EMC und Kontraktion

Abstract

Development of force in a muscle occurs via activation of new motor units and by an increase of their firing rates. The electrical activity increases in parallel, because both depend on the number and cross sectional area of activated muscle fibers. Force is futhermore influenced by the metabolic profile of the motor units and by mechanical properties like the initial length of the muscle fibers. Similarly the potential size is determined by the spatial distribution of the fibers within the territory of a motor unit and their orientation to the recording electrode, by the degree of synchronisation, and by the characteristics of the recording technique. The slope of the relationship between force and emg varies physiologically with muscle, species, level of activation and the applied technique. The frequency spectrum, interference analysis and recruitment pattern at a given activation level can preferentially be studied in a whole muscle. Intramuscular microstimulation or the spike triggered averaging method produces contractions of single motor units. The combination with macro emg allows to characterize their electromechanical relationship.