the way a muscle contracts has different roles in a typical muscle contraction when the muscle contract the muscle actually shortened um example here is when a person is trying to um bring the cup to the mouth um the muscles in charge of this movement is typically we can see here is the bicep muscles the bicep muscles um um contracts that uh create elbow faction that would help this person to bring the cup to the mouth when this typical muscle contraction happen you can see that the the biceps moving from the insertion toward the origin of the biceps muscles and this can be seen in a typical open chain movement however if a person is doing a pull up like this when this person is trying to pull his body up still the prime mover for this movement is still the uh biceps however in this situation we can imagine that the movements actually the biceps moving from the origin toward the insertion but still it's the uh biceps uh function as the the prime mover here so we can see this type of movement is typically uh observed in a close chain movement so it can it can be confused at times but when when we uh look closer it's not hard to understand uh when we look at the type of muscle contraction here so there are several type uh types of muscle contraction that we typically see uh when a muscle contract but it produce no change uh in muscle length we call this is isometric contraction so example for this is when we are holding the tray um and then carry the tray to from A to B um we we uh contract the muscle to hold the tray but we don't move the tray up and down or you know to the right or to the left this is actually the isometric contractions going on um there are when there's movement observed it can be isotonic or isokinetic isotonic is a a a muscle contraction that apply the same resistance but because of the the same resistance and the uh contraction speed May differ and the isokinetic uh contraction is the opposite isokinetic uh contraction is uh the speed of the contraction remain the same however the resistance in respond to the speed may be different um so so uh one example for the isotonic uh contraction is concentric versus Ecentric concentric contraction produce shortening of a muscle where Ecentric contraction produces a lengthening of a muscle take the example here uh when a person is trying to do a bicep curl uh the resistance of the dumbbell remain the same when the person is bending the elbow it produce shortening of the bicep muscles um this is what we call concentric uh contraction when this person is trying to lower down the dumbbell that um producing elbow extension but because this person is trying to control um the speed making it very slow um the prime mover in this elbow extension is still the bicep um muscles and this actually produce lengthening of bicep muscles and that's why we uh call it an Ecentric contraction uh another way to look at this is uh concentric contraction usually work against gravity and Ecentric contraction is usually work with gravity when we imagine the gravity is always uh pull uh things down or toward the Earth or the ground here so when we move against gravity typically is a concentric contraction when we move with gravity we have to control the speed to make it slowly slowly down lower the the object down that's the Ecentric contraction um the example for the isokinetic um contraction um the speed may stay the same but the resistance may may be different this is typically done through um an external device to do it so in clinical uh practice we have a device that help uh our client to do passive Ral motion but because we set the speed of the machine to be the same right and depending on the person's uh um strength level um that may create some kind of different isokinetic um muscle contraction so this is another um examples or uh clarifications for concentric versus Ecentric contractions so concentric contractions um they uh actually move against gravity uh the muscle is getting uh shortened whereas Ecentric contraction the muscle is actually being lengthened a bit and is moving with gravity the speed of the concentric contraction can be uh quick uh um uh however the Ecentric contraction is slowly uh moving so this is uh quite different between concentric and Ecentric contraction there are different roles for a muscle a muscle can be The Agonist uh also called the prime mover um you can see that this muscle is in charge of this Mission um a muscle can also be the end teist which uh function on the opposite side to counteract with to The Agonist in the movement we also need muscle to function as the synergist um to help um in um the muscle movement um some muscle can function as the stabilizer for example uh when we bring the cup to our mouth the core muscles actually uh function as the stabilizer so that the bicep can function as the prime mover to bring the cup to our mouth right um some muscles May function as the neutralizer uh doing the mission in in here so for example biceps we know it's a a big uh muscle for U elbow flexion but biceps are also the muscle um that function as a strong uh forearm superation but in this mission that we uh of bringing the cup to the mouth we don't need much super superation in in in in this task so to do so uh the pronators like the pronator Terrace and pronator quadratus are functioning as the neutralizer to neutralize uh the superator function of the biceps so that we don't um have The Unwanted motion doing uh the uh activity of bring the cup to our mouth depending on the situation a muscle can be Agonist uh in other situation the same muscle can be the antagonist or um synergist uh for example here if we're trying to do a bicep curl um with the elbow flexion in this movement the bicep Breaky eye uh functions as the um Agonist and the anagist is the triceps when we do the elbow extension in a pushup because we're not doing it in a very slow um motion so uh triceps ex actually The Agonist and the biceps here are the antagonist and our core our back muscle uh and our abdominal muscles functioning as the stabilizer a lot of times we focus on The Agonist which is the the prime mover however we cannot ignore the function of a muscle uh to be the antagonist or the stabilizer again uh the role of a uh antagonist is to counteract the function or uh the tension that created by the eist to facilitate a smooth or a much coordinated movement a stabilizer um is actually support the movement for The Agonist to work more uh efficiently so again uh when we trying to do pushup uh the elbow extensors which is uh the triceps Breaky ey are The Agonist right and the stabilizer is our core muscle so that when our core is strong then uh the person's performing this elbow uh extension or pushup is can be more efficient um and some muscle May functioning as the neutralizer uh we just talk about one example for the biceps uh to uh how to say uh reduce uh the superation by recruiting a PR terrorist to counteract with the superation the another example that we can see is when we are doing when we're trying to do the wrist fraction and extension uh Movement we don't don't want risk uh deviation to to to happen if we want to counteract the risk owner deviation the extensor carai onys and flexor carai onys can cancel out each other so that they don't produce any unwanted uh owner deviation while the person is producing the risk reflection and extension movement here so a lot of times uh uh The Agonist and an tagonist are are are required to contract at the same time in this situation we call this as a CO contraction why do we need a muscle uh sorry the muscle groups to Pro uh to produce co- contraction is when we need a uh the accurate movement or the accuracy is the key for this movement here the example um here that I offer is um to be able to um to hold the hammer and perform um you know the nail uh the nail down this person needs to recruit the extensors of the wrist and flexor of the wrist together to be able to hold the hammer in place and the finger flexors and extensors are trying to uh Co contract together to be able to hold the nail in place so that this uh person can accurately perform um this uh Mission which is uh to nail uh this nail down so you can see uh depending on the type of muscle contractions uh a muscle can perform differently or the functioning as differently and these are all keys for our clinical practice