Microvibrations: an interrelation between heart beat, muscle tremor and resting muscle tone

The phenomenon of microvibrations was described by Rohracher in Vienna in the 1950s. Microvibrations consist of oscillationns in the frequency range of 7 to 13 Hz which can be observed on the surface of the body during a complete muscle relaxation. We had the opportunity to study the changes of microvibrations and physiological tremor under the condition of weightlessness in the Russian Space Station MIR during the so called "Austromir" project and the following Russian long term flights including the record flight of cosmonaut Polyakow. The recordings have been made by accelerometers from the body surface. It was found that during wieghtlessness the typical 7 to 13 Hz oscillations disappeared as well from microvibrations as from physiological tremor. By the application of a simple model it can be shown that microvibrations are due to mechanical resonance. The oscillations are apparently elicited by the heart beat. Therefore it appears that microvibrations are cardioballistic phenomena. It can be shown that cardioballistic forces are transmitted by osseous structures to soft tissues like e.g. relaxed muscles. Local resonance finally leads to the oscillations as mentioned above. From the model calculations we conclude that the relaxation is much more pronounced during weightlessness. Thus, resonance is abolished in the frequency region mentioned above. On the ground even during muscle relaxation there is still some muscle tone with an elastic component which under this condition permits the generation of resonance phenomena. Our results permit a new interpretation of microvibrations. Furthermore, the results may have importance for the interpretation of the generation of certain pathological forms of tremor.