In reply to Rampikino:
This is covered well in Julian Goater's book (I didnt pay massive attention as I run forward).
Anyway, he is adamant that it is faster. The jist of his advice is:
- lean forward slighltly, head up
- increase your cadence (he suggests some drills to help with this), be light and 'peppy'
- get a feeling that you are 'falling forward' and need to increase cadence to stay upright
- try to get the knee a bit higher and think about the whole cycle and driving through like you would on a bike.
Might be worth a look to see if any of it chimes with you.