Dehydration robbed him of his ability to physically function. After multiple attempts at standing up and finishing, he crawled across the line and into his brother's arms. Here's a local TV station's recap:
If you've never seen the following videos from some of the Ironman championship races, they are incredible. These are finely-tuned athletes, who do their best to optimize performance through training and nutrition over months and years. But sometimes their tanks just get down to zero.
I honestly get choked up every time I revisit these.
Man, I love sports.