The aroused state of sympathetic nervous system doesn't prevail forever. When the stress stimuli is eliminated, there is activation of parasympathetic nervous system which gradually enables the body return to a state of calm and relaxation. 
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No one is immune to stress and as a matter of fact the things which push us more to the edge because of their demands can be used to define our success. It is the hustles in life that makes us prone to stress.
Yoga embodies integration of physical poses, breathing technique and concentration of the mind into the present. It focuses on alleviation of stress and negative emotions that have been the back bone of chronic diseases. 
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Lets contrast this biological yoga phenomenon to other aerobic exercises. Bearing in mind that meditation and breathing technique is crucial in activation of peripheral nervous system and have a dominant effect to sympathetic nervous system. During aerobics, the activation of sympathetic nervous system may persist to dominate since the exercise doesn't engage the mind and may propagate into a full fledged stress vis-a-vis yoga poses. 
Mastering the technique of breathing and concentration of the mind to present can be an awesome course. Research has shown that during inhalation there is a slight sympathetic activation and heart rate races, and during exhalation there is a slight parasympathetic activation bringing a feeling of calm.
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2. Explaining the therapeutic effect of Yoga and its ability to increase quality of life- PubMed. By Catherine Woidyard. Address:http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3193654/. Viewed on: 19/06/2015.Health
3. Yoga for stress relief; Reduce stress with Yoga- Yoga Journal. By Kelly Mcgonigal. Feb 14, 2011. Address:http://www.yogajournal.com/article/ayurveda/tame-stress/
4. Article Explains Importance of Heart Rate Variability for Your Health- HeartMath Institute. Jan 26, 2015. Address:https://www.heartmath.org/articles-of-the-heart/science-of-the-heart/article-explains-importance-of-heart-rate-variability-for-your-health/ Viewed on; June 22nd, 2015.