A very interesting paper was just published by the Karl Zelik lab on soft tissue work during early gait (see below ) . Such soft tissue work would include the deformation of the heel pad and compression / distortion of the other tissues of the foot .

It seems to me that the compression of the tissues that lie between the bony arch of the foot and the plantar fascia would also play a large role in the soft tissue work done by the foot .
If that is indeed the case then one might expect to see a lower contribution from this source when walking uphill but a higher , and later contribution when walking downhill (foot slapping action ) .

I would be very interested to hear what Karl and Eric think of the above .

Gerry

Paper Foot and shoe responsible for majority of soft tissue work in early ...

https://www.ncbi.nlm.nih.gov/pubmed/30769210

by EC Honert - ‎2019
12 Feb 2019 - Foot and shoe responsible for majority of soft tissue work in early stance of walking. Honert EC(1), Zelik KE(2). Author information: (1)Dept. of ...