How to Stay in Shape at Any Age

Let's put this archaic idea to bed, once and for all: Your physique is not destined for a downhill slide as you age.

Sure, your body changes as the decades go by, but there's plenty of proof that good diet and exercise habits can override your chronological age, says Barbara Bushman, Ph.D., an exercise physiologist at Missouri State University. After all, a 25-year-old who subsists on junk food and shuns the gym doesn't score a free pass to a sexy bodgenetic freaks aside. Just as the 45-year-old who eats healthfully and makes it to spin class isn't doomed to get frumpy.

"By simply staying active, it's amazing how you can slow down the decline that would otherwise happen," says Bushman.

The key to maintaining your hotness as you rack up birthdays is knowing your body's ever-evolving strengths and weaknesses. Things that can be a struggle at 20, like finding a routine you enjoy, can be second nature by your forties. And stuff you took for granted early on, like recovering quickly from a workout, doesn't come as easily in future decades.

Knowing what you'll encounter will help keep you looking your best at any, and every, age. (Discover how to sculpt a lean body in just 15 minutes a day!)

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In Your 20s

Ah, youth!

Your body is surging with everything it needs to help you perform your best and get into amazing shape. For starters, hormones that aid muscle buildingsuch as testosterone, insulin-like growth factor, and growth hormoneare generally most plentiful in this decade, says Mark Tarnopolsky, M.D., director of the Neuromuscular and Neurometabolic Unit at McMaster University Medical Center in Ontario.

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Not to worrynormal levels of these hormones won't make you look like the Hulk. They just enhance your body's natural ability to build lean muscle and blast fat. And thanks to ample stores of mitochondria (your cells' powerhouses that help drive oxygen consumption, tissue building, and recovery), you're able to rebound from tough gym sessions easily, says Tarnopolsky.

Enjoy your reduced need for ice packs while you can: Studies show that mitochondrial capacity drops with age. Likewise, your fast-twitch muscle fibers (used for quick bursts of speed) are most powerful nowthey tend to shrink and weaken over time, says Tarnopolsky.

Your bone density is also at its highest in your twenties, and your reaction time and balance are at their prime too.

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But this decade isn't without challenges.

In fact, for some it can come with a host of unhealthy habits: Eating for one can mean lots of takeout meals, maintaining a bustling social life can translate to regular bar crawls, and getting ample sleep doesn't usually rank high on the list of priorities.

While it's true your body seems to tolerate greasy food, hangovers and all-nighters when you're young, Tarnopolsky says there are still ramifications.

For instance, a study published in The American Journal of Clinical Nutrition found that just one night of lost sleep can cut your calorie burn the next day. And while one night of gorging on bottomless nachos and margaritas won't kill your figure, making a ritual of it could.

With so many natural advantages stacked in your favor, "this is the optimal time to form positive habits," says Bushman. Make your fitness and health a priority now, and you'll have a strong foundation to build on in the years to come.

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Sharpen Your Skills

Home In on Cross-Training

Young fitness buffs sometimes feel invincible, says Hollywood-based trainer Jeanette Jenkins, creator of the Sexy Abs with Kelly Rowland workout DVD. "That can lead to doing too much or going too hard, which can cause injuries." Keep your routine balanced with cardio, strength training, and yoga or Pilates.

Watch Your Weight

Researchers found that women ages 20 to 25 who were too thin were at increased risk for bone loss. Determining your body mass index (BMI) helps gauge if you're in a healthy range. Use an easy BMI Calculator to determine your body mass index.

Try a New Bedtime Snack

In a small study, participants who had two kiwifruit each night before bed went to sleep faster and slept longer. Raw kiwi contains high levels of serotonin and folate, both of which could contribute to the improved Z's.

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