Which is an example of humans adapting to their environment?
developing air conditioning to cool homes in hot climates
cutting down forests to create open land to build a factory
relying on government agencies to clean up after natural hazards
building a fish ladder so salmon can swim past a dam to get to spawning grounds

Telling them to either contract or relax

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)