# Physical Activity and Redox Balance in the Elderly: Signal Transduction Mechanisms
## 2 Physical Activity and Redox Balance in the Young and Adults  
In young people, the majority of papers correlated obesity with oxidative stress. In fact, obesity is often associated with high levels of free fatty acids. This increases the levels of  
Figure 1: Flow diagram according to Prisma 2009 guidelines. A total of 500 records were identified for this study in three online databases (Pubmed, Scopus, Web of Science) using this search expression: “Redox AND Balance AND Physical activity OR Exercise AND Age AND Signal transduction”. After removing duplicates, we found 430 articles, and after first screening, 130 were excluded. 300 full-text articles were assessed for eligibility, and 209 were excluded because results were partially redundant. Finally, 91 studies were included in qualitative synthesis. We did not use any date limit. NADH that generate high oxidative stress. In obese young subjects (males of 20-26 years), ROS levels are significantly higher than in non-obese, while (SOD) antioxidant activity is significantly lower [15]. After training (aerobic: 40 min treadmill, three times/week for 8 weeks; 70% Heart Rate reserve), ROS decreases and SOD increases. Interestingly, the authors also found a significant increase in Brain-Derived Neurotrophic Factor (BDNF), but not in Glial-cell-line-Derived Neurotrophic Factor (GDNF) or in Nerve Growth Factor (NGF) after aerobic training. At the same time, blood markers of blood-brain barrier (BBB) damage decreased. Notably, BDNF is lower in obese subjects, compared to non-obese. In non-obese subjects, the authors did not find significant changes in the levels of neurotrophines. Finally, [PERSON] et al. (2019) [16] reviewed the effect of physical activity on brain health. They found that BDNF is produced in the periphery of the nervous system in a physical-activity-dependent manner. A very recent review [17] showed that overweight/obesity does not affect exercise lipid-oxidation systems, suggesting that physical activity could have a positive effect, not directly on lipid oxidation, but on blood-brain barrier damage. Interestingly, three months of Crossfit training increased BDNF in active men [18]. In particular, they observed improvements in endurance performance (expressed by VO2 max) and the levels of plasma antioxidant markers such as SOD, glutathione reductase (GSH), Uric Acid (Uric Acid), the ferric reducing ability of plasma and BDNF. Altogether, these data suggest that physical activity exerts a positive effect on brain health, both reducing damages that can occur to the blood-brain barrier and increasing the levels of the antioxidant BDNF. Besides physical activity, antioxidant supplementation is widely distributed to counteract oxidative stress. In fact, the antioxidant effect of polyphenolic compounds is related to the inhibition/inactivation of several pathways such as the Nuclear-factor kappa light-chain enhancer pathway of activated B cells (Nf-kB), and the kappa kinase/c-Jun amino-terminal kinase pathway (IKK/JNK), that are involved in oxidation [19]. Moreover, polyphenolic molecules inhibit the activity of the enzymes responsible for ROS production, such as cyclooxygenase, lipoxygenase and xanthine oxidase. Of note, the effects of polyphenols can affect the activation of antioxidant pathways by exercise. For example, [PERSON] et al. (2018) [20] studied the effect of cocoa polyphenols in elite football players practising intense physical exercise. After 30 days of chocolate intake, the elite football players showed a significant decrease in their levels of muscle-damage markers such as Creatin Kinase (CK), Lactate dehydrogenase (LDH) and Myoglobin and an increased antioxidant power, suggesting that polyphenols positively modulated redox balance and reduced muscle tissue injury in elite football players.