Reactive oxygen and nitrogen species (RONS), also known as free radicals, are continually produced within the body as part of normal oxidative metabolism (Finaud et al. 2006; Powers et al. 2011). These molecules act as intracellular messengers and are necessary for proper physiological function (Dröge 2002; Niess 2005). However, high concentrations of RONS can be toxic and cause significant oxidative damage to the cellular structure of lipids, protein and DNA (Halliwell and Gutteridge 1999; Powers et al. 2004). The concentration of RONS within the body is controlled by an extensive antioxidant system, which works to scavenge free radicals (Halliwell and Gutteridge 1999; Powers et al. 2004). Antioxidants (AOX) are present in both the intra- and extra-cellular matrix forming a complex defence system to protect cells and tissue against oxidative damage (Powers and Lennon 1999). The antioxidant defence system is commonly divided into enzymatic (endogenous) and non-enzymatic (exogenous) AOX.
Seifried et al. (2007) define AOX as a group of compounds characterised by their ability to be oxidised in place of other compounds present. The main enzymatic AOX include superoxide dismutase, catalase and glutathione peroxidase. Vitamin A, vitamin C, vitamin E, thiols, flavonoids and ubiquinones represent the main non-enzymatic AOX, which can be obtained in a conventional diet and with supplementation. This has led to the suggestion that AOX supplementation may result in an acute improvement in skeletal muscle contractile performance (MacRae and Mefferd 2006; Oh et al. 2010). This hypothesis is based on the finding that the rapid elevation of oxidant concentration during exercise may be a contributory factor to muscle fatigue (Reid et al. 1994; Gomez-Cabrera et al. 2008). However, other reports have stated that AOX supplementation in combination with exercise training may blunt exercise-induced biochemical adaptations to exercise (Reid 2001; Watson et al. 2005). This chapter provides a comprehensive overview of the acute exercise responses and longer term adaptations to the common antioxidant supplements.
Prolonged exercise training induces marked changes in physiological function and skeletal muscle contractile performance (Kubukeli et al. 2002; Laursen and Jenkins 2002). The oxidant–antioxidant balance during exercise has been shown to greatly influence muscular contraction (Clarkson and Thompson 2000) and adaptation to physical training (Palazzetti et al. 2003). It has been proposed that optimising skeletal muscle oxidant concentration by consuming antioxidant substances (acutely) results in a greater force production and power output during prolonged high-intensity endurance exercise (Poulsen et al. 1996; Alessio et al. 2000). However, studies have also shown that physiological adaptations to exercise may be blunted when oxidant production is suppressed by AOX (Palazzetti et al. 2003; Watson et al. 2005). Therefore, consideration should be made of the research concerning both acute supplementation with AOX and exercise performance and also more chronic consumption and the possible consequences. The type of AOX substance/content is also important when evaluating the potential use and physiological significance of the different AOX supplements.
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