The Anatomy of Leg and Thigh Muscles, Explained | Fitness Magazine
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.
Thinner Thighs in 30 Days
Last fall, with the help of the UCLA Center for Human Nutrition's Risk Factor Obesity Program lab, I tried an experiment. I did every exercise I routinely avoid on the chance it would make my legs look like Schwarzenegger's: dozens and dozens of squats and lunges each week combined with the stairclimber and Spinning classes. And a funny thing happened. I lost 10 percent of the fat from each thigh in four weeks, according to the lab's DEXA (dual energy X-ray absorptiometry) body scanner. By eight weeks, during which I also stuck to around a 1,500-calorie-a-day diet, I'd lost more than an inch from each thigh. Try that with Spanx.
"You can change the composition of your legs — the ratio of fat to lean mass," Dr. Wright says."Increasing your strength and endurance will lead to a change in how your legs look. Strong legs are shapely legs." And there was my proof in the form of the X-ray-like DEXA readouts, which showed that the grayish halo representing the fat on my thighs was shrinking.
But here's the kicker: The darker center consisting of my quads and hamstrings wasn't busting at the seams after those gazillion squats. In fact, it had pretty much stayed put, which is the moral of this story. If I hadn't done those thigh-frying reps while I was dieting, my muscles probably would have shrunk a little, too, and along with them, my metabolism. (You can find the 1,500-calorie diet I followed as well as the Love Your Legs workout at fitnessmagazine.com/sexylegs.)
The Love Your Legs Workout
Stronger legs may indeed be a secret to staying slim. "When you increase the strength and endurance of your legs, it generally makes it easier to exercise and move around, leading to greater physical activity throughout the day. You burn more calories overall," McCarthy says. In fact, a University of Alabama at Birmingham study found that women who maintained weight loss one year after dieting had much greater leg strength than those who didn't.
Certain data from the SizeUSA study seem to back up this research. It found that the circumference of an average woman's thigh ranged from 24 inches for active women under age 45 to 26 1/2 inches for less active women of the same ages. That's a two-and-a-half-inch difference. (Of course, there are cases in which bigger can mean better — see the superfit thighs of Serena Williams.)
As for me, my legs are now about as lean as they were when I was a competitive distance runner. For the first time in 10 years I fit into my favorite pair of Levi's, the ones I bought right after college, and I finally zipped my athletic calves into a pair of tall boots. But the best part of all? Becoming a shank steak.
Anatomy of Your Leg Muscles
No, your glute muscles are not officially part of your legs (get the full 411 on your rear view at fitnessmagazine.com/behind), but here we take a below-the-cheeks look at the major players that are.
Hamstrings
These muscles, which form the back of the thigh, flex your knee and extend your hip.
Adductors
Also known as inner thigh muscles; squeeze a pencil between your knees to feel these fire.
Quadriceps
This muscle at the front of your thigh is made up of four sections and is the main mover when you extend knees.
Gastrocnemius
The uppermost of your two calf muscles, it gives your feet push-off power with each step.
Soleus
This calf muscle works with and lies underneath the gastrocnemius.
Tibialis anterior
The strip of muscle that makes up your shin and helps you flex your ankle to move your foot toward your knee.
Can Cankles Be Cured?
The region between our calves and ankles is not defined by muscle but rather by the Achilles tendon, which connects the two. For some women, this area cinches in dramatically from a well-toned calf muscle, while for others it slopes down gradually. And then there are those whose lower legs appear to drop in a straight line, with no indentation at all, inspiring the unflattering label cankles.
"Cankles are essentially a visual effect," orthopedic surgeon Vonda Wright, MD, says. "Models often look as if they have cankles because their legs are tubes from the knee to the ankle. It's all relative."
For the calf to taper, there has to be a shapely muscle to begin with. Yet, again, many women are reluctant to strengthen their calf muscles for fear that they will thicken and produce a cankle effect. "That's a myth," Dr. Wright says. "Cankles don't come from muscle, because by the time you get to the ankle, it's all tendons. Cankles come from fat accumulation."
It's partly a matter of genetic roulette. Obese women can have skinny ankles, for example, while for other women the lower leg may be the last place where they lose fat.
Your strategy to rid yourself of cankles should be to slim down all over through diet and exercise like cardio and to firm up your calf muscles with the proven toners in the Love Your Legs workout.