By Nanci Hellmich, USA TODAY

Fitness guru Jack LaLanne has pushed people to strengthen the muscles in their bellies, backs and hips for years. So have physical therapists and personal trainers.

Now everyone’s talking about an exercise regimen called “core strength training,” or core stabilization, that targets those muscles.

It’s an element of many Pilates, yoga and other popular fitness programs. Sports-medicine researchers are conducting studies to determine whether building a strong torso can help prevent knee injuries, backaches, ankle injuries and other problems.

Some experts say that having a firm and stable core – the trunk and hip region – helps the other muscle groups and limbs move more effectively in both daily living and athletic performance, says Cedric Bryant, chief exercise physiologist for the American Council on Exercise, a non-profit group that certifies fitness professionals.

Many experts believe people with a weak core have poor posture. Those with strong core muscles can function better in all aspects of their daily lives, so they are better able to lift groceries out of the trunk of a car, carry a toddler, or lift luggage and place it in the overhead compartment on an airplane, Bryant says.

“I think everybody could use a stronger core,” says Mary Lloyd Ireland, an orthopedic surgeon and president of the Kentucky Sports Medicine Clinic in Lexington.

Bert Mandelbaum agrees. He is an orthopedic surgeon in Santa Monica, Calif., and a physician for the U.S. national soccer team.

“You are only as strong as your weakest link,” Mandelbaum says, “so if you have a weak abdomen you are setting yourself up for possible injuries.”

He and Ireland are researching whether core strengthening can reduce knee injuries in female athletes. They believe that women often have weaker hips and abdomens and therefore are more prone to kneecap injuries and ACL (knee ligament) tears. These injuries sometimes occur when athletes come down from a jump or fall, landing straight and hard without bending their knees, Ireland says. Although athletes are encouraged to bend their knees during sports, it’s difficult to do for long periods of time without adequate core strength, she says.

There are many different ways to do core exercises. “Jack LaLanne was the founding father, but there is no patent on this concept,” Mandelbaum says.

There are a variety of techniques and equipment, including special fitness balls, resistance bands, machines and challenging floor exercises, Ireland says.

She recommends seeing a licensed physical therapist, certified athletic trainer or certified personal trainer for a few sessions to get the right exercises for your body. Or she suggests checking out the many Pilates and yoga classes and DVDs that stress core training.

There’s no one right approach for everyone, Bryant says. But he warns that people should be careful not to use overly challenging techniques or devices that leave them at risk of injury.

In the meantime, to feel the core muscles in your abdomen, sit up straight and pull your stomach in, as if you are trying to touch your belly button to your spine. “It almost feels like you are arching your back like an angry cat,” Ireland says.