Pack Protein to Drop Pounds

The more regularly you use these pathways, the more your muscle memory solidifies, even if you slack off for a while. Ohio University researchers put a group of women on a two-days-a-week strength-training program for 20 weeks, then let them lounge around for eight months. When they called them back to the gym along with a group of women who'd never lifted before, they found that the previously trained women had retained most of their muscle fibers. When they started pumping iron again, they made gains more rapidly than the women who had no history of strength training.

The same principle applies to any exercise, says Lee Hong, Ph.D., an assistant professor of kinesiology and neuroscience at Indiana University at Bloomington. "If you lay off an activity for too long, you'll get rusty, but those patterns are locked in," says Hong. "That's why, even after 10 or 20 years, you can get back on a bike and ride."

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Get Smarter Every Day

Until recently, researchers believed that these ingrained neuromuscular patterns were the primary reason for the rebound-after-a-layoff effect. But Norwegian scientists recently discovered something else that may be a game changer in the way we understand how the body gets—and stays—fit. Turns out, exercise also triggers longterm, possibly permanent, changes in your cells. In a study of mice, researchers found that after just six days of simulated strength training, the mice generated new nuclei in their muscle cells. This is a big deal, since these nuclei contain the DNA blueprint necessary to make new muscle. And months after the mice stopped training, even though their muscles had shrunk, those newly formed nuclei were still hanging around, waiting to be reactivated by exercise, says study leader Kristian Gundersen, Ph.D., of the University of Oslo. "It's not unrealistic to suspect that human muscles respond as quickly and that those nuclei last for decades, or even a lifetime," he says.

The more exercise you do, the more memory you can bank and the easier it is to make deposits. "It's like a health savings account," says Hong. And as with any savings account, it's best to start early—like now. Gundersen's research found that the ability to make new muscle decreases as you age. "The earlier you start and the more you build, the better off you'll be later in life," says Hong.

Your Body Never Forgets
There's no getting around this: If you take a few months (or years!) off from exercise, you will huff and puff and feel achy as your body gets back into the swing of things. But if you establish a history of fitness, your pain will be a lot more manageable. Any sweat equity you invest forges a cardiovascular and strength blueprint that helps you make gains faster and be less prone to soreness and injury than someone who has never lifted anything heavier than a glass of merlot or has run only when chased.

Lose More Weight

And there's more good news: Muscle memory's impact extends beyond general fitness. The physical changes your body undergoes while building a fitness platform help speed up your metabolism, make you more resilient to stress, and bolster your immune system, says Kraemer. "All these adaptations become ingrained physiologically," he adds. Muscle memory not only helps you get more from every workout but also "spills into your everyday life, making you a better-functioning human being."

Up Your Retention
Muscle memory has an evil alter ago called "the plateau." As you repeatedly do a task, your body becomes more efficient at it. This has upsides (see "Getting Better with Age," below) along with downsides. Your body can become so efficient that it actually recruits fewer muscle fibers to do the job.

To make your muscle memory last, you need to shake things up. On the strength side, "daily undulating periodization" (like the plan on the following pages) will help keep your muscles on their toes. Changing your cardio (going for a swim or taking a Zumba class, for instance) will challenge your body in fresh ways. Also, add intervals to your cardio routine once or twice a week. It's as simple as tossing in 30 seconds of speed. Research shows that max-effort 30-second sprints (four to six of them, with a few minutes of rest in between) are as effective as longer one-speed workouts for building and maintaining fitness.

Getting Better with Age
To understand the impact of muscle memory, look at the women who are crossing the finish line in first place these days. Of the 40 elite female athletes who competed in the 2008 New York City Marathon, nearly three-quarters were over 30, and more than a third were over 35. Women, it seems, are finding their stride in their thirties. Or in the case of swimmer Dara Torres, who won three Olympic silver medals in '08, even their forties!

Be Happy

It all comes down to efficiency, says Wayne Westcott, Ph.D. "Mature athletes have an enormous fitness base and perfectly ingrained movement patterns, so they're amazingly efficient. Being able to go very hard and very fast while not wasting an ounce of energy gives them the advantage over competitors who are younger and less experienced."

That's also why it's not unusual for average women who weren't star athletes back in high school to start winning medals at local road races and triathlons once they hit their thirties. Years of steady exercise and fitness accumulate and give them an edge.