[quickben]

If all else fails, bend the knees and go down few cm. Then try to kick you butt with the heel going up. This will naturally lean you forward and your striking leg won't heel in first on the next strike.

Also, try to keep your head in the same virtual horizontal line. Head/torso going up and down can cost up to 40% more energy.

For extra points, your torso shouldn't be swaying, arms moving should be enough.

YouTube marathon runners for Olympics and look at some training videos for in depth info.