The New York Times was the first to report the story earlier today:
Hall, 33, who was one of the last remaining hopes for an American front-runner in this summer’s Olympic marathon, is succumbing to chronically low testosterone levels and fatigue so extreme, he says, that he can barely log 12 easy miles a week.
“Up to this point, I always believed my best races were still ahead of me,” Hall, who has faced a series of physical setbacks since the 2012 London Olympics, said. “I’ve explored every issue to get back to the level I’ve been at, and my body is not responding. I realized that it was time to stop striving, to finally be satisfied and decide ‘mission accomplished.’ ”
Read the full article via http://www.nytimes.com/2016/01/17/sports/ryan-hall-fastest-us-distance-runner-is-retiring.html.