13 years old is in the developmental period, this case does not advocate weight loss, can be done through exercise, diet control to do appropriate conditioning, at this age is developing if excessive weight loss on the future development of great impact, so do not advocate weight loss. Do the right exercise can eliminate the muscles of the legs, like the most common is swimming, the best exercise for thin legs, if running legs will also become thicker, it is recommended to swim exercise, its a great help to thin legs, or do skillful exercise is also better for thin legs.