Great article about the need for impulsion and how to break it down into those important and incremental two steps. What the article implies (and which I think is equally important) is that after asking for that bust of energy, you need to leave your horse alone and not nag him. I think a lot of horses become dead to the leg because their riders are constantly bumping and nudging them along. Better to ask for the surge and then go with it. You can always ask for more later.
