It is well established that the increase in reactive oxygen species (ROS) and free radicals production during exercise has both positive and negative physiological effects. Among them, the present review focuses on oxidative stress caused by acute exercise, mainly on evidence in healthy individuals. This review also summarizes findings on the determinants of exercise-induced oxidative stress and sources of free radical production. Moreover, we outline the effects of antioxidant supplementation on exercise-induced oxidative stress, which have been studied extensively. Finally, the following review briefly summarizes future tasks in the field of redox biology of exercise. In principle, this review covers findings for the whole body, and describes human trials and animal experiments separately.

The phenomenological strain energy density function (W) for the elastomeric networks of end-linked poly(dimethylsiloxane) (PDMS) has been investigated as a function of the first and second invariants I 1 and I2 of the Green's deformation tensor on the basis of the quasi-equilibrium stress-strain relationships of general biaxial deformations varying independently each of two principal strains. The Ii dependence of ∂W/∂Ij (i,j ) 1,2) was obtained from the biaxial stress-strain data using the Rivlin-Saunders method. In the 3-dimensional plots of ∂W/∂Ii (i ) 1,2) against both the (I1 -3)-and (I2 -3)-axes, the data points of each derivative at large deformations appear to fall on a plane inclining against the (I1,I2) plane, which suggests that both the derivatives linearly depend on each of I1 and I2. The formula of W is reasonably deduced from such linear dependence of ∂W/∂Ii on Ij (i,j ) 1,2) as W ) C10(I1 -3) + C01(I2 -3) + C11(I1 -3)(I2 -3) + C20(I1 -3) 2 + C02(I2 -3) 2 . Each of the numerical coefficients Cij is assigned to each of the intercepts at I1 ) I2 ) 3 and the gradients of the two fitted planes in the (I1, I2, ∂W/∂Ii) plots. The estimated W satisfactorily reproduces not only the original biaxial stress-strain data but also the data of uniaxial, equibiaxial elongation, and uniaxial compression none of which were used for the original estimation of W. It is also demonstrated that the familiar Mooney-Rivlin type of W composed of only two linear terms of each of I 1 and I2 does not even qualitatively reproduce the biaxial stress-strain data.

Five molecular models of rubber elasticity which employ different treatments of entanglement effects (the Kloczkowski−Mark−Erman diffused-constraint model, the Edwards−Vilgis (E−V) slip−link model, the tube models of Gaylord−Douglas (G−D), Kaliske−Heinrich, Rubinstein−Panyukov versions) are assessed using biaxial deformation data for an entanglement-dominated network of end-linked poly(dimethylsiloxane) (PDMS) in which trapped entanglements are dominant in number relative to chemical cross-links. The theoretical stress−strain relations were calculated from the elastic free energy (W) of each model. Using the reduced stress (the nominal stress divided by equilibrium modulus G o), the strain-dependent predictions of each model were tested from two different viewpoints, i.e., the dependence of the reduced stresses on the principal ratio and the I i dependence of (∂W/∂I j )/G o (i,j = 1,2), where I 1 and I 2 are the first and second invariants of deformation tensor (the Rivlin−Saunders method). The diffused-constraint model is relatively successful in reproducing the reduced stress−strain data over a wide range of deformations, but the model definitely underestimates the magnitude of G o because it does not consider trapped entanglements as additional cross-links contributing to G o, in contrast to the tube models and the slip−link models. The G−D tube model is more successful in reproducing the experimental data relative to the other two versions of the tube model, but the G−D model obviously underestimates the stresses at large deformations. Among the five molecular theories tested here, the E−V slip−link model shows the most successful reproducibility over large portions of the experimental results. The agreements in reduced stress−strain relations are satisfactory over the entire deformation range, although considerable disagreement is recognized in the I i dependence of ∂W/∂I 2. Also, the fitted parameter values in the E−V slip−link model are fairly well explained using the molecular considerations based on the structural characteristics of the network sample employed here.

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