The effect of vibration on EMGrms activity of skeletal muscle

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 (1).

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 (2), showed a significant enhancement (P<0.001)>.

It has been demonstrated that vibration drives alpha - motoneurons via Ia loop producing force without descending motor drive (5). 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 (6). Mechanical vibration (10-200 Hz) applied to muscle belly or tendon can elicit reflex contraction (7). 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 Methods of functional testing during rehabilitation exercises 22 (8). 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 (8). In light of the above findings, a pilot study was planned to introduce a new assessment strategy to identify muscle behaviour and possibly dysfunction.

Refferences:
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2. Augustsson J, Esko A, Thomee R, et al. (1998) Weight training of the thigh muscles using closed ve open kinetic chain exercises : a comparison of performance enhancement. J Orthop Sports Phys Ther 27, 1: 3-8
3. Burke JR, Schutten MC, Koceja DM, et al. (1996). Age-dependent effects of muscle vibration and the Jendrassik maneuver on the patellar tendon reflex response. Arch Phys Med Rehabil 77 ,6:600-604
4. Lebedev MA, Peliakov AV (1991). Analysis of the interference electromyogram of human soleus muscle after exposure to vibration. Neirofiziologia 23, 1: 57-65 (article in Russian).
5. Rothmuller C, Cafarelli E (1995). Effects of vibration on antagonist muscle coactivation during progressive fatigue humans. J Physiol 485: 857-864
6. Kasai T, Kawanishi, Yahagi S (1992) The effects of wrist muscle vibration on human voluntary elbow flexionextension movements. Exp Brain Res 90: 217–220
7. Hagbarth KE, Eklund G(1965) Motor effects of vibratori stimuli. In: Granit R (Ed.) Muscular afferents and motor control. Proceedings of the First Symposium, Almqvist and Wiksell, Stockholm pp 177–86
8. Bongiovanni LG, Hagbarth KE, Stjenberg L (1990) Prolonged muscle vibration reducing motor output in maximal voluntary contractions in man. J Physiol (Lond) 423:15-23.