Although orange juice does not naturally contain a significant amount of calcium, some companies add calcium to help support nutritional needs. This is an example of ?

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)