Hi, I'm hoping someone here could shed light on this for me as google is telling me all sorts. So I'm training for London marathon, all going well apart from the odd aches and pains in my lower legs. This morning I set out to train on the Hastings half route, a race I've run the last 3 years and planned to run again next month in prep for London. I got to about 8 miles, up the dreaded Hastings hills and felt really good fitness wise, thinking I could possibly knock 20 mins or so off last years time. I got to the brow of a hill, and as I started coming down I felt what I can only describe as an explosion in the back of my left leg. All of a sudden my calf muscle was in agony, hamstring and a dreadful shooting pain in the back and round the side of my knee. I couldn't continue, the pain made me feel physically sick and I had to ring someone to pick me up and drive me back to my car. On the way home, because I was sitting still I suppose, I had no pain but random spasms all over my leg muscles. This was around 1pm, at about 3pm my leg gave way and I've never felt pain like it. Fast forward to now, all the time I'm sitting, nothing but pins and needles down the back of my leg. But when I walk, oh god the pain!! I should add that my right leg, not so much as an ache. Anyone else experienced this and can help me with a diagnosis? Please? I'm happy to pull out of Hastings if the hills are going to make this worse but the thought of pulling out of my first London marathon actually makes me want to cry. Thank you if you made it this far, apologies for the long explanation.