I dont buy the intense workouts as better alternative to more "slow burn" workouts. I'm a runner and I used to do fast 5k runs 3-4 times a week. I would feel very tired at the end of each run, just depleted. Didnt wanna do anything else but just relax. Had headaches too and most likely due to burning carbs at fast rate (intense workout, high heart rate) and basically depleting my carb reserves, which i think are about 2500 calories in a person. Then I stumbled upon a book, i think here on HN, called Slow Burn by Stu Mittleman [1]. It changed the way i look at the cardio exercise dramatically ! You wanna be healthy - burn fat (slow pace, long time, low HR). You wanna be fit - burn carbs (fast pace, short runs, high HR). These are very different goals as you can imagine ! So which one do you want really ?

[1] http://www.amazon.ca/Slow-Burn-Stu-Mittleman/dp/0062736744

Edit: Just wanted to add, now I run 10k easily, feel great after each run and dont have any headaches and I think, though i dont really care, i loose weight too. Just keeping the HR under control during the run, thats all you need.

+Newton's Principia as a masterpiece of marketing and for creating the modern scholasticism http://en.wikipedia.org/wiki/Philosophiæ_Naturalis_Principia...

+Descartes' Geometry where he declares that you can choose any line as a unit to measure other lines (your knowledge depends on what you already know, your unit) (p.1) http://www.gutenberg.org/files/26400/26400-pdf.pdf

+Galileo's Dialogues for the realization that real understanding of nature does not come from academic gibberish and research is actually fun http://en.wikipedia.org/wiki/Dialogue_Concerning_the_Two_Chi...

+Dana Densmore's Newton book to understand Principia http://www.greenlion.com/cgi-bin/SoftCart.100.exe/principi.h...

+Slow burn by Stu Mittleman to understand how human body deals with fat and sugar http://www.amazon.com/Slow-Burn-Faster-Exercising-Slower/dp/...

+The Answer John Assaraf about habits http://www.amazon.com/Answer-Business-Achieve-Financial-Extr...

+Paul Graham's essays on education and dropping out of school for early startup http://www.paulgraham.com/mit.html

+Ernst Mach's History of mechanics for its incredible lucidity and classic simplicity http://books.google.com/books?id=8bI3-JSarecC&dq=ernst+m...

+Euclid for its complete lack of physics in it and its beautiful diagrams http://aleph0.clarku.edu/~djoyce/java/elements/elements.html +Aristotle for appreciation of curiosity http://books.google.com/books?id=WWyF4vS8P7UC&pg=PA154&#...

+Bertrand Russel for his humor http://en.wikiquote.org/wiki/Bertrand_Russell and for his Introduction to Mathematical Philosophy Really beautiful book so simple and fun to read... http://books.google.com/books?id=9GK_Fhz5RDUC&dq=introdu...

+Tolstoy's Confessions http://flag.blackened.net/daver/anarchism/tolstoy/confession... For his intellectual quest going in circles

I believe that if you continue long enough in your quest, your research and understandings will describe such a circle. That's not a bad thing, I guess.

How does the world work? The world works the way you look at it. http://news.ycombinator.com/item?id=210104 We see what we believe.

Ooops, I think I am steering away from your question. But I learned something about how the world works from each one of these books.

I totally appreciate your approach to the question from a wholistic view (including the social and human elements) by disregarding academic boundaries.