scholarly journals Cortical and Spinal Modulation of Antagonist Coactivation During a Submaximal Fatiguing Contraction in Humans

2008 ◽  
Vol 99 (2) ◽  
pp. 554-563 ◽  
Author(s):  
Morgan Lévénez ◽  
S. Jayne Garland ◽  
Malgorzata Klass ◽  
Jacques Duchateau
Keyword(s):  
Evoked Potentials ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
H Reflex ◽  
Elbow Flexors ◽  
Triceps Brachii ◽  
Task Failure ◽  
Antagonist Muscles ◽  
Antagonist Coactivation ◽  
Stimulation Of

This study investigates the control mechanisms at the cortical and spinal levels of antagonist coactivation during a submaximal fatiguing contraction of the elbow flexors at 50% of maximal voluntary contraction (MVC). We recorded motor-evoked potentials in the biceps brachii and triceps brachii muscles in response to magnetic stimulation of the motor cortex (MEP) and corticospinal tract (cervicomedullary motor-evoked potentials—CMEPs), as well as the Hoffmann reflex (H-reflex) and maximal M-wave (Mmax) elicited by electrical stimulation of the brachial plexus, before, during, and after the fatigue task. The results showed that although the coactivation ratio did not change at task failure, the MVC torque produced by the elbow flexors declined by 48% ( P < 0.01) with no change in MVC torque for the elbow extensors. While the MEP and CMEP areas (normalized to Mmax) of the biceps brachii increased (∼50%) over the first 40% of the time to task failure and then plateaued, both responses in the triceps brachii increased (∼150–180%) gradually throughout the fatigue task. In contrast to the monotonic increase in the MEP and CMEP of the antagonist muscles, the H-reflex of the triceps brachii exhibited a biphasic modulation, increasing during the first part of the contraction before declining subsequently to 65% of its initial value. Collectively, these results suggest that the level of coactivation during a fatiguing contraction is mediated by supraspinal rather than spinal mechanisms and involves differential control of agonist and antagonist muscles.

scholarly journals Arm posture-dependent changes in corticospinal excitability are largely spinal in origin

2016 ◽  
Vol 115 (4) ◽  
pp. 2076-2082 ◽  
Author(s):  
James L. Nuzzo ◽  
Gabriel S. Trajano ◽  
Benjamin K. Barry ◽  
Simon C. Gandevia ◽  
Janet L. Taylor
Keyword(s):  
Evoked Potentials ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Compound Muscle Action Potential ◽  
Corticospinal Excitability ◽  
Triceps Brachii ◽  
Upper Arm ◽  
Muscle Action Potential ◽  
Subcortical Stimulation ◽  
Stimulation Of

Biceps brachii motor evoked potentials (MEPs) from cortical stimulation are influenced by arm posture. We used subcortical stimulation of corticospinal axons to determine whether this postural effect is spinal in origin. While seated at rest, 12 subjects assumed several static arm postures, which varied in upper-arm (shoulder flexed, shoulder abducted, arm hanging to side) and forearm orientation (pronated, neutral, supinated). Transcranial magnetic stimulation over the contralateral motor cortex elicited MEPs in resting biceps and triceps brachii, and electrical stimulation of corticospinal tract axons at the cervicomedullary junction elicited cervicomedullary motor evoked potentials (CMEPs). MEPs and CMEPs were normalized to the maximal compound muscle action potential (Mmax). Responses in biceps were influenced by upper-arm and forearm orientation. For upper-arm orientation, biceps CMEPs were 68% smaller ( P = 0.001), and biceps MEPs 31% smaller ( P = 0.012), with the arm hanging to the side compared with when the shoulder was flexed. For forearm orientation, both biceps CMEPs and MEPs were 34% smaller (both P < 0.046) in pronation compared with supination. Responses in triceps were influenced by upper-arm, but not forearm, orientation. Triceps CMEPs were 46% smaller ( P = 0.007) with the arm hanging to the side compared with when the shoulder was flexed. Triceps MEPs and biceps and triceps MEP/CMEP ratios were unaffected by arm posture. The novel finding is that arm posture-dependent changes in corticospinal excitability in humans are largely spinal in origin. An interplay of multiple reflex inputs to motoneurons likely explains the results.

Spinal Mechanisms Contribute to Differences in the Time to Failure of Submaximal Fatiguing Contractions Performed With Different Loads

2008 ◽  
Vol 99 (3) ◽  
pp. 1096-1104 ◽  
Author(s):  
Malgorzata Klass ◽  
Morgan Lévénez ◽  
Roger M. Enoka ◽  
Jacques Duchateau
Keyword(s):  
Biceps Brachii ◽  
Motor Evoked Potential ◽  
H Reflex ◽  
Time To Failure ◽  
Elbow Flexors ◽  
Task Failure ◽  
Constant Torque ◽  
Rate Of Increase ◽  
Position Task ◽  
Fatiguing Contractions

This study compared the mechanisms that limit the time to failure of a sustained submaximal contraction at 20% of maximum when the elbow flexors either supported an inertial load (position task) or exerted an equivalent constant torque against a rigid restraint (force task). The surface electromyogram (EMG), the motor-evoked potential (MEP) in response to transcranial magnetic stimulation (TMS) of the motor cortex, and the Hoffmann reflex (H-reflex) and maximal M-wave (Mmax) elicited by electrical stimulation of the brachial plexus were recorded in biceps brachii during the two tasks. Although the time to failure for the position task was only 44% of that for the force task, the rate of increase of the average EMG (aEMG; % initial MVC) and MEP area (% Mmax) did not differ significantly during the two tasks. At task failure, however, the increases in normalized aEMG and MEP area were significantly ( P < 0.05) greater for the force task (36.4 and 219.9%) than for the position task (22.4 and 141.7%). Furthermore, the superimposed mechanical twitch (% initial MVC), evoked by TMS during a brief MVC of the elbow flexors immediately after task failure, was increased similarly in both tasks. Although the normalized H-reflex area (% Mmax) decreased during the two fatiguing contractions, the reduction was more rapid and greater during the position task (59.8%) compared with the force task (34.7%). Taken together, the results suggest that spinal mechanisms were a major determinant of the briefer time to failure for the position task.

Output of Human Motoneuron Pools to Corticospinal Inputs During Voluntary Contractions

2006 ◽  
Vol 95 (6) ◽  
pp. 3512-3518 ◽  
Author(s):  
P. G. Martin ◽  
S. C. Gandevia ◽  
J. L. Taylor
Keyword(s):  
Evoked Potentials ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Voluntary Contraction ◽  
Flexor Muscle ◽  
Spinal Level ◽  
Motoneuron Pool ◽  
Wide Range ◽  
Voluntary Contractions ◽  
Stimulation Of

This study investigated transmission of corticospinal output through motoneurons over a wide range of voluntary contraction strengths in humans. During voluntary contraction of biceps brachii, motor evoked potentials (MEPs) to transcranial magnetic stimulation of the motor cortex grow up to about 50% maximal force and then decrease. To determine whether the decrease reflects events at a cortical or spinal level, responses to stimulation of the cortex and corticospinal tract (cervicomedullary motor evoked potentials, CMEPs) as well as maximal M-waves (Mmax) were recorded during strong contractions at 50 to 100% maximum. In biceps and brachioradialis, MEPs and CMEPs (normalized to Mmax) evoked by strong stimuli decreased during strong elbow flexions. Responses were largest during contractions at 75% maximum and both potentials decreased by about 25% Mmax during maximal efforts ( P < 0.001). Reductions were smaller with weaker stimuli, but again similar for MEPs and CMEPs. Thus the reduction in MEPs during strong voluntary contractions can be accounted for by reduced responsiveness of the motoneuron pool to stimulation. During strong contractions of the first dorsal interosseous, a muscle that increases voluntary force largely by frequency modulation, MEPs declined more than in either elbow flexor muscle (35% Mmax, P < 0.001). This suggests that motoneuron firing rates are important determinants of evoked output from the motoneuron pool. However, motor cortical output does not appear to be limited at high contraction strengths.

Arm-cycling sprints induce neuromuscular fatigue of the elbow flexors and alter corticospinal excitability of the biceps brachii

2016 ◽  
Vol 41 (2) ◽  
pp. 199-209 ◽  
Author(s):  
Gregory E.P. Pearcey ◽  
David J. Bradbury-Squires ◽  
Michael Monks ◽  
Devin Philpott ◽  
Kevin E. Power ◽  
...  
Keyword(s):  
Evoked Potentials ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Neuromuscular Fatigue ◽  
Corticospinal Excitability ◽  
Voluntary Activation ◽  
Elbow Flexors ◽  
Mean Power ◽  
Arm Cycling ◽  
Spinal Excitability

We examined the effects of arm-cycling sprints on maximal voluntary elbow flexion and corticospinal excitability of the biceps brachii. Recreationally trained athletes performed ten 10-s arm-cycling sprints interspersed with 150 s of rest in 2 separate experiments. In experiment A (n = 12), maximal voluntary contraction (MVC) force of the elbow flexors was measured at pre-sprint 1, post-sprint 5, and post-sprint 10. Participants received electrical motor point stimulation during and following the elbow flexor MVCs to estimate voluntary activation (VA). In experiment B (n = 7 participants from experiment A), supraspinal and spinal excitability of the biceps brachii were measured via transcranial magnetic and transmastoid electrical stimulation that produced motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs), respectively, during a 5% isometric MVC at pre-sprint 1, post-sprint 1, post-sprint 5, and post-sprint 10. In experiment A, mean power output, MVC force, potentiated twitch force, and VA decreased 13.1% (p < 0.001), 8.7% (p = 0.036), 27.6% (p = 0.003), and 5.6% (p = 0.037), respectively, from pre-sprint 1 to post-sprint 10. In experiment B, (i) MEPs decreased 42.1% (p = 0.002) from pre-sprint 1 to post-sprint 5 and increased 40.1% (p = 0.038) from post-sprint 5 to post-sprint 10 and (ii) CMEPs increased 28.5% (p = 0.045) from post-sprint 1 to post-sprint 10. Overall, arm-cycling sprints caused neuromuscular fatigue of the elbow flexors, which corresponded with decreased supraspinal and increased spinal excitability of the biceps brachii. The different post-sprint effects on supraspinal and spinal excitability may illustrate an inhibitory effect on supraspinal drive that reduces motor output and, therefore, decreases arm-cycling sprint performance.

scholarly journals Corticospinal excitability to the biceps and triceps brachii during forward and backward arm cycling is direction- and phase-dependent

2020 ◽  
Vol 45 (1) ◽  
pp. 72-80
Author(s):  
Anna. P. Nippard ◽  
Evan. J. Lockyer ◽  
Duane. C. Button ◽  
Kevin. E. Power
Keyword(s):  
Evoked Potentials ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Elbow Flexion ◽  
Corticospinal Excitability ◽  
Extension Phase ◽  
Triceps Brachii ◽  
Arm Cycling ◽  
Spinal Excitability ◽  
Flexion And Extension

The purpose of this study was to evaluate corticospinal excitability to the biceps and triceps brachii during forward (FWD) and backward (BWD) arm cycling. Corticospinal and spinal excitability were assessed using transcranial magnetic stimulation and transmastoid electrical stimulation to elicit motor evoked potentials (MEPs) and cervicomedullary evoked potentials (CMEPs), respectively. MEPs and CMEPs were recorded from the biceps and triceps brachii during FWD and BWD arm cycling at 2 positions, 6 and 12 o’clock. The 6 o’clock position corresponded to mid-elbow flexion and extension during FWD and BWD cycling, respectively, while 12 o’clock corresponded to mid-elbow extension and flexion during FWD and BWD cycling, respectively. During the flexion phase, MEP and CMEP amplitudes of the biceps brachii were higher during FWD cycling. However, during the extension phase, MEP and CMEP amplitudes were higher during BWD cycling. For the triceps brachii, MEP amplitudes were higher during FWD cycling regardless of phase. However, CMEP amplitudes were phase-dependent. During the flexion phase, CMEPs of the triceps brachii were higher during FWD cycling compared with BWD, but during the extension phase CMEPs were higher during BWD cycling compared with FWD. The data suggest that corticospinal and spinal excitability to the biceps brachii is phase- and direction-dependent. In the triceps brachii, spinal, but not corticospinal, excitability is phase-dependent when comparing FWD and BWD cycling. Novelty This is the first study to assess corticospinal excitability during FWD and BWD locomotor output. Corticospinal excitability during arm cycling depends on the direction, phase, and muscle being assessed.

scholarly journals Indirect Vibration of the Upper Limbs Alters Transmission Along Spinal but Not Corticospinal Pathways

2021 ◽  
Vol 15 ◽  
Author(s):  
Trevor S. Barss ◽  
David F. Collins ◽  
Dylan Miller ◽  
Amit N. Pujari
Keyword(s):  
Median Nerve ◽  
Presynaptic Inhibition ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
H Reflex ◽  
Cutaneous Reflexes ◽  
Spinal Pathways ◽  
Median Nerve Stimulation ◽  
The Right ◽  
Stimulation Of

The use of upper limb vibration (ULV) during exercise and rehabilitation continues to gain popularity as a modality to improve function and performance. Currently, a lack of knowledge of the pathways being altered during ULV limits its effective implementation. Therefore, the aim of this study was to investigate whether indirect ULV modulates transmission along spinal and corticospinal pathways that control the human forearm. All measures were assessed under CONTROL (no vibration) and ULV (30 Hz; 0.4 mm displacement) conditions while participants maintained a small contraction of the right flexor carpi radialis (FCR) muscle. To assess spinal pathways, Hoffmann reflexes (H-reflexes) elicited by stimulation of the median nerve were recorded from FCR with motor response (M-wave) amplitudes matched between conditions. An H-reflex conditioning paradigm was also used to assess changes in presynaptic inhibition by stimulating the superficial radial (SR) nerve (5 pulses at 300Hz) 37 ms prior to median nerve stimulation. Cutaneous reflexes in FCR elicited by stimulation of the SR nerve at the wrist were also recorded. To assess corticospinal pathways, motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation of the contralateral motor cortex were recorded from the right FCR and biceps brachii (BB). ULV significantly reduced H-reflex amplitude by 15.7% for both conditioned and unconditioned reflexes (24.0 ± 15.7 vs. 18.4 ± 11.2% Mmax; p &lt; 0.05). Middle latency cutaneous reflexes were also significantly reduced by 20.0% from CONTROL (−1.50 ± 2.1% Mmax) to ULV (−1.73 ± 2.2% Mmax; p &lt; 0.05). There was no significant effect of ULV on MEP amplitude (p &gt; 0.05). Therefore, ULV inhibits cutaneous and H-reflex transmission without influencing corticospinal excitability of the forearm flexors suggesting increased presynaptic inhibition of afferent transmission as a likely mechanism. A general increase in inhibition of spinal pathways with ULV may have important implications for improving rehabilitation for individuals with spasticity (SCI, stroke, MS, etc.).

scholarly journals Corticospinal excitability to the biceps and triceps brachii during forward and backward arm cycling is direction- and phase-dependent

2019 ◽  
Author(s):  
Anna Nippard ◽  
Evan Lockyer ◽  
Duane Button ◽  
Kevin Power
Keyword(s):  
Evoked Potentials ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Elbow Flexion ◽  
Corticospinal Excitability ◽  
Extension Phase ◽  
Triceps Brachii ◽  
Arm Cycling ◽  
Spinal Excitability ◽  
Flexion And Extension

The purpose of this study was to evaluate corticospinal excitability to the biceps and triceps brachii during forward (FWD) and backward (BWD) arm cycling. Corticospinal and spinal excitability were assessed using transcranial magnetic stimulation (TMS) and transmastoid electrical stimulation (TMES) to elicit motor evoked potentials (MEPs) and cervicomedullary evoked potentials (CMEPs), respectively. MEPs and CMEPs were recorded from the biceps and triceps brachii during FWD and BWD arm cycling at two positions, 6 and 12 o’clock. The 6 o’clock position corresponded to mid-elbow flexion and extension during FWD and BWD cycling, respectively, while 12 o’clock corresponded to mid-elbow extension and flexion during FWD and BWD cycling, respectively. During the flexion phase, MEP and CMEP amplitudes of the biceps brachii were higher during FWD than BWD cycling. However, during the extension phase, MEP and CMEP amplitudes were higher during BWD than FWD cycling. For the triceps brachii, MEP amplitudes were higher during FWD cycling compared to BWD regardless of phase. However, CMEP amplitudes were phase-dependent. During the flexion phase, CMEPs of the triceps brachii were higher during FWD cycling compared to BWD, but during the extension phase CMEPs were higher during BWD cycling compared to FWD. The data suggests that corticospinal and spinal excitability to the biceps brachii is phase- and direction-dependent. In the triceps brachii, spinal, but not corticospinal, excitability is phase-dependent when comparing FWD and BWD cycling.

scholarly journals Indirect Vibration of the Upper Limbs Alters Transmission Along Spinal but not Corticospinal Pathways

2020 ◽  
Author(s):  
Trevor S. Barss ◽  
David F. Collins ◽  
Dylan Miller ◽  
Amit N. Pujari
Keyword(s):  
Median Nerve ◽  
Presynaptic Inhibition ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
H Reflex ◽  
Cutaneous Reflexes ◽  
Spinal Pathways ◽  
Median Nerve Stimulation ◽  
The Right ◽  
Stimulation Of

AbstractThe aim of this study was to investigate whether indirect upper limb vibration (ULV) modulates transmission along spinal and corticospinal pathways that control the human forearm. All measures were assessed under CONTROL (no vibration) and ULV (30 Hz; 0.4 mm displacement) conditions while participants maintained a small contraction of the right flexor carpi radialis (FCR) muscle. To assess spinal pathways, Hoffmann reflexes (H-reflexes) elicited by stimulation of the median nerve were recorded from FCR with motor response (M-wave) amplitudes matched between conditions. An H-reflex conditioning paradigm was also used to assess changes in presynaptic inhibition by stimulating the superficial radial (SR) nerve (5 pulses at 300Hz) 37 ms prior to median nerve stimulation. Cutaneous reflexes in FCR elicited by stimulation of the SR nerve at the wrist were also recorded. To assess corticospinal pathways, motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation of the contralateral motor cortex were recorded from the right FCR and biceps brachii (BB). ULV significantly reduced H-reflex amplitude by 15.7% for both conditioned and unconditioned reflexes (24.0±15.7 vs 18.4±11.2 % Mmax; p<0.05). Middle latency cutaneous reflexes were also significantly reduced by 20.0% from CONTROL (−1.50 ± 2.1 % Mmax) to ULV (−1.73 ± 2.2 % Mmax; p<0.05). There was no significant effect of ULV on MEP amplitude (p>0.05). Therefore, ULV inhibits cutaneous and H-reflex transmission without influencing corticospinal excitability of the forearm flexors suggesting increased presynaptic inhibition of afferent transmission as a likely mechanism. A general increase in inhibition of spinal pathways with ULV may have important implications for improving rehabilitation for individuals with spasticity (SCI, stroke, MS, etc).

Increased corticospinal excitability prior to arm cycling is due to enhanced supraspinal but not spinal motoneurone excitability

2013 ◽  
Vol 38 (11) ◽  
pp. 1154-1161 ◽  
Author(s):  
Kevin E. Power ◽  
David B. Copithorne
Keyword(s):  
Magnetic Stimulation ◽  
Corticospinal Tract ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Corticospinal Excitability ◽  
Quiescent State ◽  
M Wave ◽  
Arm Cycling ◽  
Intention To Move ◽  
Stimulation Of

Human studies have not assessed supraspinal or spinal motoneurone excitability in the quiescent state prior to a rhythmic and alternating cyclical motor output. The purpose of the current study was to determine whether supraspinal and (or) spinal motoneurone excitability was modulated in humans prior to arm cycling when compared with rest with no intention to move. We hypothesized that corticospinal excitability would be enhanced prior to arm cycling due, in part, to increased spinal motoneurone excitability. Supraspinal and spinal motoneurone excitability were assessed via transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid stimulation of the corticospinal tract, respectively. Surface electromyography recordings of TMS motor evoked potentials (MEPs) and cervicomedullary MEPs (CMEPs) were made from the relaxed biceps brachii muscle prior to rhythmic arm cycling and at rest with no intention to move. The amplitude of the MEPs was greater (mean increase: +9.8% of maximal M wave; p = 0.006) and their onset latencies were shorter (mean decrease: –1.5 ms; p < 0.05) prior to cycling when compared with rest. The amplitudes of the CMEPs at any of 3 stimulation intensities were not different between conditions. We conclude that premovement enhancement of corticospinal excitability is greater prior to arm cycling than at rest because of increases in supraspinal but not spinal motoneurone excitability.

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