Momentum

"The [afterburn] hypothesis goes something like this: When you exercise, you rev up your body's metabolism. Because things in motion want to stay in motion, even after you stop exercising, your body's engine continues to rev for some time following the workout. Thus, even once you stop running, you continue to burn up more fuel for some period following exercise. The only problem with this hypothesis is that it hasn't always held up in research studies. Some have found no post-exercise effect. Others obtained results that were negligible. Yet others identified significant afterburn - to the tune of hundreds of extra calories."—Adam Cohen and Dr. Stephen Prescott, The Oklahoman, "Is exercise 'afterburn' real?" 24 May 2011. (link)

"This is your body on chairs: Electrical activity in the muscles drops — “the muscles go as silent as those of a dead horse,” Hamilton says — leading to a cascade of harmful metabolic effects. Your calorie-burning rate immediately plunges to about one per minute, a third of what it would be if you got up and walked. Insulin effectiveness drops within a single day, and the risk of developing Type 2 diabetes rises. So does the risk of being obese. The enzymes responsible for breaking down lipids and triglycerides — for “vacuuming up fat out of the bloodstream,” as Hamilton puts it — plunge, which in turn causes the levels of good (HDL) cholesterol to fall. […] Sitting, it would seem, is an independent pathology. Being sedentary for nine hours a day at the office is bad for your health whether you go home and watch television afterward or hit the gym. It is bad whether you are morbidly obese or marathon-runner thin. “Excessive sitting,” Dr. Levine says, “is a lethal activity.”—James Vlahos, New York Times, "Is Sitting a Lethal Activity?" 14 April 2011. (link)

"The brain is ravenous. Though just 2 percent of the body’s mass, it uses 20 percent of its resting energy, and the body’s other main sources of energy—amino acids, which are broken down from proteins, and fatty acids and glycerol, which are broken down from fats—cannot power the brain. This is a bother, because we store pound on pound of fat, which most of us would just as soon burn for fuel, whereas we store only a few ounces of glycogen. Our brains are thus on a nearly constant prowl for sugar. There is, however, a fallback: ketone bodies, which are highly acidic compounds created when fatty acids are broken down for energy. The best-known ketone is acetone, as in the clear flammable liquid used to remove nail polish and scour metal surfaces before painting. Once thought to be waste products, ketones are in fact fuel—and fuel that can power the brain.—Steve Hendricks, Harper's Magazine, "Starving your way to vigor." (page 51)