After signing up for Jae Gruenke's "Balanced Runner" newsletter, I've recently been experimenting with my own running form. Specifically, I've been initiating my runs, as she suggests, by standing tall and leaning forward to precipitate a subtle forward fall, then maintaining that.
There's nothing new about all this. Thomas S. Miller talked about forward lean in PROGRAMMED TO RUN, and of course the Romanov and his Pose method are all about this.
The result of my own experiments with forward lean have been amazing. My easy pace sped up by 30 seconds a mile at no increase in subjective effort.
The experiment also led me to come up with two analogies that might help others transform their running in the same way I've just transformed my own.
The first analogy is this: imagine that you're balancing a table knife on your index finger. Now move your finger in such a way that the knife starts to tilt away from you. Then, adjusting your hand position under the knife while simultaneously walking TOWARDS the knife, chase that knife. Keep the slight tilt, but walk briskly with it.
Your body is the knife. The slight forward lean--with straight back--that you initiate at the beginning of your run is the knife tilting on your index finger. Your run is following after that slightly tilted knife. You're chasing the knife. You're constantly and subtly adjusting your stride rate and your forward lean until you have the subjective impression, moving forward, that you're in equilibrium and that the run is running YOU rather than the other way around.
The other analogy is the Segway. Here's how I described it in my email to Gruenke:
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As I finished the run, shaking my head in amazement, I suddenly thought: Segway. The forward tilt you've encouraged runners to cultivate is, I believe, exactly the same slight, straight-backed forward lean that makes a Segway move forward. I've never ridden on a Segway, but I've observed them up close. You stand straight up and down to remain at rest. To move forward, you lean slightly forward--and, importantly, you maintain a slight forward lean--although slightly LESS lean than is required to initiate forward motion--in order to continue moving forward. When you want to slow, you pull back slightly.
All these Segway motions are, I believe, essentially identical to the motions that you're encouraging runners to make. Here's a video of a Segway. Start at the :50 point:
https://www.youtube.com/watch?v=rmlg5QkusFQ
So you MIGHT teach the technique you're trying to teach by asking runners to imagine themselves as a human/Segway dyad: a runner's head and shoulders as the "operator," the runner's trunk, legs, and feet as the Segway itself.
Conceiving of the runners-forward-lean thing in this way would help runners understand that "forward lean" is a terribly imprecise phrase for what is actually going on. What is actually going on is that you're initiating an off-balance moment and then rebalancing--like the Segway's human operator in conjunction with the Segway's own internal gyro mechanism--in a way that creates stable forward motion. It's a dynamic process and requires constant attention and adjustment--at least, I suspect, until it has become the new normal, a "natural" way of running.
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The chasing-the-knife and Segway analogies are my own, not Gruenke's. They're simply the best way I have of conveying the subjective feeling of getting the forward leaning thing working for you. They're imperfect analogies, but they might get you there.