yes, that's what I was thinking. I am a vigorous proponent of hard, stiff treadmills for scientific testing. The Lieberman group used a cushy treadmill for a barefoot vs. shod study and that led to flawed conclusions in my opinion.
I've talked with Iain and his force-treadmill has a belt that was quite slippery for the Vaporfly outsole.
I think Barnes used a slat treadmill in part because he was testing spikes. It is hard to beat an old Quinton. Like the 18-60 from the 1970s used by Costil, EC Frederick, Daniels and many many others. We finally sent our last 18-60 to the salvage yard about 6 months ago. The 1990s Quintons actually can flex a fair bit, I'd want to shim up the middle of the span.
As I tweeted, your study looks like a ton of careful work. It was plenty hard to find runners who could run 18 km/hr with RER <1.0 in Boulder, can't imagine finding/trying to get 16km/hr guys in Nacogdoc!
I imagine/hope that your manuscript is in review somewhere.
re: Jack Tupper Daniels, Ph.D. Oops, I've confused SFASU with AT Still University (ATSU) which is in Arizona, not Tejas. You should take my erroneous suggestion that your study seemed to have a JT Daniels influence as a big compliment.