Wondering about the calluses I have had behind my second toe balls on both feet (though very rarely do I get any pain/tenderness from these - if I do it's after wearing my KSOs all day) I have had the calluses for as long as I can remember - long before any barefoot shoe wearing, perhaps since my teen years.
Doing some searching about I came across something called 2nd Metatarsal Overload Syndrome. It's very specific and seems to be caused by the first metatarsal/big toe being hyper-mobile and lifting upwards as the foot touches down, leaving all the pressure of walking and running to fall onto the 2nd, 3rd and 4th toe balls. Though of course the 2nd metatarsal gets the greatest amount of impact.
This sounds kind of familiar to me - my big toes have always felt kind of weak somehow - and if they are not bearing much weight then this would explain it. (FYI both big toes are straight, I have no bunions, and have very rarely worn heels in my life. My arches are low to flat though, and people have observed in the past that I 'run funny' - or flat footed.
The possibilities/cause of my big toes not bearing weight are more complicated though - anything from me having shorter first ray bones in my big toes, to just my joints being over flexible. It's all a big guess.
The problem is explained a third of the way down this page here -http://www.northcoastfootcare.com/pages/Ball-of-Foot-Pain.html
It's also looked at in detail in this podiatry website - http://www.podiatrytoday.com/article/4733?page=1
And I've just found this which explains the cause of flat feet or fallen arches is an instability in the first ray of the big toe - leading to flat feet and weight transfer on the second toes. http://books.google.co.uk/books?id=OcHq05vQGDwC&pg=PA7&lpg=PA7&dq=2nd+metatarsal+overload+strengthening&source=bl&ots=mQOK1-uWmX&sig=8Leh3W-TWYsQxGQ26yHKUWxuRfg&hl=en&ei=2y3JTeyCEdSy8QP586HoBg&sa=X&oi=book_result&ct=result&resnum=9&ved=0CEUQ6AEwCA#v=onepage&q&f=false
Anyone else thinks this sounds familiar to them too? Has anyone else always had calluses behind their second toes, with or without pain - or big toes that feel weaker than the other toes, or unsupportive of the foot?
Any advice....? The good news I guess is that they rarely cause discomfort for me, and never in my Vivo Barefoot shoes, but the bad news it can while wearing KSOs... I also worry if it might flare up as I age.... :-\