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Dynamic Elasticity in the Initial Phase of an Isotonic Twitch

1960; Wiley; Volume: 49; Issue: 2-3 Linguagem: Inglês

10.1111/j.1748-1716.1960.tb01944.x

1365-201X

Fritz Buchthal, Poul Rosenfalck,

Cellular Mechanics and Interactions

Abstract A method is described which allows a continuous determination of the elastic and viscous component of the dynamic stiffness of isolated frog muscle fibres in vibration experiments. Elastic and viscous stiffness increased gradually in the initial phase of preloaded isotonic twitches. The increase started already within the mechanical latent period. Within 25 per cent of the time to maximum shortening elastic stiffness increased by 100 per cent and viscous stiffness by 50 per cent. In slightly stretched fibres, at the length in the body, the increase in dynamic stiffness during tetanic contraction was identical with that found in a twitch. In highly stretched fibres dynamic stiffness in a tetanus exceeded that of a twitch, presumably due to the redistribution of load between the contractile substance and the sarcolemma. The increase in dynamic stiffness during a twitch immediately after a prolonged tetanus was markedly lower than in a twitch performed before the tetanus. The contributions to the dynamic stiffness from the parallel elastic, the series elastic and the contractile component were evaluated. Although the periodical deformations were essentially confined to the series elastic component, the dynamic elastic properties give information about the contractile substance as the series elastic component mainly represents the elasticity of the contractile material.