To start your swinging motion, you must push off the ground to create some type of energy you wish to increase. As you swing backwards to get a starting swing from gravity, your potential energy will increase as your body moves forward. Going backwards, your potential energy decreases and increases in kinetic energy. Whether you're increasing or decreasing in kinetic or potential energy, the increase or decrease is the same amount of either energy. So for example, the amount of kinetic energy you lose is the amount of potential energy you will obtain.