Visuals show Iffrig’s legs being swept out from under him by the impact of the explosion.
A race official helped him back to his feet, and Iffrig, determined to reach his goal, went on to finish the race.
“I got down to within 15 feet of the finish apron and heard this tremendous explosion,” he said.
“The shockwaves hit my whole body and my legs started jittering around. I knew I was going down.”
But, he said after running 26 miles he wasn’t going to give up.
Iffrig, who sustained a scrape on his knee, described his proximity to the blast as scary.
His son, Mark, said Iffrig was a bit dazed by the explosion. After recovering from the blast Iffrig walked further half a mile to his hotel still wearing the bright orange tank top.