 Hey everybody, Dr. O here. In this video I'm going to do a quick overview of the major muscles of the body. I'm going to cover different regions and mine deeper in the following videos, but I wanted all of the key muscles in one place. Let's start with some general rules. First of all, the muscles on the front of your body, they're almost always involved in flexion, so decreasing the angle between two structures. So think of the front of the body, they're almost all involved in flexion. The front of the arm flexes the elbow, front of the forearm flexes the wrist, front of the neck, flexes the neck, et cetera. The only exception there is going to be the quadriceps. Your quadriceps muscles, they extend the knee. Muscles on the back are going to be your extensors. They're going to extend the back, extend the neck, extend the arms, et cetera. The exception there would be the hamstrings. So they're involved in the flexion of the knee. There's always going to be an exception. Muscles on the outside, on the lateral surface, they're usually involved in abduction, taking body parts away from your body, or else lateral flexion, flexion to the side, like with my trunk here or my neck like I just did. Muscles on the medial surface, they're usually going to be involved in abduction, bringing body parts closer to the midline. So just keep that in mind. If you don't know the function of a muscle, look at where it is. That may tell you at least one of its key functions. Let's go ahead and dive in how I'm going to break this up. I'm going to show you all the muscles of the upper half of the body on the front and in the back, and then I will jump down to the muscles of the lower half on the front and the back. So we'll be looking at four different slides here. Let's start right here on the front with the frontalis. So notice this image calls this the frontal belly of the occipitofrontalis. That's absolutely correct. But calling it the frontalis works, and to me, if it's easier, we'll do it that way. So I will actually call this the frontalis muscle. Its action is to raise your eyebrows. So that's the frontalis or the frontal belly of the occipitofrontalis muscle. Next we have the sternocleidomastoid, perfect example of why terminology is important. It sounds like quite a mouthful, but it tells you exactly where it is. Sternom means sternum, clidom means clavicle, and mastoid is the mastoid process of the temporal bone. So sternocleidomastoid. Its action, if they're both contracting, it will flex the neck. If only one is contracting, so if my right sternocleidomastoid is contracting, it will rotate my head to the left. So rotation if one of them contracts, flexion if they're both contracting. That's the sternocleidomastoid. Next we have the pectoralis major or your big pec muscles. They're involved in flexion, forward flexion, and then medial or internal rotation of the humerus. So think of pushup. When you do a pushup, your arms start here. They end up getting flexed forward and rotated forward in that pushup position. So that's your pectoralis major. From a terminology standpoint, anytime you see a major, that means there will also be a minor. So on the other side, you do see the pectoralis minor. This job is to depress the scapula, not as important, but whenever you see a major, you're going to see a minor. That's just kind of a general rule there. Next we have the deltoid. Deltoid means triangle. So it's a triangular muscle on the shoulder, and its job is abduction of the shoulder. I'll go into more detail in a separate video about how there is an anterior, middle, and posterior delt. But for now, just think deltoid, abduction of the shoulder, taking them away from the midline. Next we have the biceps brachii, the biceps muscles everyone thinks of. So biceps tells you that it has two heads, brachii tells you it's in the brachio region. So the biceps brachii, its primary function is flexion of the elbow, but don't forget that it's also a supinator. So flexion and supination of the elbow, that's what tricks up a lot of students. Next we have the brachialis, which is underneath the biceps brachii. This is also an elbow flexor. It's called the workhorse of the elbow here, because there are many several muscles that flex the elbow, but this one is the strongest elbow flexor we have in any position. So that's called the brachialis muscle. Next we have the brachioradialis. So like the name implies, it starts in the brachium, the upper arm, and then travels down the radius, which is on the thumb side of your arm. So the brachioradialis crosses the elbow, so it is an elbow flexor as well. If you work out and you've heard of hammer curls, so hammer curls are used to specifically strengthen that brachioradialis muscle. Next we let's move into the trunk there, the core. We have the rectus abdominis. That's right, rectus means straight, so it's the abdominal muscles that travel straight up and down. It flexes the trunk and the spine. It's the six-pack that everybody thinks about. We all have. Most of us have them. It's covered with a lot of icing, as I like to say. So that's your rectus abdominis. You'll notice that the core muscles are going to run in all different directions. The rectus abdominis travel straight up and down. Then we have the internal and external oblique muscles. They're going to be involved in rotation of the trunk and they're going to run at an oblique angle, which is why they're called the obliques. So you have the obliques running this way and this way. So you have muscles running straight up and down. You have obliques running this direction and this direction. Then underneath all of them, you have what's called the transversus abdominis. Transverse meaning running this way. The action of the transversus abdominis is to compress the abdomen. So I like to think about those muscles. Your abdominal muscles and the muscles of your spine, they basically form like, imagine wearing a back brace. Like it's a muscular brace. You have muscles going up and down, obliquely both different ways, and side to side. And they cinch up and strengthen your core. And that's why having these strong abdominal muscles is the best way to protect your low back. You would think that strengthening your low back would help the low back more, but it doesn't. If you strengthen these abdominal muscles, it's like cinching your spine and your abdomen in a back brace and it stabilizes things and keeps them getting hurt. All right. So those are the key muscles on the front of the body, on the top half. Now we're looking at the posterior surface. We see the occipitalis. Now notice here, it's called the occipital belly of the occipitofrontalus muscle. You can call it that. But I like to call it the occipitalis muscle. It retracts the scalp. Some people can control it better than others and they can get more scalp retraction. So that's the occipitalis muscle. Then you have the trapezius. Like with the deltoid, I will treat the trapezius like three separate muscles in a more detailed video. But for now, just know that it's a trapezoid or kite shape and it moves the scapula. Next we have the latissimus dorsi, which basically means like the widest and broadest muscle on your back. It's a massive muscle. The actions of the latissimus dorsi are extension. So bringing the arms down back towards your body, adduction, bringing your arms back towards your sides of the shoulder. So extension and adduction of the shoulder. So think about doing a pull-up. If you do a pull-up, you start with your arms up and you pull them back and down to your sides. The latissimus dorsi is the most important muscle there for doing a pull-up. Okay. Deltoid, we already covered. That triangular shaped muscle on the side of your shoulders, abduction of the shoulder. Now we have the triceps brachii. So triceps tells us that this one has three heads. Brachii tells us it's on the upper arm. This muscle is on the back of the upper arm, so its job is to extend the elbow to straighten your arm out. Brachioradialis, you can see it here again, but we already covered it. Flexion of the elbow. It runs down the thumb side of your forearm. Next we have the next four muscles are going to make up your rotator cuff. I'll do a separate video on them, so I'll go through them pretty quickly here. We have the supraspinatus, which is right above the spine of the scapula. Its job is abduction of the shoulder. It covers the top of the head of the humerus. That's the first muscle in your rotator cuff. Then we have the infraspinatus, which is below the spine of the scapula. Its job is lateral or external rotation, along with the teres minor. The teres minor, also on the back of the scapula, and its job is also external rotation. Then we do have the subscapularis. You can't see it here, but it's on the under surface or the anterior surface of the scapula, and its job is medial rotation. When I was in clinical practice, I know a lot of golfers had problems with this muscle. Those four muscles make up your rotator cuff, supraspinatus, infraspinatus, teres minor, minor being very important in there, and subscapularis. You might say, teres minor, where's the teres major? The teres major is right there above it, but it attaches on the front of the humerus. The teres major, its actions are the same as the latissimus dorsi, not the teres minor. The teres major extends and adducts the shoulder. It works with your latissimus dorsi there. All right. Now let's go back to the front and we'll look at the lower half of the body here. First we have your quads or your quadriceps. The quadriceps are not a muscle. It's a group of four muscles. So there isn't a muscle called a quadricep. It's the group of four muscles on the front of the thigh, and that's going to be the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius. So rectus meaning straight, so the one that runs straight up and down the front of the thigh is they're all going to be involved in the extension, so I'll just say that quickly here. So the rectus femoris runs straight up and down. Vastus medialis is going to be on the inside, also extends the knee, but it can help pull the patella that direction, so strengthening that muscle can help a lot of people that have issues with patella tracking, where the patella actually tracks too far on the outside and rubs on the femur, and that can actually wear away the cartilage underneath the patella. It's called chondromalacia patella. You do see it more with females because of the wider pelvis for birthing a child, so the q-angle is increased. I covered that in a separate video. So that's the vastus medialis. On the outside, you have the vastus lateralis, and then you have the vastus intermedius, but you can't see it here. You have to remove the rectus femoris, and it's underneath it, so the intermedius is in the middle between the medialis and lateralis. So those are your quadriceps, rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius. Then we have the sartorius. So sartorius means tailor's knee. So think about if you were sitting down and you put your right ankle on your left knee. That's the action or function of this muscle. I guess tailors must sit like that. At least that's where the name comes from. This is the longest muscle in your body because it runs the length of your thigh and also crosses it. So kind of the trivia type question you might see somewhere. So the sartorius or tailor's knee, longest muscle in the body, it's involved in flexion and lateral or external rotation of the hip. Next we have the tensor fascialata. Now in class you've got to call it that, but in clinical practice they call it the TFL. It's easier to say, less than a mouthful. But tensor fascialata, what it's basically saying is it has a really big tendon. So you notice it's a small muscle, but it actually has a very long, very, very big tendon. So the function of the tensor fascialata is going to be flexion of the hip and then medial or internal rotation of the hip. But that really long tendon actually fuses with the tendon of the gluteus maximus muscle and makes up the IT band or iliotibial band. And that can cause a lot of lateral knee pain in runners if that gets real tight. So loosening that, massaging it, breaking it down appears to be helpful. Just kind of a little tip there. Next we have the adductors or the groin muscles. So you have the adductor longus and adductor magnets are the key ones. So adductor longus, like the name implies, is the longest adductor muscle. So it involved in hip adduction. The adductor magnets is the largest. It's actually so large that it's involved in both flexion and extension of the hip because it's just got so many attachment points, but also hip adduction. That's the key there. Then we have the gracilis there in the middle. The gracilis is the most medial muscle in the thigh. So it's going to be involved in adduction, but also because of where it inserts a little bit of flexion as well. That's called the gracilis. And the last one here on the front is in the shin there, the tibialis anterior involved in dorsiflexion. So standing on your heels or picking up your toes if you're sitting, that's dorsiflexion. Okay, now let's look at the last one here for this video. Let's look at the posterior side of the bottom half of the body. We have the gluteus maximus. It has been cut away, but you know what that muscle looks like. That's the largest gluteal muscle. So notice we don't have a major and minor. And that's because there's not two options. There's three. We have gluteus maximus, gluteus minimus, which is the smallest of the three gluteal muscles, and then the gluteus medius. So that's why you see it called maximus and medius here. So gluteus maximus is involved in extension of the hip. Then we have the gluteus medius, very important, very involved in abduction of the hip. If this muscle is weak and you try to stand on one leg, your pelvis will basically drop because you can't, you can't stabilize the pelvis without this muscle. That's the gluteus medius. Then we have your hamstrings. Again, they're hamstrings and not a muscle. It's a group of three muscles. So there's no hamstring muscle. The hamstring is made of hamstrings are made of the biceps, femoris, semi-membranosis, and semi-tendinosis. I'll do a separate video where I cover them in more detail. But biceps, femoris, two heads, why it's called the biceps, in the femoral region, on the back, and all three of these are involved in knee flexion, semi-membranosis, and then semi-tendinosis. And again, I'll cover these in more detail. But how you remember the difference between the two, semi-tendinosis has a longer tendon. So look down by the knee. You can try to figure out which one is which. Semi-membranosis has a big, membranous, sheath-like tendon, but you can't usually see it unless other muscles have been cut away. So those three muscles make up your hamstrings, biceps, femoris, semi-membranosis, semi-tendinosis. Then down in the calf, we have the gastrocnenius and the soleus. Gastro means like stomach or belly. So the gastrocnemius has two large bellies, a medial and lateral belly. And then they're going to be involved in plantar flexion, so standing on your tippy toes. The soleus is underneath that muscle or deep to it, also involved in plantar flexion. The key there is the soleus is a postural muscle. So if you're just like standing for hours at a time, the soleus is doing most of the work. The gastrocnemius is more of an explosive phasic muscle. So if you're running or climbing stairs, the gastrocnemius would be more important, but they work together. All right, that's the gastrocnemius and soleus. Then we have, what else can we see here? You can see the, we already covered the gracilis, but you can see the gracilis there, that medial most muscle, but we already hit that one. So, okay, that is it for this video. Like I said, I'm going to come back through and cover all the important ones in detail where you can really get a better look. But I wanted all the key muscles that I expect you to know in one place, and there they are. I hope this helps. Have a wonderful day, be blessed.