An analysis of the heat production during a contraction in which work is performed

Abstract

RECENT experiments by Fenn(l, 2) have shown that when a muscle is allowed to shorten and do work there is a further output of energy beyond that liberated in an isometric contraction. When the load was held by the muscle during contraction only, and not during relaxation, the total extra energy liberated was approximately equal to the work done, so that the energy liberated as heat was constant. If the load rested on the muscle during relaxation then still more heat was given out. It seemed desirable to consider the matter in greater detail, and to make an attempt to follow the course of the heat production during the contraction by analysing the curve of galvanometer deflection usinag the method explained elsewhere(3). By such means it was hoped to determine in which phase the extra energy associated with work was liberated. With a view to this, and to other measurements of the kind, considerable improvements have been made in the technique.The thermopile, constructed by soldering, has been improved by making it in one sheet, zig-zag fashion, holding each outer junction by thread to the supports, instead of winding the wire either round a sheet of insulator or round the arms of a U-shaped frame. If the same wire were used the new method would give only half the number of junctions per unit length, but by using finer wire (36 S.W.G. iron and constantan) the number of junctions per unit length has been maintained (35 to 40 junctions per centimetre) without making the electrical resistance excessive. Using as little insulation as possible the thermal capacity of the part of the thermopile under the muscle is now much less than before, so that its temperature changes follow more quickly those of the muscle.A further great improvement has been made by introducing a new suspension into the Paschen galvanometer used. This magnet system was constructed, with much stronger magnets of cobalt steel, by

The analysis of the initial heat production of muscle

“…That the relaxation heat does really represent mechanical potential energy dissipated during relaxation is confirmed by experiments [Hartree, 1925;Hartree and Hill, 1928] in which it has been shown that when work is done by a stimulated muscle the relaxation heat is correspondingly reduced. This mechanical energy is probably far less than the area of the tension-length curve [see Hartree and Hill, 1928, p. 13, etc.…”

“…Later, however, quicker thermopiles consisting of a single layer of thin wire were made, and the galvanometer was improved, the resulting analyses being much more definite. An example was published [Hartree, 1925], unfortunately without numerical details; these, however, have been supplied since [Hill, 1930a: Appendix by Hartree]. In various other investigations [e.g.…”

Croonian Lecture:—The laws of muscular motion

“…The full amount of work cannot be done-owing to the " viscosity " of the muscle substance-unless the shortening be slow, unless, that is, the con ditions be, in the thermodynamic sense, reversible. Now, Hartree (16) found-in confirmation of Fenn-that in a frog's muscle allowed to shorten, doing or without doing work, the heat set free is the same as in an isometric contraction, an extra amount of energy being liberated to provide for the work, if any, performed. He ascertained, however, that when shortening was allowed there was 15 per cent, extra heat in the first (contraction) phase and a corresponding deficit in the second (relaxation).…”

The free energy of glycogen-lactic acid breakdown in muscle

“…In a paper by Hartree and A. V. Hill to appear shortly, the manuscript of which was kindly shown to the writer, the view receives support that the truest measure of the mechanical potential energy is the heat liberated in relaxation, rather than the tension length diagram area as used by A. V. Hill (35) and others before. Such a view, for which Meyerhof (38) has always contended, upon other grounds, however, has received this new support as a result of further investigation of the Fenn effect (36,37). The determination of the theoretical maximum work is further complicated and rendered un certain by the possibility suggested by A. V. Hill (35, p. 261, lines 18-21) and later by Wyman (39), that part of the potential energy of tension may be used in reconversion processes rather than all being converted quantitatively into heat.…”