scholarly journals Menstrual cycle-associated modulations in neuromuscular function and fatigability of the knee extensors in eumenorrheic women

2019 ◽  
Vol 126 (6) ◽  
pp. 1701-1712 ◽  
Author(s):  
Paul Ansdell ◽  
Callum G. Brownstein ◽  
Jakob Škarabot ◽  
Kirsty M. Hicks ◽  
Davina C. M. Simoes ◽  
...  
Keyword(s):  
Oral Contraceptive ◽  
Transcranial Magnetic Stimulation ◽  
Menstrual Cycle ◽  
Magnetic Stimulation ◽  
Motor Nerve ◽  
Oral Contraceptive Pill ◽  
Intracortical Inhibition ◽  
Neuromuscular Function ◽  
Voluntary Activation ◽  
Knee Extensors

Sex hormone concentrations of eumenorrheic women typically fluctuate across the menstrual cycle and can affect neural function such that estrogen has neuroexcitatory effects, and progesterone induces inhibition. However, the effects of these changes on corticospinal and intracortical circuitry and the motor performance of the knee extensors are unknown. The present two-part investigation aimed to 1) determine the measurement error of an exercise task, transcranial magnetic stimulation (TMS)-, and motor nerve stimulation (MNS)-derived responses in women ingesting a monophasic oral contraceptive pill (hormonally-constant) and 2) investigate whether these measures were modulated by menstrual cycle phase (MCP), by examining them before and after an intermittent isometric fatiguing task (60% of maximal voluntary contraction, MVC) with the knee extensors until task failure in eumenorrheic women on days 2, 14, and 21 of the menstrual cycle. The repeatability of neuromuscular measures at baseline and fatigability ranged between moderate and excellent in women taking the oral contraceptive pill. MVC was not affected by MCP ( P = 0.790). Voluntary activation (MNS and TMS) peaked on day 14 ( P = 0.007 and 0.008, respectively). Whereas corticospinal excitability was unchanged, short-interval intracortical inhibition was greatest on day 21 compared with days 14 and 2 ( P < 0.001). Additionally, time to task failure was longer on day 21 than on both days 14 and 2 (24 and 36%, respectively, P = 0.030). The observed changes were larger than the associated measurement errors. These data demonstrate that neuromuscular function and fatigability of the knee extensors vary across the menstrual cycle and may influence exercise performance involving locomotor muscles. NEW & NOTEWORTHY The present two-part study first demonstrated the repeatability of transcranial magnetic stimulation- and electrical motor nerve stimulation-evoked variables in a hormonally constant female population. Subsequently, it was demonstrated that the eumenorrheic menstrual cycle affects neuromuscular function. Changing concentrations of neuroactive hormones corresponded to greater voluntary activation on day 14, greater intracortical inhibition on day 21, and lowest fatigability on day 21. These alterations of knee extensor neuromuscular function have implications for locomotor activities.

scholarly journals Effect of graded hypoxia on supraspinal contributions to fatigue with unilateral knee-extensor contractions

2010 ◽  
Vol 109 (6) ◽  
pp. 1842-1851 ◽  
Author(s):  
Stuart Goodall ◽  
Emma Z. Ross ◽  
Lee M. Romer
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Motor Cortex ◽  
Maximal Voluntary Contraction ◽  
Magnetic Stimulation ◽  
Voluntary Contraction ◽  
Corticospinal Excitability ◽  
Voluntary Activation ◽  
Severe Hypoxia ◽  
Knee Extensors ◽  
Moderate Hypoxia

Supraspinal fatigue, defined as an exercise-induced decline in force caused by suboptimal output from the motor cortex, accounts for over one-quarter of the force loss after fatiguing contractions of the knee extensors in normoxia. We tested the hypothesis that the relative contribution of supraspinal fatigue would be elevated with increasing severities of acute hypoxia. On separate days, 11 healthy men performed sets of intermittent, isometric, quadriceps contractions at 60% maximal voluntary contraction to task failure in normoxia (inspired O2 fraction/arterial O2 saturation = 0.21/98%), mild hypoxia (0.16/93%), moderate hypoxia (0.13/85%), and severe hypoxia (0.10/74%). Electrical stimulation of the femoral nerve was performed to assess neuromuscular transmission and contractile properties of muscle fibers. Transcranial magnetic stimulation was delivered to the motor cortex to quantify corticospinal excitability and voluntary activation. After 10 min of breathing the test gas, neuromuscular function and cortical voluntary activation prefatigue were unaffected in any condition. The fatigue protocol resulted in ∼30% declines in maximal voluntary contraction force in all conditions, despite differences in time-to-task failure (24.7 min in normoxia vs. 15.9 min in severe hypoxia, P < 0.05). Potentiated quadriceps twitch force declined in all conditions, but the decline in severe hypoxia was less than that in normoxia ( P < 0.05). Cortical voluntary activation also declined in all conditions, but the deficit in severe hypoxia exceeded that in normoxia ( P < 0.05). The additional central fatigue in severe hypoxia was not due to altered corticospinal excitability, as electromyographic responses to transcranial magnetic stimulation were unchanged. Results indicate that peripheral mechanisms of fatigue contribute relatively more to the reduction in force-generating capacity of the knee extensors following submaximal intermittent isometric contractions in normoxia and mild to moderate hypoxia, whereas supraspinal fatigue plays a greater role in severe hypoxia.

scholarly journals Methodological issues with the assessment of voluntary activation using transcranial magnetic stimulation in the knee extensors

2018 ◽  
Author(s):  
Jeanne Dekerle ◽  
Paul Ansdell ◽  
lisa Schäfer ◽  
Aaron Greenhouse-Tucknott ◽  
James Graeme Wrightson
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Maximal Voluntary Contraction ◽  
Magnetic Stimulation ◽  
Voluntary Contraction ◽  
Face Validity ◽  
Voluntary Activation ◽  
Knee Extensors ◽  
Post Exercise ◽  
Smallest Detectable Change ◽  
Fatiguing Exercise

Purpose: The assessment of voluntary activation of the knee extensors using transcranial magnetic stimulation (VATMS) is routinely performed to assess the supraspinal function. Yet methodological scrutiny of the technique is scarce. The aim of the present study was to examine face validity and reliability of VATMS and its two main determinants (superimposed twitch during a maximal voluntary contraction [SIT100%] and estimated resting twitch [ERT]). Methods: SIT100%, ERT, and VATMS were measured on 10 healthy males (age: 24 ± 5 years) before and following intermittent isometric fatiguing exercise on two separate occasions. Results: The findings indicated issues regarding the accuracy of ERT and suggested a three-point relationship should not be used to determine ERT. Reliabilities for VATMS, SIT100% and ERT were acceptable pre- but much weaker post-exercise (especially for SIT100%). Despite statistically significant changes in main neuromuscular variables following the intermittent isometric fatiguing exercise (P&lt;0.05), when post-exercise reliability was considered, the exercise effect on VATMS was smaller than the smallest detectable change in 18 of the 20 individual tests performed, and for the whole sample for one of two visits. Finally, Maximal voluntary contraction was reduced significantly following the neuromuscular assessment (NMA) pre-exercise but recovered during the NMA post-exercise. Conclusion: This is the first study to demonstrate a lack of sensitivity of key neuromuscular measurements to exercise and to evidence both presence of neuromuscular fatigue following the NMA in itself, and recovery of the neuromuscular function during the NMA post-exercise. These results challenge the face validity of this routinely used protocol.

Voluntary activation of knee extensor muscles with transcranial magnetic stimulation

2020 ◽  
Author(s):  
James Louis Nuzzo ◽  
David S. Kennedy ◽  
Harrison T. Finn ◽  
Janet Louise Taylor
Keyword(s):  
Electrical Stimulation ◽  
Transcranial Magnetic Stimulation ◽  
Magnetic Stimulation ◽  
Motor Evoked Potentials ◽  
Vastus Lateralis ◽  
Test Validity ◽  
Femoral Nerve ◽  
Voluntary Activation ◽  
Knee Extensors ◽  
Stimulation Of

We examined if transcranial magnetic stimulation (TMS) is a valid tool for assessment of voluntary activation of the knee extensors in healthy individuals. Maximal M-waves (Mmax) of vastus lateralis (VL) were evoked with electrical stimulation of femoral nerve (FNS); Mmax of medial hamstrings (HS) was evoked with electrical stimulation of sciatic nerve branches; motor evoked potentials (MEPs) of VL and HS were evoked with TMS; superimposed twitches (SIT) of knee extensors were evoked with FNS and TMS. In Study 1, TMS intensity (69% output(SD 5)) was optimized for MEP sizes, but guidelines for test validity could not be met. Agonist VL MEPs were too small (51.4% Mmax(SD 11.9); guideline ≥70% Mmax) and antagonist HS MEPs were too big (16.5% Mmax(SD 10.3); guideline <10% Mmax). Consequently, the TMS estimated resting twitch (99.1 N(SD 37.2)) and FNS resting twitch (142.4 N(SD 41.8)) were different. In Study 2, SITs at 90% maximal voluntary contraction (MVC) were similar between TMS (16.1 N(SD 10.3)) and FNS (20.9 N(SD 16.7)), when TMS intensity was optimized for this purpose, suggesting a procedure that combines TMS SITs with FNS resting twitches could be valid. In Study 3, which tested the TMS intensity (56% output(SD 18)) that evoked the largest SIT at 90%MVC, voluntary activation from TMS (87.3%(SD 7.1)) and FNS (84.5%(SD 7.6)) were different. In sum, the contemporary procedure for TMS-based voluntary activation of the knee extensors is invalid. A modified procedure improves validity, but only in individuals who meet rigorous inclusion criteria for SITs and MEPs.

scholarly journals Measurement of voluntary activation based on transcranial magnetic stimulation over the motor cortex

2016 ◽  
Vol 121 (3) ◽  
pp. 678-686 ◽  
Author(s):  
Gabrielle Todd ◽  
Janet L. Taylor ◽  
Simon C. Gandevia
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Motor Cortex ◽  
Magnetic Stimulation ◽  
Voluntary Activation ◽  
Knee Extensors ◽  
Muscle Twitch ◽  
Antagonist Muscles ◽  
Ideal Situation ◽  
Technical Challenges ◽  
Muscle Groups

This article reviews the use of transcranial magnetic stimulation (TMS) over the motor cortex to make estimates of the level of voluntary drive to muscles. The method, described in 2003 (Todd et al. J Physiol 551: 661-671, 2003), uses a TMS pulse to produce descending corticospinal volleys that synaptically activate motoneurons, resulting in a muscle twitch. Linear regression of the superimposed twitch amplitude and voluntary force (or torque) can generate an “estimated” resting twitch for muscles involved in a task. This procedure has most commonly been applied to elbow flexors but also to knee extensors and other muscle groups. Data from 44 papers using the method were tabulated. We identify and discuss five major technical challenges, and the frequency with which they are addressed. The technical challenges include inadvertent activation of the cortical representation of antagonist muscles, the role of antagonist torques at the studied joint, uncertainty about the effectiveness of the TMS pulse in activating the motoneuron pool, the linearity of the voluntary force (or torque) and superimposed twitch relationship, and variability in the TMS-evoked EMG and force/torque responses. The ideal situation in which the descending corticospinal volleys recruit all of the agonist motoneurons and none of the antagonist motoneurons is unlikely to ever occur, and hence results must be carefully examined to assess the authenticity of the voluntary activation estimates in the context of the experimental design. A partial compromise lies in the choice of stimulus intensity. We also identify aspects of the procedure that require further investigation.

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

2009 ◽  
Vol 106 (2) ◽  
pp. 556-565 ◽  
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.

scholarly journals Long-interval intracortical inhibition as biomarker for epilepsy: a transcranial magnetic stimulation study

Brain ◽  
2018 ◽  
Vol 141 (2) ◽  
pp. 409-421 ◽  
Author(s):  
Prisca R Bauer ◽  
Annika A de Goede ◽  
William M Stern ◽  
Adam D Pawley ◽  
Fahmida A Chowdhury ◽  
...  
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Magnetic Stimulation ◽  
Intracortical Inhibition
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