Tension development in highly stretched vertebrate muscle fibres

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Abstract
An apparatus is described by which the length of a selected part of an isolated muscle fiber can be held constant, giving isometric conditions, or alternatively Its length can be measured while tension is held constant (isotonic). Control can be switched between length and tension to carry out afterloaded contractions with a shortening stop. When a part of a fiber with uniform strlation spacing is stretched so far that there is no overlap of fiJements, the tension developed during an isometric tetanus with this apparatus is very small (not more than 3-5% of the tension developed at optimum length). If the tendon ends are held stationary, a fiber with the same initial length slowly develops a large amount of tension (order of 30-40% of tension at optimum length). This additional tension is dhe fiber, where the strtation spacing is smaller and overlap of filaments still exists. The resistance to elongation of a part of fiber where there is no overlap is only slightly increased on stimulation. The development of detectable amounts of tension, and of a slight increase of stiffness on stimulation are not expected, possible explanations are discussed.