Good question and I have often pondered this myself.
I don't have the answer however but consider this:
Try pushing a wheelbarrow over 400m. with a 14 stone person it and then try the same thing with a 10 stone person.
Pull a loaded trailer uphill with your car and then repeat with half the load.
In relation to a harness driver, whether a few pounds makes a difference is problematical.
A 14 stone man however, compared to a 7 stone female, for example, and the difference could be significant.
I guess this question could be answered by someone expert in the laws of physics.

[ This Message was edited by: Imagele on 2004-01-21 12:40 ]