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Assessment of Homonymous Recurrent Inhibition during Voluntary Contraction by Conditioning Nerve Stimulation

View Article: PubMed Central - PubMed

ABSTRACT

In humans, the amount of spinal homonymous recurrent inhibition during voluntary contraction is usually assessed by using a peripheral nerve stimulation paradigm. This method consists of conditioning the maximal M-wave (SM stimulus) with prior reflex stimulation (S1), with 10 ms inter-stimulus interval (ISI). The decrease observed between unconditioned (S1 only) and conditioned (S1+SM) reflex size is then attributed to recurrent inhibition. However, during a voluntary contraction, a superimposed SM stimulation leads to a maximal M-wave followed by a voluntary (V) wave at similar latency than the H-reflex. This wave can therefore interfere with the conditioned H-reflex when two different stimulation intensities are used (S1 and SM), leading to misinterpretation of the data. The aim of the present study was to assess if conditioning V-wave response instead of H-reflex, by applying SM for both stimuli (test and conditioning), can be used as an index of recurrent inhibition. Conditioned and unconditioned responses of soleus and medial gastrocnemius muscles were recorded in twelve subjects at 25% and at 50% of maximal voluntary contraction at the usual ISI of 10 ms and an optimal inter-stimulus of 15 ms determined upon M- and V-wave latencies. Conditioned H-reflex (obtained with S1+SM paradigm) was significantly lower than the unconditioned by ~30% on average, meaning that the amount of inhibition was 70%. This amount of recurrent inhibition was significantly lower at higher force level with both methods. Regardless of the level of force or the conditioning ISI, results obtained with V-wave conditioning (SM+SM) were similar at both force levels, linearly correlated and proportional to those obtained with H conditioning. Then, V-wave conditioning appears to be a reliable index of homonymous recurrent inhibition during voluntary contraction.

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Representative results.Typical traces of SOL muscle in two representative subjects. Six traces for each condition are superimposed. The presence of two conditioned responses in subject 1 (e.g. at 15 ms ISI and 25% MVC) can be noticed, indicated by dashed squares.
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pone.0167062.g005: Representative results.Typical traces of SOL muscle in two representative subjects. Six traces for each condition are superimposed. The presence of two conditioned responses in subject 1 (e.g. at 15 ms ISI and 25% MVC) can be noticed, indicated by dashed squares.

Mentions: Finally, it can be noticed that for some subjects (4 out of 12), a prior response to H’ or V’ appeared (Fig 5 subject 1). Interestingly, these subjects were the 4 smallest subjects of the group (height ≤ 1.75 m). The latency of this response (SOL: 34.96 ± 1.72 ms; MG: 33.52 ± 1.04 ms), measured from the onset of S1 stimulus artefact on EMG signal, was not different from the latency of H1 and V1. These responses were consistently observed before H’ and before V’ in the same four subjects and not in the other subjects.


Assessment of Homonymous Recurrent Inhibition during Voluntary Contraction by Conditioning Nerve Stimulation
Representative results.Typical traces of SOL muscle in two representative subjects. Six traces for each condition are superimposed. The presence of two conditioned responses in subject 1 (e.g. at 15 ms ISI and 25% MVC) can be noticed, indicated by dashed squares.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120836&req=5

pone.0167062.g005: Representative results.Typical traces of SOL muscle in two representative subjects. Six traces for each condition are superimposed. The presence of two conditioned responses in subject 1 (e.g. at 15 ms ISI and 25% MVC) can be noticed, indicated by dashed squares.
Mentions: Finally, it can be noticed that for some subjects (4 out of 12), a prior response to H’ or V’ appeared (Fig 5 subject 1). Interestingly, these subjects were the 4 smallest subjects of the group (height ≤ 1.75 m). The latency of this response (SOL: 34.96 ± 1.72 ms; MG: 33.52 ± 1.04 ms), measured from the onset of S1 stimulus artefact on EMG signal, was not different from the latency of H1 and V1. These responses were consistently observed before H’ and before V’ in the same four subjects and not in the other subjects.

View Article: PubMed Central - PubMed

ABSTRACT

In humans, the amount of spinal homonymous recurrent inhibition during voluntary contraction is usually assessed by using a peripheral nerve stimulation paradigm. This method consists of conditioning the maximal M-wave (SM stimulus) with prior reflex stimulation (S1), with 10 ms inter-stimulus interval (ISI). The decrease observed between unconditioned (S1 only) and conditioned (S1+SM) reflex size is then attributed to recurrent inhibition. However, during a voluntary contraction, a superimposed SM stimulation leads to a maximal M-wave followed by a voluntary (V) wave at similar latency than the H-reflex. This wave can therefore interfere with the conditioned H-reflex when two different stimulation intensities are used (S1 and SM), leading to misinterpretation of the data. The aim of the present study was to assess if conditioning V-wave response instead of H-reflex, by applying SM for both stimuli (test and conditioning), can be used as an index of recurrent inhibition. Conditioned and unconditioned responses of soleus and medial gastrocnemius muscles were recorded in twelve subjects at 25% and at 50% of maximal voluntary contraction at the usual ISI of 10 ms and an optimal inter-stimulus of 15 ms determined upon M- and V-wave latencies. Conditioned H-reflex (obtained with S1+SM paradigm) was significantly lower than the unconditioned by ~30% on average, meaning that the amount of inhibition was 70%. This amount of recurrent inhibition was significantly lower at higher force level with both methods. Regardless of the level of force or the conditioning ISI, results obtained with V-wave conditioning (SM+SM) were similar at both force levels, linearly correlated and proportional to those obtained with H conditioning. Then, V-wave conditioning appears to be a reliable index of homonymous recurrent inhibition during voluntary contraction.

No MeSH data available.


Related in: MedlinePlus