Anatomy of Leg Muscles — Plus, How to Make the Most ...

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," warns Marc Hamilton, Ph.D., a professor of biology and biochemistry at the University of Houston.

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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," he adds.

As he speaks, I flashback 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 makeshift desks about waist-high that we would belly up to bar height.

Turns out my hipster coworkers were onto something. "Standing while talking on the phone or filing isn't exercise by anybody's standard, yet compared with sitting, it increases your metabolic rate a bit," says Hamilton. In case you were wondering, doing "light office work" while sitting burns 96 calories an hour for an average 140-pound woman as opposed to 147 calories while standing, according to a widely accepted compendium of physical activity.

But more importantly, "when we're sitting for extended periods, hundreds of 'bad' genes are turned on, including ones that stimulate muscle atrophy," adds Hamilton.

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 leg muscles. Once there, Barry R. Chi, M.D., 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 of the body are now engaged in isometric contractions," says Dr. Chi, pointing to the elevated lines. "Standing for two hours can be the equivalent of going for a two-mile run," he explains.

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 side effects of wearing heels, such as back pain.

How Genetics Alter Your Leg Muscles

The length of your legs is basically a matter of genetics — and this could mean way, way back in the family tree.

In general, women are slightly leggier than men: The latest body-measurement statistics from a 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.

Main Muscle Groups

Leg muscles are another story. They depend greatly on your genes and what you do with them. The latter half of that equation will be discussed later — i.e. diet, exercise, couch-sitting habits — but for now, a quick leg muscle anatomy lesson.

Everyone has the same main leg muscles:

• Quadriceps are large muscles of the front upper legs.
• Hamstrings are muscles of the back upper legs.
• Adductors are located along the inner thigh.
• Shins are along the front of the lower leg.
• Calves are along the back of the lower leg.

Leg Muscle Functions

Within those larger muscle groups, though, there are several smaller muscles, each with their own unique function(s), such as:

• Adduction: Moving toward the mid-line of the body
• Flexion: Bending of a joint
• Extension: Straightening of a joint
• Rotation: Twisting movement either toward or away from mid-line of body

It's worth noting that while adductor muscles are located on the inner thigh and help to move your leg into the mid-line of your body, abductors are not merely "outer thigh" muscles, but rather muscles located in the glutes that help rotate your hip. This story will be sticking to the muscles below the booty. (But here's a guide to your butt muscles if you're interested.)

Muscle Fibers

There are two types of muscle fibers:

• Slow-twitch muscle fibers are used for lower intensity activities and endurance activities since they can fire for a longer time.
• Fast-twitch muscle fibers are used for short, explosive movements like sprints or squats.

But there's a wide range of sizes and muscle fiber makeup among people that even experts debate. "Muscle fibers in humans evolved so that most of us have leg anatomy with a majority of slow-twitch fibers, which give us our staying power during long runs," according to Daniel Lieberman, Ph.D., professor of human evolutionary biology at Harvard University. "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," says Lieberman. "Cheetahs can run 25 meters per second. The fastest human, [Jamaican world champion sprinter] Usain Bolt, runs only 10.4 meters per second," he adds. (See also: Everything to Know About Slow- and Fast-Twitch Muscle Fibers)

It turns out that the quadriceps, or quads, are the real wild cards of your leg muscles, 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, Ph.D., former professor of physical therapy at the University of Alabama at Birmingham.

On the other hand, 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.

Sources of Bulk

The problem is that many people are often so afraid of getting bulky thighs and calves that they neglect to strength-train their legs. But 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, M.D., a double board-certified orthopedic surgeon based in Orlando, Florida. "It's a snowball effect when we start accumulating fat, and it affects the function and strength of muscle," she continues. (See: Fire Up Your Lower Body with This Beginner-Friendly Workout)

Body Composition of Your Leg Muscles

If you were assigned female at birth, your hormones have been signaling fat cells to be stored around your butt and thighs since puberty, 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, M.D., professor and chief of plastic and reconstructive surgery at the University of California, Los Angeles. The most common of those parts is the outer thigh, he says.

There are two levels of fat in the legs: a superficial layer and a deeper layer, explains Dr. Da Lio. The superficial layer is where you'd find cellulite when fat pushes through between the tissues that connect the skin to the underlying muscle.

Gain too much of the deeper leg fat and it can actually begin to infiltrate your leg muscles, says Dr. Wright. The good news? This deeper layer is also typically the first layer of fat to shrink when you exercise. (For more: Try This No-Equipment Leg Workout When You Can't Make It to the Gym)

How to Strengthen Your Leg Muscles

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 stair climber and cycling 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 a low-calorie diet, I'd lost more than an inch from each thigh.

"You can change the composition of your leg muscles — the ratio of fat to lean mass. Increasing your strength and endurance will lead to a change in how your legs look," says Dr. Wright. 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 reps while I was dieting, my muscles probably would have shrunk a little, too, and along with them, my metabolism.

Stronger legs may indeed be a secret to maintaining a healthy body. "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," says McCarthy.

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. (Also: The Best Leg Day Exercises Trainers Want You to Add to Your Workouts)

But What About Your Ankles?

The region between your calves and ankles is not defined by muscle but rather by the Achilles tendon, which connects the two. For some, 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 and totally body-shaming label: cankles.

"Cankles are essentially a visual effect," says Dr. Wright. "Models often look as if they have cankles because their legs are tubes from the knee to the ankle. It's all relative," she says. (More importantly, here's how weak ankles and ankle mobility affect the rest of your body.)

For the calf to have the appearance of tapering, there has to be a bit of muscle size to the calves. Yet, again, many are reluctant to strengthen their calf muscles for fear that they will thicken and produce a cankle effect. "That's a myth. Cankles don't come from muscle, because by the time you get to the ankle, it's all tendons," explains Dr. Wright. It's a matter of genetic roulette, fat accumulation, and body composition.

Okay, now that you've gotten a lesson on how and why leg muscles look and act as they do, here's a breakdown of exactly what your leg muscles are and where you find them.

The Anatomy of the Leg Muscles

Take a look at the labeled leg muscle diagrams below for a more detailed look at the front, side, and back of your leg muscles.

Front Leg Muscles

When it comes to the front of your legs, there are two muscle groups — the anterior upper leg muscles (i.e. your thigh) and the anterior lower leg muscles (i.e. your shin). There are four parts of your quadriceps: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The tibialis anterior is the strip of muscle that makes up your shin and helps you flex your ankle to move your foot toward your knee.The peroneus longus runs down the outside of your anterior lower leg.

Kailey Whitman

Side Leg Muscles

Your inner leg muscles or inner thigh muscles are known as your adductor muscles, which include the pectineus, adductor longus, adductor brevis, and gracilis. This group of leg muscles is responsible for bringing your thigh toward the center of your body, as well as rotating the thigh bone.

Kailey Whitman

Back Leg Muscles

The posterior leg muscles (below the glutes, at least) are what make up your hamstrings and calves. The three hamstring muscles — biceps femoris, semitendinosus, and semimembranosus —are responsible for flexing your knee and extending your hip.

The calf muscles include the gastrocnemius, the uppermost of your two that gives your feet power with each step, and the soleus, which lies underneath the gastrocnemius. The tibialis posterior is a very small muscle deep inside the calf that helps stabilize your foot.

Kailey Whitman

How Often Should I Train My Lower Body?

Some call it “leg day”, others call it lower body strength training, but no matter how you slice it, exercising your lower body is vital for building a strong base for every movement. 

Think of your lower body as both your foundation and your power system, guiding and propelling all your movements no matter how small or large. Building strength and mobility in your lower body creates a firm, solid base, which plays a vital role in both your balance and stability, helping improve your overall posture and form. It’s also beneficial for cardiovascular health, along with building muscle. 

From your glutes to calves, and everything in between, lower body strength training encompasses every muscle below the waist, including your glutes (your largest muscles), quadriceps, hamstrings, and calves. Your lower body workout can even incorporate your core and back muscles because your lower body helps to stabilize these. There is a huge selection of exercises to choose from, each using different combinations of these muscles. 

Here’s what you need to know. 

Key Benefits of Lower Body Exercises

Whether you’re adding lower body strength training to your routine to benefit other types of workouts, like cycling or running, you’re hoping to further define muscles in your lower body, or you want to feel stronger in your everyday activities like climbing stairs and walking, there are many benefits to lower-body workouts. 

Importance for Daily Movement

As strength or resistance training can help promote better bone health and improve bone density, lower body strength training can help reduce the risk of potential injury and lower the likelihood of developing osteoporosis. A recent study found that 15 to 20 minutes of strength training, three days a week, can significantly help improve bone density. Along with bone health, building muscle around weak joints and helping to condition muscles can contribute to functional strength, and help prevent injuries or strains.

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Cardiovascular Health Benefits

While you may not immediately think of lower body exercises as having direct heart health benefits, strength training has a positive impact on many aspects of cardiovascular health. Over time, strength training can decrease blood pressure and create a leaner muscle mass, improving circulation by strengthening the heart and blood vessels, which reduces the risk of heart attacks and strokes. And, studies have also found that sustained strength training can help reduce levels of “heart fat” which is linked to cardiovascular disease. 

Reduces Your Risk of Injury

Lower body strength training works on your core stability, improving your range of motion and mobility. It builds stronger muscles around key joints such as hips and knees, to help protect against strains and sprains. Strengthening glutes, hamstrings, and your core also helps with posture alignment, correcting any muscle imbalances which can lead to postural issues and pain. 

Increases Your Resting Metabolic Rate

With lower body strength training, you’re building muscle mass over time. As muscle mass needs more energy to maintain, this boosts your resting metabolism, effectively helping you burn more calories, even when you’re not working out. 

How Often Should I Train My Lower Body?

How often you do lower body training sessions will be based on your fitness level and goals. “If you’re brand new to strength training or looking to maintain your strength, once a week is plenty. Just make sure to focus on hitting all the main parts of your leg: quads, hamstrings, glutes, and calves,” says Austin Cagley, who leads Global Instructor Development at Peloton. “As you become more comfortable in the weight room and look to add strength or muscle, you can up the frequency to two to three days a week.” 

You can choose workouts that focus solely on the lower body aka your “leg days” on rotation with upper body strength training on different days, or you can integrate as part of a full body strength training workout. 

“I find people like to do two legs days, with an emphasis on quads during the first one (along with accessory exercises that hit hamstrings, adductors/abductors, and glutes) and an emphasis on hamstrings during the second one (along with accessory exercises that hit quads, adductors/abductors, and glutes),” says Cagley, adding, “Just give yourself enough time to recover between leg days.”

If you prefer to do strength training on rotation, Peloton instructor Ben Alldis offers plenty of advice on creating a well-rounded strength training program, so you can focus on different muscle groups each time.

Warm-Ups For Lower Body Strength Training

All strength training starts with a proper and thorough warm-up. So, to get the most out of your lower body strength training you’ll want to tailor your warm-up to prep the lower body muscles.

By warming up your muscles, joints, and connective tissues you’re slowly increasing your heart rate and blood flow, ensuring more oxygen reaches your muscles. By gradually raising your body temperature, your muscles become warmer and their elasticity improves. Warm muscles also contract more easily, creating better mobility for your workout and reducing the risk of strains or injury.

One way to approach your lower body strength training warm-up exercises is to choose ones that will complement what you’ll be doing in your actual workout. This could be bodyweight squats for any workout using your glutes, quads, or hip flexors or a lunge with hip opener for any hinging exercises like a good morning or a deadlift. 

That said, any lower body warm-up will be better than none, so always make sure you build in time for at least 5 to 10 minutes of warm-up exercises.

Here are a few lower-body strength training warm-ups to help you get started:

1. Jogging in Place or Jumping Jacks

Both will get your heart rate up while moving your lower body at a faster pace. 

1. For jumping jacks, stand with your feet together and arms by your sides. 

2. Then jump up kicking your legs outwards and raising your arms above your head. 

3. Jump back to the starting position. Repeat.

Muscles worked: Glutes, hip flexors, quads, calves, hamstrings, abs, and shoulders.

2. Lunge with Hip Opener

This is not your standard lunge but makes a great warm-up if your workout includes lunges. 

1. Stand with feet hip-width apart.

2. Step one foot forward, bending the front knee to 90 degrees.

3. Lower your back knee to the ground, keeping the weight in your front foot. 

4. Gently open your front knee outwards while keeping your foot firmly in place. 

5. Switch sides. Repeat.

Muscles worked: Glutes, hip flexors, quads, hamstrings, calves, and core. 

3. Forward or Lateral Leg Swings

Both of these swings will activate the hips and glutes.

1. Stand with your feet together and arms either at your sides or out to a “T” for balance. 

2. Place your weight on one leg and then raise the other off the floor.

3. Swing raised leg front and back, increasing the range of motion as you swing.

4. Swing raised leg side to side, in front of your opposite leg, increasing the range of motion as you swing.

5. Switch legs and repeat, doing at least three sets per side.

Muscles worked: Glutes, hip flexors, quads, hamstrings, calves, and core.

4. High Knees

This will get your heart rate up, depending on how fast you pace it.

1. Start with your feet hip-width distance apart.

2. For high knees bring one knee up as high as it goes and raise the opposite arm.

3. Switch quickly to the other foot and arm, and repeat. 

4. Speed it up as you see fit. 

Muscles worked: Glutes, hip flexors, quads, hamstrings, calves, and core. 

5. Butt Kicks

Butt kicks are a great way to warm up the glutes, quads, and hamstrings. 

1. Start with your feet hip-width distance apart.

2. Bring your one heel up to your butt then put your foot down.

3. Switch feet and repeat.

4. Build up speed as you go.

Muscles worked: Glutes, hip flexors, quads, hamstrings, calves, and core. 

Most Effective Lower Body Strength Training Exercises

Once you’ve got your warm-up down, it’s time to get your lower body strength training workout on. Here are some of the most effective lower body exercises you can do to start to make great strides in your fitness journey. 

1. Squats

1. Stand with your feet shoulder to hip-width apart with a slight bend in your ankles, knees, and hip.

2. Ensure knees are tracking above your second and third toe at 11 and 1, making sure your knees aren’t falling inwards.

3. Engage your core and keep your chest upright as you sit your hips back, until thighs are parallel to the floor.

4. Return to start, activating your glutes at the top of the movement.

For an extra challenge, this move can also be done with weights.

Muscles worked: Glutes, hip flexors, quads, calves, hamstrings, and abs.

2. Deadlifts

Performing deadlifts with proper form will help protect all areas of your back during this movement.

1. Stand with your feet shoulder to hip-width apart.

2. Hinge at the hips to keep your spine in a neutral position.

3. With a flat back, bring your torso towards the floor.

4. Engage your glutes and hamstrings to return to standing, being careful to keep your spine neutral—although the movement is generated from the hip hinge, make sure to not lock out your knees.

Muscles worked: Glutes, hamstrings, core, back, and traps.

3. Lunges

Follow the form below while you’re moving through either a forward lunge or reverse lunge.

1. Stand with your feet shoulder to hip-width apart with your toes facing forward.

2. Take one step forward, and lower your weight straight down towards the floor, ensuring both your front leg and back leg create 90-degree angles.

3. Make sure that your back knee doesn’t hit the ground--it should just be hovering over the floor.

4. This movement can be performed with or without a weight.

Muscles worked: Glutes, hamstrings, quads, and calves.

4. Bulgarian Split Squats

This one takes some balance and coordination so you’ll want to spend some time getting your footing placement comfortable and stable.

1. Stand in front of a chair or bench with feet hip-width distance apart and a straight back and shoulders. 

2. Pick a foot to start with and place it on the chair or bench behind you. Keep it at the hip-width distance apart to maintain balance.

3. Keep your eyes looking straight ahead, bend your front knee, ensuring the weight is on that front leg not the back—which is there for balance. 

4. Hinge a little forward at the hips and ensure your front knee is in line with your toes and isn’t moving inwards or outwards.

5. Lower until your front quad is parallel to the ground and stay down for a beat.

6. Use that front leg to push upwards to standing, then bring your back leg down. Switch legs and repeat.

Muscles worked: Glutes, hamstrings, quads, calves, and abs.

5. Glute Bridges

This move can be done without weights or by holding dumbbells across your hips for additional resistance.

1. Start with your back flat on the floor and your feet placed shoulder-width apart flat on the floor, creating a 90-degree angle with your knees.

2. Engage your core and lift your hips up by contracting your glutes and pushing your heels into the floor, keeping a neutral spine and neck. 

3. Make sure your back is not arched; your body should be in a straight line from the knees to your shoulders. 

4. Pause at the top, then slowly move your hips down to start position. Repeat.

Muscles worked: Glutes, hamstrings, quads, and adductors.

6. Good Mornings

Depending on your strength training goals, you can add weights to this or keep it just about the movement. Start without weights and build up from there. 

1. Start standing with feet hip-width distance apart. 

2. If you’re using dumbbells, place them on your shoulders or hols one dumbbell at chest height..

3. Bend your knees slightly, then hinge forward at the hips bringing your upper body parallel to the floor. 

4. Keep your core engaged and a straight back. 

5. Slowly return to start. Repeat.

Muscles worked: Hamstrings, glutes, and abs.

7. Box Step-Ups

Combining the effects of a lunge and a squat, box step-ups are challenging move to progress your training. This exercise can be done with or without dumbbells. You can also progress it by increasing the height of the step.

1. Using a stable box or a raised platform, place one foot on top of the box and one on the ground. 

2. Shift your weight onto the foot that’s on the box. 

3. Drive your weight into your box foot and pull upwards bringing your other foot onto the box. 

4. Bring your foot back to the floor and your other to join it, then repeat.

5. Alternate your leading leg or do repeating reps on one side followed by the other. 

6. You can also change the way you do your stepping to target different muscles and add more weights, as well as varying the speed to get your heart rate up. 

Muscles worked: Glutes, quads, hamstrings, adductors and abductors, calves, and core.

As with any new exercise program, make sure you start off at a comfortable pace adding a few lower body strength training exercises and warm-ups into your workouts and build it up from there. Don’t forget to rotate it with upper body strength training too, or do a full body strength training workout to really get all the muscles working together. 

Depending on how you want to strength train and your fitness goals, you’ll find everything you need over on the Peloton App.

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