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A decline in physical fitness is not a consequence of aging, according to the National Institute on Aging (NIA). Many frail older adults got that way because they stopped exercising. Many chronic health conditions are made worse by lack of physical activity. Even if you haven't been active, it's not too late to start. Be sure to check with your doctor before beginning an exercise program. Start slowly and build up gradually. That might mean exercising for only five to 10 minutes at first, but over several months, you can increase your time to 30 minutes a day.

Getting enough exercise during the day can actually help ease insomnia, according to the National Institute on Neurological Disorders and Stroke. It is best to avoid vigorous exercise in the evening before bedtime, as this can cause you to be more awake.

You don't have to get all your exercise for the day at one time, according to the CDC. You can break up exercise into short periods -- in 10-minute chunks, for example -- with rest in between. You might garden in the morning, for instance, and swim in the afternoon. An exercise log can help you keep track of how active you are. Another benefit is that you can track your progress over time, which can help keep you motivated to exercise regularly.

The NIA says that even if you must spend most of your time in a wheelchair, you can still exercise. Here's a sampling of exercises you should be able to do: flexibility exercises for fingers, wrists, and feet; neck extensions; simulated swimming strokes with your arms (crawl, breast stroke, back stroke) to stretch your shoulders; back stretches; leg extensions; and arm curls.

A set of dumbbells is nice to have, but you can use substitute items: a bucket of soil, a stone, a brick, or a can of food, the NIA says. For many strength exercises, such as leg extensions and heel raises, you can simply use the weight of your body as the resistance.

These are the core parts of any good exercise program, no matter what your age, the CDC says. Flexibility exercises help maintain your range of motion. As you age, your muscles tend to lose their elasticity, and tissues around the joints thicken. These exercises help counteract this, as well as slow down the development of arthritis. Strength training helps halt the loss of muscle tissue that occurs as you age and helps prevent back problems. Endurance exercise, also called aerobic exercise, boosts the health of your heart, lungs, and blood vessels, as well as giving you more energy. Weight-bearing aerobic exercise also can stimulate bone growth and make your bones healthier.

The CDC says that walking is a great aerobic exercise because it's easier on your joints than running, and the massaging action of your leg muscles on your leg veins improves the flow of blood back to the heart. Walking also strengthens your leg muscles and improves your balance, helping you avoid falls. Other advantages to walking: It's free, it can be done just about any time, and it has the lowest rate of injury of any exercise. Other good choices for aerobic exercise include biking and golfing (as long as you're walking the fairways). Activities like gardening and playing with your grandchildren also can count toward your daily activity time.

You can get a great workout by doing water aerobics, or walking in the water, the NIA says. A bonus is that the buoyancy of the water is easy on your joints. Swimming can be a better exercise than walking for people with diabetes who have lost feeling in their feet. For most people, however, an aerobic program should also include weight-bearing exercises, such as walking or dancing, to maintain good bone health.

Huffing and puffing can mean you're pushing yourself too hard. The CDC says that you should be able to maintain a conversation at the pace you've set. If you can't, slow down.

No matter what your age, if you sweat, it means you're losing fluids, the NIA says. Older adults may not feel thirst as quickly as younger people, so it's especially important to make sure you drink water before, during, and after exercise.