The simplest way to start Jogging in the morning. Choose a place for Jogging (the nearest Park), get an alarm clock. Jog for a few days, and then, suddenly, the second half will catch up. And if you are not interested - invite her along, focusing on the fact that without it you sad.
If you run yourself completely does not work, and buy literature about healthy way of life. Read aloud, discuss. In conversation often mention that a sedentary lifestyle is very bad for health.
Give her a very beautiful and fully-open dress. Dress must be good for her, she should want to wear. Even if it would need to lose a few pounds.
Or another option - buy an outdoor swimsuit. Hand it to her with the words: "You look great in that thing." And then her concern as to match your words.
Perhaps your relationship has gone far enough, strengthened by marriage and children. In this case, promise her that you will mess with the children a few hours a day. Reapply this time for yourself, including Jogging. And strictly fulfill its obligations, so she didn't have to worry about children.