I have seen people test the stiffness of frames for years by putting one foot on a pedal in the 12 O'Clock position and pushing on it. I have tried to explain that all they are seeing is how much air is in their tires.
There are still a lot myths and foolishness in our hobby, I think the one about frames going soft is one of the silliest, Chucks description a few years ago, of a pile of discarded Merckx's frames rusting away in a field because they had gone soft, was quite a parody of this foolishness.
Jim McCoin
Fremont Ca.