# Physical Activity and Redox Balance in the Elderly: Signal Transduction Mechanisms
## 4 Insights into Signal Transduction
### Plasma and Adipose Tissue  
Increased oxidative stress is related to abnormal activation of the renin-angiotensin-aldosterone system [49]. Resistance exercise increases the level of Triacylglycerglycerol Lipase Activity (TGLA), the level of plasma glycerol and the level of oxidative stress in obese with respect to lean subjects [49; 50]. This is associated with higher levels of serum non-esterified fatty acid and increased lipolysis in adipose tissue [50]. The relationship between exercise and obesity is under study in a clinical trial (current controlled trials, ISRCTN95488515). In particular, they are investigating the effects of endurance and high-intensity intermittent endurance exercise on plasma concentrations of glycerol, Atrial Natriuretic Peptide (ANP) and Brain Natriuretic Peptide (BNP). In fact, ANP and BNP are potent lipolytic agents. The results of this trial will be useful for optimizing training protocols for the prevention and treatment of obesity [51].  
Contrasting results have been obtained on the role of exercise on plasma levels of cytokines [52; 53; 54]. For example, triathlon competitions like Ironman or Half Ironman significantly increase the levels of oxidative stress markers, Interleukin-6 (IL-6), Interleukin-1 (IL-1) and Tumour Necrosis Factor alpha (TNF-alpha). However, the training hours spent before the competitions were inversely correlated with the level of IL-6 found, suggesting that only IL-6 is related to the time of training [52]. In aged subjects affected by rheumatoid arthritis, 10 weeks of a walking-based high-intensity interval training (HIIT) increased ROS production, but there were no significant changes in the levels of inflammatory markers such as IL-1, IL-6, TNF-alpha and Interleukin-10 (IL-10) [53]. On the other hand, a study performed in post-menopausal women observed a significant decrease in IL-2, IL-4, IL-6 and TNF-alpha levels, both after 3 months of aerobic training (60-70% of maximal heart rate on treadmill, with low speed and without inclination) and after 3 months of resistance training with better results in terms of BMI and quality-of-life in subjects performing aerobic training [54]. In contrast, a single short bout of resistance exercise in healthy untrained men increased catecholamines, Epidermal Growth Factor (EGF), IL-2 and TNF-alpha, with the levels of IL-1\(\alpha\), IL-1\(\beta\), IL-6, IL-8 and IL-10 maintained constant levels [55]. Additionally, [PERSON] et al. (2017) [49] observed that a single bout of physical activity does not induce changes in plasma cytokine levels. Instead, they observed a decrease of EGF and an increase of the antioxidant enzyme Glutathione Reductase (GR).  
Eccentric exercise of the elbow flexors does not induce significant change in plasma cytokine levels, even in the presence of significant muscle damage as demonstrated by the increase in Creatine Kinase (CK) activity and myoglobin [56]. In any case, a transient increase in oxidative stress and cytokines is considered relevant for improvements induced by regular exercise, in a process called mitohormesis, because mitochondria are necessary for energy production and associated with oxidative stress induction [57]. All these data suggest that, since the role of cytokines in response to oxidative stress and exercise has not been definitively clarified, the aerobic, resistance, endurance and strength training sessions should be carefully set up within physical-activity programs for adults and elderly people in order to avoid undesirable effects in inflammation-signalling pathways.