In which stage of the family life cycle does the family dynamic begin to form?

Unattached young adult joining of families through marriage. Newly carried couple family with young children family with adolescents launching children and moving on family in later life.

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)