Proposes a two-stage cross-bridge attachment model to explain the non-monotonic relationship between energy liberation and shortening speed in muscle contraction.
Two-stage cross-bridge model may refine muscle energetics predictions; extends single-stage theory but leaves applicability to cardiac contraction open.
It has been widely assumed that the rate-limiting step in actomyosin ATPase activity during contraction is a single-stage attachment of the myosin head to a site on the thin filament. This assumption leads to a rate of energy liberation that increases monotonically with speed of shortening, in agreement with pre-war estimates of the output of work and heat; it does not explain the fall in energy release at high speeds that has been found more recently. This fall can be explained by assuming that the attachment is a two-stage process.
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Andrew Huxley (1973) studied this question.
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