As we age, our bodies change. As time goes by, we need to pay attention to new health concerns�things we may never have given much thought to in younger years. One such concern is remaining mobile, a paramount consideration as we age. Being active may even enhance our brainpower. Some studies suggest that activities such as jogging create new cells in parts of the brain that are important for learning and memory not to mention the healthy effect on our cardiovascular systems. But while walking and running are great for the heart, they don�t do much for strength, particularly in upper body muscles, which is why you still may have trouble lifting a box of books even though you�ve been walking 20 minutes a day, three times a week.

The body contains 600 muscles that power our every move. Muscles are comprised of tiny tissue bundles clustered into units. When these units receive nerve impulses, they release chemicals that cause the muscle fibers to contract and relax repeatedly. But our bodies do not maintain unused muscle. Hence, muscle wastes away, and we get flabby. Strength training stimulates muscle cell growth and increases enzyme production that helps store and use energy.

No matter what your age, strength training can turn back the clock and make your body physically and metabolically more youthful. Strength training can help you stay healthy and agile, adding a vital dimension to any present running or walking routine. Still not convinced? At Tufts University in Boston, researchers put a group of people up to age 80 on a weight-training regimen that included 30 minutes of strengthening exercises three days a week. After 12 weeks, the group gained 3 pounds of muscle and lost 4 pounds of fat. And if your goal is thwarted by a lack of time, you can notice a difference in how you look and feel with just 20 minutes twice a week. Actually, there are plenty of reasons to hoist a barbell, dumbbell, or hand weight:

• Limits body weight. Fat just sits there, but muscles take energy to maintain, and that means calories burned.

• Protects joints. They get less wear if muscles around them are strong.

• Preserves bones. As they adapt to weight training, bones gain strength.

• Improves process of sugar. Studies indicate that this may help stave off a form of diabetes.

• Boosts body functions. Balance, coordination, and agility improve.

Here�s the plan: You need to work your major muscle groups with either weight machines or free weights in just one set of six to eight repetitions. (Although any form of strength training can help you get strong, free weights�used properly�provide a full range of motion and work both sides of your body.) Major muscle groups include three areas: upper body (arms and shoulders), lower body (hips and legs), and trunk muscles (abdomen and spine). The trick is to lift the heaviest weight you can and work those muscles to the point of fatigue. Tip: Use enough weight so you�re making an effort but not straining. If you have never lifted weights before, you may need a partner to act as a "spotter."

A beginner�s routine of eight to 10 exercises should take 15 to 45 minutes, depending on the number of repetitions and sets. If all goes well, you should feel the benefits in four to six weeks. Whether you decide to join a gym or lift weights in your bedroom, remember that the benefits include feeling and looking strong and healthy. If nothing else, a weight lifting routine practiced twice a week will not only help you climb stairs more swiftly, it will help you lift your grandchildren more easily. And that fact alone makes it all worthwhile.