What is an example of extra cellular fluid

Simple answer
Extra cellular fluid denotes all body fluid outside any multicellular organism

The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)

Answercapillaries;