I’ve been running since I’ve been a teen and am now into my 50s….almost 52. Overall I’ve had a good ride qualifying for Boston a few times and running it once back in 2006. Last fall I missed by just a couple minutes. I have completed a couple half marathons this spring….may and July both in a 1:49. However after a track workout and than hyper extending my hamstring at yoga, I am trying to come back to train for my 20th marathon in January. How long can I expect my upper hamstring to need. I recently started incorporating some of the chi principles…..I have a 185 candence…..but working on breathing. Mid foot strike. I’ve been a toe runner. My stride could use a bit of shortening too?