Explain a relationship that exists between the following group of terms: 1) SA node
2) Purkinje fibers
3) Myocardium
4) Ventricles *

Depression is lifelong, though you can get medication to with it. the difference between sadness and depression is that sadness lasts a little bit, depression last a long time and it goes on and off. people usually get depression through experiences they have been through, or genetics.

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)