Your 40s continued...
One of the best ways to strengthen quad muscles, she says, is to ride a stationary bike -- and you can get results from just 10 minutes twice a week. Don't have a bike handy? Litman says you can get similar results by sitting in a chair, then standing up, 20 times -- using only the power of your legs to lift your body.
"I always encourage my patients in their 40s to start protecting their knees with the quad workouts, especially if they have a family history of knee problems," says Litman.
In terms of cardio workouts, Carmichael says, it's safe to continue the routines you started in your 20s and 30s. This can include any form of activity that gets your heart beating faster -- like power-walking on a treadmill or doing step aerobics -- at least twice a week.
To get the most benefits from these workouts in your 40s, Carmichael suggests, work out shorter but harder.
"Studies show if you cut down on duration but increase intensity after age 40, you get more benefits than if you do that before age 40," says Carmichael. "The cardiovascular benefits will increase and that can help reduce the onset of hypertension."
If you were an avid exerciser in your 20s, 30s, and 40s, by age 50 you may begin to experience the cumulative effect of wear and tear on joints and bones. So you might not be able to participate in the kind of fitness activities you enjoyed before.
But if you haven't worked out much, experts say you're likely to begin feeling an entirely different set of aches and pains -- those that result from years of inactivity. And this can curtail your daily activities.
The good news is that no matter where you find yourself on the fitness scale, there's a safe and healthy workout for you. But where do you begin?
"By age 50, women start to experience some serious loss in muscle tone and bone density, so these are two of the areas your fitness routines should focus on," says Carmichael.