Welcome back. This is the musculoskeletal system and we'll be talking about the bones, muscles and the joints. So yoga is perfect for this module because it makes the muscles most efficient. So you need proper muscles so that you can have the proper posture and of course, you look good when you have good muscles. So how does the muscles become super efficient? It is all about circulating the nutrients and the oxygen so that the muscles can be super efficient. So this is the reason why yoga is extremely important for the muscle, and the proper functioning, of course, the bones and the joints. Later on, Dr. [inaudible] , will be joining us and talking about how joint health is very important. So there are three types of muscles found in your body. There's the cardiac muscle, there's the skeletal muscle, and there's the smooth muscle. The cardiac muscle of course pumps the heart and makes your circulation efficient. The skeletal muscle is the one that are moving all of your bones so that you have proper movement. Of course, the smooth muscle is found throughout your digestive track and therefore it will be propelling all of your food from your mouth, all the way down to the other end of your digestive tract. So the skeletal muscle is made up of, the muscle itself is covered in a sheath or covering called the epimysium. If you cut the belly of the muscle, you'll see a lot of little fascicles. They are little groups of tissues that you think that is triangular or circular in structure, those are the fascicles that make up the larger muscle. The fascicles, as we said, is made up of a group of muscle fibers. The muscle fibers when you pull them out, you'll see that it is covered by another covering called the endomysium. So when you take a look at the muscle fiber, it's made up of smaller tube called the myofibril. So in this module, I will say muscle fiber even though by Greek it will be called the myofiber. So in the textbook you might see the term myofiber and the myofibril. But, of course, the myofibril is the protein tubes that are found within inside the muscle fiber or the myofiber. So I'll tend not to use the term myofiber and use the term muscle fiber instead. So the types of skeletal muscles exists. What are they? They are classified by their ability to twitch. What's a twitch? It's a single muscle contractions. So anytime you are touching your shoulder, that is a single twitch. If you smile and then let go of your facial expression, that is a twitch. So if you can do these things fast they're known as a fast-twitch fiber. Like the one that's found on your thumb, and notice how fast your thumb can twitch. Most of the time you can make your thumb without any exercise or any kind of training. It could be moving as fast as seven times a second. So this is what's really needed for those of you who are playing video games, you want to press the button as fast as you can. The second type that you find in your skeletal muscles is the intermediates. Who are the intermediates? They're the types that you find in your shoulder, or your deltoids. They have slower speed of contraction than the muscles of the finger. But they are longer lasting. In other words, for them to fatigue, it takes a little longer time. So in other words, what can you do with your arm? You can raise your arm and keep it there for a longer period of time and it will fatigue slowly. But if you're talking about your thumb, you can keep pressing a button all day long and eventually, within minutes, your thumb will start to slow down like mine. So the third type is called the slow twitch fiber. So where do you find these? They are your back muscles and they're the ones that give you the best posture. Of course, when you're doing yoga, this is what you're probably going after. You are making sure that the slow twitch fibers are really optimized and really trained. So, they're not only rated for their twitch, as I said before, they're rated for their fatigue resistance. So the ones on your finger, therefore they're very fast. So why would you have the three types? So in other words, if you're falling down from a mountain, would you want slow twitch fibers? No, the timing that it will take to grab a branch as you're sliding down will be too slow for you. So this is the reason why the body, ingeniously, have placed fast-twitch fibers in your hands and slow twitch fibers on your back so that once you have grabbed onto a branch, you can sit up on a ledge and wait for help. Otherwise, you'll be holding onto a ledge with your fingertips and that, as most of you will probably know, you'll will not be on that ledge for a long period of time. So what makes these muscles very different? It is what their fuel is. So we call them the glycolytic muscles versus the oxidative muscles. The glycolytic, just like the name implies, utilizes glucose. So in other words, all you need is sugar for your thumbs to move. They do not require any other fuels. So in other words, what is the oxidative ones? This is the ones that we'll be utilizing fat, amino acids, and sugars at the same time. So whatever is available to them, they will be utilizing it. So these are the major muscles types that you have in your body that gives you your posture. Again, some examples of the fast twitch fibers are your fingers, the intermediate types are your deltoids, or your shoulder muscles and of course the slow ones are the back muscles or your postural muscles. So because they do not have any myoglobin content, the fast type will always appear, when uncooked, light pink. When you take the slow ones and you look at it uncooked, it would appear red. So the intermediate are going to be utilizing mixture of glycolytic and oxidative muscle. So therefore, they do require some oxygen but it's not a whole lot. Who utilizes all of the oxygen in your body? It is the slow type. So if you really want to think about it, you are really breathing for your muscles, because they are going to be making a lot of energy using the oxidative process. So what makes skeletal muscles function? So there are really two components in skeletal muscles. What's called the elastic element and the other one called the contractile element. The elastic elements are parts of the cell and parts of the muscle that can stretch. A good example of this is a tendon. The contractile elements are the actual proteins that makes the muscle become shorter, such as the Actin and the Myosin.