Very well said, it really is something that will vary from person to person. I run every day and lift 5days a week...and lift heavy..to the point when I leave the body part I have trained is shot. For me personally, If it is a match day I will still run, if it's a day that I should be at the gym I will just go in and do abbs. So I don't end up with major muscle fatigue. Like Jake said, it is about knowing your body. Just start trying different things and see how your body reacts and make corrections from there.