There are many piezo crystals available where we need to chpose which one will have a greater efficiency.
I have worked upon piezo on RC gliders but I could hardly glow few LED without any batteries. Selecting suitable piezo under shoe can yield more power.
An single layered/crystal of piezo materials produce very less power which might have barely glow the few LED’s. for even more output u need to use several layers or network of piezo electric materals so u can gain mare o/p