Sure, it can feel all too relaxed, even indulgent compared to the intense stuff. But don’t be so quick to disparage. Low level aerobic activity, I’m here to tell you, is the crucial base of Primal Blueprint fitness (Rule #3 in my book for those of you who are currently reading it). It’s the base, the foundation, the keystone to the big fitness picture.(These Mark's Daily Apple articles were written by Mark Sisson, and are narrated by Brock Armstrong)