Vancouver physiotherapist Katie Steele says almost every gym has one: a muscular guy whose six-pack abs pop through his shirt, yet who nevertheless has a massive, distended belly.
Physiques like his, she says, are the prime example of how not to approach core fitness. A strong core will pull the belly in like a corset, Ms. Steele says, whereas a six-pack pertains only to the superficial layer of muscles on top.
So no matter how many sit-ups he can perform, that guy at the gym typifies someone "whose inner core is non-existent," she says.
"It's very easy to work the wrong things if you don't know what you're supposed to be doing," Ms. Steele says.
These days, it's rare to flip through a health magazine or attend a fitness class without encountering the term "core." A glut of workout DVDs are devoted to shaping up the core, and at every turn, six-pack-busting fitness models advertise the myth that a strong core equates to a slim waistline and sculpted abs.
However, among fitness trainers, instructors and health professionals, there are discrepancies over what the buzzword actually means, leading to general core confusion.
The core refers to an entire group of trunk muscles, not just the rectus abdominis that make up a six-pack.
It also includes the transversus abdominis, which are the corset-like muscles that wrap around the belly, the deep lower back muscles, the gluteal muscles, and the pelvic floor muscles, says Agnes Makowski, chairwoman of the sport physiotherapy division of the Canadian Physiotherapy Association.
Some of these deeper muscles don't actually conduct the movements of one's limbs. Rather, they prepare the body for movement, providing control and stability, Ms. Makowski says.
"I think that term is being used quite freely by lots of different fitness and health professionals," she says. "Pilates people are using it. People doing yoga are referring to it. ... There's a lot of different health philosophies that hold [the core]in high regard."
Many fitness industry professionals continue to perpetuate the myth that abdominal exercises, like crunches, are the key to building a strong core, Ms. Makowski says.
"That's pretty old-school training," she says, noting that crunches only help strengthen the superficial rectus abdominis muscles. "The true core [muscles] if you look at it from a scientific medical point of view, are quite deep ... and they're difficult to see."
Toronto kinesiologist Angela Pereira, who uses the terms "core" and "trunk" interchangeably, explains that since the core is made up of several different layers of muscles, it's important to start with the inner-most layer, consisting of the diaphragm and transversus abdominis, which aid in breathing.
As president of Toronto's First Line Kinesiologists, Ms. Pereira says, she frequently sees clients who have injured themselves, straining their backs, shoulders, necks and hamstrings, by performing core exercises incorrectly.
"People [are]pushed in ways that they aren't quite ready for ... so they compensate just to get the movement done," she says.
Pilates and yoga instructors often start off by teaching deep-belly breathing techniques, which require people to expand their bellies as they breathe in and exhale as they bring their belly buttons toward their spines.
But, Ms. Pereira says, "That's actually not the proper way to breathe." Instead, she says, proper breathing involves the expansion and contraction of the rib cage, without any notable movement in the stomach area.
Done incorrectly, core workouts can make people more susceptible to injury over time, since repeatedly stressing the wrong muscles can cause shearing forces on the joints, leading to wear and tear, Ms. Steele says.
That's no reason to think the core is overrated, however, she says. A weak core is often the culprit behind those injuries that seem to occur later in life without any apparent reason.
"It'll be like, 'I twisted wrong,' or 'I went to pick up a shirt off the floor and I hurt my back.' So an awareness of your core is very important and should start right away," Ms. Steele says.
Fortunately, Ms. Pereira says, activating the core is easier than most people think. Whether you realize it or not, you engage your core muscles with almost any movement you make, if you maintain a good posture, she says.
"You can be standing and lifting dumbbells and your trunk muscles all have to turn on to keep that trunk stable, otherwise you'd be like a piece of spaghetti," Ms. Pereira says. "You don't necessarily have to do trunk exercises to have a strong trunk."
Still, for those looking to further improve their core strength and stability, Ms. Steele stresses the importance of clearing up any lingering confusion.
"It's always a great idea if you're going to start core, or if you're training with someone and they say they're going to give you some core exercises, just to ask 'Well, what is the core?' " Ms. Steele says. "And if you don't understand, ask them again."
How to work that core
Abdominal crunches alone won't develop a strong core, but Angela Pereira, president of Toronto's First Line Kinesiologists, offers these three basic exercises as part of a well-rounded core workout:
Opposite arm and leg raise
On your hands and knees, extend one arm and the opposite leg. Hold for up to 10 seconds, and repeat for 10 to 15 repetitions. Do the same on the other side. Pay close attention to the shoulders and hips, ensuring the trunk is flat with no rotations.
Modified side plank
On your side, bend your bottom elbow, propping it beneath the shoulder. With both knees bent, push the upper part of your body off the floor with the other hand, so your hips are shifted forward and the spine is in a straight line. Face directly ahead of you so that a straight line can be drawn from the top of your head to your pelvis. Hold and repeat with the other side.
Lie on your back, with knees bent. Contract your rear muscles to lift the hips. At the same time, slightly push forward onto the balls of your feet to contract the thigh muscles at the same time. Make sure you're sparing your lower back and hamstring muscles.
You should feel this most in the thighs and rear.