Atividade Física e Plasticidade da Musculatura Esquelética

The vertebrate skeletal musculature of contemporary humans, responsible for most of their locomotor activity, expresses a common basic structure and mechanism, which resulted from a long evolutionary process. However, the type of physical activity performed may alter these structural and functional patterns. Athletes engaged in different types of training such as velocity, force and endurance express different phenotypes. Athletes engaged in velocity and force sport modalities, like the 100 meters sprint and the shot put, respectively, show predominantly fast twitching muscle fibers, which function in the absence of oxygen (glycolytic pathway), whereas athletes engaging in long term (endurance) modalities, like the marathon, show predominantly slow twitching muscle fibers whose function depends on oxygen (oxidative pathway). These different muscle fiber expressions are known as phenotypic plasticity, which occurs both within the same species as well as among different species.A musculatura esquelética do ser humano contemporâneo, responsável por grande parte de suas atividades locomotoras, apresenta um desenho estrutural e um mecanismo básico comum resultante de um longo processo evolutivo. Entretanto, o tipo de atividade física realizada pode alterar esse padrão estrutural e funcional. Atletas que realizam treinamentos específicos de velocidade, força e resistência expressam fenótipos diferentes. Isto é, atletas que realizam provas esportivas de velocidade e força, como a prova dos 100 metros rasos e o arremesso de peso, respectivamente, apresentam predomínio de fibras de contração rápida, cujo metabolismo não depende do oxigênio (via glicolítica), enquanto atletas que realizam provas de longa duração (resistência), como a maratona, apresentam predomínio de fibras de contração lenta e dependentes do oxigênio (via oxidativa). Essas diferentes expressões da musculatura esquelética são conhecidas como plasticidade fenotípica, a qual ocorre tanto dentro de uma mesma espécie assim como, de modo mais amplo, entre espécies diferentes

On the cardiac control in the South American lungfish, Lepidosiren paradoxa

1. 1. The mechanisms behind cardiac control were investigated in the South American lungfish, Lepidosiren paradoxa, using fish with chronically implanted cannulae and electromagnetic flow probes. In addition, a preliminary study was made of the cardiovascular events associated with air breathing. 2. 2. The study suggests that the heart of Lepidosiren is controlled by cholinergic vagal fibres which, in some animals, exert a tonic influence in the resting fish. Cyclic changes in heart rate in association with air breaths is due to modulation of this cholinergic tonus. 3. 3. In addition to the variable cholinergic tonus, there appears to be a relatively stable adrenergic tonus on the heart, which causes an elevated heart rate. The adrenergic tonus is likely to be due to local release of catecholamines from endogenous chromaffin cells within the atrium. 4. 4. Preliminary results suggest that pulmonary arterial flow increases by about 50% immediately following an air breath. The mechanism behind this increase probably involves both an elevation of the heart rate and a redistribution of blood flow into the pulmonary circuit. © 1989

Temperature effects on energy metabolism: a dynamic system analysis.

Q(10) factors are widely used as indicators of the magnitude of temperature-induced changes in physico-chemical and physiological rates. However, there is a long-standing debate concerning the extent to which Q(10) values can be used to derive conclusions about energy metabolism regulatory control. The main point of this disagreement is whether or not it is fair to use concepts derived from molecular theory in the integrative physiological responses of living organisms. We address this debate using a dynamic systems theory, and analyse the behaviour of a model at the organismal level. It is shown that typical Q(10) values cannot be used unambiguously to deduce metabolic rate regulatory control. Analytical constraints emerge due to the more formal and precise equation used to compute Q(10), derived from a reference system composed from the metabolic rate and the Q(10). Such an equation has more than one unknown variable and thus is unsolvable. This problem disappears only if the Q(10) is assumed to be a known parameter. Therefore, it is concluded that typical Q(10) calculations are inappropriate for addressing questions about the regulatory control of a metabolism unless the Q(10) values are considered to be true parameters whose values are known beforehand. We offer mathematical tools to analyse the regulatory control of a metabolism for those who are willing to accept such an assumption