Running

I lost big toenail running (well fair bit of walking) Athens Marathon after having no problems during training. Since then I have notice the toe sits up a little higher at the front than the other, meaning the nail would have been hitting the top of the shoe rather than the front of the toe taking the impact (of course being a fat git and taking 6 hours might have played a part).

Thinking that lighter shoes with a sock like top might be better to reduce impact (using Asics at the moment).

fundamentally, you shouldn't be losing toenails every time you run a half marathon, and its likely to be from repeated impact of the top or front of the offending toe which despite not having seen you run i'd imagine is not part of your normal gait, so something is causing impact and it could be sliding, it could be fit, it could be the seam of your socks, or it could be that they are too small.

its not likely to be something you notice when you first put your shoes on or first set off, or indeed be something that causes you a lot of pain while running so it might be hard to identify when looking at your feet in the shoes in the cold light of day..

I've never actually lost a nail, what happens (seems to be) that the nail(s) are folded backward on themselves, this causes a crease in the nail and the front of the nail lifts away from the nail bed.

Christmas before last this was definitely caused by wearing shoes that were too small, which I have since got rid of.

My own view is that something in my gait changes when I am fatigued - I've been running 5k's recently, the odd 10k, so 22k was well above what my body was/is used to.

I'm basing this on having none of these nail issues, in the same shoes, at 5/10k distance.