Goes up 100 arms and legs! (6)
I believe the answer is:
climbs
'goes up' is the definition.
('climb' can be a synonym of 'go up')
'100 arms and legs' is the wordplay.
'100' becomes 'C' (Roman numeral).
'arms and legs' becomes 'limbs' (your limbs are your arms and legs).
'c'+'limbs'='CLIMBS'
(Other definitions for climbs that I've seen before include "Moves upward gradually" , "Goes up" , "Advances" , "Moves upward slowly" , "Scales" .)