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Energetics of Shortening Muscles in Twitches and Tetanic Contractions : I. A Reinvestigation of Hill's Concept of the Shortening Heat
Shortening heat was defined by Hill as the "difference between heat produced when shortening occurs and that produced in a similar contraction without shortening." For the tetanus the "similar contraction" was an isometric one at or near l(o). By contrast, in a twitch the "s...
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Formato: | Texto |
Lenguaje: | English |
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The Rockefeller University Press
1973
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2226140/ https://www.ncbi.nlm.nih.gov/pubmed/4548713 |
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author | Homsher, Earl Rall, Jack A. |
author_facet | Homsher, Earl Rall, Jack A. |
author_sort | Homsher, Earl |
collection | PubMed |
description | Shortening heat was defined by Hill as the "difference between heat produced when shortening occurs and that produced in a similar contraction without shortening." For the tetanus the "similar contraction" was an isometric one at or near l(o). By contrast, in a twitch the "similar contraction" was one in which only activation heat was produced. The applicability of Hill's concept of the shortening heat has been reexamined in both the twitch and tetanus of Rana pipiens semitendinosus muscles. Results of this investigation confirm the existence of an extra heat production accompanying shortening in the twitch and tetanus. In both cases, this shortening heat was proportional to distance shortened and relative afterload. However, at a given afterload the amount of shortening heat produced per distance shortened was greater in the twitch than the tetanus. This difference suggests that the base lines or "similar contractions" employed for the twitch and tetanus are not equivalent. The discrepancy is not remedied by utilizing in the tetanus the activation heat as the myothermic baseline and suggests that some heat producing factor(s) has been omitted in Hill's formulation of the shortening heat. Finally, the existence of Hill's feedback heat, an energy liberation associated with the presence of tension during mechanical relaxation, was not confirmed. This result strongly indicates that relaxation is energetically passive. |
format | Text |
id | pubmed-2226140 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 1973 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-22261402008-04-23 Energetics of Shortening Muscles in Twitches and Tetanic Contractions : I. A Reinvestigation of Hill's Concept of the Shortening Heat Homsher, Earl Rall, Jack A. J Gen Physiol Article Shortening heat was defined by Hill as the "difference between heat produced when shortening occurs and that produced in a similar contraction without shortening." For the tetanus the "similar contraction" was an isometric one at or near l(o). By contrast, in a twitch the "similar contraction" was one in which only activation heat was produced. The applicability of Hill's concept of the shortening heat has been reexamined in both the twitch and tetanus of Rana pipiens semitendinosus muscles. Results of this investigation confirm the existence of an extra heat production accompanying shortening in the twitch and tetanus. In both cases, this shortening heat was proportional to distance shortened and relative afterload. However, at a given afterload the amount of shortening heat produced per distance shortened was greater in the twitch than the tetanus. This difference suggests that the base lines or "similar contractions" employed for the twitch and tetanus are not equivalent. The discrepancy is not remedied by utilizing in the tetanus the activation heat as the myothermic baseline and suggests that some heat producing factor(s) has been omitted in Hill's formulation of the shortening heat. Finally, the existence of Hill's feedback heat, an energy liberation associated with the presence of tension during mechanical relaxation, was not confirmed. This result strongly indicates that relaxation is energetically passive. The Rockefeller University Press 1973-12-01 /pmc/articles/PMC2226140/ /pubmed/4548713 Text en Copyright © 1973 by The Rockefeller University Press This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/). |
spellingShingle | Article Homsher, Earl Rall, Jack A. Energetics of Shortening Muscles in Twitches and Tetanic Contractions : I. A Reinvestigation of Hill's Concept of the Shortening Heat |
title | Energetics of Shortening Muscles in Twitches and Tetanic Contractions : I. A Reinvestigation of Hill's Concept of the Shortening Heat |
title_full | Energetics of Shortening Muscles in Twitches and Tetanic Contractions : I. A Reinvestigation of Hill's Concept of the Shortening Heat |
title_fullStr | Energetics of Shortening Muscles in Twitches and Tetanic Contractions : I. A Reinvestigation of Hill's Concept of the Shortening Heat |
title_full_unstemmed | Energetics of Shortening Muscles in Twitches and Tetanic Contractions : I. A Reinvestigation of Hill's Concept of the Shortening Heat |
title_short | Energetics of Shortening Muscles in Twitches and Tetanic Contractions : I. A Reinvestigation of Hill's Concept of the Shortening Heat |
title_sort | energetics of shortening muscles in twitches and tetanic contractions : i. a reinvestigation of hill's concept of the shortening heat |
topic | Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2226140/ https://www.ncbi.nlm.nih.gov/pubmed/4548713 |
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