How to Stay Fit Over 40

Why time is key (even for celebrities).

Jemal Countess/Getty ImagesHalle Berry

Jennifer Aniston, Courteney Cox, Halle Berry ... these days, when a 40-something woman steps out in a bikini, it makes news.

Turns out, there's a scientific explanation for why we're so fascinated by these lean, toned, impossibly supple bodies. In some ways, these apparent genetic wonders are defying the aging process.

"Once a man or woman gets beyond their 30s, they're in a situation where unless they are really proactive about what they do from an exercise standpoint as well as eating sensibly, they are going to lose some muscle tissue," says Cedric Bryant, Ph.D., FACSM, Chief Science Officer for The American Council on Exercise.

But that extra pudge is not all your fault -- really. Research shows that about half of these changes in appearance can be attributed to the normal aging process, and the other half is often due to simply not having enough time to exercise.

"One of the things that tends to happen for women -- particularly because of the demands that women around that age tend to have from their kids and at work -- time becomes a tremendous challenge for them to maintain whatever fitness habits they may have had until that point," Bryant explains.

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In fact, even the stars are watching the clock when they work out.

"Celebrities, just like you and I, are always looking for what will yield the best results in the least amount of time, period," reveals celebrity trainer Gunnar Peterson, who has worked with 40-somethings like Jennifer Lopez as well as younger stars like Kim Kardashian.

In other words, rocking a six-pack like J-Lo at 42 has less to do with being genetically gifted and more to do with hitting the gym on a regular basis. Or more importantly, having the time to hit the gym on a regular basis. Which most women in this age group don't have.

"[Typical 40-something women] start to exercise less, they eat on the go more and the body composition of lean tissue and fat tissue gets flipped, meaning there's greater fat and less muscle tissue, which doesn't support the same level in terms of metabolism," Bryant says. (Because muscle is more metabolically active than fat, if you maintain more normal body composition, you're going to be able to maintain a more normal metabolism.)

"All these factors combined lead to that creeping fat development known as middle-aged spread. That gradual subtle weight gain that happens where by the time you're in your 50s, you're like, 'How did I become my mom?'

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