Events, situations, or surroundings that make a demand on the body are known as:

environment
adrenalines
stressors
hormones

Stressors.Hope this helps.Great luck mate!

The los angeles must have 500 to 900words

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)