Question 5 In normal,
circumstances, the reward circuit responds to healthy, pleasurable
activities by releasing the neurotransmitter
which teaches other parts of
the brain to repeat those activities
O a. non-drugged, serotonin
O b. drugged, dopamine
O c. drugged, serotonin
O d. non-drugged, dopamine

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)