I wore toe spreaders inside shoes for about two years. However, whenever running, I prefer being unencumbered. The result was that my toes were more flexible as far as splay was concerned, but not extension or flexion. However, my toes weren't any stronger, and it was still challenging to try to splay them without the toe spreaders.
Incidentally, I found that my feet became stronger, when I started wearing a heavy backpack to try to burn some extra calories while walking. It seemed that I learned how to move more efficiently. Eventually, I got a weight vest that was 1/3 of my bodyweight, but I didn't really notice any further improvement after about 1/4 bodyweight. 6-8 weeks of this did more to strengthen my feet than a 1000 miles of barefoot running.
Maybe this makes sense. Rehabilitative strength training seems to be about slow, purposeful, controlled movements against resistance. Maybe it's no different for toes!
Incidentally, I found that my feet became stronger, when I started wearing a heavy backpack to try to burn some extra calories while walking. It seemed that I learned how to move more efficiently. Eventually, I got a weight vest that was 1/3 of my bodyweight, but I didn't really notice any further improvement after about 1/4 bodyweight. 6-8 weeks of this did more to strengthen my feet than a 1000 miles of barefoot running.
Maybe this makes sense. Rehabilitative strength training seems to be about slow, purposeful, controlled movements against resistance. Maybe it's no different for toes!