> The picture shows you with quite a bit of forward lean.
Well, maybe 4 - 5 degrees, yes.
> So bending forward at the ankles with a straight back is an economical posture
> to assume with the forward lean.
I agree, of course.
But I find it hard to imagine some bending forward from the ankles at 26 degrees, as your first posting stated. OK, maybe a severely overloaded SAS trooper carrying his FULL load of munitions and water might do that for 100 m from the chopper which landed him, but a walker with a reasonably light-weight pack???? Photographic proof would be needed.
As noted in some other postings, the backwards tension in the shoulder straps has been measured as not all that high *in practice*. This suggests to me that a reasonably light-weight load carried upright in a reasonably good pack is not really going to present that much of a problem. The amount of tilt needed to balance this will not be high.
Now, do we lean forward some more when going forward? Yes, we do, but that is needed to keep the CoG of the whole walker somewhere between the front and back feet. You would fall flat on your face if you didn't do this. And it may also be that the faster you go, the further forward the CoG needs to be.
That necessary forward displacement of the CoG has to be assessed in combination with the weight of the pack *relative to the walker's weight*. I weigh 64 kg; my pack weighs 10 kgs. The influence of the pack weight on how much my CoG has to move is not going to be all that large. This suggests that the change in position of the CoG due to a light-weight pack is not supremely important.
If there are other factors coming into play, such as the ability to see one's feet, than any small benefit from a shift forwards of the CoG due having front packs in place may *in practice* be inconsequential. This seems to be the experience of many walkers: they rate being able to see their feet far higher, especially in rough terrain.
Other factors which can detract from the front-mounted load include the increased heat load on the body from the reduction in ventilation, the increased difficulties experienced in swinging a pack on and off one's shoulders when there are large weights on the shoulder straps, and the increased problems when scrambling with a bulky thing at the front pushing you off the face. The importance of these factors will depend very much on the individual and what he is doing.
So while some people undoubtedly like having front-mounted packs to alter the CoG, the market place seems to be putting other factors higher in importance. Well, that's what the sales figures and walker preferences indicate, anyhow.
I hope this explains my thinking.