- The word "up" is a general term used to describe a higher position. In this case is narrowed to a the higher position on gains in jumping vertically upwards, so to speak.
up's
other word formation type narrowing (specialization)
This is in reference to a person's vertical, the vertical distance in which a person can jump.
Source : "Yeah, I'm working on my up's." -Roomate at the gym
Last modified: 5 December 2011