I can't believe I have not googled this problem before - I am sooo relived to have found this thread. I have been running for 6 years now injury free with one marathon, one half and many 10ks under my belt. I did the Great North Run last year and all was fine....running tailed off and then picked it back up again at the start of 2007. On my first run back, I noticed my right foot started to go numb after 10 mins and every run since then, it has gone numb always after 10 mins. Both feet now do it and once I have felt a tingling up my left calf. It also happens for me when cycling (after an hour), cross trainer (after 10 mins). I have generally tight calves and on my right foot, I sometimes feel like my achilles is near snapping point. I also have what feels like a permanatly spasmed muscle just under my bum on my right leg. I went to the physio for my achilles and he said it was to do with my lower back which may have been causing the numbness......after weeks of treatment, nothing was changing and he started to get worried about compartment syndromme. He then didnt want to treat me any more in case he caused more damage. I was sent to a neurologist who was baffled - he sent me for an MRI scan of lower back....nothing. Then I was sent for a nerve function test....nothing again. I have an MRI scan on upper back coming up to see if there is anything there. So none the wiser and very frustrated but very hopefull now I have found there are so many others with this problem. I am going to go back to a new physio and show this thread to them - I also plan to send to the neurologist to prove I am not the only one out there suffering from this. If anyone has had any miracle diagnosis that have helped, please please let me know as I really want this gone - beggining to feel like running career is over.