If the muscles of your body have a first sergeant, it’s the core.

The muscles of your core – in less trendy times, called your trunk – comprise the most important muscles in your body, say experts, because all the other muscles rely on them being strong and stable.

The weaker your core, the weaker you are. If you have disabilities, your core is often what determines your level of disability; if you think you’re a rough, tough athlete, a weak core will shorten your career.

That’s why experts say if you’re going to pay attention to one area of your body, the core is the place to start.

The core is an array of muscles from your chest to your hips. They maintain balance, ensure stamina, keep you upright and protect the routes between your brain and your appendages.

There’s some disagreement on the scope of the core. Some say it’s the midsection from the neck to the pelvis – about 50 muscles. The more common definition is that it starts at the diaphragm to just above the pelvis, or the “pelvic floor.” Some say it includes parts of the gluteus (buttocks) muscles.

The National Institutes of Health describes it as the center of everything, composed of 29 muscles.

Tricia Austin, assistant professor of physical therapy at St. Louis University, likes the NIH description. She says you should think about the core as a box that keeps you upright.

“It acts like a stabilizer, a belt that helps stabilize our midsection and back, the spine,” she said. “It can add stability so that we get good motion with our arms and legs in the activities we do throughout the day, particularly with athletes and sports performance.”

Austin specializes in physical therapy and training of athletes, working mostly on SLU athletes.

However, “It’s not just athletes who need the core. People also need the core to pick up their child, get groceries out of the car or do yard work,” she said.

Even athletes can be fooled about their core strength.

“It’s not just strengthening them, it’s also being able to (use) them,” she said. “Someone may look strong having (nice abs), but in reality, they don’t use the other muscles of the core, so the strength in their midsection may not be as strong.

“And it might be strong, but they don’t know how to use those muscles, to recruit them, when we need to. An example is swinging a bat. How do you get all of the muscles that come into play to work together?”

Contrary to common belief, the abdominal muscle – the rectus abdominis – that gives you the six-pack is not by definition a true core muscle, because it runs vertically instead of horizontally, according to Keath Hausher. He’s a St. Louis-area athletic trainer who runs fitness boot camps and helps design athletic training programs for the U.S. Military Academy at West Point.

More than ab work

Experts agree that true core muscles wrap around the midsection and hold everything inside together. Still, the same exercises that work the ab muscles can certainly help the core muscles. But you need to do more than just ab work.

When it comes to developing the core, one size doesn’t fit all, said Renee Ivens, a physical therapist at Washington University School of Medicine. Ivens explained that someone who’s built with wider hips will have different needs than someone with a more flexible spine. Shorter midsections can be exercised differently than longer midsections.

The vast majority of her patients’ problems start with core weakness. In other cases, problems start with overexercising parts of the core without exercising other parts enough, which can lead to soreness, imbalance and strain.

Get a referral

It’s a good bet to start with your family doctor before starting a core exercise program. Depending on what you need, you could get a referral to a physical therapist.

Otherwise, you can visit a physical therapist for an evaluation without a doctor’s referral, but you’ll probably pay from $50 to $150 for an evaluation.

Personal trainers – even those with good credentials – aren’t trained to work with any information that you don’t bring to them, experts said, which is why you want to start with an evaluation by a licensed medical professional.

But at the most basic level, Ivens said you can do some core exercises that don’t require much preparation.

“Just pull in the abdominals a bit,” she said. “That would be good for almost anyone to do.”