Knee Anatomy Explained: The 14 Muscles Every Trainer Should Know

Want to truly understand the knee and pain, not just train around it?

In this episode of the Show Up Fitness Podcast, we break down knee anatomy in a way that actually applies to real-world training, rehab, and performance. We cover the 14 key muscles around the knee and how they influence stability, movement, and injury risk.

Whether you’re a personal trainer, kinesiology student, nurse, physical therapy professional, or coach, this episode will help you connect anatomy to function—so you can better assess, cue, and program for your clients and patients.

You’ll learn:

• The 14 muscles that support and move the knee
• How these muscles impact knee stability and pain
• Common misunderstandings about knee function
• How to apply anatomy to training and rehab settings
• Why most trainers overlook key structures around the knee

If you want to level up from basic programming to true movement understanding, this is a must-listen.

Want to become a high-level personal trainer?

The Show Up Fitness CPT (SUF-CPT) is designed for trainers who want to stand out with real-world coaching skills and career opportunities in top gym environments.

Learn more about the SUF-CPT and how to build a successful training career.

📘 Recommended reading: How to Become A Successful Personal Trainer Vol. 2 by Chris Hitchko (available on Amazon)

Want to become a SUCCESSFUL personal trainer? SUF-CPT is the FASTEST growing personal training certification in the world!

Want to ask us a question?  Email info@showupfitness.com with the subject line PODCAST QUESTION to get your question answered live on the show!

Website: https://www.showupfitness.com/
Become a Successful Personal Trainer Book Vol. 2 (Amazon): https://a.co/d/1aoRnqA
NASM / ACE / ISSA study guide: https://www.showupfitness.com

Transcript

Why Anatomy Builds Coaching Confidence

SPEAKER_00 0:00

Haddy all, welcome back to the Show Up Fitness podcast. Today we're coming at you helping you level up your knee anatomy and the importance of understanding the fundamentals as a professional, which you are. I'm coming at you live on Instagram as well. If you are a trainer struggling, my challenge to you is how great is your anatomy? I've interviewed so many trainers in my book over a 10-year period surveying trainers who are struggling. The common denominator, they lack confidence, they're afraid of sales, but they can't even tell you basic anatomy. Could you imagine going to a doctor and he asks a nurse, can you give me that little uh the little that the thing that makes the little cutty thingy? Or that that stuff where I'm supposed to put on the heartwork, what is that called? If you don't know the basics, how can you confidently deliver a product that value add to your clients? It comes to anatomy because most of us overlook this because you have some survivorship bias where a trainer says, Oh, your clients don't care about anatomy, they just want a great workout. You know how many gyms are out there today where a client can go out there and get a more intense workout than what you deliver. I don't want to compete with that nonsense. That's a circus show out there. I'm a competent coach. Whatever your goals are, I will help you get there. If you have pain, I have a process for that. With the SUF STM, our certification that's level two, we teach you general assessments for general population, pain, as well as athletes. When you come in, I'm like a master chef. What do you want to eat? I'm not preparing all this food, not knowing what my market wants. I ask you, what are your goals? What are your expectations for today? What does success look like six months from now? I plant the seeds, I get my client to think, but I listen. I give a great workout. I'm professional, not sitting on the side of the wall with my phone out, counting a minute plank. I'm getting engaged. I'm getting them a towel and water. I'm asking stimulating questions, learning about their career, their families, and providing value. One of the first questions when we do lower body seminars, it's our level two. When we're excited, we're launching our level one seminars around programming and assessments. We'll have our first one at the end of April in Santa Monica. And as we progress month to month, we will have more of those. Trainers, zero to five years of experience. The level two, that's when we get into the soft tissue stuff. So when we do the lower body seminars, I start with can you tell me the 14 muscles around the knee? Most trainers will look at you and be like, 14 muscles? What? I didn't even know the quad was four muscles. I thought it was just one. Let's start there. Quadriceps. We have four muscles. One is biarticulate. Rectus in Latin means straight, because the muscle is straight, starts at the hip, comes down to the patella tendon. We have the vastus lateralis, vastus intermedius, which is underneath the rectus femoris, and then the vastus medialis. Those are four quad muscles. On the posterior side, if you were to use your hand like this and you use your ring finger, you will feel two guitar strings. Those are your hamstring muscles, the lateral, the medial part, which are the semimembranosus and semitendinosus. The larger one on the lateral side is your biceps femoris. Femoris, femoris, tomato, tomato, whatever makes you sound spancy, use that pronunciation. There's three muscles there. That's seven. And then we're going to add in the gluteus maximus, and I'll tell you why here in a second. The gastrocnemus is the only biarticulate knee and calf muscle. The soleus is a calf muscle, but it's deep to the gastroc and it does not cross the knee joint. Then we need to look at these five over here. So we're at four, three. Now we are at nine. The last five are the sartorius, my favorite muscle. When I get a big dog, sartorius, come here. Oh, it just sounds like an awesome name. This dog comes over like Beethoven. Sartorius is the longest muscle in the human body. And I love it because it does a lot of cool stuff. It flexes the hip and the sagittal plane. It also AB ducts, it externally rotates because it crosses the knee joint, it works with knee flexion as well as lateral rotation. So that sucker is really, really important. It crosses two joints as well, as does the gracillus, which is a medial thigh muscle and it crosses on the medial side of the knee. And then we have the TFL tensor fascia lata. And the last two behind the knee, the popliteus and plant terrace. Those are the 14 muscles of the knee. Now, some may start at the hip, and as I said, the gluteus max is because it goes into your IT band. So if you were pretending like you're in sand, hot as hell out there in Santa Monica, if you want to go down to the beach, don't get in the water. It's toxic right now. But if your feet were in the sand and you pull your knees apart, you will feel your glutes fire up. So that's a little nuance there. You could say there's 13 muscles around the knee, but understanding knee anatomy is really, really important as a personal trainer because you're going to have clients that come in with knee discomfort, and you have to be smart enough, competent enough to look at the ankle, to look at the hip. And that's the process that we take you through with the STM certification, soft tissue mobilization techniques. You look at the ankle for mobility deficits, stability deficits. We do a TKAE test, which is terminal knee extension. If you can't own that, then maybe that's why you have discomfort. We got to look at the hip as well. So there's a process of understanding why you're in discomfort, looking at the biopsychosocial model of pain. It's not just you have knee pain, walk on a fucking treadmill backwards, and you're going to clear it all up. That may help because that person wasn't doing anything because their doctor told them rest for the next six months. And you have someone with a couple million followers saying, you just have to go knees over your toe for these two exercises and clear everything up. It gave that person hope. A lot of Western medicine doesn't give people hope. They're going to say your knee's jacked up, they take an MRI. They're going to find something, all MRIs do. And you have some type of steniosis or osteoformation, but they scare the hell out of you. You have arthritis and you go, holy shit, I'm broken. I suck. The mindset is so important when it comes to understanding pain. And that's why you have a physical therapist on your team. You have an RD on your team. And you're constantly meeting with these individuals because it levels up your knowledge and your confidence as well as your competence. You don't need to go out there and get some corrective exercise certification where you learn 38 exercises and you don't know why behind it. Why are you doing that test? Why are you doing that exercise? That's what competent coaches can tell you. So if you're new into training and you got that textbook cert and you're completely lost, that's what the level one seminars are about. We're going to level up your anatomy, your assessment process, but more importantly, give you confidence around programming. Most trainers are thrown clients and your manager is going to say, go and train them. And you look at your textbook and you go, stability ball, squat, curl, press, single leg scaption. What the hell? I'm uh uh like I don't have that. I don't know what to do. You need to be able to think on the fly. So when you have a system with your programming, like we used at the CCA, it makes your life so much easier and you have way less stress. So when we look on the posterior side for the lower body, gluteus maximus, we all know where that is. That's the big badonkadonk on the posterior side. But you have upper fibers and lower fibers. The upper fibers work with abduction in the frontal plane. The lower fibers work with that posterior tilt. If you want to see my belt buckle, bam, bam, that's a posterior tilt. Anterior tilt is coming forward, posterior is coming back. And then on the lateral side, you'll see it goes into that white tissue. That's your IT band. So it's going to come down into your tibia, ilio-tibial tract. Posterior side, we have the semis, semimembranosis, semitendinosus, and the biceps femoris. There's two heads of the biceps, but it's three muscles of the hamstrings. On the anterior side, we have the quads, rectus femoris, vastus lateralis, vastus medialis, the teardrop. And then we have the vastus intermedius, which is underneath the biarticulate rectus femoris. On the medial side here, we have that very thin muscle, the gracillus, which is also an adductor. The five muscles that adduct the femur. Major league baseball has great pitching. We saw that with Skeens the other night. Smoke the DR. Woo! We're in the final game. It's exciting. Stop. One of the best games I've ever seen. Major League Baseball, Magnus Longus Previs, has great pitching. Gracillus and the pectinius. Those are adductors of the femur. And then we also have the gastrocnemius, you see on the top one here. Biarticulate goes into your calcaneous bone via your Achilles tendon along with the soleus. The soleus is not part of the knee, nor is the anterior tibialis or posterior tibialis. It's a common mistake people will think. Oh, the anterior tib, because I saw some dipshit doing them, that must work at the knee. No, it's just movement, is what's helping. It's not stabilizing the knee joint because it doesn't cross the knee joint. If you want to stabilize that joint, you need to strengthen the entire joint and all planes of motion. So then we also have the sartorius on the lateral side of the hip, anterior superior iliac spine, crosses medially into your tibia. That's why it works with flexion, like leg curls, but also external rotation of the tibia. And then we also have behind the knee the popliteus and plantaris. The plantaris, like 40% of the population, doesn't have fun little factoid. Next time you're playing bar trivia. And then the last one being the tensor fascia lata. It's like you're holding a latte, tensor fascia lata, starts on the lateral side of the hip, and then it goes down lateral as well. So those three bar articulate ones, they stabilize the hip and the knee. That's why one of my favorite exercises is to bend the knee and to do a little airplane because you're just strengthening the gluteus medius as well as the upper fibers of the gluteus maximus. When you bend the knee, you take out the gracillus, the TFL, and the sartorius. My challenge for you is to know the 14 muscles around the knee, 17 muscles around the shoulder. And that's going to be specific to the scapula. Because when you can confidently name them and also their actions, your confidence level drives up. And when you have conversations with physical therapists, they say, wow, you actually knew the rotator cuff muscles. Oh, you knew the names of the hamstring muscles. You know there's an ACL and a PCL, anterior cruciate ligament, cruciate in Latin means cross. And you have a posterior cruciate ligament, you have a lateral collateral ligament and a medial collateral ligament. You know what a menisci is. You have these C-shaped connective tissue that allows for shock absorption. So if a client were to say, I have a blown-out ACL and they don't have that terminal knee extension, you can reach out to your therapist and say, What are some suggestions that you think I should do? Are there any contraindications? Just getting involved and sharing that information showcases that professional that you are a professional. We are all within the medical community. If you look in the sports world, the medical community, athletic trainer, strength coach, dietitian, the doctor, they work together for the team. Why don't you have a team? I ask that question all the time. How many people in here can text a physical therapist and within an hour get a response back? Crickets. No one raises their hand. So if you want to be like everyone else who's fighting on social media and doing a bunch of bullshit exercises without a cause because they're not competent and they're fighting in this Red Sea, great book, by the way, Blue Ocean Strategy. If you have a team and you're looking out for the best interests in your clients, you will build a book of business. You will charge what you want and you can turn this into a career. I guarantee it. That's why I wrote the book, How to Become a Successful Personal Trainer. If you enjoyed today's podcast, throw this into your story. Let trainers know there is hope for them. Putting a bunch of acronyms in your bio only shows that you are insecure and you're competing with that social media world. Great trainers are, in fact, trainers, and they're competent in the assessment process and they have a team and they charge what they're worth. Remember, big biceps are better than small ones. Okay, show it up.