I haven’t read “Born to Run,” the most popular running book ever written if you can judge by best-seller numbers, two years old but still in the Top 35, but you’d have to seriously question the impact it has had because despite the outsized role running as recreation plays among the book-reading public there are only a modest number of born-to-run enthusiasts who purchase those glove-like shoes, and more incredibly, run in them, a tiny majority of true believers in the message of “Born to Run” author Christopher McDougall, an advocate of one-hundred mile races and one-hundred-twenty-mile training weeks, with nothing else below the ankle than what God provided, a glorious invention, the foot, so you would think that a running-mad place like 2011 Park Slope, Brooklyn, I would see more than the occasional finger-foot runner, and maybe now I will as I push out in the finally snow-clear roads, the most telling weeks of Boston training regimen, Week Three of Seven, because the final one before April 18 doesn’t count, it is a tapering one, but my guess is I won’t, so what conclusion can we come to, that readers are buying this book as an inspiration for young althetes, encouragement for middle-aged shirkers, or vicarious pleasure for the elderly, with perhaps a single marathon once run, or a college history of track, because it can’t be just runners who are buying; in 2009, only 467,000 runners completed a US marathon, and if Pittsburgh 2010 is any guide, just 4,058 out of 7,620, or 53 percent, finished the whole grueling route, 26.2 miles.