Modulation of soleus corticospinal excitability during Achilles tendon vibration

Abstract

Soleus (SOL) corticospinal excitability has been reported to increase during Achilles tendon vibration. The aim of the present study was to further investigate SOL corticospinal excitability and elucidate the changes to intracortical mechanisms during Achilles tendon vibration. Motor-evoked potentials (MEPs) were elicited in the SOL by transcranial magnetic stimulation (TMS) of the corresponding motor cortical area of the leg with and without 50-Hz Achilles tendon vibration. SOL input-output curves were determined. Paired-pulse protocols were also performed to investigate short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) by conditioning test TMS pulses with sub-threshold TMS pulses at inter-stimulus intervals of 3 and 13 ms, respectively. During Achilles tendon vibration, motor threshold was lower than in the control condition (43 ± 13 vs. 49 ± 11 % of maximal stimulator output; p = 0.008). Input-output curves were also influenced by vibration, i.e. there was increased maximal MEP amplitude (0.694 ± 0.347 vs. 0.268 ± 0.167 mV; p < 0.001), decreased TMS intensity to elicit a MEP of half the maximal MEP amplitude (100 ± 13 vs. 109 ± 9 % motor threshold; p = 0.009) and a strong tendency for decreased slope constant (0.076 ± 0.04 vs. 0.117 ± 0.04; p = 0.068). Vibration reduced ICF (98 ± 61 vs. 170 ± 105 % of test MEP amplitude; p = 0.05), but had no effect on SICI (53 ± 26 vs. 48 ± 22 % of test MEP amplitude; p = 0.68). The present results further document the increased vibration-induced corticospinal excitability in the soleus muscle and suggest that this increase is not mediated by changes in SICI or ICF.

Intermediate Muscle Length and Tendon Vibration Optimize Corticospinal Excitability During Knee Extensors Local Vibration

“…One may only speculate about the mechanisms involved in the LV-induced increased MEPs amplitude since MEPs depends on the synaptic relays of the corticospinal projections at both the cortical and spinal levels ( Devanne et al, 1997 ). Although cortical mechanisms have been suggested to increase corticospinal excitability during LV ( Kossev et al, 1999 ), potentially through long-loop reflexes involving transcortical circuits ( Matthews, 1984 ), we previously reported increased soleus MEPs during LV without concomitant changes in intracortical inhibition and facilitation suggesting that increased corticospinal excitability would be rather spinal in origin ( Lapole et al, 2015a ). Hence, vibration-induced Ia afferent activity may have partially depolarized motoneuronal cells without causing them to discharge, as confirmed by the unaltered EMG background activity reported during vibration.…”

“…It is now well accepted that activation of Ia afferents from muscle spindles during LV increases corticospinal excitability as indicated by increased MEPs size during LV in various upper- ( Kossev et al, 1999 , 2001 ; Siggelkow et al, 1999 ; Rosenkranz et al, 2003 ; Steyvers et al, 2003a ) and lower-limb muscles ( Lapole et al, 2015a , b ). The present study further reports such findings for the KE and confirms the potential for LV to modulate corticospinal excitability of lower-limb muscles, despite weaker corticomotoneuronal projections compared with upper-limbs ( Brouwer and Ashby, 1990 ).…”

“…The sample size was calculated at the outset using G ∗ Power software (version 3.1.9.2; Kiel University, Kiel, Germany) for a statistical power of 0.80 and an alpha risk of 0.05. Considering the results of several studies on upper- ( Kossev et al, 1999 ; Siggelkow et al, 1999 ; Steyvers et al, 2003a ) and lower-limb muscles ( Lapole et al, 2015a , b ), the main criterion of our study was the increase in MEPs amplitude during LV. A minimum of 20 subjects was necessary to reach the desired power for a two-way repeated-measures ANOVA.…”

“…Modulations of corticospinal excitability during short-time LV (4–60 s) has been reported, e.g., an increase in motor evoked potentials (MEPs) size in extensor ( Kossev et al, 1999 ; Siggelkow et al, 1999 ; Kossev et al, 2001 ) and flexor carpi radialis ( Rosenkranz et al, 2003 ; Steyvers et al, 2003b ) as well as soleus ( Lapole et al, 2015a , b ) and gastrocnemius medialis muscles ( Lapole et al, 2015b ). Such an increase in MEPs during LV exposure is thought to be directly mediated by the vibration-induced discharge of Ia afferents ( Roll et al, 1989 ).…”

Differential Effect of Visual and Proprioceptive Stimulation on Corticospinal Output for Reciprocal Muscles

“…Our results showed that: (a) the ECR MEP amplitudes increased during the control condition rather than the resting condition, but the FCR MEP amplitudes did not; and (b) the ECR MEP amplitudes further increased during the static condition rather than the dynamic condition, but the FCR MEP amplitudes further increased during the dynamic condition rather than the static condition. Many previous reports have shown that vibratory proprioceptive stimulation increases the MEP amplitude evoked in the muscle stimulated by vibration (Rosenkranz and Rothwell, 2003; Rosenkranz et al, 2003; Lapole et al, 2015; Souron et al, 2018), and this increase is considered to be due to increased excitability of spinal mechanisms (Eklund and Hagbarth, 1966; Hagbarth et al, 1980; Claus et al, 1988). In the present study, the ECR MEP amplitudes increased during the control condition, consistent with the findings of previous studies, and probably this increment was mainly due to spinal Ia-α loop excitation by tendon vibration.…”