The angle of muscle pull is know as following?

The angle of muscle pull is the angle between the line of pull of the certain muscle and in bone which it inserts :)

The angle of pull may be defined as the angle between the line of pull of the muscle and the bone on which it inserts.

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)