Factual error: When Ted is having a flashback about the first road trip in the Fiero, which would have happened around 1997or 1998, they are passed by a 2002 GMC Sierra. (00:06:10)
Continuity mistake: In this episode we learn that Barney doesn't know how to drive. But throughout the whole series there are reference that he actually does, such as: In 'Come On' (22nd episode 1st season) : Penelope says to Barney: "We had sex twice in your car." In 'Moving Day' (18th episode 2nd season) : Barney drives away with Ted's rental van. In 'The Bracket' (14th episode 3rd season) : Barney stole Holly's SUV as they were camping.
Answer: After running the marathon for Marshall with no training, he's allowed to ride the subway for free. While sat on the train, the muscles in his legs start to seize up after the marathon to the point it is painful to move his legs. This is why he can't move them. It's the same reason your body aches after a good session at the gym the day before.
Ssiscool ★