It's not enough to build muscle and achieve aerobic fitness. You need to think about flexibility, too. Stretching can help.

You may think of stretching as something performed only by runners or gymnasts. But we all need to stretch in order to protect our mobility and independence. "A lot of people don't understand that stretching has to happen on a regular basis. It should be daily," says David Nolan, a physical therapist at Harvard-affiliated Massachusetts General Hospital.

Why stretching is important

Stretching keeps the muscles flexible, strong, and healthy, and we need that flexibility to maintain a range of motion in the joints. Without it, the muscles shorten and become tight. Then, when you call on the muscles for activity, they are weak and unable to extend all the way. That puts you at risk for joint pain, strains, and muscle damage.

For example, sitting in a chair all day results in tight hamstrings in the back of the thigh. That can make it harder to extend your leg or straighten your knee all the way, which inhibits walking. Likewise, when tight muscles are suddenly called on for a strenuous activity that stretches them, such as playing tennis, they may become damaged from suddenly being stretched. Injured muscles may not be strong enough to support the joints, which can lead to joint injury.

Regular stretching keeps muscles long, lean, and flexible, and this means that exertion "won't put too much force on the muscle itself," says Nolan. Healthy muscles also help a person with balance problems to avoid falls.

Where to start

With a body full of muscles, the idea of daily stretching may seem overwhelming. But Nolan says you don't have to stretch every muscle you have. "The areas critical for mobility are in your lower extremities: your calves, your hamstrings, your hip flexors in the pelvis and quadriceps in the front of the thigh." Stretching your shoulders, neck, and lower back is also beneficial. Aim for a program of daily stretches or at least three or four times per week.

Find a physio who can assess your muscle strength and tailor a stretching program to fit your needs. If you have chronic conditions such as arthritis, you'll want to clear a new stretching regimen with your doctor before you start.

The cumulative effect of stretching

Stretching once today won't magically give you perfect flexibility. You'll need to do it over time and remain committed to the process. "It may have taken you many months to get tight muscles, so you're not going to be perfectly flexible after one or two sessions," says physical therapist David Nolan of Massachusetts General Hospital. "It takes weeks to months to get flexible, and you'll have to continue working on it to maintain it."

A hamstring stretch will keep the muscles in the back of your thigh flexible. Sit on the floor with your legs in front of you. Slide your hands down your legs until you feel a burning sensation. Hold for 30 seconds, then slowly return to a sitting position.

Proper execution

We used to believe that stretching was necessary to warm up the muscles and prepare them for activity. However, mounting research has shown that stretching the muscles before they're warmed up can actually hurt them. "When everything is cold, the fibers aren't prepared and may be damaged. If you exercise first, you'll get blood flow to the area, and that makes the tissue more pliable and amenable to change," says Nolan. All it takes to warm up the muscles before stretching is five to 10 minutes of light activity, such as a quick walk. You can also stretch after an aerobic or weight-training workout.

Hold a stretch for 30 seconds. Don't bounce, which can cause injury. You'll feel tension during a stretch, but you should not feel pain. If you do, there may be an injury or damage in the tissue. Stop stretching that muscle and talk to your doctor.