Neither is a major source of heat here, most of this is friction, the running mat drags against a static surface and with the weight of a human on it it has a LOT of friction and that generates heat.

I'd say that all of the yellow on the tread is friction from running on it

Probably friction from the fact that it has to constantly slide while being pressed into the plate under the tread with the force of an adult human.

Neither. It's friction.