Free radicals are normally produced during numerous physiological processes and play important roles as regulatory mediators in signalling processes (Strobel et al. 2011). Under physiological conditions, the body has adequate antioxidant defences to cope with the production of free radicals. However, oxidant species can become toxic when generated in excess or in the presence of a deficiency in the naturally occurring antioxidant defences. Specifically, the imbalance between free radical generation and antioxidant defence leads to an oxidative stress state, which may be involved in ageing processes and in many pathological conditions (e.g. cardiovascular and neurodegenerative disease, and cancer) (Valko et al. 2007).
Exercise can have positive or negative effects on redox biology depending on the type (acute or chronic), and on training specificity, load and the basal level of training. Beneficial changes on multiple physiological and laboratory parameters have been generally observed as a result of regular moderate training (Haskell et al. 2007). Conversely, acute and strenuous exercise may paradoxically induce oxidative stress and adverse effects on health (Neubauer et al. 2008, Suzuki et al. 2006). Antioxidant nutrients by diet and exogenous supplementation may be helpful to cope with adverse implications on health and performance (Whayne and Maulik 2012, Braakuis 2012). However, caution should be taken against excess antioxidant supplements.
The complexity of the human antioxidant defence/oxidant system and their delicate balance renders it extremely difficult to estimate the oxidative stress status (Lee et al. 2012). A number of oxidative stress biomarkers (belonging to both antioxidant and oxidant counterparts and also to inflammatory processes) have been identified and measured in biological fluids (Lee et al. 2012). The choice of a specific biomarker and the analytical method used may have a great impact on the results obtained (Lee et al. 2012). Moreover, it is clear that the choice of specific markers depends on the function affected by the exercise and/or by the deficit of the nutrient intake. At the moment, no shared consensus exists on which biomarkers or group of biomarkers must be used to estimate exercise effects as well as bioefficacy of dietary/supplemental antioxidants in sport.
In this chapter, aspects related to the effect of exercise on oxidative stress, diet/antioxidant supplementation and biomarkers in trained subjects will be discussed. Moreover, possible future strategies to answer still open questions and to solve problems in the assessment of these complex issues will also be proposed.
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