scholarly journals Intensity-dependent alterations in the excitability of cortical and spinal projections to the knee extensors during isometric and locomotor exercise

2015 ◽  
Vol 308 (12) ◽  
pp. R998-R1007 ◽  
Author(s):  
J. C. Weavil ◽  
S. K. Sidhu ◽  
T. S. Mangum ◽  
R. S. Richardson ◽  
M. Amann
Keyword(s):  
Evoked Potentials ◽  
Exercise Intensity ◽  
Motor Evoked Potentials ◽  
Vastus Lateralis ◽  
Femoral Nerve ◽  
Rectus Femoris ◽  
Knee Extensors ◽  
Electromyographic Activity ◽  
Dependent Manner ◽  
Cycling Exercise

We investigated the role of exercise intensity and associated central motor drive in determining corticomotoneuronal excitability. Ten participants performed a series of nonfatiguing (3 s) isometric single-leg knee extensions (ISO; 10–100% of maximal voluntary contractions, MVC) and cycling bouts (30–160% peak aerobic capacity, Wpeak). At various exercise intensities, electrical potentials were evoked in the vastus lateralis (VL) and rectus femoris (RF) via transcranial magnetic stimulation (motor-evoked potentials, MEP), and electrical stimulation of both the cervicomedullary junction (cervicomedullary evoked potentials, CMEP) and the femoral nerve (maximal M-waves, Mmax). Whereas Mmax remained unchanged in both muscles ( P > 0.40), voluntary electromyographic activity (EMG) increased in an exercise intensity-dependent manner for ISO and cycling exercise in VL and RF (both P < 0.001). During ISO exercise, MEPs and CMEPs progressively increased in VL and RF until a plateau was reached at ∼75% MVC; further increases in contraction intensity did not cause additional changes ( P > 0.35). During cycling exercise, VL-MEPs and CMEPs progressively increased by ∼65% until a plateau was reached at Wpeak. In contrast, RF MEPs and CMEPs progressively increased by ∼110% throughout the tested cycling intensities without the occurrence of a plateau. Furthermore, alterations in EMG below the plateau influenced corticomotoneuronal excitability similarly between exercise modalities. In both exercise modalities, the MEP-to-CMEP ratio did not change with exercise intensity ( P > 0.22). In conclusion, increases in exercise intensity and EMG facilitates the corticomotoneuronal pathway similarly in isometric knee extension and locomotor exercise until a plateau occurs at a submaximal exercise intensity. This facilitation appears to be primarily mediated by increases in excitability of the motoneuron pool.

scholarly journals Fatigue diminishes motoneuronal excitability during cycling exercise

2016 ◽  
Vol 116 (4) ◽  
pp. 1743-1751 ◽  
Author(s):  
Joshua C. Weavil ◽  
Simranjit K. Sidhu ◽  
Tyler S. Mangum ◽  
Russell S. Richardson ◽  
Markus Amann
Keyword(s):  
Evoked Potentials ◽  
Muscle Activation ◽  
Motor Evoked Potentials ◽  
Vastus Lateralis ◽  
Femoral Nerve ◽  
Central Fatigue ◽  
Rectus Femoris ◽  
Constant Load ◽  
Corticospinal Excitability ◽  
Cycling Exercise

Exercise-induced fatigue influences the excitability of the motor pathway during single-joint isometric contractions. This study sought to investigate the influence of fatigue on corticospinal excitability during cycling exercise. Eight men performed fatiguing constant-load (80% Wpeak; 241 ± 13 W) cycling to exhaustion during which the percent increase in quadriceps electromyography (ΔEMG; vastus lateralis and rectus femoris) was quantified. During a separate trial, subjects performed two brief (∼45 s) nonfatiguing cycling bouts (244 ± 15 and 331 ± 23W) individually chosen to match the ΔEMG across bouts to that observed during fatiguing cycling. Corticospinal excitability during exercise was quantified by transcranial magnetic, electric transmastoid, and femoral nerve stimulation to elicit motor-evoked potentials (MEP), cervicomedullary evoked potentials (CMEP), and M waves in the quadriceps. Peripheral and central fatigue were expressed as pre- to postexercise reductions in quadriceps twitch force (ΔQtw) and voluntary quadriceps activation (ΔVA). Whereas nonfatiguing cycling caused no measureable fatigue, fatiguing cycling resulted in significant peripheral (ΔQtw: 42 ± 6%) and central (ΔVA: 4 ± 1%) fatigue. During nonfatiguing cycling, the area of MEPs and CMEPs, normalized to M waves, similarly increased in the quadriceps (∼40%; P < 0.05). In contrast, there was no change in normalized MEPs or CMEPs during fatiguing cycling. As a consequence, the ratio of MEP to CMEP was unchanged during both trials ( P > 0.5). Therefore, although increases in muscle activation promote corticospinal excitability via motoneuronal facilitation during nonfatiguing cycling, this effect is abolished during fatigue. We conclude that the unaltered excitability of the corticospinal pathway from start of intense cycling exercise to exhaustion is, in part, determined by inhibitory influences on spinal motoneurons obscuring the facilitating effects of muscle activation.

Motor cortex excitability does not increase during sustained cycling exercise to volitional exhaustion

2012 ◽  
Vol 113 (3) ◽  
pp. 401-409 ◽  
Author(s):  
Simranjit K. Sidhu ◽  
Andrew G. Cresswell ◽  
Timothy J. Carroll
Keyword(s):  
Motor Cortex ◽  
Evoked Potentials ◽  
Cortical Neurons ◽  
Cortical Excitability ◽  
Motor Evoked Potentials ◽  
Vastus Lateralis ◽  
Rectus Femoris ◽  
Cycling Exercise ◽  
Motor Cortex Excitability ◽  
Stimulation Of

The excitability of the motor cortex increases as fatigue develops during sustained single-joint contractions, but there are no previous reports on how corticospinal excitability is affected by sustained locomotor exercise. Here we addressed this issue by measuring spinal and cortical excitability changes during sustained cycling exercise. Vastus lateralis (VL) and rectus femoris (RF) muscle responses to transcranial magnetic stimulation of the motor cortex (motor evoked potentials, MEPs) and electrical stimulation of the descending tracts (cervicomedullary evoked potentials, CMEPs) were recorded every 3 min from nine subjects during 30 min of cycling at 75% of maximum workload (Wmax), and every minute during subsequent exercise at 105% of Wmax until subjective task failure. Responses were also measured during nonfatiguing control bouts at 80% and 110% of Wmax prior to sustained exercise. There were no significant changes in MEPs or CMEPs ( P > 0.05) during the sustained cycling exercise. These results suggest that, in contrast to sustained single-joint contractions, sustained cycling exercise does not increase the excitability of motor cortical neurons. The contrasting corticospinal responses to the two modes of exercise may be due to differences in their associated systemic physiological consequences.

scholarly journals The effect of rolling massage on the excitability of the corticospinal pathway

2018 ◽  
Vol 43 (4) ◽  
pp. 317-323 ◽  
Author(s):  
Saied J. Aboodarda ◽  
Rebecca M. Greene ◽  
Devin T. Philpott ◽  
Ramandeep S. Jaswal ◽  
Guillaume Y. Millet ◽  
...  
Keyword(s):  
Compound Muscle Action Potential ◽  
Vastus Lateralis ◽  
Femoral Nerve ◽  
Motor Evoked Potential ◽  
Silent Period ◽  
Knee Extensors ◽  
Electromyographic Activity ◽  
Muscle Action Potential ◽  
Central Excitability ◽  
Electrical Stimuli

The aim of the present study was to investigate the alterations of corticospinal excitability (motor evoked potential, MEP) and inhibition (silent period, SP) following rolling massage of the quadriceps muscles. Transcranial magnetic and femoral nerve electrical stimuli were used to elicit MEPs and compound muscle action potential (Mmax) in the vastus lateralis and vastus medialis muscles prior to and following either (i) 4 sets of 90-s rolling massage (ROLLING) or (ii) rest (CONTROL). One series of neuromuscular evaluations, performed after each set of ROLLING or CONTROL, included 3 MEPs and 1 Mmax elicited every 4 s during 15-s submaximal contractions at 10% (experiment 1, n = 16) and 50% (experiment 2, n = 10) of maximal voluntary knee extensions (MVC). The MEP/Mmax ratio and electromyographic activity recorded from vastus lateralis at 10% MVC demonstrated significantly lower values during ROLLING than CONTROL (P < 0.05). The ROLLING did not elicit any significant changes in muscle excitability (Mmax area) and duration of transcranial magnetic stimulation-induced SP recorded from any muscle or level of contraction (P > 0.05). The findings suggest that rolling massage can modulate the central excitability of the circuitries innervating the knee extensors; however, the observed effects are dependent on the background contraction intensity during which the neuromuscular measurements are recorded.

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 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 Regional and muscle-specific adaptations in knee extensor hypertrophy using flywheel versus conventional weight-stack resistance exercise

2019 ◽  
Vol 44 (8) ◽  
pp. 827-833 ◽  
Author(s):  
Tommy R. Lundberg ◽  
Maria T. García-Gutiérrez ◽  
Mirko Mandić ◽  
Mats Lilja ◽  
Rodrigo Fernandez-Gonzalo
Keyword(s):  
Resistance Exercise ◽  
Muscle Hypertrophy ◽  
Vastus Lateralis ◽  
Knee Extensor ◽  
Rectus Femoris ◽  
Knee Extension ◽  
Knee Extensors ◽  
Cross Sectional ◽  
Proximal Site ◽  
Before And After

This study compared the effects of the most frequently employed protocols of flywheel (FW) versus weight-stack (WS) resistance exercise (RE) on regional and muscle-specific adaptations of the knee extensors. Sixteen men (n = 8) and women (n = 8) performed 8 weeks (2–3 days/week) of knee extension RE employing FW technology on 1 leg (4 × 7 repetitions), while the contralateral leg performed regular WS training (4 × 8–12 repetitions). Maximal strength (1-repetition maximum (1RM) in WS) and peak FW power were determined before and after training for both legs. Partial muscle volume of vastus lateralis (VL), vastus medialis (VM), vastus intermedius (VI), and rectus femoris (RF) were measured using magnetic resonance imaging. Additionally, quadriceps cross-sectional area was assessed at a proximal and a distal site. There were no differences (P > 0.05) between FW versus WS in muscle hypertrophy of the quadriceps femoris (8% vs. 9%), VL (10% vs. 11%), VM (6% vs. 8%), VI (5% vs. 5%), or RF (17% vs. 17%). Muscle hypertrophy tended (P = 0.09) to be greater at the distal compared with the proximal site, but there was no interaction with exercise method. Increases in 1RM and FW peak power were similar across legs, yet the increase in 1RM was greater in men (31%) than in women (20%). These findings suggest that FW and WS training induces comparable muscle-specific hypertrophy of the knee extensors. Given that these robust muscular adaptations were brought about with markedly fewer repetitions in the FW compared with WS, it seems FW training can be recommended as a particularly time-efficient exercise paradigm.

Can Hip Joint Position affect Quadriceps Muscle Responses during Knee Extension Exercise?

2020 ◽  
Vol 41 (13) ◽  
pp. 929-935
Author(s):  
Denis César Leite Vieira ◽  
Marco Aurélio Araujo Dourado ◽  
Lucas Ugliara ◽  
Joao Luiz Quagliotti Durigan ◽  
Brad J. Schoenfeld ◽  
...  
Keyword(s):  
Vastus Lateralis ◽  
Muscle Thickness ◽  
Rectus Femoris ◽  
Peak Torque ◽  
Quadriceps Muscle ◽  
Knee Extension ◽  
Knee Extensors ◽  
Work Output ◽  
Before And After ◽  
Knee Extension Exercise

AbstractThis study investigated the acute effects of seated and supine knee extension exercise on muscle swelling, torque, and work output. Twelve resistance-trained men performed two isokinetic concentric-only knee-extension training protocols at different hip positions in a counter-balanced order. They completed the knee extension exercise in the seated (hip angle at 85°) and supine (hip angle at 180°) positions. The torque and work output were assessed during each set. Moreover, muscle thickness of the middle and proximal vastus lateralis and rectus femoris were evaluated before and after each protocol and used as an indicator of muscle swelling. Middle rectus femoris and proximal vastus lateralis thickness increased significantly (p=0.01) with no difference between exercise variations. However, the middle vastus lateralis thickness increased (p=0.01) only after the seated knee extension exercise (~7%). Knee extensors’ peak torque and work output were approximately 8% higher (p=0.04) in the seated when compared to the supine hip position. There was a similar decrease in torque and work output throughout both protocols (p=0.98). In conclusion, seated knee extension exercises produced greater torque, work output, and muscle swelling in the vastus lateralis when compared to the supine knee extension exercise.

Activity of spindle afferents from cat anterior thigh muscles. II. Effects of fusimotor blockade

1985 ◽  
Vol 54 (3) ◽  
pp. 565-577 ◽  
Author(s):  
G. E. Loeb ◽  
J. A. Hoffer
Keyword(s):  
Stance Phase ◽  
Femoral Nerve ◽  
Knee Extensor ◽  
Muscle Spindles ◽  
Swing Phase ◽  
Knee Extensors ◽  
Electromyographic Activity ◽  
Force Output ◽  
Anterior Thigh ◽  
Proprioceptive Signal

Chronically implanted electrodes and nerve cuff catheters were used to record the activity of individual muscle spindle afferents during treadmill walking as low doses of lidocaine were infused around the femoral nerve to progressively block gamma motoneuron activity. Both primary and secondary endings from both the monarticular knee extensors and the biarticular hip/knee muscles of the anterior thigh showed large decreases in afferent activity, usually well before changes in the electromyographic activity, force output, or length and velocity were seen in the parent muscles. This decline in the proprioceptive signal feeding back onto the spinal cord, which we presume to have involved most of the spindles supplied by the femoral nerve, did not cause noticeable irregularities or instability of the walking gait. At the peak of the fusimotor blockade, spindle afferents from knee extensor muscles lost about half of their usually brisk activity during the near-isometric contraction of the stance phase. Significant decreases in the response to passive stretch during the flexion phase also occurred. At the peak of the fusimotor blockade, spindle afferents from the biarticular muscles lost all of their activity during the rapidly shortening swing phase and about half of their activity during the rapidly lengthening stance phase. For both monarticular and biarticular muscle spindles, the activity decreases in stance and swing phase often occurred at distinctly different stages of the progressive fusimotor blockade, indicating several different sources of fusimotor control. From these data, we infer that the sensitivity of most spindle afferents is substantially influenced by fusimotor activity during phases of both extrafusal activity and extrafusal silence. At least some of this influence appears to come from fusimotor neurons whose recruitment is independent of the extrafusal recruitment. The extent and type of fusimotor effects on spindle afferent sensitivity (dynamic or static) appear to be specialized for the mechanical events that tend to occur during those phases.

scholarly journals Spinal excitability is increased in the torque-depressed isometric steady state following active muscle shortening

2017 ◽  
Vol 4 (11) ◽  
pp. 171101 ◽  
Author(s):  
Caleb T. Sypkes ◽  
Benjamin Kozlowski ◽  
Jordan Grant ◽  
Leah R. Bent ◽  
Chris J. McNeil ◽  
...  
Keyword(s):  
Steady State ◽  
Evoked Potentials ◽  
Motor Evoked Potentials ◽  
Muscle Length ◽  
Electromyographic Activity ◽  
Active Muscle ◽  
Isometric Condition ◽  
Compound Muscle Action Potentials ◽  
Muscle Shortening ◽  
Spinal Excitability

Torque depression (TD) is the reduction in steady-state isometric torque following active muscle shortening when compared with a purely isometric contraction at the same muscle length and level of activation. The purpose of the present study was to assess spinal and supraspinal excitability in the TD state during submaximal contractions of the dorsiflexors. Eleven young (24 ± 2 yrs) males performed 16 contractions at a constant level of electromyographic activity (40% of maximum). Half of the contractions were purely isometric (8 s at an ankle angle of 100°), whereas the other half induced TD (2 s isometric at 140°, a 1 s shortening phase at 40° s −1 and 5 s at 100°). Motor evoked potentials (MEPs), cervicomedullary motor evoked potentials (CMEPs) and compound muscle action potentials (M-waves) were recorded from tibialis anterior during the TD steady-state and purely isometric contractions. When compared with values in the purely isometric condition, following active shortening, there was a 13% decrease in torque ( p  < 0.05), with a 10% increase in normalized CMEP amplitude (CMEP/Mmax) ( p  < 0.05) and no change in normalized MEP amplitude (MEP/CMEP) in the TD state ( p  > 0.05). These findings indicate that during voluntary contractions in the TD state, the history-dependent properties of muscle can increase spinal excitability and influence voluntary control of submaximal torque production.

Muscle coordination in cycling: effect of surface incline and posture

1998 ◽  
Vol 85 (3) ◽  
pp. 927-934 ◽  
Author(s):  
Li Li ◽  
Graham E. Caldwell
Keyword(s):  
Lower Extremity ◽  
High Speed ◽  
Vastus Lateralis ◽  
Activity Patterns ◽  
Gluteus Maximus ◽  
Rectus Femoris ◽  
Biceps Femoris ◽  
Knee Extensors ◽  
Emg Activity ◽  
Muscle Coordination

The purpose of the present study was to examine the neuromuscular modifications of cyclists to changes in grade and posture. Eight subjects were tested on a computerized ergometer under three conditions with the same work rate (250 W): pedaling on the level while seated, 8% uphill while seated, and 8% uphill while standing (ST). High-speed video was taken in conjunction with surface electromyography (EMG) of six lower extremity muscles. Results showed that rectus femoris, gluteus maximus (GM), and tibialis anterior had greater EMG magnitude in the ST condition. GM, rectus femoris, and the vastus lateralis demonstrated activity over a greater portion of the crank cycle in the ST condition. The muscle activities of gastrocnemius and biceps femoris did not exhibit profound differences among conditions. Overall, the change of cycling grade alone from 0 to 8% did not induce a significant change in neuromuscular coordination. However, the postural change from seated to ST pedaling at 8% uphill grade was accompanied by increased and/or prolonged muscle activity of hip and knee extensors. The observed EMG activity patterns were discussed with respect to lower extremity joint moments. Monoarticular extensor muscles (GM, vastus lateralis) demonstrated greater modifications in activity patterns with the change in posture compared with their biarticular counterparts. Furthermore, muscle coordination among antagonist pairs of mono- and biarticular muscles was altered in the ST condition; this finding provides support for the notion that muscles within these antagonist pairs have different functions.

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