Study the diagram of a cell
Which structure is found only in plant cells and functions in
the process of photosynthesis?
OW
ФХ
OY
Z
XN
Y
W

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)

Around the ages of 7-12