Your body—and fitness—changes a lot sooner than you thought.
Read on to learn when you burn the most calories, if your muscle is
already waning, and how you can become fitter, stronger, and faster with
every decade.
In Your 20s...
Your Body's Built for Exercise
The 20s are prime time for fitness. (Okay, maybe you’ve gained a few
pounds since you ran high
school track, but some of that weight is probably from muscle.) That’s
because, during your 20s, estrogen, progesterone, testosterone, human
growth hormone, and thyroid hormone are all working together to keep you
in tip-top baby-making shape. As an added bonus, they improve your
body’s muscle-building power, she says.Meanwhile, during your 20s, you
are at your peak cardiorespiratory capability, says board-certified
internist Sue Decotiis, M.D., a medical weight-loss and
bioidenticial hormone-replacement therapy expert in New York City. Bring
on the endurance races.
But Your Metabolism Is Already Slowing
Womp, womp. After 20, the average basal metabolic rate (BMR), the number
of calories you’d burn if you stayed in bed all day, drops by one to
two percent per decade, according to the American Council on Exercise.
Most of that dip may be due to the unfortunate fact that when most women and men
enter the “real world,” they sit at a desk more and walk around less.
At any age, increasing your activity levels and muscle mass can help
keep your BMR high. Muscle makes up a large part of your body’s
“engine,” so the more muscle you have, the more fuel you’ll burn,
whether you are hanging out with friends or powering through a workout.
In Your 30s...
DHEA Declines
Levels of this guy, which is a precursor to both estrogen and
testosterone, peak in your 20s and start tapering off once you hit the
big 3-0. While it’s not clear if DHEA supplementation can have any
effect on anti-aging, according to the National Institute on Aging, the
loss of DHEA as you age may slow your exercise recovery time and
increase your body’s muscle-to-fat ratio, says Decottis. To help combat
fat gain, focus on strength training. In a new study from Harvard University,
men who lifted weights each day for 20 minutes put on less belly fat as
they aged compared to guys who spent the same amount of time doing
cardio.
Babies Block Your Workout
With your doctor’s permission, you can keep up your workout routine with
a bun in the oven. But pregnancy is not the time to start a
high-intensity training program. Your body is going through enough
changes as it is. During pregnancy, your hormones shift, and your body
focuses the bulk of its energy on the pregnancy, not your muscles, says
Kaehler. After the baby comes, breastfeeding can burn crazy calories,
which helps some women lose the pregnancy weight. But still, it’s not
the right time to push your workout to the max, says Hamilton. “Trying
to train at a high level immediately after giving birth is risky because
hormones are not balanced back to ‘normal’ as long as you’re
breastfeeding," she says. "I’ve seen an increased incidence of stress
fractures in women who push to train at a high level during the
postpartum period. I recommend training be moderated until after
breastfeeding has ceased and normal menstruation has returned, which to
me signals that the woman’s hormonal balance is back.” Once your baby
has permanently detached from your nipples, though, you can crank up
your workout’s intensity.
In Your 40s...
Sarcopenia Sets In
A fancy word for muscle loss, sarcopenia is a natural part of the aging
process—but it still sucks. While it doesn’t hit full force until around
75, The Journal of Nutrition, Health & Aging suggests
that it can start as early as 40. Researchers believe most muscle loss
comes from your fast-twitch muscle fibers, the ones that are responsible
for powering high-intensity, largely anaerobic exercise. “In order to
minimize the effects of sarcopenia, it is helpful to do strength
training, which recruits different muscle fibers [your fast-twitch
ones], compared to endurance training activities like biking, swimming,
and running," as those train your slow-twitch, endurance-focused ones,
says Hamilton. Increasing your protein intake may also help. Eating
twice the current RDA of protein (1.5 grams instead of 0.8 grams of
protein per kilogram of body weight) increases the rates of muscle
growth and lessens muscle breakdown due to aging, according to research from the University of Arkansas for Medical Sciences.
You Enter Perimenopause
Menopause isn’t an on-off phenomenon. It happens gradually, typically in
the 40s (or sometimes even earlier) with perimenopause. Common
symptoms, like irregular periods, are due to fluctuations in estrogen
and progesterone, which can also cause weight gain and a lower
metabolism, says Decottis. What’s more, during perimenopause, insomnia
and night sweats can make finding the energy to work out more
challenging, says Hamilton. Still, continuing to exercise will not only
help you feel younger—after all, exercise can ease your hot flashes and
sleep troubles—it may help you look and perform even better than you did
at 20. “Some women don’t even start training until later in life,” says
Hamilton. “Whatever your age, you can improve your fitness.”
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