There are many benefits of yoga, like stress reduction, increased energy and flexibility, and it's great for your metabolism, cardiovascular and circulatory health. It's also good for strengthening and toning the muscles. Yoga is not just stretching; it's much more than that. I read this really great book for my yoga teacher traning course called Asana Pranayama Mudra Bandha by Swam Satyananda Saraswati. The postures, or asanas, have been practiced for hundreds of years and are meant to prepare the body for meditation and sitting for long periods of sitting/stillness. The postures open the energy centres (nadis), increases the flow of vital energy (prana) and stimulates the chakras (energy centres). There's often tension and stiffness in the body due to built up toxins and blocked prana. Yogasana helps to open the enegy channels and release dormant energies.
There are many ways in which yoga and exercise are different. Exercise is obviously really good for your body and mind, improving mental health, mood, confidence and self-esteem. It helps you to control weight and improves cardiovascular and respiratory health. Yoga has similar benefits and was designed to have “specific effects on glands and internal organs and to alter electrochemical activity in the nervous system” as Saraswati says in the book. They're so complimentary! Exercise speeds up metabolism and breath, the body gets hot and oxygen consumption increases. But with yoga, respiration and metabolic rates slow down and the consumption of oxygen and body temperature decreases. The combination of yoga and exercise provides a healthy balance.