What are then functions of the nervous system

The four primary functions of the nervous system are the sensory, communicative, integrative and motor functions. The nervous system allows the body to respond quickly to various stimuli.

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)