In Your 30s
Many women face the big 3-0 with dread and anxiety. But you don't need to enter this decade kicking and screaming.Bone mass and the growth hormones that were bursting in your twenties won't dip dramatically just yet. So don't sweat it if you're only now starting to work out—your body still is brimming with natural muscle-building, fat-fighting juices. And if you were hitting the gym regularly in your twenties, the fitness base you developed can really pay off now, especially if you have something like a marathon or triathlon on your bucket list.
There's a reason endurance athletes often peak in their thirties—it's a time when your body's strength, endurance, and coordination come together to create an optimal performance, says Bushman.
More: Why It's Important to Strength Train at Any Age
Also, oxygen efficiency—which helps you knock off longer, harder efforts with ease—often improves with age and training, and it could give you an advantage over your juniors on the racecourse or even just in spin class.
That said, what you've heard about your metabolism stalling and muscle mass slowly shrinking in the later half of this decade is true.
But buck up! Your metabolism is directly correlated to your lean muscle mass, meaning you can stop—and even reverse—the decline with regular exercise. The weight wars people often experience now aren't solely the result of some inevitable physiological process. Rather, they're commonly associated with a drop in physical activity, specifically of the endurance-and muscle-building variety, says Tarnopolsky.
More: 5 Cross-Training Ideas
With families and careers in full swing, "this is a time when a lot of women start to sacrifice their own health, putting other things and people first," says Bushman.
But neglect your diet or exercise regimen for too long and the pounds will creep up--faster than the freshman 15 did.
Music to a busy woman's ears: You can stay fit at this age by working out smarter, not longer.
To get the most out of your precious workout minutes, you have to focus on intensity. In one study, participants who did four to six 30-second all-out sprints on a bike (for a total exercise time of one and a half hours per week) saw fitness increases similar to those of another group who cycled at a moderate pace for a total of four and a half hours per week. Do less, gain more? Tough to argue with that.
(Learn to work out more efficiently by trying these 14 Shape-Up Shortcuts.)
More: How to Lose Those Last Stubborn 10 Pounds
Sharpen Your Skills
Push Your Limit
Add three to five 30-second sprints during cardio sessions, which will rev up your metabolism and allow your body to keep burning calories hours after your workout, says Jenkins. (Or get a similar effect by adding 30-to 60-second cardio blasts, like jumping jacks, in between moves of a strength workout.)
Bonus: High-intensity intervals also strengthen your bones, which will make you less prone to fractures and osteoporosis.
Curb Excess Salt and Caffeine
Both can promote bone loss, says Tanya Zuckerbrot, R.D., founder of the F-Factor Diet. She recommends limiting sodium to 1,300 milligrams a day and caffeine to 200 to 300 milligrams to help reduce that risk.
Muscle Up
A study found that the rate of muscle loss tends to be greater in the lower body than in the upper body.
Adding exercises like squats, lunges, and deadlifts to your weekly routine (at least twice a week) can help slow and even prevent that loss. Beware of the top strength-training mistakes most athletes make to avoid workout injuries.