A lot of people are relatively well-versed on what happens to their legs after a race or hard workout. You break down muscle, your connective tissue is damaged ever so slightly, etc., and you ultimately come back stronger.
What I, along with a lot of other people, don't understand is what happens to the rest of your body in the hours and days following a very hard effort. I have a few questions I'm hoping you can answer. Even if you can only answer one or two, that will be greatly appreciated.
-Can the heart muscle be damaged by back-to-back hard efforts, or too many hard efforts?
-If the body can continue to adapt and get stronger after six (or so) weeks of hard training, why does it eventually get overwhelmed?
-If you feel completely fine after a very hard effort -- say a half marathon -- several days after the fact, is there anything beyond your legs you have to worry about damaging by undergoing another hard effort?
-Why do aerobic bases take so long to kick in?