let me tell you something about muscles and it's pretty disappointing muscles can only pull okay that's all they can do now we're saying that's all they can do i mean the contractile proteins within muscle fibers are actually quite stunning but that's the whole of the story now muscles can only pull that's their limitation that's what they can do but what if i was to say to you but they need to do all of the following they need to produce contractions of all of the following they need to produce contractions where the muscle is shortening there's lots and lots examples of that and we'll come back to that in a second they need to produce movement where the muscle is lengthening almost pushing it sort of sounds like but it's not and it they need to produce contractions where the muscle stays completely stationary or still okay so how can it be that a muscle can do nothing but pull but can shorten can lengthen and produce stationary contractions now that is an interesting question and that's the one we're going to try and address here i must stress we're not going to answer answer it biologically down in the cellular structure we're going to answer it almost in kind of like subheadings and here we go we effectively have got three types of contractions please note there is another one that we might refer to we don't cover in this course called an isokinetic contraction but we're going to look at these three types of contractions and then we're going to have a look at some specific examples of them so first of all i want you to familiarize yourself i want you to familiarize yourself with the term isotonic we have two types of isotonic contractions in the human body we have an isotonic concentric and we have an isotonic eccentric now can i stress you if i go back to my original points an isotonic contraction is when movement is occurring so if movement occurs the contraction is isotonic which type of isotonic depends on the nature of the movement so if the muscle shortens under tension that is an iso isotonic concentric contraction and it's the most common type of contraction in sporting movements whereas if the muscle is contracting and changing length but this time the muscle lengthens under tension that therefore is an isotonic eccentric contraction so start to familiarize yourself with the language i'll give you examples of this finally if we look at the third type of contraction we've got isometric which literally translates to equal length and this is where the muscle will contract but it will remain stationary under tension it will not move think about examples where stillness balance moments where the body must remake completely static a sprint start a downhill skiing position for example now they are the concepts i want to get across to you before we sort of get much further then i want to start to consider some examples so let's look at a football throwing so first of all i want to look at the football throwing as if this is happening what we're seeing in the picture here in other words what's happened here is the elbow has been moving back into this flexed position here there's that flex position how has that happened well in essence we've got a bicep brachii muscle here which is pulling and it's pulling on this forearm in fact specifically the radius to pull the arms back when it pulls it shortens and because it shortens this of course is an isotonic concentric contraction it's an ic contraction a constant contraction the bicep brachii it is shortening and it is doing that work now as this arm now at the elbow starts to extend what's going to be happening here well now the tricep which i've drawn completely outside the arm it is now going to shorten it is now going to shorten and it's going to cause this extension of the elbow the tricep brachii this again is an isotonic concentric contraction because we've got shortening of the prime move of the agonist muscle so you might be thinking about what hang on a second we initially in phase one we've got an isotonic concentric contraction of the bicep brachii and then phase two the elbow extension we've got an isotonic concentric contraction of the triceps brachii exactly that now you might want to be asking yourself what is happening to the antagonistic pair whilst the concentric track contraction is taking place and the answer to that is it's relaxing it is not contracting doing none of those contractions we looked at before the antagonist is relaxing the antagonistic pair is relaxing so if in the first phase the bicep bracha is contracting isotonically concentrically the tricep brachii is relaxing now that is what we call a completely standard antagonistic pair movement but it gets a bit more interesting when we look at our second example so let's imagine that in phase a our performer is on the upwards movement now we are particularly interested in here now the tricep brachii because that is the prime mover in elbow extension so what's happening here is the prime mover is shortening under tension it's effectively causing elbow extension pushing our performer upwards into the upright position and of course this is once again an isotonic concentric contraction lovely nice and simple exactly what we've looked at before but now in phase b the performer is now lowering themselves to the ground so typically with elbow flexion which is what we've got here the prime mover is the bicep bracha right not here the tricep brachii now remains as the prime mover is the tricep bracket and now what it's doing it's lengthening it's lengthening under tension now that makes it an isotonic eccentric contraction now where we tend to find isotonic eccentric contractions is in things like lowering lowering the body down it could be in landing you know imagine the the four quadriceps muscles for example impacting a landing we're talking about slowing the body this is where essential contractions tend to happen we're talking about what we would call and make sure you know which type of breaking i'm talking about breaking actions so effectively what's happening here is on the way down this body is that the the tricep brachii is lengthening under tension and acting as a break to prevent this head of hitting the ground right that's what that muscle is doing excuse me sorry i have a bit of a tickly cough at the moment now let's go for a couple more here we're going to look at the leg muscles a second excuse me sorry what we're going to do here is we're going to focus on let's say the rectus femoris okay so we'll stick with hinge joints but let's imagine we're looking at the rectus femoris here and here can you see going from movement once i know it's a different performer can you see that here in order to cause this knee to extend at the knee this rectus femoris is shortening under tension it shortens under tension it causes the knee extension this is an isotonic contraction okay now let's look at our example over here what we're getting now is we're gonna imagine that this is phase one and this is phase two so in essence what's happening here is this person is landing back down on the ground and what i want to imagine now is the rectus femoris muscle now over here what's happening with this in order to act as a break it's lengthening under tension it's lengthening under tension so we of course know that that is an isotonic e-center contraction it's slowing the downward movement towards the ground now the final point i want to make here i don't think i included any other images i don't know the final point i want to make here is now imagine that this performer is holding this position completely still so imagine they're holding that almost like a hand-based plank what we would find that's not going either up nor down what we'd find now is that both the tricep bracket and the bicep bracket would both contract with an isometric contraction so notice that with isometric contractions both muscles have to be contracting isometrically in the antagonistic pair to hold that station stationary now we've actually we've got a mechanical concept term for that it's called the principle of moments we're not going to cover that here but this is effectively two levers operating with the same amount of torque operating against each other and it produces an isometric stationary contraction anyway i hope that's helpful for you and i hope that gets the concept of contractions across you neatly thank you