Now that I'm a regular at the gym, coming up on a year, I am quite comfortable concluding that the "cardio craze" is complete bunk. It's of virtually no value whatsoever, and the downsides far outweigh any advantages. I'd love it if my gym -- which is a 5-minute walk, so I'm not about to switch -- would dump all but a few of the cardio machines that take up enormous space, and use the space for crossfit training. How did I come to this conclusion? Well, Art's essay on Evolutionary Fitness (PDF) clued me in and made me aware, so it was in my field of view and I've observed. The adaptive and variable energy demands of our ancestral existence are gone. We live a low energy flux and metabolically unvaried existence in bodies designed for another lifeway. We are hunter/gatherers in pin-stripe suits, living a sedentary life and it is killing us in ways our ancestors never experienced. Virtually all the degenerative diseases–atherosclerosis, diabetes, high blood pressure, osteoporosis, declining muscle mass–of modern civilization are unheard of among hunter-gatherers and were not part of our ancestral experience. Most modern fitness prescriptions are static and agricultural. These programs model the...