I'm definitely no expert, I'm afraid. Perhaps others can chime in. But notice how, in this gif, the maximum force is applied just as the heel starts to lift:
https://i.makeagif.com/media/3-05-2014/hQcYHP.gif
I think it's hard to imagine in part because it involves such a radical shift in the center of gravity, bringing the body over the knee, so the foot can act as a springy lever, minimizing the impact of your heel on the ground.
http://www.barefootbruce.com/images/100_Barefoot_Biomechanic...
It's also something I found >literally< impossible to do when I started, because in addition to the lack of knowledge, my tendons and muscles had never performed the motion before. So, please be careful anyone who tries to pick this up, and don't overdo it until you are limber and strong enough in the small stability muscles of your feet. But >do< pick it up. Such a more efficient, and less painful way to run.
