I'm sure this has been asked before but I don't feel like searching through the forum, so here it is again.  Why do we have a 1mn rest in between sets?  For me, I'm really into more of a cardio heart rate when I only rest for 1mn and I'm wondering if I should increase it or is that what the system is designed for, more of a cardio/weight routine?   If the program is designed for more of a cardio/weight routine, then why not do a full blown circuit training? 

After today's upper body (C1W3D1), I am completely exhausted and found it difficult to get through all the reps.  Perhaps I need to start lower because it feels like 9-10 intensity on each set (a great workout today, btw).  Love to hear your thoughts!