|Z-Coil Freedom shoe|
It is a "Freedom" model from Z-Coil, who makes elaborate footware for people with sore feet. I found them at a store in Dearborn.
The company is based in Arizona, but the shoes themselves are made in Korea. They have a whole line of shoes with different styles, but all with the big bulky spring in back. They make different strengths of springs for different people, and the springs do wear out.
I don't really have a foot problem, but I did have an Achille's tendon injury last August, and I have not really come back. Unlike my Nikes, this running shoe is rigid, and so tendons in my foot don't flex. All the cushioning is done by the big spring.
The hope is that as time passes, my foot will get stronger, and I won't have to wear them all the time.