You gently place your body into a yoga posture. Done correctly, there's very little chance of injury or muscle stress. A particular asana is not repeated dozens of times, nor are you ever encouraged to push yourself too much.
A yoga session is designed for balance. You stretch to the right and then to the left. You bend back and then forward. You learn to recognize when one side is stronger or more flexible than the other. Thus harmony and balance are achieved with yoga practice.
People of all ages can practice yoga exercises. They are easily modified to meet your needs and physical condition. Don't be put off by the difficult looking postures you may see in a yoga book. A skilled teacher can adapt most asanas by using chairs, cushions, even a wall or other props. A yoga practice can be tailor-made just for you. If something is really impossible for you to do, just forget it. Never compete with yourself or others. Yoga is a stress-free but powerful way to exercise.
Yoga is good for increasing your flexibility and relieving stress, but it doesn't take the place of aerobic exercise. You should still do regular, aerobic exercise, which increases your cardiovascular fitness, helps you lose weight, and, for people with non-insulin-dependent (type II) diabetes at least, improves blood glucose control.
Proponents of yoga exercise argue that it has a multiplicity of techniques to counter that cause and, unlike drug therapy, attack the cause, not just the symptoms. It offers, they say, a holistic approach to health and fitness. Many professional athletes, looking for the edge have turned to yoga as a supplementary form of training. They have found that yoga aids their state of mental and physical relaxation between training sessions, and their crucial build-up to big meets, where a competition is usually won or lost in the mind.