 Hey everybody, Dr. O here. In this video I'm going to cover all the key muscles of the lower leg, both front and back. All right, let's start with the tibialis anterior. So you can see that one right there, front and center. Tibialis anterior is involved in dorsiflexion and inversion. So dorsiflexion would be standing on your heels or pulling your toes up, as you can see from the picture there. And inversion is drawing the sole of the foot medially, so like the way I'm sitting right now, the soles of my feet are pointing in, so that's inversion. Those terms are important when you're looking at like inversion or eversion ankle sprains. So that's the tibialis anterior. Then we have the fibularis longus and fibularis brevis. Remember, longus means long, brevis, think brevity, brief, short. So they both do the same things, just one muscle is longer than the other. You may also see these called peronius. I learned them as peronius longus and peronius brevis, but fibularis longus and brevis is fine. So fibularis longus, the longest muscle running on the fibular side or the outside of the leg. It's going to be involved in eversion and plantar flexion. So pushing your toes to the earth, standing on the tippy toes. And eversion is the fibularis longus, fibularis brevis or peronius brevis. Same thing. So eversion and plantar flexion. Next we have extensor digitorum longus. So like the name implies, it will extend your toes. And then we have the extensor halusus longus. Remember, halux is your big toe. I always remember when you walk down a hall, you use your big toe, your halux. When you take a pole, thumbs up or thumbs down, you use your pollux. So the extensor halusus longus is the long muscle that extends your big toe. Next image on the back here, now we have the gastrocnemius has been cut away here as you can see underneath it. But the gastrocnemius is the largest calf muscle. Notice it has a medial and lateral head or a medial and lateral belly. That's where the name gastrocnemius comes from. Gastro means stomach or belly. So the gastrocnemius, large explosive muscle involved in plantar flexion, but also knee flexion. As you can see there with those heads, they do cross the knee joint. So the gastrocnemius is involved in both plantar flexion and flexion of the knee, whereas the soleus underneath it, this large broad postural muscle that's involved in sustained contraction if you're standing up for long periods of time, does not cross the knee. So it's only involved in plantar flexion. Then you can see a little plantarus muscle there, pretty small muscle with that long tendon that runs down. The plantarus muscle, it does cross the knee as well, so it's involved in plantar flexion and knee flexion. I remember I had a couple of patients, one was a letter carrier that had partially torn this plantarus muscle a lot more pain than you think from a little muscle like this. But those are the muscles there on the back, gastrocnemius, which most has been cut away there. The soleus, they both do insert on the Achilles tendon or Calcaneal tendon together than your plantarus muscle. As a group, those would be called your triceps surae, but I don't use that terminology anymore. And then now we're going to go a little deeper here and we see the popliteus muscle. So kind of interesting, the popliteus muscle, it basically, it can flex the knee, but also internally rotates it. The way I like to look at it is the popliteus muscle has to unlock the knee before it can flex. So before the hamstrings can actually bend the knee, the popliteus has to twist it, internally rotate it to unlock it. But then it also has to put that, so external rotation would be how the knee locks. So your knee kind of locks and unlocks prior to being able to move. That's the job of the popliteus. So it unlocks the knee by internally rotating it at the bottom half of it. And then also plays a role in knee flexion. Then we see, again, the fibularis longus and fibularis brevis again. So they can also be called peroneus longus and brevis. That's eversion. So taking the soles of your feet laterally and plantar flexion. So eversion and plantar flexion for those two muscles. The tibialis posterior. So on the back of the tibia, notice that it's involved in plantar flexion, planting your toes to the ground. So the tibialis anterior is a dorsiflexor involved in dorsiflexion. The tibialis posterior is involved in plantar flexion. But both of them are involved in inversion. So whereas these fibularis muscles, the foot, the ankle, the tibialis muscles, anterior and posterior, work together to invert the foot. So the tibialis anterior and posterior, they're agonist. They're synergist. They work together when it comes to inversion, but they're antagonist. They have opposing effects when it comes to plantar flexion and dorsiflexion. Then we see, again, flexor digitorum longus, which is going to flex your toes. That's on the back of the leg. The extensors are on the front. And flexor halosus longus will flex your big toes. If you're curling your toes, you're using your flexor digitorum longus and flexor halosus longus. If you're extending your toes up, then you're using the extensor digitorum longus and halosus longus there. There are other deeper foot muscles, but I'm not going to do a video on the foot yet. That's probably going to be sometime next year. All right, but those are all the key muscles there of the lower leg. I hope this helps. Have a wonderful day. Be blessed.