Key result
Short-range stiffness of smoothly contracting isometric soleus muscles in anesthetized cats was found to be a function of tension only, independent of muscle length and stimulus rate.
The study demonstrates that muscle stiffness is a function of tension only, independent of length and stimulus rate, consistent with crossbridge theory.
Should not alter clinical muscle assessment; hypothesis-generating for tension-dependent stiffness models in mammalian muscle.
The short-range stiffness of smoothly but submaximally contracting isometric soleus muscles of anesthetised cats was measured by applying small fast stretches. The ratio of isometric tension to stiffness was plotted against tension over a wide range of muscle lengths and stimulus rates. The results fitted a straight line well, as predicted from crossbridge theory, showing the stiffness to be a function of tension only, independent of the combination of length and stimulus rate used to generate the tension. The major deviation from this line was attributed to incomplete fusion at low frequencies of stimulation. Values believed to be tendon compliance and crossbridge tension per unit of stiffness were found from the graph, and the tendon compliance correlated with the maximum muscle tension. Shortening the tendon by attaching nearer to the muscle changed the results in a manner consistent with the theory, provided that appropriate precautions were taken against slippage.
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David L. Morgan (1977) studied this question. Small fast stretches was evaluated on Ratio of isometric tension to stiffness. Short-range stiffness of smoothly contracting isometric soleus muscles in anesthetized cats was found to be a function of tension only, independent of muscle length and stimulus rate.
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