You're the envy of the female world with a well-proportioned top and bottom body and a narrow waist. When you gain weight you gain it all over - especially on your chest and bottom. Hourglasses body shapes tend also to be endomorphs or mesomorphs.
If you're an hourglass body shape, you should focus on both cardio and resistance exercises. Cardio will assist in keeping your weight in check, while resistance exercises will help to maintain balance between your upper and lower body. Vary your repetitions (in other words, the amount of times you do the exercise) and keep your resistance weights light so as not to build too much muscle mass. Here are some great exercises that you may want to try as an hourglass body shape: