Nature or nurture? Outgrowing my running shoes

A growing problem

A couple of weeks ago I gave away three pairs of running shoes to someone with same shoe size. My collection of running shoes had reached a point where I needed to store them in four different locations. When I made the exchange I had a total of 13 pairs. Now it's down to 10. I should probably get rid of most of the rest because, remarkably, the majority of them no longer fit me.

When I finished growing (at around 19 years old) I naively assumed that I'd never need to buy clothing again. Over the years I've had to replace worn clothes and buy more occupationally appropriate attire, but I'd always assumed that I would fit into the same shoes forever. Four years ago I started running again and bought a pair of Nike shoes. They fit me well and I liked them.

A lot has changed since that purchase in 2008. I no longer care for Nike's and I doubt I could even fit my foot into those shoes. It's strange, but since I started running, my shoe size has increased a full size and a half. I started at 9.5, moved up to 10's about a year later and, by early 2010, I needed 10.5's. Now most 10.5's are too tight in the toe for me to use, except on shorter runs.

The Spira's and the Kinvara 3's are both 11's and they fit me well. I was still thinking I was a 10.5 when  Brooks picked me to test a pair of prototype shoes a few months back. I really like the shoes but the fit is annoyingly snug on the outside toes. Had I asked for 11's, I'd probably be rotating these shoes with the Kinvaras on almost every run. Happily, the Saucony's provide me with a quality running experience and I appreciate them more every day.

Outgrowing shoes gives me an opportunity to buy new ones (and as my wife would point out, a reason to get rid of old ones). I'm wondering why this has happened. Is running flattening or spreading the volume of my feet? More importantly, when does it stop!?