The exercise principle that states that a muscle must have more resistance than it is accustomed to in order to be conditioned is called the exercise specificity principle law of reversibility overload principle muscle adaptation principle

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)