Chubby Yoga pants Virginia

The two figures standing in front of me one recent winter morning could not look more different. On the right is Carrie McCulloch, MD, a musculoskeletal anatomy expert and the medical director for Kinected Pilates studio in New York City, who is sizing up the shape of my waistline. Dr. McCulloch's own midsection happens to be perfectly rounded because she is only weeks away from giving birth to her first child. On the left is her assistant, Mr. Bones, one of those hanging skeletons that teach medical students how the thigh bone's connected to the hip bone. Mr. Bones doesn't actually have a waist, just a hollow space between his ribs and pelvis.

Dr. McCulloch is demonstrating how this inner bony foundation can set the stage for your torso's outer appearance, tapping the stacked bones that make up her assistant's spine.

I ask Dr. McCulloch how I ended up with a relatively slim 26-1/2-inch waist that has forced me to belt every pair of pants I've ever bought in order to cinch the gap created by wearing sizes big enough to fit my more ample bottom. The answer includes factors like body type, fat composition, and possibly even the shape of the pelvic bone, where your ab muscles attach, she says. Theoretically, a wider pelvis can translate into a broad lower abdomen and hips, compared with what's north of the belly button. "These are all variations on normal, and genetics can play a big role, " she assures me.

But even though I weigh less now than I did in my twenties — thanks to a mostly vegetarian diet and a love of Zumba Fitness classes — I notice something new: a muffin top, a spare tire, love handles. Whatever you call it, I've got it. And I'm about to loan my body to science to get rid of it.

Middle Management

When it comes to ab flab, there are two ways to tackle the problem: Either burn blubber or suck it in with stronger muscles. "Even if you don't lose fat, you can improve your waistline by toning your muscles, " says Michele Olson, PhD, a FITNESS advisory board member and professor of physical education and exercise science at Auburn University at Montgomery in Alabama.

The skinny on abs is that they're actually hard to fatigue because they work all day long to keep you upright. But you don't come home after a long day at the office with a tummy ache from all that typing, so how busy could they really be?

"When we're seated, our back muscles and spine help keep us upright and the abs are in a slack position, especially if you slouch, " explains Joseph Herrera, a doctor of osteopathic medicine and the director of sports medicine at Mount Sinai School of Medicine Department of Rehabilitation Medicine in New York City. "Although we would end up reclining without the opposing muscle forces they provide, intentionally contracting your abs is the only way to activate them as you sit." As I stand in his office, Dr. Herrera tapes electrodes beneath my rib cage and just above my belly button. Cables connect those electrodes to an electromyography (EMG) machine, which makes a whooshing sound every time the underlying abdominal muscles — my external obliques and rectus abdominis — are activated.

The external obliques are the V-shaped muscles running diagonally down your sides that, along with the internal obliques underneath them, help you rotate your spine when a Ryan Gosling look-alike walks by. The rectus abdominis, meanwhile, is the straight-down-the-center muscle which, yes, can make you appear to have a six-pack if you have a seemingly single-digit body-fat percentage like Ryan Gosling's. The one remaining ab muscle, which Dr. Herrera's surface EMG won't be picking up, is the transversus abdominis. The deepest-down of all, it does a complete wraparound of your midsection and pulls it in like a corset.

When I sit in my chair with the electrodes in place, nothing happens. So I switch over to sit on a pumped-up stability ball, like the kind every office health nut uses. No whoosh. But then I lean slightly backward and all of sudden — whoosh — my rectus abdominis activates to support my spine because there is no backrest to do the job. "The stability ball requires your torso to balance on an unsteady surface. It forces your abs to fire, " Dr. Herrera says. I find I can also activate the rectus abdominis, not to mention my heretofore-napping obliques, by pulling in my belly button. I feel like a living Wii game avatar as I subsequently walk around Dr. Herrera's office trying to get a reaction from the EMG. Walking itself produces only a weak whoosh, but by carrying a bag of groceries in front of me, slinging my purse over one shoulder, or climbing stairs, I get the electrical activity on the EMG monitor to increase.

Of course none of this multitasking is making my abs burn or getting them closer to bounce-a-quarter-off-'em shape. For that, you have to do the type of middle-cinching muscle toning that Olson was referring to.

Olson has in fact used this same sort of EMG machine to test just about any ab exercise you can name. Thanks to her, for the next four weeks I'll be doing the mother of all ab workouts: a routine that contains her and her fellow scientists' greatest hits. (Spoiler alert: You get to do it, too, with the Flat Abs Fast workout below.)