Yoga and stretching can help maintain muscle tone and keep you flexible with little if any impact on your joints. However, you may have to augment a yoga regime by walking a few times a week to give your heart a workout. Be careful not to overdo the stretching. You will be more supple as a result of the effects of relaxin, which causes your ligaments to be more pliable. Don't hold the stretches for too long or try to develop your flexibility too much.