– For more information and a full transcript of this video, check out fun4thedisabled.com. When joining us for this video, you need to take some precautions as your health and safety are the most important. To avoid any injury or harm, you need to check your health with your doctor before exercising. By performing any fitness exercises without supervision, like with this video, you are performing them at your own risk. See a fitness professional to give you advice on your exercise form. Strategy for Access Foundation NFP and Dark Room Ballet will not be responsible or liable for any injury or harm you sustain as a result of this video. 


– Hi everybody. I’m Krishna Washburn, and I’m here to present another No Diagram Anatomy class for all of you good folks. So who am I? I am the Dark Room Ballet ballet teacher. I have a Masters of Education and I have special certifications through the American College of Sports Medicine. And I have a particular interest in biomechanics, and I’m a blind professional dancer. So welcome everybody. Today’s class topic is actually “Biomechanics 101,” also known as, “Joint Actions.” That is our topic today. 

A little bit about my surroundings, I’m recording here from the Dark Room Ballet studio, which is a garden-level apartment in a little brownstone house in Sugar Hill, up in the heart of Harlem in New York City. I’m recording from my little professional dance floor. It’s about six feet by six feet, two meters by two meters. Some sounds that you might notice, you might hear a little bit of New York excitement on the window on the other side of my camera. You’ll definitely hear the chirping of my four little birds that are under their covers. They haven’t fallen asleep yet so you might hear them chirping along with me cause when I talk, they talk. You might also hear the pitter-patter of little feet, ‘cause there’s a little bunny rabbit living in the kitchen with me as well, and her name is Flora. So if a little bunny rabbit comes onto the scene, don’t worry, she’s supposed to be here. So here I am, this is my dance studio/kitchen/everything place, my home with my animals, and I’m ready to dance with you in your home. 

So let’s talk about joints. A joint is a place on the body where two bones meet. That’s what a joint is. It’s a place where two bones meet and there’s three kinds of joints. The first kind of joint are called fibrous joints. Fibrous joints are more or less attached to each other with really tight connective tissue, maybe even fibers of bone tissue, and that includes the plates of the skull, and it also includes how the long bones of the forearm and our lower leg attach to each other. We have two bones in those parts of our bodies, those analog lower halves of our limbs. Fibrous joints are not really considered to have a range of motion. So we’re not gonna talk too much about them today, but they do exist and they are places where bones meet. 

The second kind of joint is called cartilaginous joint. Some of the cartilaginous joints that we have in the body are our spine, in our pelvis. We also have cartilaginous joints in our ribcage. They’re considered to have somewhat less capacity for motion, but we’ll see about that. We’ll talk about that a little bit more in depth later on in class. The third kind of joint is the synovial joint. That’s the most common joint in the body. A synovial joint has a very special and specific structure. Think of you have a little plastic capsule around the place where the two bones meet, and inside that plastic capsule is synovial fluid. Synovial fluid, I like to think of as shampoo or soap, and actually has a lot of very similar chemical properties to shampoo or soap. And it gets firmer when it is cool, and it gets more fluid when it is warm. So if you’ve ever gone to ballet class and you have to do your pliés to get ready for the rest of class, what you are doing is you are warming up that synovial fluid in your synovial joints, so that way those joints can move smoothly and be lubricated. So a little bit of rules relating to how these synovial joints work. Synovial joints are moved by muscles and muscles only function when they are enervated. That means the nerves in that part of the body have a signal that comes from our brain, through our peripheral nervous system, into those nerves, and those nerves enervate the muscles, and tell us that we want to move it. 

Now how those muscles act on the joints is very particular. Muscles can only pull on bones. They can’t push, they can only pull. So you need to think, all right, I will think about a pulling sensation, or a shortening sensation, to determine what muscle is acting on a joint in order to cause it to move. Muscles at synovial joints tend to work in opposition. They work in pairs. The family of muscles that do one movement are not gonna be the same family that does the opposite movement. A different family of muscles is going to be doing the opposite movement. 

So now let’s start talking about the three categories of synovial joints. The first kind is called single axis joints. They’re also sometimes known as hinge joints. Single action joints, single axis joints, can only move in one prescribed axis of motion. And in general, what that means is it can bend and it can unbend, and that’s all it can do. Or, keep your ear open for this, that’s all it ought to do. There’s several hinge joints, or single axis joints in the human body. The most well known is probably your elbow. Your elbow can bend, or flex, and it can extend, or it can unbend. Flexion is when you bring one part of the body close to another part of the body, and extension is when you move them farther apart. So I bend my elbow: I flex it. I extend my elbow: I unbend it.

The other hinge joints in the body are our knees. So our knees, I bend my knee, my lower leg gets closer to my upper leg. And a different set of muscles bends my knee than straightens my knee out again. It’s a different set of muscles doing those two movements. The other hinge joints are on our four fingers, the two top knuckles. So the middle knuckle and the top knuckle, the one closest to your fingernail. So those are also hinge joints. Those are hinge joints. And also the one at your thumb as well, the top tip, tip of your thumb. That is a hinge joint. Also your toes are hinge joints. If you are a ballet student, let’s say, and you are very experienced now doing pointed feet, you will be using, through the flex and point of your foot, your toes, are hinge joints. You can curl those toes up to a certain amount and you can also curve them down. Those are hinge joints in your toes. So those are all of the hinge joints in our bodies. 

Let’s take a minute and think, in particular, about elbow and knee. So we’ve got elbow. I bend my elbow, I flex it. What muscle does that? Something has to be pulling and shortening, “contracting” is the scientific word, in order for that to happen. Now, I think about, all right, I’m gonna really focus and take my time and do this very slow. I feel this part of my arm, the inside part where the skin is very thin, that is shortening. It’s contracting. It’s flexing. Now, if I’m gonna straighten my arm out again, what is doing that? It’s not going to be my inner arm muscle. If I straighten it out again, it’s the one on the back of my arm that I feel, shortening, flexing, contracting. This muscle now on the inside of my arm is stretching. The one on the back is shortening. If I bend my elbow again, the muscle on the back of my arm is lengthening. The one on the inside is shortening, flexing. Now how about knees? If I check with my knee, I’m gonna stand on my left leg and I’m gonna bend my right knee. What set of muscles is doing this? What is doing this? I feel it on the back of my leg, shortening, contracting, acting on the bone, making that lower leg move closer to the upper leg. Then when I straighten my leg out, especially if I go slowly, I know that’s the muscle in the front of my leg that’s doing the opposite motion. I bend the knee, muscle in the back, straighten the knee, muscle in the front. Now you’ll notice a theme with both our elbow and our knee. The muscle that moves the joint is the muscle that is next closest to the joint that is closer to the torso or closer to the middle of the body. 

So I have a forearm, and my forearm does move when I bend my elbow, but my forearm is not doing the work here. It is the muscles surrounding my upper arm that is doing the work. Same thing with my legs. It’s the muscles surrounding my upper leg, that bend and unbend my knee. My lower leg is in motion, but the muscles in my lower leg are not the ones acting on the joint. It’s always going to be the muscles closer to your torso or closer to the middle of your body. So let’s do a little bit of independent practice time with these thoughts in mind about single axis joints. Can you do dance improvisation that really helps you get a sense, a feeling, for how these single axis joints, our toes, our fingers, our elbows, our knees, how they function in the system of your body. Let’s catch back up in two minutes, and let’s practice our movement. 

(upbeat electronica) 

Okay. So what are some of the things that you’ve picked up on through your exploration of your single axis joints? Let me tell you a couple things that I started to think about. We talked in depth about how our muscles act on our elbows and our knees. So I really started to think a lot about my finger joints and also my toes. I started really paying attention. I picked a foot up off the floor and I let that foot point in the air as hard as I could. I started really feeling, Okay. When I point to my foot, I feel the sole of my foot in action. When I flex my foot and I let my toes reach upwards, I can really feel the top of my foot doing the action there. And there is a reason why. That is the locations of the muscles that act on our toe hinge joints. They are absolutely on the tops and bottoms of our feet. Now the sole of our foot has also somebody to help it out, which is our big set of calf muscles. All of those muscles in the family, they all work as a team, the sole of the foot, and the whole complex at the calf muscle, really work together to help you activate those toes. It’s not something that’s easier to, as easy to pull apart as the, how the elbow and the knee work together. 

Now, hands and the fingers, little upper knuckle joints on our fingers, that’s also really interesting because I think a lot of people don’t realize your hand itself does not have muscle tissue in it. Your hand is all full of connective tissues and nerves. The muscles that control any and all movements of your hands, they’re in your forearms. That’s what’s going on. And if I was able to really concentrate and move one middle knuckle at a time, and I could start to sense, I had my palm facing upward and I was concentrating my energy bending the middle knuckle of the index finger, bending the middle knuckle of the middle finger, and the ring finger, and the pinky finger, and I could feel small changes on the inside of my forearm. And then when I straightened those fingers out again, I could feel a stretch. It was very, very informative and really interesting to try. 

Now, let’s talk about the next set of joints. They are called the double axis joints. So single axis joints means they move in one way, bending and unbending. Double axis joints means it can move in two ways. Double axis joints can bend and unbend, but they can also move in towards the midline of the body, or away. Those are called adduction, moving in towards, and abduction, moving away. So what I just did is I stood with my arms down and my palms facing backward. I can tilt my hands in towards the midline and then going through neutral, out towards the outside edge. So my thumbs come up a little bit. My pinky fingers come up a little bit from hanging down, thumbs come up, pinky fingers come up. It’s this windshield washer kind of feeling from the wrist. And the wrist can also flex, bring the hand closer to the arm, and extend, bring it away. It can flex. It can extend. 

Now people have different ranges of motions, especially in their wrists. Some people can flex their hand a lot and bring their palm very close to their arm. Some people can extend their hand a lot and bring the top of their hand really close to the back side of their forearm. But this is something that is very different for every person. Same thing with the adduction, in towards the middle, and abduction, out towards the sides. That is so unique and personal to each person. So we know we’ve got the wrist, that is a double axis joint. What’s the other double axis joint we’ve got? We’ve got our ankles. Now, I’m not gonna be moving the soles of my feet, but I’m gonna pick up my right foot here, and right now I’m flexing my ankle. I’m using the muscles in the front of my shin to bring the top of my foot as close to my shin as I possibly can. And now I’m gonna extend, I’m not activating the sole of my foot. I’m moving just from the ankle. I extend, the top of my foot is now far away from my shin bone. So flex, top is getting closer. Extend, top goes farther away. So that is one action. 

Now my left foot, I’m gonna demonstrate how ankles can adduct and abduct. And ankles have to be able to adduct and abduct in order to respond well to uneven ground. But sometimes it causes us some problems. So if I have all my weight on my right foot and my left foot is on the floor but there’s really no weight on it, that’s a safe way for me to show you adduction and abduction of the ankle. So if I pick up my pinky toe and I roll so only the inside edge of my foot is touching the floor, that is my adduction. Bringing that ankle in towards the midline, I go through the middle, whole foot lightly touching the floor, and now pinky toe stays in contact, the big toe and inside edge of my foot comes up. That is abduction, going away from the midline of the body. 

Now for ankles, we have an extra set of fancy antonyms to describe these movements. And they are inversion, that is adduction of the ankle, and eversion, that is abduction of the ankle. It’s really easy to remember because inversion sounds like “in,” so it brings the ankle shape in closer to the midline of the body. Eversion brings it away from the midline of the body. Now being able to do that as a response to uneven surfaces, how we evolved to be able to walk, not only on sidewalks, and tile floors, and carpets, but you know, through the forest, and the plains, and all the natural landscapes. But sometimes these things can go awry and we use those other set of antonyms, inversion and eversion, to describe types of sprained ankle when things go wrong. So inversion sprained ankles means the sole of foot pops out at the side. Eversion sprained ankles means sole of the foot pops up on the inside. Sprained ankles are really bad. So actually a lot of dancers not only have to train awareness of these more subtle movements of the ankle, but learn how to use it sparingly, and carefully, and never when there is weight on the foot. It always has to be weightless foot. Even if the foot is touching the floor, it must always be weightless. 

Now there’s one more kind of joint in your body that is double axis, and that is the base knuckles of your fingers. So your fingers can flex. They can come down, and they can extend. They can flex and extend, fingers get closer to the palm of the hand, they get farther away from the palm of the hand. Flex and extend, bending the knuckles, unbending the knuckles, the ones that attach your fingers to your palm. But they can also spread apart, that is our abduction, and come close together, that is abduction. So if you’ve ever, you know, know like when people scold little kids or little animals and stuff, and they had the index finger pointing up and it waves side to side, they’re going through abduction and adduction, one after the other at the base of that knuckle joint of the finger. And remember, all of these movements, whether it is flexion or extension, adduction or abduction, it is all coming from enervated muscles that are closer to the center of the body. So another opportunity to dance and explore movements that really clarify the wrists, the ankles, these fingers, and really make their origins of energy present to you. Two minutes to dance everybody. And then we’ll regroup. 

(soft electronica) 

Okay folks. Let’s regroup. Let’s think about some of the things that we noticed as we were connecting with our ankles, our wrists, and our fingers. Now, something that I’m sure at least one of you experimented with was thinking, “Hey, what’s this thing? Why can I make this circley type shape with my wrist? Why can I make this circley type thing with my ankle? What’s that all about?” Now this is a great big debate in biomechanics. There are some biomechanists who say, oh, well this is just smooth transition from flexion, to adduction, to extension, to abduction, and that’s why you can go through that pattern with your wrist or your ankle. You’re just transitioning between the extreme destinations of those joint actions. But there’s a team of different biomechanical scientists who say, “No, no, no, no, no. This is another movement. Something we haven’t considered before. And we’re gonna call it circumduction.” We’re going to call it circumduction because I think, me, the opposing biomechanical scientist, think that this is a circle and it’s not just, oh, I’m making smooth transitions between four different shapes. I’m making circumductive movements. 

Now I also wonder if there’s anybody out there who, regardless of whichever side of the debate you fall on, whether this, you think, okay, this is just moving through four discrete shapes in a smooth way, or whether you think this is circumduction or not, I wonder was there anybody who did this movement and brought an arm out front with the palm facing down and then rotated their wrist to bring their palm to face up, and wondered to themselves, “Huh? What is that all about? What kind of wrist movement is that?” Now, do you remember earlier in class when I said, “Oh yeah, fibrous joints, they don’t really move.” A fibrous joint, the joint that connects the two long bones in your forearm, enables you to do that. So it’s not at your shoulder, your upper arm does nothing. You can have your palm facing the floor and then rotate, in your forearm, those two bones in your forearm, cross each other at their fibrous joints, so then your palm can rotate up. Put a hand under your elbow, really check this out, where you can have a palm face the floor, you can have a palm face up. Now put your hand right in the middle of the forearm, underneath, palm facing down, palm facing up. You can almost feel those two bones making an X shape in your forearm. Now that movement of the wrist is called supination and pronation. So pronation, palm faces down, palm down, pronation. Supination, palm faces upward. Some people say, “Oh, if you have a supinated palm, you could pour soup into your palm.” 

(makes a singing, doubtful noise) 

That’s not something I would recommend, maybe gazpacho, I don’t know, but that is how that joint action works. That’s not a synovial joint making that movement possible. It’s actually a fibrous joint making that movement possible. Is that not wild and exciting? I get excited about joint actions. What can I say? 

But as exciting as the double axis joints are, there’s nothing that’s more exciting than the triple axis joints. So what do we have, joints that can move a minimum of three different ways. Now we’ve got three triple axis joints in the body. They are the shoulder. Now the shoulder can do all of the things that a double axis joint can do. It can flex. That means it can bring that arm close up into you. It can extend, bring it behind you into the back space. Away from you, out in front of you and up, back behind you, that’s flexion and extension of the shoulder joint. It can also adduct and abduct, meaning that I can bring my arm out to the side and up, and then back down again. And I can cross my midline with my upper arm, so I have this huge range of motion. My arm can go all the way up, arm against my ear, abduction. Adduction, cross almost all the way to the other side of my body. I can bring my elbow almost like it’s right at my navel, it’s right at the middle of my body. Now that can do one more nifty thing, which is that our shoulder joint, because it’s a ball and socket joint, our upper arm bone can rotate inside the shoulder socket. So let’s say I begin with my palm facing my torso, and my arm down. I can rotate it outwards, and I can rotate it inwards. I can rotate it out, turn it out. I can rotate it in, turn it in. And that is a third way that a joint can move. 

The other ball and socket joint in the human body is the thigh bone connecting to the pelvis, the hip joint. So I can flex. I can bring my leg up out in front of me. I can bring it behind me, I can extend. I can bring my leg away from the midline, abduct. I can cross my midline, my knee is all the way over on the other side of my body, that is adduction. And I can rotate it in the socket. I can turn it out. I can turn it in. I can turn it out. I can turn it in. And the muscles doing these actions are all wrapped around the pelvis. The muscles doing the actions of the shoulder are all wrapped around the upper torso, and really almost our entire back is in charge of moving our whole chest. Most of our back is all dedicated to moving our upper arm bones, activating our shoulder joints. 

Now the third triple axis joint is the most human of the joints. It’s the thumb. Now the thumb is not a ball and socket joint like your shoulder or your hip. It is what’s known as a saddle joint, and it has a crazy number of movements that it can do. So my thumb can flex, it can come upwards. It can extend, it can go downward. It can abduct, it can move away from my hand. It can adduct, it can move inward. It can circumlocute, go in a circle, and it can also do this amazing thing called oppose, which is that my thumb can fold in on itself on the palm and it can do a precision grip with any of my four fingers. That is what makes our thumb probably the most unique joint in our human body. And also the joint that has the greatest number of kinds of movements that it can execute. It’s what? Thumb: infinite possibilities! 

Now, this is important for me to mention. Just like with our wrists and ankles, our double axis joints, triple axis joints have different ranges of motion depending on the person. And sometimes we will lose range of motion because of injury, or illness, or maybe your disability limits the number of ways in which your joint can move, or it makes the range of motion for your joint a little smaller. None of those things actually change the capacity. Even if your range of motion is small, it’s still there. There’s still always ways to connect with the range motion of a joint. There’s always ways to find it. So let’s dance a little bit together, and let’s take some time and think about how we can sense these versatile, almost infinite, triple axis joints in our bodies. Talk to you in a couple moments. 

(upbeat electronica) 

Well, that was a lot of fun for me. I don’t know if that was a lot of fun for you, but when I connect to my triple axis joints, I feel so free. I just really want to play and sense all of the changes in my joints. At one point, I was just making these big, windmill circles with my arms, and doing it at different speeds. If I bring my arm in a circle, coming forward, over and back, really fast, it almost feels like I’m not doing anything, like almost like momentum is moving that bone, but I know that that’s not true. What’s moving that bone are my muscles. So if I go slower, and I take my time I can notice, all right, as I reach forward, I feel my shoulder, the front part of my shoulder, shortening, contracting, as my arm comes up and up and up and up, and as I reach the top something changes. As it starts to reach back, I feel now in my back, just in my upper back and the muscles take over there and keep my arm moving. It was a change, same thing I was making circles that go across the front with my arm, playing with adduction and abduction, things were different there too. If I go out to the side, slow, I feel the middle of my shoulder doing that job all the way up to the top, but then, as I cross the midline, I feel my chest taking over. And then as I reach the bottom, I feel something else happening, some transition. And then I feel my shoulder take it over again. It’s so wonderful to come to understand what pulls on those bones. 

With my lower legs, I really played. How much to the front can I flex that leg? How much to the back can I extend that leg behind me? I can feel the back of my pelvis shorten as I bring that leg behind me. And I can feel all of these muscles in the front of my pelvis contract so strong when I bring that leg out in front. It’s so clear who’s doing that job. And for my thumb, I took my time and I let it touch each finger, and paid attention, to all the tiny little piano string muscles in that forearm and let them burst away, feeling not only my fingertips become so vibrant, and the palms of my hands, all the nerves living in there become vibrant and awake, but also noticing the radiation through my forearms as those changes were happening. So much fun. So exciting. 

Now let’s talk about you thought I was talking big controversy when I was talking about circumduction of wrists and ankles. Here’s the biggest controversy of them all. In biomechanics, are the movements that happen at cartilaginous joints, movements? Discuss everybody. Now there’s some debate. Some scientists say that cartilaginous joints don’t move. I know that that’s not true. Here is the truth about our cartilaginous joints. Cartilaginous joints require mental focus and concentration to move, but they move. And if you are a trained communicator with your nervous system, like a lot of my folks who are dancers are, and you can treat your nervous system like a wild bird, and tame it, and treat it with positive reinforcement, and patience, and gentleness. And you can ask it and say, “Hey, spine, can you change shape?” And you know what your spine’s gonna do? It’s gonna change shape in the way that you want. Our spine is the largest collection of cartilaginous joints. Every vertebra, we have five in the lower back, 12 in the thoracic, middle back where our ribs are, and seven in the neck, they are all cartilaginous joints. 

Now there’s all different types of movement that can happen in the spine. So we have spinal flexion, that’s when we make a curve in the spine or in the neck even, that makes a C shape into the back space. And then we have spinal extension, that’s when we make a C shape that reaches into the front space. We have lateral flexion, that’s what we call tilting from the spine. So we have lateral flexion to the right, lateral flexion to the left. That is what we call tilting. If we do (speaking Sanskrit) that’s lateral flexion of the spine. We also have spinal rotation. We can rotate. We can even just rotate at one vertebra. I can rotate just at my top vertebra of my neck and the rest of my neck is totally still. It’s not that big of a movement, but I can do that. I can move from just the vertebra at my waist and rotate my torso, keep my lower body totally still. I can rotate and I can make big, yoga spinal rotations where I can rotate as much as I want to and move all of vertebra, and rotate all of them. There’s a lot of possibilities with our spine. 

Now, as for our other cartilaginous joints, we also have our shoulder blades. Our shoulder blades are attached to our ribcage by cartilage and our shoulder blades have the capacity to move, also a lot. We have to ask it to. Our shoulder blades can elevate, they can come up and bring our shoulders closer to our ears. They can depress. They can push down. They can spread apart. That would be abduction. They can pinch in towards each other. That would be adduction. And another nifty thing. Do you remember when we were moving our arms out to the side and doing abduction at the shoulder? Feel and sense, really carefully in your back, what are your shoulder blades doing? Are they still? Or can you ask them to rotate too? They can rotate upwards and rotate downwards. 

Now our rib cage, people say you can’t move your rib cage. It can at least inwardly flex, and outwardly extend. You need to ask it to. It can do at least that. My sternum bone is attached to my ribs. That’s what covers my heart. Cartilage attaches my sternum bone to my ribs in the front. I’m gonna ask my sternum bone to come inward. It is coming in. I need to focus to do that. And I can also ask it to extend outward. But I have to be patient. I have to ask my nervous system to do something about it. So this they call, either they call it inward flexion or they call it inward adduction, or they call it outward extension, or outward abduction, meaning that our sternum bone is moving in towards our spinal column, and out away from it. It takes focus and concentration to move these cartilaginous joints carefully and with care, and to do it safely. We have to take time. That’s one of the beauties of dance. That it’s a lifelong adventure. You can take as much time as you need to tame these parts of the body. So let’s take a little time together and really explore the possibilities of these cartilaginous joints together. 

(upbeat electronica) 

Welcome back everybody. Here’s something that you may have observed that caught my attention as I was really focusing my attention on those cartilaginous joints. Unlike our synovial joints, where it’s pretty easy to figure out the location of the muscles causing those joint actions, with our cartilaginous joints, it might feel a little more vague. It might just be like, “Okay, I’m using, I know it’s the front of my torso. Maybe the back of my torso? Maybe opposite sides?” The reason for this is because our cartilaginous joints are supported by the core muscle system. This is a lot more complicated and is in layers and layers of sheets and sheets of muscle tissue of all different kinds of stripes and patterns. So it may be a little bit less obvious to you what precise muscle is doing the task, but you’ll know, if your nerves are helping those bones pull into the shape that you want your spinal flexion, your spinal extension, all the different play of the shoulder blades. Even the sternum bone, it’s all there. It’s all possible.

So with that, we’re gonna wrap it up. Enjoy your improvisations, enjoy the internal feelings of all the different joint movements you have in your body. And come back next time, for more dancing, here in the Dark Room, with more No Diagram Anatomy. Bye, everybody.

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