Continuity mistake: In the scene at the bar where Robin is describing looking after Marshall as being like having a baby, Barney's drink moves from in his hands to on the table and back again instantly between shots. (00:06:30)
Continuity mistake: When Robin and Ted are at the bar planning their weekend away together, the level of beer in the glass next to them goes up and down between shots. (00:10:00)
Continuity mistake: In the scene at the hotel bar, the red straws lying on the table next to Ted change position between shots without being touched.
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 ★