2greysdad, our girl Beka is 6 1/2 months post amp and had six rounds of chemo, finishing 2 months ago and she now enjoys 30 minute walks, twice a day. She gets tired, but she loves it. Plus, as Chris said, she needs to go a little faster because the momentum makes it much easier for her. She goes into a trot, which is a run for me! I let her have as much sniffing time as she wants, since it gives her a little rest between trots (and runs). She also runs in the house, chasing our other grey through the hall, living room and dining room! It just takes time for them to build up the stamina for longer walks (and runs).
Twiggy is definitely an inspiration! I met her years ago at GiG and was so impressed. I thought of her often after Beka's surgery!