Bloom says that sciatica for runners does not come from the actual movements but from simple errors or anything related to posture. He noted that runners often have the tendency to lean back to control their descent during downhill stretches; this can test the spine. Sciatic pain, which is also traceable to tightness in the piriformis muscle (found in the buttocks) is not evident even during the run itself. Symptoms of sciatica include numbness in the lower extremities, and tingling sensations. Some people say that in worst cases, the legs might suddenly shut down from severe sciatic attack, which can be dangerous in the middle of a crowd of runners.
http://painreliefexperts.com/info-articles/paramus-nj-sciatica-treatment-makes-the-difference-for-avid-runners/
