CURRENT REGIMEN: Yoga, 2-4 times/week

The practice of yoga has stood the test of time because it does an excellent job teaching the body total balance and flexibility, as well as tuning you in to the connection between breath and movement. It strengthens the torso's core muscles and, from there, allows you to connect, say, the power of your legs to your ground strokes on the tennis court. Yoga also heightens the mind-body connection, says Mohr. “And being in tune like that makes every movement easier.”

What's missing

“Yoga's not a weight-bearing exercise,” says Hyman. “And that's a critical need for women — especially postmenopausal women, who need to worry about osteoporosis. The impact of running spurs your bones to grow stronger.”

Although moving through yoga poses does provide some aerobic benefit, it doesn't compare to the high-intensity cardiovascular workout that comes from Spinning class or a run. Those efforts do more than nuke fat and leave you breathless; they strengthen the most important muscle in your body — the heart.

“A good, hard bit of cardio completes what I call the circle of fitness,” says Hyman. “Endurance, flexibility, strength, and a strong heart are all necessary to grow healthier.”

The fix

Hyman recommends running at least three times a week for 30 minutes or longer. After a 10-minute warm-up, do 15 minutes of high-intensity intervals, then take 5 to 10 minutes to cool down. Vary the length of your intervals: One week, do 1-minute sprints followed by 1 minute of easy jogging. The next week try 3-minute sprints followed by 3 minutes at a slower pace.

If running is too hard on your joints, do intervals by hiking up a steep hill. “You'll get your heart rate up, and the hike down will provide some stimulus for bone growth,” says Hyman. Or get your interval workout on a bike, elliptical trainer, or in the pool. To strengthen your bones, though, you need to do a couple of sets of multijoint weight-bearing exercises such as lunges. Start with ten lunges per leg and work up to 30, making sure your front knee never bends past your ankle. Keep your back straight and your chest open. For a bigger challenge, hold 5- to 10-pound free weights in each hand.

Fitness and health writer Grant Davis runs marathons, races mountain bikes, and does 100-mile bike rides from his home in Colorado Springs.