G.S. stands for General Strength. You should have some General Strength and Mobility at the end of every run.
If you want to run faster, you should consider running more miles and running some of those miles at a higher intensity. Your life may or may not allow this. Be honest about the amount of training your life will allow.
I’m an advocate of running a hard and running a lot of miles. But to do those two things you need to be healthy. AIF and G.S. help you stay healthy.