Both brown fat tissue (BAT) and skeletal muscle experience large increases of oxygen consumption and
oxygen radical generation during activation. This, together with the relatively low activities of
antioxidant enzymes in these two tissues and the high
lipid content and
free fatty acid liberation of BAT, can produce a physiological oxidative stress. Increases of in vivo or in vitro (BAT) lipid peroxidation have been described in these tissues after activation. They react to this oxidative stress in an adaptive way after chronic stimulation. Cold acclimation increases
antioxidant enzymes, ascorbate, and especially
reduced glutathione (GSH) in BAT. There is controversy about the variations of
antioxidants in skeletal muscle after acute exercise. Nevertheless, exercise training seems to increase muscle
antioxidant enzymes and GSH. Many reports show that
vitamin E levels decrease in the muscle and increase in plasma during exercise. Studies of
vitamin E deficiency and supplementation strongly suggest that this
vitamin is of protective value during exercise.