This is because exercises like squats and deadlifts use
more muscle groups under a heavy load than almost any other weight bearing exercises known to man.
Not exact matches
Also, training only one
group of
muscles for a few days in a row was proven to be
more effective
under certain conditions.
But to get the most out of your resistance training program make sure you use exercises that involve
more than on
muscle group, keep the rest
under 45 seconds, and make sure the exercises aren't too easy.