The heat production in isometric and isotonic twitches

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Abstract
The total energy in an isotonic twitch is not equal to that in an isometric one except within a narrow range of initial loads. With small initial loads the isotonic heat may be much less than the isometric, with great initial loads, much more. The conflicting results of several observers in this respect are due to variations in the range of initial loads within which they worked. The energy set free in a single twitch of a muscle does not depend only on con ditions obtaining at the moment of stimulation. Release for example, at a much later stage may considerably affect the energy, and[long dash]according to the initial load[long dash][center dot] the isotonic heat may vary almost from half tp twice the isometric. There are 2 factors determining the energy liberated by a muscle in a twitch: (a) the length of its fibers, not only at the moment of stimulation but throughout contraction, and (b) work done. With smaller initial loads (a) is the more important; with greater initial loads (b) is.

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