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      Variation in isometric force after active shortening and lengthening and their mechanisms: a review Translated title: Variação da força isométrica após encurtamento e alongamento ativo e seus mecanismos: uma revisão


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          Introduction The isometric force history dependence of skeletal muscle has been studied along the last one hundred years. Several theories have been formulated to explain and establish the causes of the phenomenon, but not successfully, as they have not been fully accepted and demonstrated, and much controversy on such a subject still remains. Objective To present a systematic literature review on the dynamics of the mechanisms of force depression and force enhancement after active shortening and lengthening, respectively, identifying the key variables involved in the phenomenon, and to date to present the main theories and hypothesis developed trying to explaining it. Method The procedure of literature searching complied the major databases, including articles either, those which directly investigated the phenomena of force depression and force enhancement or those which presented possible causes and mechanisms associated with their respective events, from the earliest studies published until the year of 2010. Results 97 references were found according to the criteria used. Conclusion Based on this review, it is suggested that the theory of stress inhibition of actin-myosin cross-bridges is that better explain the phenomenon of force depression. Whereas regarding the force enhancement phenomenon, one theory have been well accepted, the increased number of actin-myosin cross-bridges in strong binding state influenced by the recruitment of passive elastic components, which hole is attributed to the titin filament.

          Translated abstract

          Introdução A dependência entre a produção de força isométrica do músculo esquelético e o histórico da contração precedente vem sendo objeto de estudo nos últimos cem anos. Diversas teorias têm sido formuladas para explicar e estabelecer as causas do fenômeno, obtendo pouco sucesso, uma vez que não foram completamente aceitas e comprovadas, suscitando ainda muita controvérsia sobre o tema. Objetivos Apresentar uma revisão sistemática da literatura sobre a dinâmica dos mecanismos de depressão (DF) e de aumento (AF) da força isométrica após encurtamento e alongamento ativos, respectivamente, identificando as principais variáveis intervenientes nos fenômenos, e as principais teorias e hipóteses elaboradas para explicá-los até a presente data. Métodos O procedimento de busca da literatura foi composto por uma pesquisa nas principais bases de dados, incluindo artigos que observaram diretamente os fenômenos DF e AF, ou possíveis mecanismos e causas associadas a suas respectivas manifestações, desde os primeiros estudos sobre o tema até o ano de 2010. Resultados Foram encontradas 97 referências que atenderam aos critérios adotados. Conclusão Com base na revisão produzida, sugere-se a teoria da inibição por estresse induzido das pontes cruzadas de actina-miosina para explicar o fenômeno DF. Quanto ao fenômeno AF uma teoria tem sido bem aceita, a do aumento do número de pontes cruzadas de actina-miosina em estado forte de ligação influenciado pelo recrutamento dos componentes elásticos passivos, atribuindo-se aos filamentos de titina este papel.

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          Most cited references 108

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          Ki-67: level of evidence and methodological considerations for its role in the clinical management of breast cancer: analytical and critical review

          Clinicians can use biomarkers to guide therapeutic decisions in estrogen receptor positive (ER+) breast cancer. One such biomarker is cellular proliferation as evaluated by Ki-67. This biomarker has been extensively studied and is easily assayed by histopathologists but it is not currently accepted as a standard. This review focuses on its prognostic and predictive value, and on methodological considerations for its measurement and the cut-points used for treatment decision. Data describing study design, patients’ characteristics, methods used and results were extracted from papers published between January 1990 and July 2010. In addition, the studies were assessed using the REMARK tool. Ki-67 is an independent prognostic factor for disease-free survival (HR 1.05–1.72) in multivariate analyses studies using samples from randomized clinical trials with secondary central analysis of the biomarker. The level of evidence (LOE) was judged to be I-B with the recently revised definition of Simon. However, standardization of the techniques and scoring methods are needed for the integration of this biomarker in everyday practice. Ki-67 was not found to be predictive for long-term follow-up after chemotherapy. Nevertheless, high KI-67 was found to be associated with immediate pathological complete response in the neoadjuvant setting, with an LOE of II-B. The REMARK score improved over time (with a range of 6–13/20 vs. 10–18/20, before and after 2005, respectively). KI-67 could be considered as a prognostic biomarker for therapeutic decision. It is assessed with a simple assay that could be standardized. However, international guidelines are needed for routine clinical use.
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            New insights into the behavior of muscle during active lengthening.

             D.L. Morgan (1990)
            A muscle fiber was modeled as a series-connected string of sarcomeres, using an A. V. Hill type model for each sarcomere and allowing for some random variation in the properties of the sarcomeres. Applying stretches to this model led to the prediction that lengthening of active muscle on or beyond the plateau of the length tension curve will take place very nonuniformly, essentially by rapid, uncontrolled elongation of individual sarcomeres, one at a time, in order from the weakest toward the strongest. Such a "popped" sarcomere, at least in a single fiber, will be stretched to a length where there is no overlap between thick and thin filaments, and the tension is borne by passive components. This prediction allows modeling of many results that have previously been inexplicable, notably the permanent extra tension after stretch on the descending limb of the length tension curve, and the continued rise of tension during a continued stretch.
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              The relation between force and speed in muscular contraction.

               Ellen Katz (1939)

                Author and article information

                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Fisioterapia em Movimento
                Fisioter. mov.
                Pontifícia Universidade Católica do Paraná (Curitiba )
                March 2014
                : 27
                : 1
                : 141-153
                [1 ] Universidade Salgado de Oliveira Brazil
                [2 ] Universidade Salgado de Oliveira Brazil
                [3 ] Vrije Universiteit Brussel Belgium
                [4 ] Universidade do Estado do Rio de Janeiro Brazil
                [5 ] Universidade Salgado de Oliveira Brazil
                [6 ] Universidade Gama Filho Brazil
                [7 ] Universidade do Estado do Rio de Janeiro Brazil
                [8 ] Universidade Salgado de Oliveira Brazil
                [9 ] Universidade Federal do Rio de Janeiro Brazil
                Product Information: website

                Orthopedics, Physiotherapy

                Lengthening, Active, Força, Encurtamento, Alongamento, Ativo, Force, Shortening


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