I have “foot drop” in both feet - I can push my feet down (tip-toe like), but can’t lift them up. For years, I had carbon fiber orthotics, including a carbon fiber foot sole. I can say that in my experience, in no uncertain terms, that the carbon fiber stored energy when flexed, and released it when let go. It was a “spring” effect (the term for that energy is elastic potential energy), and my orthotics guy pushed that as a plus when I first got them.
The “spring” was extremely helpful! I switched to an external orthotic recently, though, because the “in the shoe” requirements of the old orthotics were fairly painful - they rubbed and irritated my ankle and foot, fairly common for active people.
The new orthotics don’t hurt, but they’ve got no “spring”. I don’t think this was psychological.
That’s somewhat obliquely referred to here:
The shoes weigh about 6.5 ounces and feature a thick but lightweight midsole that is said to return 13 percent more energy than more conventional foam midsoles. Some runners have said the shoes reduce fatigue in their legs.
“The shoes have springs in them” would be clearer.