THE POWER OF PERTURBATION

Let's slow down for a moment, and ask ourselves why strength training has a bigger effect on metabolism and post-exercise fatburning than endurance exercise. I think there are two key reasons. First, there's the inefficiency factor. When you hear your boss use a word like "inefficiency," you know someone in the office will soon be using monster. com as her home page, and you hope it's not you. But when we talk about inefficient exercise, we're talking about routines that require more effort. Your body isn't used to the exercises yet, or hasn't fully adapted to the exercise parameters, and thus has to work harder to get through the routine. Harder work means better results-you'll burn more calories during the workout, and you'll burn more afterward, when your body is recovering. In other words, inefficiency is the ideal. The problem with a repetitive routine, like running or cycling, is that your body makes adaptations and gets progressively more efficient. Those adaptations allow you to go farther and faster in your runs or rides, which is good if your goal is to be an endurance athlete who goes farther and faster. If your goal is to be leaner, then greater endurance isn't really to your benefit; the increased efficiency means you use fewer calories per unit of exercise. Here 's a study that illustrates the problem: Back in 1990, researchers at the u.s. Department of Agriculture published a study that compared the effects of diet and exercise versus exercise alone for overweight women. The diet was extreme, cutting the women's daily calorie intake by 50 percent. Both groups of women did six days a week of steadypace endurance exercise, thirty-five to forty minutes a day. The diet-pIus-exercise group lost a boatload of weight, as you can imagine-29 pounds in twelve weeks, on average. Unfortunately, a third of it was muscle, which meant their resting metabolic rates slowed down by an average of 9 percent. The exercise group also lost weight, about 13 pounds per person, but only 14 percent of it was lean tissue, and their metabolic rates stayed the same. But the really, really startling finding is that the first group became so efficient at endurance exercise that they burned 16 percent fewer calories when doing it at low intensities. The exercise group also got more efficient, but only burned 8 percent fewer calories. (I should note that the effect disappeared at higher intensities of exercise, which gets back to what I said earlier about the importance of working harder versus longer.) One more negative effect of chronic endurance exercise: Your body will adapt to the increased efficiency by selectively shrinking your type I muscle fibers. Yes, literally, those fibers get smaller as they get better at running or riding. The effect may not be dramatic, but it illustrates how endurance exercise makes your body more efficient, which is to say better at going longer distances with less fuel. If you're trying to get your body to burn more fuel, you can see the problem here. The same problem arises with strength training, if you forget the "strength" and focus on the "training." Doing high-repetition work with light weights simply makes your muscles more efficient at lifting light weights, which is a surefire way to shrink your muscles and reduce their ability to burn calories. Heavier lifts, as you can imagine, are inherently less efficient than lighter lifts . They require a bit more energy to perform, but consume a lot more energy as your body recovers from them. Imagine a lower-body workout that includes leg presses versus one in which you do squats with a barbell on your shoulders. For the leg press, you're merely straightening your legs by pushing on a platform that, by virtue of its 45-degree angle, is designed to be easy to push. Contrast that with barbell squats, in which most of your body's muscle fibers are involved in either lifting the weight or keeping your body upright while you lift it. The squatting movement is natural-we do it every time we jump or get up from a chair-but the heavy weight and the difficulty of keeping it balanced on your shoulders make it extraordinarily inefficient. That inefficiency flips all the switches on what's called your sympathetic nervous system. Again, forget that the word "sympathetic " has warm and fuzzy connotations in most of its uses. When we're talking about our nervous system, "sympathetic " involves the heavy-duty stuff, the stress hormones that trigger our fight-or-flight responses. It's your body's internal equivalent of a smoke detector. Activating the sympathetic nervous system means your adrenal glands are kicking out adrenaline and other stress hormones, your heart rate and blood pressure increase, and your bronchial passages widen. Your body's core temperature increases, your sweat glands open, your pupils dilate, and you might even get goose bumps. We're conditioned to think that all these things are bad, but in the context of a workout, they're actually good, since without this festival of stress, you wouldn't be able to work as hard in the weight room. And your body wouldn't burn as many calories, or use as much fat for energy, while you' re recovering. In other words, the real key to successful strength training is metabolic perturbation. You're shaking things up in your muscle cells, your nervous system, and your hormones. The calories you burn while throwing so much of your body into the spin cycle can be modest or substantial, but they're only part of the effect. What your body does afterward, when it's trying to recover, has at least as big an impact on your physique as the calories used while you're actually lifting. Could you shake things up with endurance exercise? Sure, if you do intervals, which are a mix of all-out and easy efforts, rather than running or riding at a steady pace. But at that point, you're shifting away from your exclusive use of your aerobic energy system and using one or both of your anaerobic systems. In other words, you've stopped doing "aerobics" and started doing something that resembles strength training, at least in terms of energy. You're selectively using glycogen-fueled movement with the goal of forcing your body to use more fat while it recovers. And that's exactly what Alwyn wants you to do.This is as good a place as any to emphasize something that books like this usually ignore: the way your genes influence your results. Those who study weight loss acknowledge that no two people will process calories the exact same way, unless those people are identical twins. If you set out to compose a list of every exercise- and diet -related variable that's genetically dependent, you'd start with these: • strength • aerobic capacity • body-fat percentage • body-fat distribution • spontaneous physical activity (how much you move on any given day) • how many calories you burn during digestion (a phenomenon I'll address in the next chapter) • resting metabolic rate Different studies attach different numbers to all those variables, but most seem to settle into the range of 30 to 40 percent. So when you lift, for example, your genes probably determine about 30 to 40 percent of the results you get. When you diet, your genes weigh in on how your body reacts-how much fat you lose, where the fat comes off, the degree to which your metabolism slows down. But here's a cool fact to know: Exercise intensity trumps genetics. The harder you work, the less influence your genes have on the results of that work. The tipping point seems to be when you're working at a pace that requires six times the energy you'd use at rest, which researchers abbreviate as "6 METs." (For a list of exercises and activities and their MET values,