How I Met Everyone Else - S3-E5
Other mistake: In the scene where Barney is describing The Vicky Mendoza Diagonal of The Hot-Crazy Scale, his words describe her getting hotter, (i.e. lost ten pounds) not less crazy. On the diagram shown, she goes down in craziness, not up in hotness.
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 ★