activation and motoneuron excitability following 2-min isometric maximal contractions in humans occur only when fatigue is produced through voluntary contractions and not through electrically stimulated contractions. This is contrary to studies that suggest that changes in the superimposed twitch and therefore voluntary activation are explained by changes in peripheral factors alone. Thus, the interpolated twitch technique remains a viable tool to assess voluntary activation and central fatigue.

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Reliability of Tibialis Anterior Muscle Voluntary Activation Using the Interpolated Twitch Technique and the Central Activation Ratio in People with Stroke

Brain Sciences ◽

10.3390/brainsci11020176 ◽

2021 ◽

Vol 11 (2) ◽

pp. 176

Author(s):

Sharon Olsen ◽

Nada Signal ◽

Imran Khan Niazi ◽

Gemma Alder ◽

Usman Rashid ◽

...

Keyword(s):

Electrical Stimulation ◽

Lower Bound ◽

Tibialis Anterior ◽

Tibialis Anterior Muscle ◽

Central Fatigue ◽

Chronic Stroke ◽

Voluntary Activation ◽

Central Activation Ratio ◽

Interpolated Twitch Technique ◽

Activation Ratio

Voluntary activation (VA) is measured by applying supramaximal electrical stimulation to a muscle during a maximal voluntary contraction (MVC). The amplitude of the evoked muscle twitch is used to determine any VA deficit, and indicates incomplete central neural drive to the motor units. People with stroke experience VA deficits and greater levels of central fatigue, which is the decrease in VA that occurs following exercise. This study investigated the between-session reliability of VA and central fatigue of the tibialis anterior muscle (TA) in people with chronic stroke (n = 12), using the interpolated twitch technique (ITT), adjusted-ITT, and central activation ratio (CAR) methods. On two separate sessions, supramaximal electrical stimulation was applied to the TA when it was at rest and maximally activated, at the start and end of a 30-s isometric dorsiflexor MVC. The most reliable measures of VA were obtained using the CAR calculation on transformed data, which produced an ICC of 0.92, and a lower bound confidence interval in the good range (95% CI 0.77 to 0.98). Reliability was lower for the CAR calculation on non-transformed data (ICC 0.82, 95% CI 0.63 to 0.91) and the ITT and adjusted-ITT calculations on transformed data (ICCs 0.82, 95% CIs 0.51 to 0.94), which had lower bound confidence intervals in the moderate range. The two ITT calculations on non-transformed data demonstrated the poorest reliability (ICCs 0.62, 95% CI 0.25 to 0.74). Central fatigue measures demonstrated very poor reliability. Thus, the reliability for VA in people with chronic stroke ranged from good to poor, depending on the calculation method and statistical analysis method, whereas the reliability for central fatigue was very poor.

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Comparison Between Isometric and Concentric Motor Fatigability in Persons With Multiple Sclerosis and Healthy Controls – exploring central and peripheral contributions of motor fatigability

Neurorehabilitation and Neural Repair ◽

10.1177/15459683211017502 ◽

2021 ◽

pp. 154596832110175

Author(s):

Tobias Gaemelke ◽

Morten Riemenschneider ◽

Ulrik Dalgas ◽

Tue Kjølhede ◽

Cuno Rasmussen ◽

...

Keyword(s):

Multiple Sclerosis ◽

Regression Analysis ◽

Knee Extensor ◽

Voluntary Contraction ◽

Voluntary Activation ◽

Knee Extensors ◽

Healthy Controls ◽

Isokinetic Dynamometer ◽

Interpolated Twitch Technique ◽

Group Regression

Background Motor fatigability (i.e. contraction-induced reduction in muscle strength) from a concentric task associate stronger to walking and perception of fatigue in persons with multiple sclerosis (pwMS), compared with an isometric task. However, the central and peripheral contributions of motor fatigability between these tasks have not been investigated. Objective Compare the central and peripheral contributions of motor fatigability in the knee extensors in a sustained isometric fatigability protocol versus a concentric fatigability protocol and in pwMS versus healthy controls (HCs). Methods Participants (n=31 pwMS; n=15 HCs) underwent neuromuscular testing before and immediately after two knee extensor fatigability tasks (sustained isometric and concentric) in an isokinetic dynamometer. Neuromuscular testing of fatigability consisted of maximal voluntary contraction, voluntary activation (central/neural contributor), and resting twitch (peripheral/muscular contributor) determined by the interpolated twitch technique. Results Sustained isometric and concentric fatigability protocols resulted in motor fatigability for both pwMS and HCs, with no between-protocols differences for either group. Regression analysis showed that motor fatigability variance in pwMS was mainly attributed to central fatigability in the sustained isometric protocol and to both central and peripheral fatigability in the concentric protocol. In HCs, the variance in sustained isometric and concentric fatigability were attributed to both peripheral and central fatigability. Conclusion Central and peripheral contributions of motor fatigability differed between sustained isometric and concentric protocols as well as between pwMS and HCs. These between-protocol differences in pwMS provide a neuromuscular dimension to the reported difference in the strength of associations of concentric and isometric tasks to walking and perception of fatigue in pwMS.

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Delayed recovery of velocity-dependent power loss following eccentric actions of the ankle dorsiflexors

Journal of Applied Physiology ◽

10.1152/japplphysiol.01254.2009 ◽

2010 ◽

Vol 109 (3) ◽

pp. 669-676 ◽

Cited By ~ 25

Author(s):

Geoffrey A. Power ◽

Brian H. Dalton ◽

Charles L. Rice ◽

Anthony A. Vandervoort

Keyword(s):

Power Loss ◽

Muscle Power ◽

Low Frequency ◽

Eccentric Contraction ◽

Voluntary Contraction ◽

Voluntary Activation ◽

Shortening Velocity ◽

Interpolated Twitch Technique ◽

In Series ◽

Ankle Dorsiflexors

Unaccustomed eccentric exercise has been shown to impair muscle function, although little is known regarding this impairment on muscle power. The purpose of this study was to investigate changes in neuromuscular properties of the ankle dorsiflexors during and after an eccentric contraction task and throughout recovery in 21 (10 men, 11 women) recreationally active young adults (25.8 ± 2.3 yr). All subjects performed 5 sets of 30 eccentric contractions at 80% of maximum isometric voluntary contraction (MVC) torque. Data were recorded at baseline, during the fatigue task, and for 30 min of recovery. There were no significant sex differences for all fatigue measures; thus data were pooled. After the fatigue task, MVC torque declined by 28% ( P < 0.05) and did not recover fully, and voluntary activation of the dorsiflexors, as assessed by the interpolated twitch technique, was near maximal (>99%) during and after the fatigue task ( P > 0.05). Peak twitch torque was reduced by 21% at 2 min of recovery and progressively decreased to 35% by 30 min ( P < 0.05). Low-frequency torque depression (10-to-50 Hz ratio) was present at 30 s of recovery, increased to 51% by 10 min, and did not recover fully ( P < 0.05). Velocity-dependent concentric power was reduced by 8% immediately after task termination and did not recover fully within 30 min ( P < 0.05). The main findings of an incomplete recovery of MVC torque, low-frequency torque depression, and shortening velocity indicate the presence of muscle damage, which may have altered excitation-contraction coupling and cross-bridge kinetics and reduced the number of functional sarcomeres in series, ultimately leading to velocity-dependent power loss.

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Quadriceps neuromuscular function and self-reported functional ability in knee osteoarthritis

Journal of Applied Physiology ◽

10.1152/japplphysiol.00947.2011 ◽

2012 ◽

Vol 113 (2) ◽

pp. 255-262 ◽

Cited By ~ 14

Author(s):

M. J. Berger ◽

C. A. McKenzie ◽

D. G. Chess ◽

A. Goela ◽

T. J. Doherty

Keyword(s):

Knee Osteoarthritis ◽

Functional Ability ◽

Muscle Power ◽

Voluntary Contraction ◽

Voluntary Activation ◽

Knee Oa ◽

Interpolated Twitch Technique ◽

Multiple Regression Models ◽

General Power ◽

Isometric Torque

The purposes of this study were to determine 1) the relationships of self-reported function scores in patients with knee osteoarthritis (OA) to both maximal isometric torque and to isotonic power at a variety of loads, and 2) the degree to which muscle volume (MV) or voluntary activation (VA) are associated with torque and power measures in this population. Isometric maximal voluntary contraction (MVC) torque and isotonic power [performed at loads corresponding to 10, 20, 30, 40, and 50% MVC, and a minimal load (“Zero Load”)] were measured in 40 participants with knee OA. Functional ability was measured with the Western Ontario and McMaster Osteoarthritis Index (WOMAC) function subscale. MV was determined with magnetic resonance imaging, and VA was measured with the interpolated twitch technique. In general, power measured at lower loads (Zero Load and 10–30% MVC, r2= 0.21–0.28, P < 0.05) predicted a greater proportion of the variance in function than MVC torque ( r2= 0.18, P < 0.05), with power measured at Zero Load showing the strongest association ( r2= 0. 28, P < 0.05). MV was the strongest predictor of MVC torque and power measures in multiple regression models ( r2= 0.42–0.72). VA explained only 6% of the variance in MVC torque and was not significantly associated with power at any load ( P > 0.05). Quadriceps MVC torque and power are associated with self-reported function in knee OA, but muscle power at lower loads is more predictive of function than MVC torque. The variance in MVC torque and power between participants is due predominantly to differences in MV and has little to do with deficits in VA.

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Supraspinal fatigue impedes recovery from a low-intensity sustained contraction in old adults

Journal of Applied Physiology ◽

10.1152/japplphysiol.00799.2011 ◽

2012 ◽

Vol 112 (5) ◽

pp. 849-858 ◽

Cited By ~ 24

Author(s):

Tejin Yoon ◽

Bonnie Schlinder-Delap ◽

Manda L. Keller ◽

Sandra K. Hunter

Keyword(s):

Young Adults ◽

Pressor Response ◽

Motor Evoked Potential ◽

Silent Period ◽

Voluntary Activation ◽

Age Difference ◽

Task Failure ◽

Old Adults ◽

Sustained Contraction ◽

Low Intensity

This study determined the contribution of supraspinal fatigue and contractile properties to the age difference in neuromuscular fatigue during and recovery from a low-intensity sustained contraction. Cortical stimulation was used to evoke measures of voluntary activation and muscle relaxation during and after a contraction sustained at 20% of maximal voluntary contraction (MVC) until task failure with elbow flexor muscles in 14 young adults (20.9 ± 3.6 yr, 7 men) and 14 old adults (71.6 ± 5.4 yr, 7 men). Old adults exhibited a longer time to task failure than the young adults (23.8 ± 9.0 vs. 11.5 ± 3.9 min, respectively, P < 0.001). The time to failure was associated with initial peak rates of relaxation of muscle fibers and pressor response ( P < 0.05). Increments in torque (superimposed twitch; SIT) generated by transcranial magnetic stimulation (TMS) during brief MVCs, increased during the fatiguing contraction ( P < 0.001) and then decreased during recovery ( P = 0.02). The increase in the SIT was greater for the old adults than the young adults during the fatiguing contraction and recovery ( P < 0.05). Recovery of MVC torque was less for old than young adults at 10 min post-fatiguing contraction (75.1 ± 8.7 vs. 83.6 ± 7.8% of control MVC, respectively, P = 0.01) and was associated with the recovery of the SIT ( r = −0.59, r2 = 0.35, P < 0.001). Motor evoked potential (MEP) amplitude and the silent period elicited during the fatiguing contraction increased less for old adults than young adults ( P < 0.05). The greater fatigue resistance with age during a low-intensity sustained contraction was attributable to mechanisms located within the muscle. Recovery of maximal strength after the low-intensity fatiguing contraction however, was impeded more for old adults than young because of greater supraspinal fatigue. Recovery of strength could be an important variable to consider in exercise prescription of old populations.

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Quadriceps activation during maximal isometric and isokinetic contractions: The minimal real difference and its implications

Isokinetics and Exercise Science ◽

10.3233/ies-203241 ◽

2020 ◽

pp. 1-13

Author(s):

Luigi Catino ◽

Chiara Malloggi ◽

Stefano Scarano ◽

Valeria Cerina ◽

Viviana Rota ◽

...

Keyword(s):

Intraclass Correlation ◽

Correlation Coefficients ◽

Voluntary Activation ◽

Real Difference ◽

Concentric Contractions ◽

Rehabilitation Programs ◽

Logit Transformation ◽

Isokinetic Contractions ◽

Electrical Stimuli ◽

Voluntary Contractions

BACKGROUND: A method of measurement of voluntary activation (VA, percent of full muscle recruitment) during isometric and isokinetic concentric contractions of the quadriceps femoris (QF) at 60∘/s and 120∘/s was previously validated. OBJECTIVE: This study aimed to quantify the test-retest minimal real difference (MRD) of VA during isometric (ISOM) and isokinetic concentric contractions of QF (100∘/s, ISOK) in a sample of healthy individuals. METHODS: VA was measured through the interpolated twitch technique. Pairs of electrical stimuli were delivered to the QF at 40∘ of knee flexion during maximal voluntary contractions. Twenty-five healthy participants (20–38 years, 12 women, 13 men) completed two testing sessions with a 14-day interval. VA values were linearized through logit transformation (VAl). The MRD was estimated from intraclass correlation coefficients (model 2.1). RESULTS: The VA (median, range) was 84.20% (38.2–99.9%) in ISOM and 94.22% (33.8-100%) in ISOK. MRD was 0.78 and 1.12 logit for ISOM and ISOK, respectively. As an example, in terms of percent VA these values correspond to a change from 76% to 95% and from 79% to 98% in ISOM and in ISOK, respectively. CONCLUSIONS: The provided MRD values allow to detect significant individual changes in VA, as expected after training and rehabilitation programs.

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Locomotor exercise induces long-lasting impairments in the capacity of the human motor cortex to voluntarily activate knee extensor muscles

Journal of Applied Physiology ◽

10.1152/japplphysiol.90911.2008 ◽

2009 ◽

Vol 106 (2) ◽

pp. 556-565 ◽

Cited By ~ 84

Author(s):

Simranjit K. Sidhu ◽

David J. Bentley ◽

Timothy J. Carroll

Keyword(s):

Motor Cortex ◽

Motor Nerve ◽

Maximum Voluntary Contraction ◽

Voluntary Activation ◽

Exercise Session ◽

Knee Extensors ◽

Central Component ◽

Control Session ◽

Cycling Exercise ◽

Human Motor Cortex

Muscle fatigue is a reduction in the capacity to exert force and may involve a “central” component originating in the brain and/or spinal cord. Here we examined whether supraspinal factors contribute to impaired central drive after locomotor endurance exercise. On 2 separate days, 10 moderately active individuals completed a locomotor cycling exercise session or a control session. Brief (2 s) and sustained (30 s) isometric knee extension contractions were completed before and after locomotor exercise consisting of eight, 5-min bouts of cycling at 80% of maximum workload. In the control session, subjects completed the isometric contractions in a rested state. Twitch responses to supramaximal motor nerve stimulation and transcranial magnetic stimulation were obtained to assess peripheral force-generating capacity and voluntary activation. Maximum voluntary contraction (MVC) force during brief contractions decreased by 23 ± 6.3% after cycling exercise and remained 12 ± 2.8% below baseline 45 min later ( F1,9 > 15.5; P < 0.01). Resting twitch amplitudes declined by ∼45% ( F1,9 = 28.3; P < 0.001). Cortical voluntary activation declined from 90.6 ± 1.6% at baseline to 80.6 ± 2.1% after exercise ( F1,9 = 28.0; P < 0.001) and remained significantly reduced relative to control 30–45 min later (80.6 ± 3.4%; F1,9 = 10.7; P < 0.01). Thus locomotor exercise caused a long-lasting impairment in the capacity of the motor cortex to drive the knee extensors. Force was reduced more during sustained MVC after locomotor exercise than in the control session. Peripheral mechanisms contributed relatively more to this force reduction in the control session, whereas supraspinal fatigue played a greater role in sustained MVC reduction after locomotor exercise.

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