The effect of vibration on EMGrms activity of skeletal muscle
Carmelo Bosco Ph. D., D. U., D. Hon .C.

 

The assessment of the neuromuscular behaviour has received in the last decades a strong improvement through the evolution of diagnostic technique. This was allowed by the creation
of new dedicated instruments and apparatus that have been used mainly in the field of
rehabilitation and sport medicine.

However, the assessment of the neuromuscular functions is steel far to be enough complete for covering the large spectrum of biological changes which occurs with injures and after surgery. In fact, there is an high percentage of patients showing a weakness of the leg extensor muscles after a long follow-up period - most likely due to the severing of propioceptors during surgery (27). Even if such problems are well known there is an inadequate and lack of specific evaluation technique that could allow the quantification and assessment of the impairment due to the proprioceptors inability to function properly. In this respect, it was conduced a pilot investigation to analyse the possibility for detecting and quantifying the operated knee joint propioceptors functional capacity. For this purpose a new diagnostic technique, consisting on monitoring the muscles EMGrms activity during vibration, was applied for identify altered neural strategies of motoneuron pool recruitment.

Previous findings of EMGrms recorded in biceps brachii of boxers (20), showed a significant enhancement (P<0.001) of the neural activity during the vibration treatment period, as compared
to normal conditions. Similar results have been noted monitoring the EMG activity of the leg extensor muscles (mm. vastus lateralis: LL (left) and LR (right) and vastus medialis: ML and
MR), of an healthy athlete during a vibration treatment period (Fig. 10).

Facilitation of the excitability of spinal reflex has been elicited through vibration to quadriceps muscle (21). It was suggested previously the possibility that vibration may elicit excitatory inflow through muscle spindle-alpha motoneurons connections in the overall motoneuron inflow (47). It has been demonstrated that vibration drives alpha-motoneurons via Ia loop producing force without descending motor drive (61).

In addition, it has been shown that vibration-induced activation of muscle spindle receptors, not only in the muscle to which vibration was applied, but also to the neighbouring muscles (43). Mechanical vibration (10-200 Hz) applied to muscle belly or tendon can elicit reflex contraction (31). This response has been named ''tonic vibration reflex'' (TVR). It has been also argued that in the presence of TVR, the vibration-induced suppression of motor output in maximal voluntary contractions probably does not depend to the voluntary command (6). It was suggested that contributing mechanism might be vibration induced pre-synaptic inhibition and/or transmitter depletion in the group Ia exitatory pathways which constitute the afferent link of the gamma-loop (6). In light of the above findings, a pilot study was planned to introduce a new assessment strategy to identify muscle behaviour and possibly dysfunction.

Fig. 10 . Electromyografic activity (EMGrms ) recorded from leg extensor muscles ( mm. vastus
lateralis : LR and LL and medialis : MR and ML of both left and right legs ) , before and during
whole vibration treatment . During the vibration treatment a remarkable enhancement of the
EMGrms was recored

 

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