This is really strange. I've been running 35 minutes and, as precise as a Swiss watch, my left foot goes numb. It happens every time I run longer than half an hour. Damn, it's frustrating! I would like to run longer and faster, I feel fit and great, but I have the impression that my foot has turned hard as a piece of wood. I must stop.
All over the last 4 years I've been trying to collect information about this awkward reaction. On the internet I found some explanations and some suggestions on how to prevent it. It seems that the most probable cause is a nerve compression, therefore many runners and doctors suggest to wear comfortable shoes and to avoid tight socks. First problem: in my case, I am sure the tingling is not caused by my shoes. How can I be so confident about it? 4 years ago, when the problem first appeared, I went running barefoot on the beach, and my foot tingled. So it could not depend on the tightness of my footwear.
Back then, I used to keep track of my daily running performances on a small diary (very useful habit indeed!). I started a training programme at the beggining of June 2011, and I detected the first signs of tingling after 3 weeks of light training, always after 35 minutes of running. It went on for around one month, then it never occurred again, and I could run long distances without suffering any problem.
In April 2015 I resumed my daily running after a sedentary winter season, and here it comes again, the damn tingling! However, my previous experience taught me to keep my spirit up. Whenever the foot got numb, (always after 35 minutes!) I bit the bullet and I kept running for 500 meters before stopping. After two weeks the tingling disappeared and now I can run any distance I like. I want to be clear: I am not suggesting you to do the same! This method worked with me and honestly I don't know why. I tend to ascribe the numb foot to the lack of training after a long stop, but being no doctor I am not 100% sure!