Task-Specific Depression of the Soleus H-Reflex After Cocontraction Training of Antagonistic Ankle Muscles

2007 ◽  
Vol 98 (6) ◽  
pp. 3677-3687 ◽  
Author(s):  
Monica A. Perez ◽  
Jesper Lundbye-Jensen ◽  
Jens B. Nielsen
Keyword(s):  
Presynaptic Inhibition ◽  
Tibialis Anterior ◽  
Motor Performance ◽  
Motor Evoked Potentials ◽  
Intracortical Inhibition ◽  
H Reflex ◽  
Emg Activity ◽  
Frequent Use ◽  
Ankle Muscles ◽  
Simultaneous Activation

Ballet dancers have small soleus (SOL) H-reflex amplitudes, which may be related to frequent use of cocontraction of antagonistic ankle muscles. Indeed, SOL H-reflexes are depressed during cocontraction compared with plantarflexion at matched background EMG level. We investigated the effect of 30-min training of simultaneous activation of ankle dorsi- and plantarflexor muscles (cocontraction task) on the SOL H-reflex in 10 healthy volunteers. Measurements were taken during cocontraction. After training, there was a significant improvement in the ability of the subjects to perform a stable cocontraction. SOL H-reflex recruitment curves and H-max/M-max ratios were decreased after cocontraction training but not after 30 min of static dorsi or plantarflexion. The decreased H-reflex size correlated with improved motor performance. No changes in SOL and tibialis anterior (TA) EMG activity or EMG power were observed, suggesting that increased presynaptic inhibition of Ia afferents is a likely mechanism for H-reflex depression. In different sessions we measured SOL and TA motor-evoked potentials (MEPs) by using transcranial magnetic stimulation (TMS), TMS-elicited suppression of SOL EMG, and coherence between electroencephalographic (EEG) activity (Cz) and TA and SOL EMG. SOL and TA MEPs were depressed, whereas TMS-elicited suppression of SOL EMG and coherence were increased after training. Decreased excitability of corticospinal neurons due to increased intracortical inhibition seems a likely explanation of these observations. Our results indicate that the depression in H-reflex observed during a cocontraction task can be trained and that repeated performance of tasks involving cocontraction may lead to prolonged changes in reflex and corticospinal excitability.

scholarly journals Physiological changes underlying bilateral isometric arm voluntary contractions in healthy humans

2011 ◽  
Vol 105 (4) ◽  
pp. 1594-1602 ◽  
Author(s):  
Demetris S. Soteropoulos ◽  
Monica A. Perez
Keyword(s):  
Tibialis Anterior ◽  
Motor Evoked Potentials ◽  
Short Interval ◽  
Intracortical Inhibition ◽  
Voluntary Contraction ◽  
Triceps Brachii ◽  
Hand Muscles ◽  
Healthy Humans ◽  
Simultaneous Activation ◽  
The Right

Many bilateral motor tasks engage simultaneous activation of distal and proximal arm muscles, but little is known about their physiological interactions. Here, we used transcranial magnetic stimulation to examine motor-evoked potentials (MEPs), interhemispheric inhibition at a conditioning-test interval of 10 (IHI10) and 40 ms (IHI40), and short-interval intracortical inhibition (SICI) in the left first dorsal interosseous (FDI) muscle during isometric index finger abduction. The right side remained at rest or performed isometric voluntary contraction with the FDI, biceps or triceps brachii, or the tibialis anterior. Left FDI MEPs were suppressed to a similar extent during contraction of the right FDI and biceps and triceps brachii but remained unchanged during contraction of the right tibialis anterior. IHI10 and IHI40 were decreased during contraction of the right biceps and triceps brachii compared with contraction of the right FDI. SICI was increased during activation of the right biceps and triceps brachii and decreased during activation of the right FDI. The present results indicate that an isometric voluntary contraction with either a distal or a proximal arm muscle, but not a foot dorsiflexor, decreases corticospinal output in a contralateral active finger muscle. Transcallosal inhibitory effects were strong during bilateral activation of distal hand muscles and weak during simultaneous activation of a distal and a proximal arm muscle, whereas GABAergic intracortical activity was modulated in the opposite manner. These findings suggest that in intact humans crossed interactions at the level of the motor cortex involved different physiological mechanisms when bilateral distal hand muscles are active and when a distal and a proximal arm muscle are simultaneously active.

Task-dependent changes of motor cortical network excitability during precision grip compared to isolated finger contraction

2012 ◽  
Vol 107 (5) ◽  
pp. 1522-1529 ◽  
Author(s):  
Nezha Kouchtir-Devanne ◽  
Charles Capaday ◽  
François Cassim ◽  
Philippe Derambure ◽  
Hervé Devanne
Keyword(s):  
Stimulus Intensity ◽  
Motor Evoked Potentials ◽  
Precision Grip ◽  
Silent Period ◽  
Intracortical Inhibition ◽  
Emg Activity ◽  
Maximum Slope ◽  
Corticospinal Pathway ◽  
Long Latency ◽  
Motor Cortical

The purpose of this study was to determine whether task-dependent differences in corticospinal pathway excitability occur in going from isolated contractions of the index finger to its coordinated activity with the thumb. Focal transcranial magnetic stimulation (TMS) was used to measure input-output (I/O) curves—a measure of corticospinal pathway excitability—of the contralateral first dorsal interosseus (FDI) muscle in 21 healthy subjects performing two isometric motor tasks: index abduction and precision grip. The level of FDI electromyographic (EMG) activity was kept constant across tasks. The amplitude of the FDI motor evoked potentials (MEPs) and the duration of FDI silent period (SP) were plotted against TMS stimulus intensity and fitted, respectively, to a Boltzmann sigmoidal function. The plateau level of the FDI MEP amplitude I/O curve increased by an average of 40% during the precision grip compared with index abduction. Likewise, the steepness of the curve, as measured by the value of the maximum slope, increased by nearly 70%. By contrast, all I/O curve parameters [plateau, stimulus intensity required to obtain 50% of maximum response ( S50), and slope] of SP duration were similar between the two tasks. Short- and long-latency intracortical inhibitions (SICI and LICI, respectively) were also measured in each task. Both measures of inhibition decreased during precision grip compared with the isolated contraction. The results demonstrate that the motor cortical circuits controlling index and thumb muscles become functionally coupled when the muscles are used synergistically and this may be due, at least in part, to a decrease of intracortical inhibition and an increase of recurrent excitation.

On the Potential Role of the Corticospinal Tract in the Control and Progressive Adaptation of the Soleus H-Reflex During Backward Walking

2005 ◽  
Vol 94 (2) ◽  
pp. 1133-1142 ◽  
Author(s):  
Roth-Visal Ung ◽  
Marie-Andrée Imbeault ◽  
Christian Ethier ◽  
Laurent Brizzi ◽  
Charles Capaday
Keyword(s):  
Motor Cortex ◽  
Large Amplitude ◽  
Corticospinal Tract ◽  
Motor Evoked Potentials ◽  
Conditioning Stimulus ◽  
H Reflex ◽  
Emg Activity ◽  
Step Cycle ◽  
Voluntary Activity ◽  
Backward Walking

When untrained subjects walk backward on a treadmill, an unexpectedly large amplitude soleus H-reflex occurs in the midswing phase of backward walking. We hypothesized that activity in the corticospinal tract (CST) during midswing depolarizes the soleus α-motoneurons subliminally and thus brings them closer to threshold. To test this hypothesis, transcranial magnetic stimulation (TMS) was applied to the leg area of the motor cortex (MCx) during backward walking. Motor-evoked potentials (MEPs) were recorded from the soleus and tibialis anterior (TA) muscles in untrained subjects at different phases of the backward walking cycle. We reasoned that if soleus MEPs could be elicited in midswing, while the soleus is inactive, this would be strong evidence for increased postsynaptic excitability of the α-motoneurons. In the event, we found that in untrained subjects, despite the presence of an unexpectedly large H-reflex in midswing, no soleus MEPs were observed at that time. The soleus MEPs were in phase with the soleus electromyographic (EMG) activity during backward walking. Soleus MEPs increased more rapidly as a function of the EMG activity during voluntary activity than during backward walking. Furthermore, a conditioning stimulus to the motor cortex facilitated the soleus H-reflex at rest and during voluntary plantarflexion but not in the midswing phase of backward walking. With daily training at walking backward, the time at which the H-reflex began to increase was progressively delayed until it coincided with the onset of soleus EMG activity, and its amplitude was considerably reduced compared with its value on the first experimental day. By contrast, no changes were observed in the timing or amplitude of soleus MEPs with training. Taken together, these observations make it unlikely that the motor cortex via the CST is involved in control of the H-reflex during the backward step cycle of untrained subjects nor in its progressive adaptation with training. Our observations raise the possibility that the large amplitude of H-reflex in untrained subjects and its adaptation with training are mainly due to control of presynaptic inhibition of Ia-afferents by other descending tracts.

scholarly journals Repetitive Peripheral Magnetic Stimulation of Wrist Extensors Enhances Cortical Excitability and Motor Performance in Healthy Individuals

2021 ◽  
Vol 15 ◽  
Author(s):  
Mitsuhiro Nito ◽  
Natsuki Katagiri ◽  
Kaito Yoshida ◽  
Tadaki Koseki ◽  
Daisuke Kudo ◽  
...  
Keyword(s):  
Neural Plasticity ◽  
Motor Performance ◽  
Magnetic Stimulation ◽  
Cortical Excitability ◽  
Motor Evoked Potentials ◽  
Short Interval ◽  
Stimulus Frequency ◽  
Intracortical Inhibition ◽  
Hoffmann Reflex ◽  
M Wave

Repetitive peripheral magnetic stimulation (rPMS) may improve motor function following central nervous system lesions, but the optimal parameters of rPMS to induce neural plasticity and mechanisms underlying its action remain unclear. We examined the effects of rPMS over wrist extensor muscles on neural plasticity and motor performance in 26 healthy volunteers. In separate experiments, the effects of rPMS on motor evoked potentials (MEPs), short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), direct motor response (M-wave), Hoffmann-reflex, and ballistic wrist extension movements were assessed before and after rPMS. First, to examine the effects of stimulus frequency, rPMS was applied at 50, 25, and 10 Hz by setting a fixed total number of stimuli. A significant increase in MEPs of wrist extensors was observed following 50 and 25 Hz rPMS, but not 10 Hz rPMS. Next, we examined the time required to induce plasticity by increasing the number of stimuli, and found that at least 15 min of 50 and 25 Hz rPMS was required. Based on these parameters, lasting effects were evaluated following 15 min of 50 or 25 Hz rPMS. A significant increase in MEP was observed up to 60 min following 50 and 25 Hz rPMS; similarly, an attenuation of SICI and enhancement of ICF were also observed. The maximal M-wave and Hoffmann-reflex did not change, suggesting that the increase in MEP was due to plastic changes at the motor cortex. This was accompanied by increasing force and electromyograms during wrist ballistic extension movements following 50 and 25 Hz rPMS. These findings suggest that 15 min of rPMS with 25 Hz or more induces an increase in cortical excitability of the relevant area rather than altering the excitability of spinal circuits, and has the potential to improve motor output.

Mechanisms modulating spinal excitability after nerve stimulation inducing extra torque

2021 ◽  
Author(s):  
Florian Vitry ◽  
Maria Papaiordanidou ◽  
Alain Martin
Keyword(s):  
Nerve Stimulation ◽  
Presynaptic Inhibition ◽  
Motor Evoked Potentials ◽  
Femoral Nerve ◽  
Common Peroneal Nerve ◽  
H Reflex ◽  
Ia Afferents ◽  
Thoracic Level ◽  
The Common ◽  
Spinal Excitability

The study included 3 experiments aiming to examine the mechanisms responsible for spinal excitability modulation, as assessed by the H-reflex, following stimulation trains delivered at two different frequencies (20 and 100Hz) inducing extra torque (ET). A first experiment (n=15) was conducted to evaluate changes in presynaptic inhibition acting on Ia afferents induced by these electrical stimulation trains, assessed by conditioning the soleus H-reflex (tibial nerve stimulation) with stimulation of the common peroneal nerve (D1 inhibition) and of the femoral nerve (heteronymous Ia facilitation, HF). A second experiment (n=12) permitted to investigate homosynaptic post-activation depression (HPAD) changes after the stimulation trains. A third experiment (n=14) analysed changes in motoneuron intrinsic properties after the stimulation trains, by electrically stimulating the descending corticospinal tract at the thoracic level, evoking thoracic motor evoked potentials (TMEP). Main results showed that in all experiments spinal excitability decreased after the 20-Hz train (P<0.05), while this parameter significantly increased after the 100-Hz stimulation (P<0.05). D1 and HF were not significantly modified after either stimulation. HPAD was significantly decreased only after the 20-Hz train, while TMEP was significantly increased only after the 100-Hz train (P<0.05). It is concluded that the decreased spinal excitability observed after the 20-Hz train cannot be attributed to D1 presynaptic inhibition but rather to increased HPAD of the Ia afferents terminals, while the increase of this parameter obtained after the 100-Hz train can be assigned to changes in intrinsic motoneuron properties allowing to maintain Ia - alpha motoneurons transmission efficacy.

scholarly journals Paired Associative Stimulation Induces Change in Presynaptic Inhibition of Ia Terminals in Wrist Flexors in Humans

2010 ◽  
Vol 104 (2) ◽  
pp. 755-764 ◽  
Author(s):  
Jean-Charles Lamy ◽  
Heike Russmann ◽  
Ejaz A. Shamim ◽  
Sabine Meunier ◽  
Mark Hallett
Keyword(s):  
Presynaptic Inhibition ◽  
Motor Evoked Potentials ◽  
Long Term Potentiation ◽  
H Reflex ◽  
Paired Associative Stimulation ◽  
Before And After ◽  
Ia Inhibition ◽  
Cortical Synapses ◽  
Postactivation Depression ◽  
Spinal Excitability

Enhancements in the strength of corticospinal projections to muscles are induced in conscious humans by paired associative stimulation (PAS) to the motor cortex. Although most of the previous studies support the hypothesis that the increase of the amplitude of motor evoked potentials (MEPs) by PAS involves long-term potentiation (LTP)-like mechanism in cortical synapses, changes in spinal excitability after PAS have been reported, suggestive of parallel modifications in both cortical and spinal excitability. In a first series of experiments ( experiment 1), we confirmed that both flexor carpi radialis (FCR) MEPs and FCR H reflex recruitment curves are enhanced by PAS. To elucidate the mechanism responsible for this change in the H reflex amplitude, we tested, using the same subjects, the hypothesis that enhanced H reflexes are caused by a down-regulation of the efficacy of mechanisms controlling Ia afferent discharge, including presynaptic Ia inhibition and postactivation depression. To address this question, amounts of both presynaptic Ia inhibition of FCR Ia terminals (D1and D2 inhibitions methods; experiment 2) and postactivation depression ( experiment 3) were determined before and after PAS. Results showed that PAS induces a significant decrease of presynaptic Ia inhibition of FCR terminals, which was concomitant with the facilitation of the H reflex. Postactivation depression was unaffected by PAS. It is argued that enhancement of segmental excitation by PAS relies on a selective effect of PAS on the interneurons controlling presynaptic inhibition of Ia terminals.

Differential effects of a flexor nerve input on the human soleus H-reflex during standing versus walking

1995 ◽  
Vol 73 (4) ◽  
pp. 436-449 ◽  
Author(s):  
C. Capaday ◽  
B. A. Lavoie ◽  
F. Comeau
Keyword(s):  
Spinal Cord ◽  
Presynaptic Inhibition ◽  
Stance Phase ◽  
Conditioning Stimulus ◽  
Background Level ◽  
H Reflex ◽  
Emg Activity ◽  
Group I ◽  
The Difference

A conditioning (C) stimulus at group I strength was delivered during standing to the common peroneal (CP) nerve before a test (T) stimulus at several C–T intervals ranging from 0 to 150 ms. At sufficiently long C–T intervals (100–120 ms) the soleus H-reflex was strongly inhibited despite little, or no change, in the background level of EMG activity. This finding indicates that a significant portion of the inhibition occurs at a premotoneuronal level, likely via presynaptic inhibition of the Ia-afferent terminals. During standing, at C–T intervals of 100–120 ms (optimal C–T interval) a conditioning stimulus to the CP nerve of 1.5 times motor threshold (MT) intensity reduced the soleus H-reflex by an average of 45.8% (n = 14 subjects). The conditioning stimulus always produced a clear inhibition of the H-reflex during standing at these C–T intervals. The effects of this conditioning stimulus on the soleus H-reflex were then determined in the early part of the stance phase of walking. In contrast to standing, the conditioning stimulus produced little or no inhibition during the early part of the stance phase of walking (average inhibition 45.8 vs. 11.6%, n = 14 subjects). The soleus background EMG, and the soleus and tibialis anterior M-waves were essentially the same during standing and walking. Furthermore, there was no shift of the optimal C–T interval during walking. The difference in the effects of the conditioning stimulus was not due to differences in the size of the test H-reflex in each task. It appears to be due to a genuine task-dependent change in the input–output properties of the underlying spinal cord circuits. There are at least two, mutually compatible, explanations of these results. Firstly, during walking the intraspinal terminals of the afferent fibres (group Ia and Ib) conducting the conditioning volley may be presynaptically inhibited, or their input gated at the interneuronal level. Secondly, on the assumption that the conditioning stimulus is acting via the presynaptic inhibitory network in the spinal cord, it is possible that during walking this network is saturated as a result of increased central or peripheral synaptic inputs. Finally, it seems unlikely that differences in the refractoriness of the CP nerve between the tasks may be involved; the reasons for this are presented in the discussion.Key words: Ia afferents, motoneurons, presynaptic inhibition, EMG, posture, locomotion, spinal cord.

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.).

Changes in Reciprocal Inhibition Across the Ankle Joint With Changes in External Load and Pedaling Rate During Bicycling

2003 ◽  
Vol 90 (5) ◽  
pp. 3168-3177 ◽  
Author(s):  
H. S. Pyndt ◽  
M. Laursen ◽  
J. B. Nielsen
Keyword(s):  
Linear Relation ◽  
External Load ◽  
Plantar Flexion ◽  
Tibialis Anterior Muscle ◽  
Reciprocal Inhibition ◽  
Tonic Contraction ◽  
H Reflex ◽  
Emg Activity ◽  
Ankle Muscles ◽  
Pedaling Rate

The purpose of this study was to investigate the role of reciprocal inhibition in the regulation of antagonistic ankle muscles during bicycling. A total of 20 subjects participated in the study. Reciprocal inhibition was induced by stimulation of the peroneal nerve (PN) at 1.2 times threshold for the M-response in the tibialis anterior muscle (TA) and recorded as a depression of the rectified soleus (SOL) EMG. Recordings were made during tonic plantar flexion and during bicycling on an ergometer bicycle. During tonic contraction, the amount of inhibition in the SOL EMG was linearly correlated to the amount of background EMG. This linear relation was used to calculate the expected amount of reciprocal inhibition at corresponding EMG levels during bicycling. During the early phase of down-stroke of bicycling at 60 revolutions per minute (RPM) and an external load of 1.0 kg, the amount of recorded reciprocal inhibition was significantly smaller than that calculated from the linear relation during tonic contraction. In nine subjects, the SOL H-reflex was used to evaluate the amount of inhibition. At a short conditioning test interval (2–3 ms), the PN stimulation depressed the SOL H-reflex when the subjects were at rest. This short latency inhibition was absent during downstroke, but appeared during upstroke just prior to and during TA activation. A positive linear relation was found between the level of SOL background EMG in early downstroke and the external load (0.5–2.5 kg) as well as the rate of pedaling (30–90 RPM at 1.0 kg external load). The amount of inhibition in the SOL EMG when expressed as a percentage of the background EMG activity decreased significantly with increasing load. During increased pedaling rate, a similar decrease was seen, but it did not reach a statistically significant level. The data illustrate that reciprocal inhibition of the soleus muscle is modulated during bicycling being small in downstroke when the SOL muscle is active and large in upstroke where the muscle is inactive and its antagonist becomes active. The depression of the inhibition in relation to increased load and pedaling rate likely reflects the need of reducing inhibition of the SOL motoneurons to ensure a sufficient activation of the muscle.

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).

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