What is gesture? Gesture is the movement of the whole form in space, not what it looks like but what it is doing. While contour drawing asks you to patiently travel over form using your sense of touch, gesture drawing requires you to -- in a moment -- extract the essential nature of a form or a pose. A line in a gesture drawing traces the movement of the whole form in space.
Extracting the essence, or the movement
My teacher Hale used to point out that even Leonardo couldn't get a man to lie under a rearing horse, nor could he get the horse to rear for an hour and a half while he drew. What he had to do was to quickly get a feeling for the gesture of that movement and then work from his memory. So this is a training in learning how to capture the essence or the movement or the life of the pose within a moment. And then build from there.