Yes, my running shoes were purchased at a running store after a professional gait analysis.

7.0 is only a little faster than a ten minute mile- certainly not a sprint. I feel very comfortable at this speed but feel like my body may just crumple out from underneath me after about a minute. My legs feel fine, my lungs feel fine, my head feels fine, but my heart races and my body gets weak.

I'm going to try to find a doctor to see about this. I'm very perplexed that it only happens running and not cycling or swimming. Perhaps it has something to do with running being weight bearing.