The most common and most likely answer to this crossword clue is the 8 letter word HEMLINES
H
E
M
L
I
N
E
S
Buddy explains!
The straight part
We know that "They go up and down on catwalk" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they go up and down on catwalk = hemlines.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HEMLINES mean?
HEMLINES noun- The line formed by the bottom edge of a skirt, dress, or coat; hem.
- The height of this line, measured from the floor.