The Amazing Stickie is amazingly efficient. When she finds an exercise that helps her meet multiple goals at once, she gets excited. Woodchoppers are one of those exciting exercises because they work the obliques while adding a cardio component.
Stickie uses a medicine ball, but a dumbbell held by the ends works just as well. She begins with the weight twisted up toward one side of her body, held with straight arms. Her arms remain straight throughout the exercise as she chops the weight through the air across her body toward her opposite calf. Her feet can pivot slightly and her knees can bend a little. Then she raises the weight back up across her body, still keeping her arms long to maximize the physics.
She usually does a set of fifteen reps on one side and then switches to the other side. Three sets are enough.