Force-Velocity Relation and Stiffness in Frog Single Muscle Fibres during the Rise of Tension in an Isometric Tetanus

  • Carlo Ambrogi Lorenzini
  • Francesco Colomo
  • Vincenzo Lombardi
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 37)


The force-velocity (T-V) relation and the force-extension (T 1 ) relation are determined at preset times and at increasing isometric tensions during a tetanic contraction in frog single muscle fibres in which the passive compliance in series with the sarcomeres was made very small

The slope of the instantaneous T 1 relation, the fibre stiffness, increases roughly in proportion to the level of the rising isometric tension at which the measurements were made.

The value of V0 (the velocity of shortening under zero load) is time-independent, whereas the force T exerted during shortening at any velocity V lower than V o increases gradually with time after the beginning of the tetanus volley and attains its steady state level before the isometric tension has attained the tetanus plateau and the fibre stiffness its final value.

It is concluded that the delay of the development of the isometric tension and of the fibre stiffness with respect to the development of the T-V relation is determined by a specific factor of the contractile process. It is interesting to note that in a cross-bridge model of contraction, in which the value of the rate constant for cross-bridge formation is moderate, the recruitment of actin sites which is measured by the characteristics of the instantaneous T-V relation, is expected to lead significantly the actual cross-bridge formation, which is measured both by the instantaneous isometric tension and by the instantaneous stiffness.


Isometric Tension Tetanic Contraction Passive Compliance Steady State Characteristic Contractile Process 
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Copyright information

© Plenum Press, New York 1984

Authors and Affiliations

  • Carlo Ambrogi Lorenzini
    • 1
  • Francesco Colomo
    • 1
  • Vincenzo Lombardi
    • 1
  1. 1.Instituto di FisiologiaUniversità degli Studi di FirenzeFirenzeItaly

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