in this section we will discuss the concept of kinetics kinetics is the analysis of the forces that create motion and maintain balance specifically in our human body um muscles uh create forces and within our human body there are three type of muscles that um that we use to generate Force the first type is the cardia muscle which we can find the card muscles in our heart and the second type of muscle is smooth muscle which we can find uh these muscles in our organ and the third type of muscle is the skeletal muscles which will be our Focus for this semester a typical skeletal muscles are in charge of voluntary actions in our human body to do this voluntary action uh a specific uh muscle need to have the ability to receive a signal from the motor neuron which you will learn more in the Neuroscience course in the fall and uh after receiving the sick note um uh the muscle needs to have the ability to contract in order to produce a movement uh through um the muscle contraction another function of the muscle is to Distributing the loads from the external environment uh by absorbing the shock uh or the impact to the human body so before we learn more about how muscle generating uh a muscle Force we need to look at the structure of a typical uh skeletal muscle in a typical skeletal muscle we uh can see there's a origin of the muscle and the insertion of the muscle the original muscle typically uh originated from the proximal part of the movement in this sense is a proximal BMP and the insertion typically um is disto from um the uh insertion why do we need to know this when we know the origin and insertion of a specific muscle we would know uh what movement that this muscle is uh functioning if you're into kinal taping or you you've heard about kinesiotaping technique you would have to know uh the origin insertion of a muscle so you can apply the kesal taping uh based on the direction of the muscle um the shape of a muscle also matters um so uh there are muscles um the shape look like the fuchia phone uh type of muscle like this uh such as biceps uh brachialis break your radialis this type of muscle because it's uh um the shape that typically uh they produce more mobility in other words they produce more muscle Excursion that you know a um helping to produce more range of motion the other type of muscle they're much more flat and short uh they uh the shape may look like the pened muscle like uni pened bip pened or multi pened muscles like this these type of muscle they don't have much more range of motion but they produce much more uh strength so the based on the shape of the muscle we can kind of expect uh what this type of muscle do to our human body when we look closer um to the structure of a uh muscle we can see when we do a crosssection to muscle uh a muscle is actually uh consisted of multiple phasical FAS each fasle they have you know uh the muscle fiber multiple muscle fiber in it when we take a segment of a muscle fiber we can see the smallest uh function unit of a muscle called sarcomere within the sere there's there are two important protein called uh actin and myosin um these two protein can uh bind to each other doing muscle contraction to produce muscle uh strength uh when we put our uh hand together like this pretending that one hand is acting the other hand is myosin um the the picture in the middle here we can see that this is when the sakr miror is at a resting position and this is also uh uh when the muscle contraction produce the most or the strongest muscle strength when the distance between AC and myosin is uh far away like the muscle is being stretched and it's hard uh for the actin and myosin to bind together to create this kind of cross bridge and similar situation when the actine and myosin um the two are too close to each other then The Binding um strength can be reduced as well because they're uh because they're too close to each other so this is uh very important concept for us to know when we position The Joint uh we can expect that when the you know uh the muscle is at the resting position that actually produce the most strong uh strongest uh muscle strength when the muscle is in the shorten or stretched position or lengthen um position then uh the muscle strength produced is not as strong as uh compared to when it is at the uh resting position a so should have an active uh component and passive component for the contraction for the muscle to have uh the Active Components for contraction the muscle needs to have several uh um properties so they need to have intact nervous system to innovate the muscle to uh transmit the or to send the signal to the muscle or from the muscle the muscle need to have a proper circulation and nutrition to make sure that the muscle is in a healthy condition and to the muscle itself the muscle needs to have the ability to contract and uh muscle needs to have the ability to be stretched or um to absorb the impact from the external U environment so when we look at a muscle typically we will see this kind of muscle right here the muscle body and um um there is a a tendon that attach um to the Bone and there's a t a muscular tendonous Junction that connects the muscle um to the tendon so this we typically see the uh unit of a muscle uh for the passive component for the of the contraction uh uh um the tendon itself is consists of the type one collagen which is resistant to uh being stretched right and this is uh good for our human body because when if the M when the muscle is being stretched the tendon is actually keep try to keep the muscle in shape so we don't lose any power to it but because of this stress this also creates some kind of passive attention to the muscle so when we look at the muscle length and its tension uh in a different uh muscle position we can see that um when the muscle is at the resting position we call it a normal position right here it is the most strongest uh muscle contraction that we can find or in other words the muscle will produce the strongest uh muscle strength when the muscle's length is at the normal uh range when the muscle is shortened because of the uh cross bridion is kind of too short and the actin and myosin they're too close to each other it it it's hard for The Binding uh action to happen so it actually reduce the muscle strength and similar situation we can see that when the actine and myosin is far away from each other and The Binding re uh reaction is kind of hard to happen right so the muscle strength also reduced um but when we look at um the active component uh with the passive component so here this uh dash line represent uh the active component which is the muscle contraction in different muscle length um and again when we look at this part it's exactly the same as the one that's on the left however when one muscle is Contracting the other side of the muscle that's say Aces and antagonist so um the other side of the muscle um is being stretched and that would create some kind of passive tension so that's why when uh some people may feel their uh their the muscle Sur is actually stronger when the muscle is being stretched and now we know this kind of situation right here it is not um the primary mover uh muscle produce more um strength it is combining with the passive tension when you see the total tension right here here and it actually goes up so please don't confuse with the active component to the passive component so this is important when we are um training our our patient sometimes we may choose uh to put the position in the close to the end range because we want um the active component and the passive component and we know that when the muscle is being stretched they don't produce much uh muscle strength but um the passive tension is increased in in a way so so this is how we use this concept in our clinical practice