Studies are revealing some pretty negative results on the effects that endurance races and extreme cardio exercises have on the heart and body. No one who does triathlons and iron mans wants to hear this, but damage is evident (most especially in the right ventricle of the heart) immediately after and sometimes long term in an alarming percentage of athletes studied. (See Dr. Mercola’s link http://fitness.mercola.com/sites/fitness/archive/2012/01/25/cardio-may-damage-heart.aspx )
Everyone can become extreme in their life about something. I myself, at one time or another have been a stringent dieter and vegan, an die-hard yogi, an habitual retreat taker, and even a marathon walker. All of my achievements have shed some light on who and what I am made of. They helped me achieve focus and raised my confidence and self-esteem, but more importantly, they gave me a reason to keep striving. I believe that everyone who works hard at whatever they do is just trying to get to the next level, whatever that may be. It is about seeing what more muscle can develop, what skill set can be reached, or what personal record can be broken. Striving is a part of life, and the day we stop is the day we can stop calling ourselves athletes.
The point to remember though is that even if our spirit, mind, and gut are all in agreement about where we want to go, it is our human body that is helping us get there. Although no one I ever heard of has collapsed from too much determination, every minute of every day there is a pro or amateur athlete suffering from a physical symptom or injury that may have been preventable.
Taking care of the vessel that houses a boundless mind and invincible spirit is the only way to allow greatness to be realized. No real champion wants to limit themselves; and as a coach, I would never want to sequester the powerful energy that drives a motivated sportsperson. So, of course, go forth and conquer! But, as you do, make sure you spend as much time and targeted energy making sure your body is going to be able to keep up with you.