Cardio Confusion

Quoting JD Johannes:

How can something so logical as burning more calories through cardiovascular exercise not result in sustained fat loss?  The answer is in your body’s ability to adapt to exercise and the complex functions of the hormone cortisol.  The conventional wisdom of cardio is the energy in vs. energy out formula.  Burn more calories than you eat and you will lose weight. ... But the simple fact remains that even if you did create a 500 calorie deficit every day through exercise, you will not be able to exercise yourself out of existence.  Your body will adapt to the workload. [...]

According the University of New Mexico’s Len Kravitz, the critical level that results in excess cortisol secretion occurs after about 45 minutes of exercise -- some people hit the critical level earlier, others later depending on a variety of genetic and other variables. ... When cortisol puts the body in a catabolic mode while doing cardio vascular exercise the muscle is burned instead of fat.  For every pound of muscle that is burned, your resting metabolism slows down a little bit.  If your energy intake from food is not adjusted to the loss of muscle, you have a calorie surplus and will gain fat while doing lots of cardio.

He goes pretty deep into the science behind these ideas, and makes the case that High Intensity Interval Training is a good way to avoid the cortisol signaling that’s caused by sustained cardio and which results in muscle burn instead of fat burn.