Your body was designed to move; walk to gather food; lift heavy objects to build shelter; and run to escape danger. All these activities activate muscle fibers which burn calories in order to contract and move your body. Health experts took note as society became more sedentary with the end of the "industrial age." These experts focused on the most "efficient" of these activities. In 1968 American physician Kenneth Cooper coined the term aerobics in his exercise book Aerobics. He used the term to describe exercises that use oxygen to keep large muscle groups moving continuously for at least 20 minutes. Based on this definition, the name aerobics came to refer to calisthenics taught to music. (Encarta) A movement was born and women all over the country bought leg warmers and danced in classes and in front of the TV sweating to the "oldies."

The biology of the "runner's high"
As their classes wore on, and the brain became starved for oxygen and fuel, a funny thing happened to these women. A region of the temporal lobe got more active, a lot more active. This is the same are area of the brain that is activated when religious people "talk to God." Dr. Michael Persinger, who is an expert on this part of the brain, reports that when this part of the brain is activated, people feel an "opiate-like effect with a substantial decrease in anxiety." and a "heightened sense of well being." Millions of women were hooked, literally stoned on aerobics.

This blissful experience is triggered by two activities, meditation/prayer and stress/lack of oxygen. This euphoria is designed so that when it's time to "meet our maker," after being chased to exhaustion, it is a peaceful transition. What this aerobic "runner's high" is covering up is the huge increase in cortisol that accompanies survival mimicking activities -- aerobics, running, spinning, stairmaster, treadmill, kick boxing, etc.

How stress makes you want to eat "junk"
These elevated cortisol levels keep your blood sugar high, and your insulin system working overtime to supply your muscles with the fuel they need to escape "danger." Chronically high cortisol levels also skew your perception of time so you feel rushed during the day and have problems turning off your brain at night so you stay up late feeling that there is more work to do and searching for sweet and starchy foods to feed this permanent "fight or flight" state.

The end result off job related stress getting pushed over the edge by heavy aerobic exercise is a damaging high cortisol state masked by the mimicking of a blissful "near death" experience all of which forces you to over eat sweets and starches, feel guilty adding more stress and more exercise. It's no wonder many people drop out after just a few months and some who get hooked on the "high" fall over dead on the treadmill.

So what's the answer
I'm not saying don't move your body, just concentrate on the other less "efficient" exercises that don't create stress or burn calories, like yoga, pilates, tai chi, weight lifting and walking.