Yoga considers the body as the vehicle of the soul in its journey to perfection. Yogic exercises - asanas- are designed to develop not only the body, but also mental and spiritual capacities.
Other physical exercises usually promote violent movements of the muscles, whereas asanas are practiced slowly and synced with breathing. Muscle development doesn't necessarily mean a healthy body, health is also related to the proper functioning of all the organs and a control of the mind.
The practice of yogic exercises has benefits beyond the muscular system; it increases spine flexibility and blood circulation, and glands and internal organs are stimulated into efficient functioning. Together with conscious breathing and concentration of mind, asanas help our vital energy -prana- to flow naturally for a general wellbeing.
One hour of yoga is more than one hour of exercise, it is one hour of deep relaxation for mental and spiritual balance, one hour to reconnect to yourself.