What is measured by the amount of time a muscle group can sustain a contraction? A.
Muscular endurance
B.
Muscular strength
C.
Cardiovascular fitness
D.
All of the above

The answer is A. Muscular endurance

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)