Get Strong, Sexy Legs: The Anatomy of Your Leg Muscles
How Your Leg Muscles Work
If you're lounging as you read this, the next sentence may scare you sit-less.
"Sitting is the new smoking; it's just as insidious," says Marc Hamilton, PhD, a physiology professor at the Pennington Biomedical Research Center in Baton Rouge, Louisiana. Hamilton is making a point about how so many Americans are letting their leg muscles -- and therefore their bodies -- turn to mush. "You've seen the flat line on an EKG, when all the doctors rush in? That's what's happening to your leg muscles when you're sitting."
As he speaks, I flash back to a job I had at a digital agency. I showed up on my first day of work in the New York City office to find half the staff standing at their computers. Because they didn't have chairs. The office consisted mostly of jerry-rigged desks about waist-high that we would belly up to like a bar.
Turns out my hipster coworkers were onto something. "Standing while talking on the phone or filing isn't exercise by anybody's standard," Hamilton says, "yet, compared with sitting, it increases your metabolic rate a bit." According to a widely accepted compendium of physical activity, doing "light office work" while sitting burns 96 calories an hour for an average 140-pound woman as opposed to 147 calories while standing. Besides, Hamilton adds, "when we're sitting for extended periods, hundreds of 'bad' genes are turned on, including ones that stimulate muscle atrophy."
Intrigued, I head to the Kaiser Permanente Los Angeles Medical Center to see firsthand the toll that opting for a chair and a laptop all day is taking on my legs. Once there, Barry R. Chi, MD, chief of physical medicine and rehabilitation, wires my leg muscles with surface electrodes that are tethered by several long cables to an electromyography (EMG) machine. I reenact a day in the life of my legs by sitting, standing, walking (in both heels and flats), rising up on tiptoe, and jogging. We cap this off with squats and lunges as a yardstick to measure everyday muscle activity against. True to the EKG analogy, the leg muscle readings on the EMG monitor are indeed flat lines when I sit in a chair. It's as if I'm not even there.
But something happens when I stand up in front of the monitor. It fills with electrical activity. "You may not feel anything, but your leg muscles are now supporting your whole body weight, and all of your big muscles are now engaged in isometric contractions," says Dr. Chi, pointing to the elevated lines. (Interestingly, when I stand or walk in heels my quads and hamstrings show greater surges than when I'm in flats, but Dr. Chi quickly warns against long-term high heel side effects like back pain.) "Standing for two hours can be the equivalent of going for a two-mile run," Dr. Chi explains.The Long and Short of Legs
By now you know that the length of your legs is basically a matter of genetics -- and we may be talking way, way back in the family tree. In general, women are slightly leggier than men: The latest body-measurement statistics from the SizeUSA study, conducted by TC², a not-for-profit apparel industry resource, show that the average 18- to 45-year-old woman's legs (determined by crotch height) make up about 45 percent of her total height versus 44 percent for the average man in the same age group. So a woman who's five foot five, as I am, would probably have about a 29-1/4-inch inseam. I head to the tailor to discover that mine is 29 1/2 inches, or a smidge taller than average for someone my height. (Who knew? To think that I've been buying the short cut of jeans all these years!)
Leg muscles are another story. Just how strong or string beany they make our gams appear depends on our genes and what we do with them. We'll get to the latter half of that equation -- diet, exercise, couch-sitting habits -- later, but for now, a quick anatomy lesson.
We all have the same main leg muscles: the quadriceps, the hamstrings, and the adductors make up the thighs, the below-the-knee tibialis anteriors make up the shin muscles, and gastrocnemius and soleus muscles make up the calves. (See the third page for your leg anatomy.)
But there's a wide range of sizes and muscle makeup among people that even experts debate. According to Daniel Lieberman, PhD, professor of human evolutionary biology at Harvard University, muscle fibers in humans evolved so that most of us have legs with a majority of slow-twitch fibers, which give us our staying power during long runs. "We're built more for endurance, whereas chimps have more fast-twitch fibers," he explains. With fewer powerhouse fast-twitch fibers, humans are at a disadvantage when it comes to speed. "As a species we're terrible sprinters," Lieberman says. "Cheetahs can run 25 meters per second. The fastest human, [Jamaican world champion sprinter] Usain Bolt, runs only 10.4 meters per second."
The quadriceps, or quads, it turns out, are the real wild cards, as they can range from predominantly fast-twitch to the complete opposite: The quads of someone like Bolt can contain up to 90 percent fast-twitch fibers, says John P. McCarthy, PhD, professor of physical therapy at the University of Alabama at Birmingham, while elite marathoners' muscles can contain up to 90 percent slow-twitch fibers. The quads of average people, or even those of swimsuit models or hulking bodybuilders, are more a fifty-fifty mix of the two.
The problem is that many women are often so afraid of getting bulky thighs and calves that they neglect to strength-train their legs. Actually, bulky legs are mainly due to fat. "Our legs can go from shank steak to marbled rump roast without our even knowing it," says Vonda Wright, MD, a FITNESS advisory board member and an orthopedic surgeon and professor at the University of Pittsburgh Center for Sports Medicine. "It's a snowball effect when we start accumulating fat, and it affects the function and strength of muscle."Fat Chances
Since puberty, your hormones have been signaling fat cells to be stored around your butt and thighs, ultimately to help serve as reserve energy for pregnancy and breastfeeding. "Women tend to gain fat in very specific body parts, mostly those from the waist to the knee," explains Andrew Da Lio, MD, professor and chief of plastic and reconstructive surgery at University of California, Los Angeles. The most common of those parts is the outer thigh, he says, even if your body type isn't specifically a pear shape.
There are two levels of fat in the legs, Dr. Da Lio explains: a superficial layer and a deeper one. The superficial layer is where we find the puckered tufted-mattress look we call cellulite when extra fat bulges out between the tissues that connect skin to underlying muscle.
Gain too much of the deeper leg fat and it can actually begin to infiltrate your leg muscles, says Dr. Wright, who has witnessed the rump roast effect firsthand in the operating room. The good news? This deeper layer is also typically the first layer of fat to shrink when we exercise.
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