Snail - I push off with my balls, if you'll pardon the expression.
I have a neutral gait/foot strike but when I started running (about 2 years ago) I used to hit the ground very, very hard with my heels and the first few miles of any run (even when doing 20 miles) hurt like hell. You could here me coming a mile off as my feet thwacked the pavement - slap,slap,slap, ouch, ouch, slap etc.
Things are a lot easier now - no pain and no heavy heel strike. Partly I think due to being fitter and stronger, but I also make a conscious effort to try to run "quietly". If I think softly, softly, I don't hit the ground as hard, which equals no pain. I also think it helps that I run about 1 minute per mile faster on most runs. If I try to run real slow, it can start to muck things up again!
Blimey, what a ramble!
Neil