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Built By Science: Legs

It's time to get serious and smart about training your legs. Learn the inner workings of your lower body to maximize your growth in the gym!

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If you're serious about building an aesthetic, athletic physique, you simply have to develop your legs. Training them not only helps them look great, but also gives you a strong, stable base for improved performance and additional physical power. In my opinion, your legs are the most important muscle group to train, hone, and build.

And let's be honest, there's no way you can build the size and strength you want without using your legs. They're literally half of your body.

I'm here to teach you more about the muscular and skeletal anatomy of your legs. I'll also teach you select exercises that can help you build a strong, shredded, and muscular lower body. This trainer brings science and squats together to help you build the lower body you've always wanted!

Built By Science Leg Anatomy & Training Program
Watch the video: 24:34

Muscular Anatomy

Yours legs are a massive collection of muscle groups, joints, and bones. To better target specific muscles and increase the overall strength and performance of your lower body, you need to know a little bit about your anatomy and how each bone, joint, and muscle work together. Let's start with the muscles.

Quadriceps Femoris

Your quads are made up of four main muscle groups—hence the prefix, "quad." These muscles are the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris. These muscles work in concert to extend your knee.

Vastus Lateralis

A lot of bodybuilders and fitness athletes covet an outer-thigh sweep. This sweep comes from developing your vastus lateralis, which sits on the outside portion of your thigh. The muscle starts at the top of your femur (thigh bone) and attaches to the patellar tendon in your knee joint.

Vastus Medialis

You want that tear-drop shape on your inner thigh? Then you want a big vastus medialis. The vastus medialis starts at the top of the femur and attaches to the patellar tendon. The tear drop sits just above your knee on the inside of your leg.

Vastus Intermedius

The vastus intermedius is deep in the middle of your thigh. You can't see it because it's covered by the rectus femoris, but it also originates on the femur and attaches to the patellar tendon.

Rectus Femoris

This muscle is unique because it's the only one of your quadriceps muscles that crosses your hip. It connects at the top of the pelvis and comes down all the way to insert at the patellar tendon in the knee.


If you want to develop big quads, you need to spend an equal amount of time developing the back of your legs. The hamstrings have three main muscle groups: the biceps femoris, semimembranosus, and the semitendinosus. These muscles work to flex your knee. In other words, they bring your heel toward your butt.

Biceps Femoris

The biceps femoris is a two-headed muscle. The long head runs from the ischial tuberosity—or the sitting bones—and attaches to the fibula. The short head originates on the back part of the femur and attaches to the fibula.


This wide, flat, and deep muscle originates at the ischial tuberosity and attaches at the tibia. It's more medial, or closer to the midline, than the semitendinosus.


The semitendinosus runs from the ischial tuberosity and also attaches to the tibia. This muscle is notable for the length of its tendon insertion, which can be partially removed to replace a torn anterior cruciate ligament (ACL).


We like to talk about glutes because of their potential beauty, but it's important to note that the glute muscles are hugely important for keeping our trunk upright. We don't have big butts just for looks, after all. The gluteal muscles are made up of the gluteus maximus, the gluteus medius, and the gluteus minimus.

Gluteus Maximus

The glute maximus is the most visible muscle and is what people spend the most time developing. The glute max starts on your sacrum (the triangular bone at the base of the spine) and your lumbar fascia (connective tissue in your lower back) and attaches to your iliotibial tract, or your IT band. It also attaches to your outer thigh.

Gluteus Medius

People aren't usually too concerned with the glute medius because it's deeper and you can't see it, but the glute medius is an important muscle. It's a critical stabilizer of the hip and thigh. It runs from the top of your hip bone (the iliac crest) and attaches to your outer thigh.

Gluteus Minimus

Even deeper than the glute medius is your glute minimus. It's a very small muscle that starts on the outer portion of your hip and attaches to the outer thigh.


We've all sat in the adductor-abductor machine and wondered, "Why am I doing this?" The adductors are actually very important muscles. There are five muscle groups to discuss here, and all of them originate at the inside of your hip (pubis) and attach to the inside of your thigh. The adductors are layered, almost like the shape of a fan.

In terms of training, the adductors are important for stabilization. They don't get much use in common movements, so it's important to work them specifically. Strong adductors help you stabilize during unilateral movements and are essential to a good squat.


The pectineus begins on the pubis and attaches to top of femur.

Adductor Brevis

This muscle lies next to the pectineus and attaches lower on the femur.

Adductor Longus

The adductor longus runs from the pubis and attaches below the brevis.

Adductor Magnus

This is probably the biggest adductor. It runs from your pubis and has attachment points at the top of your thigh and down a little lower on the inside of your mid thigh.


The gracilis is a long adductor. It originates on your pubis and attaches to the tibia, or the inside of your lower leg bone.

standing calf raise
Standing Calf Raise


You can't have great legs without a good set of calves. The two main muscles in your calves are the gastrocnemius and the soleus. These muscles work to flex and point your foot.


Your gastrocnemius is unique because it crosses the back of the knee joint. It has two heads, lateral and medial, which converge and attach to your Achilles tendon in your ankle.


The soleus is deeper than the gastrocnemius. It originates at the tibia and fibula and attaches to the Achilles tendon.

Skeletal Anatomy

With a system as large as your legs, just knowing the muscles isn't enough. Learn more about the bones and joints that are necessary for you to walk, run, and squat!


The pelvis is shaped like a bowl. It ties your lower body together and has two basic movements. Your pelvis can roll the hips forward, which is called anterior tilt, and can roll the hips backward, which is called posterior tilt.


Your hip joint is where your femur attaches to a socket in your pelvis. This ball-and-socket joint gives you freedom of motion, which is why you can flex, extend, abduct, adduct, and internally and externally rotate your legs.


The knee is a condyloid joint, which means that it does more than just flex and extend, it can also rotate. The knee is critical in almost every leg exercise you do.


Your ankles control two basic movements: Planar flexion, which is pointing your toe toward the ground, and dorsi flexion, which is pulling your toes up toward your face.

Muscular Function

I want you to have a really good understanding of how your bones, joints, and muscles work together to create seamless, fluid movement. Here's what these muscles do in the gym.


The quadriceps muscles are responsible for extending your knee. Movements like squats and leg extensions will bring out your quads. I'd like you to pay special attention to your rectus femoris because it crosses two joints, the hip and the knee. The rectus femoris helps to flex your hip. You can work it by doing step-ups or sprints.

Barbell Squat
Barbell Squat


Your hamstrings come into play when you extend your hips. You'll hit your hamstrings doing any deadlift variation. Your hammies are also used in movements with knee flexion. Leg curls, glute-ham raises, and squats will all grow the back of your legs.


Your glutes get worked when you load the hips. Heavy deadlifts can help build that glute max, while unilateral exercises like split squats will engage the smaller glute muscles for stability.


Your adductors are there for stability and control. Exercises like lunges will engage and strengthen them.


To best train your gastrocnemius, do the standing calf-raise. Your soleus is better trained when the knee is flexed, so perform seated calf-raises to work it.

Key Exercises

We can read about the muscles all day, but to actually change them, we have to do some work in the gym. Here are some great exercises that will help you target and build those leg muscles for a stronger base and a balanced physique.

EXERCISE 1 Front Squat

The cool thing about front squats is that you hit almost every muscle in your legs. As you sit down into the squat, you lengthen the quads and load the hamstrings and glutes. When you stand up, you extend the knee and fire your quads. If you're going to pick one exercise to start building your legs, this is the one I recommend. It's an exercise that will give you a lot of bang for your buck.

Front Squat
Front Squat

Set a barbell high on your sternum, almost against the bottom of your throat. It's uncomfortable, but that's the best place for the bar. Your legs should be shoulder width apart, with your toes turned slightly out. Keep your body weight in the mid foot, and then sit back. Keep your knees out. Sit down to parallel or below and then come back up to a full extension.

EXERCISE 2 Romanian Deadlift

This fantastic exercise will isolate the glutes and hamstrings. Focus on pushing the hips back. Keep your knees soft and your spine neutral. As you push your hips back, your glutes and hamstring groups stretch out. Finish the movement by popping the hips forward and flexing your glutes. Full range of motion will give you the growth and development you're looking for.

Romanian Deadlift
Romanian Deadlift


Training on one leg changes the stress on your muscles and forces your body to stabilize. Keep your torso up nice and tall, step forward on one leg, and land on the heel. Push back up from the ground and return to full extension.

We picked the lunge because it hits every muscle in your leg. Your quads will extend your knee as you step out and back. Your hamstrings and glutes will pull you down and will also help you come back out of the bottom. Yes, you're using those big muscles, but you also use those little muscles like the glute minimus and adductors to stabilize your knee and control the movement.

EXERCISE 4 Standing Calf Raise

You can use your bodyweight, dumbbells, or a barbell with this movement. The best thing about calf raises is that they're hard to mess up. Keep your knees nice and straight to stretch your gastrocnemius and your Achilles. At the bottom of the movement, give the stretch a second or two before coming up to a big squeeze at the top.

Better Legs, Built By Science

We've covered a lot of information, but I hope you understand how important your hips and legs are. If you need to, go back and watch this video again. I want you to get as much out of this trainer as you can. Put this all together and learn why we're spending time on our legs. To get the most out of our training and the most out of our physique, we need to train legs. As the saying goes: Friends don't let friends skip leg day.

Follow the Built By Science Program

Look for the exercises and techniques discussed above in the weekly legs workouts of the six-week Built by Science program. Watch all the overview videos before attacking the gym. Remember, you need to combine mind and muscle to build your best possible body.

Support your results with this muscle-building supplement combo! Go Now!

Main | Legs | Chest | Back | Shoulders | Arms | Abs | Nutrition | Supplements | Get Started