Summary
Use has been made of the method of selective leading-off of impulses from individual motor units at high isometric muscle tension, the maximum one including. Two types of motor units have been distinguished in m. biceps brachii in man on the basis of the dependence between the firing frequency and the level of the muscle tension. Characteristic of the first (tonic) type is the rise in the frequency at lower tensions and constant frequency at higher tensions. The second (phasic) type shows an approximately linear rise of the frequency with increase of tension. The tonic motor units are smaller in size, with lower threshold, they are less fatiquable and their transient pattern of firing depends on the rate of increase of tension. They contribute less to the growth of the muscle tension. The phasic motor units are bigger in size with higher threshold, more fatiguable, their transient pattern of firing does not depend on the rate of increase of tension. They contribute essentially to the growth of the muscle tension.
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Gydikov, A., Kosarov, D. Some features of different motor units in human biceps brachii. Pflugers Arch. 347, 75–88 (1974). https://doi.org/10.1007/BF00587056
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DOI: https://doi.org/10.1007/BF00587056