One of the unsolved problems of muscle contraction has been the bridging of the gap between the chemistry of the energy producing reactions involved and the physical processes of shortening and lengthening of the muscle fiber. The detailed chemical transformations of the energy producing mechanisms and their interrelationships have been elucidated during the course of the past two decades, and the energy changes involved have been measured quantitatively. The phosphorylation cycles whereby energy is transferred from carbohydrate breakdown to the muscle fiber have been worked out in detail.1 Physical studies, chiefly with the aid of x-ray analysis, have yielded a rather complete picture of the alterations which occur in the muscle fiber when subjected to varying amounts of tension in vitro. Muscle contractibility is essentially a molecular contractility of the protein (myosin) chains.2 However, the means by which the energy produced by the chemical processes is linked or
ADVANCES IN MUSCLE PHYSIOLOGY. JAMA. 1943;121(5):347. doi:10.1001/jama.1943.02840050045014
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