When establishing a basic routine, is it neccessary to have days that you are completely "off"? Days that you don't even do cardio on? This is the routine i'll be following this summer, but i'm still doing revisions on it: Mon - Pecs/Tris Tues - Legs Wed - HIIT + Abs Thurs - Bis/Fores Fri - Shoulders/Back Sat - HIIT + Abs Sun - HIIT In most of the articles ive read on interval training it says that you should do HIIT 3+ times a week, and on your non weight training days. I definitely want to incorporate running into my routine but don't know the best way of going about it. So i guess i'm asking is it essential to have days completely off? And when's the best time to do running (yes i know it's been beaten to death...)?