Thomas Panek had been a runner from a young age, so even when he lost his sight in his early 20s, he continued to compete in road races. And like any blind runner, he has relied on volunteers to guide him. Whether he was running the New York City Marathon (with Rabbi Michael Friedman of Running Rabbis) or the Boston Marathon (with the famed ultramarathoner Scott Jurek), human guides, connected by a tether, have led his way. He has enjoyed this method, despite the lack of independence.

And yet Mr. Panek, now 47, has wondered what it would be like to run with one of his guide dogs. Every trainer he posed this question to gave the same answer: guide dogs were not appropriate for long-distance running, let alone a race. “The presumption was that it wasn’t safe,” he said. “And no school had ever trained a guide dog to run.”

He had gotten wind of several blind racers who bucked the conventional wisdom, like a Denver runner named Kerry Kuck, but Mr. Panek never seriously considered doing that himself.

Then one morning in April 2014, as he was eating breakfast just before running the Boston Marathon, a friend who was guiding him brought up running with a guide dog: “Why don’t you see if it’s possible?”