hi so in today's class I'm gonna give the kind of medical side the biomechanics side to kinetics to force those kind of measurements okay so really when we think about how acceleration how velocity how Center of mass affects kind of the human body we talk a lot about biomechanics and this is kind of if you can think of how our bodies move how we walk how we control our reaches and grasps okay so there's going to be a lot about how our bodies move today so the broad learning outcomes that describe the process of gate monitoring that's actually how we monitor how someone walks the different types of walking that they might happen and and kind of what we might want to monitor in terms of when things go wrong we want to describe how Newtonian Laws of Motion affect biomechanics will typically do that in the workshops or brush through some of that in in class here we want you to compare and contrast the anatomy of how bones are formed because our bones are there to help us create movements by using or taking advantage of levers as well as they need to be able to take on the force of all the uh weight that we put on our body okay so if we have more weight on our body our bones need to grow to compensate to help out carrying that weight we want you to be able to describe the mechanical properties of the bones as well as describe what happens when we apply more Force to the bones what actually happens to the bones to grow to to allow it to strengthen so first off what is biomechanics and biomechanics is broadly the science that examines how Force acts upon and within biological structures to produce produce such forces okay so this is really that linking between the physics again and the medicine how force act upon our body okay and so force is you know broadly the influence that causes an object to move like we we can't move or objects don't move unless an external force is applied to it okay and and we think about this in terms of movement again in terms of of grasping um there are also this idea of external Forces versus internal forces so this may mean when I sit on a bus how the seat pushes me forward or uh internal forces where how do I actually generate the muscle movements to to move my legs and things like that so these can be broken down into segmental movements into each one of the breakout body down into segments uh tissue movement tissue deformation how if force is applied let's say in a rugby tackle how my tissue deforms to absorb that Force as well as tissue growth and development and broadly kind of the whole performance so uh when we talk about biomechanics broadly a lot of where it goes in in medicine is in sports performance how we use biomechanics to to help people reach their maximum potential so the biomechanics intro is it's a study of how and why our bodies move if you enter into physiotherapy or into medicine and those kind of sites it's about how we can also repair how we can fix movements uh issues with with muscles or bones we want to apply the physical physics principles of force acceleration and then the more complex kind of second order kind of measurements of talk levers what do we mean by levers like my arm there's a pivot point how we can use that as a lever uh to the mechanics of the body to understand where things might go wrong to understand how we can use uh let's say Center of Mass to help us better pick up uh heavy objects we don't use our backs to pick up objects why is that we keep things close weight close to our body when we when we lift heavy things why is that and it has to do with things like Center of mass and we'll go through those kind of calculations uh in the latest slides so this field can also be highly quantitative and that means we you know you might measure the exact speed with GPS that uh that an athlete is running or the force that they exerts on the ground when you when you jump and that's really important in sports science it's important for things like healthy aging so things like foot clearance how far up are you getting your foot off the ground is really important metric or a marker in whether or not you may have Falls as you as you get older in life it's also really important for Rehab are you getting stronger in your let's say if you've had a stroke you get muscle weakness one of the metrics that you might have is kind of the movement in your arms the force that you can still generate with with an arm that has a little bit of muscle weakness it can also be highly qualitative so like often in in the physio you're just looking for a range of movement like just seeing whether someone can move with pain or without pain just kind of characterizing those problems but still having a good understanding of the quantitative force physics behind how Levers work how arms work really allows you to open up kind of what you can do with those qualitative measures so the first thing we're going to talk about in kind of physics biomechanics is gate analysis and the word gate analysis is or gate is just a pattern of movement of the limbs during walking Locomotion so how we how we kind of have this and you might not have thought about this before but when you walk you don't really think about it but you just repeat that same pattern over and over again okay so it's the systematic study of how a subject is walking and it's used to treat diff and diagnose different conditions it may be a neurological disorder that is causing you to walk in a different fashion it may be a muscle issue where you're having a weakness on a certain side of your body which is causing uh your your muscles to or it could be you know a fracture of the bones that is also causing things like that okay it's also used a lot again and I'm going to talk about sports a bit in this class uh you know performance enhancing how can you optimize your running stance or your your movements to to to get that 100 out of your body it's used in kind of healthy aging to assess the risk as I said um what are the one of the biggest risks of or risk profiles of someone falling over when they're when they're getting older is they stop lifting their feet up off the ground and then when you stop having that clearance of your feet then you may start to hit objects on the ground trip over and that causes big issues so what are these kind of phases of the gate cycle when you walk so you've got typically a heel strike so the first thing you do is you strike the ground with your heel you then put all your weight on that or most of your weight on that foot that's called the single support phase so you know heel strike put the foot down you then kind of put your weight on that side and then you kind of move off toe off your your other foot comes off the ground and then you kind of swing your foot forward and then heel strike again and you just kind of repeat that over and over again so it's a very kind of it seems like a very simple thing when you start to think about it but you can learn a lot by someone's uh gait cycle and so the two phases that we often talk about are The Stance phase when you've got one foot kind of planted um and the other foot is kind of Levering forward and then the swing phase when that foot lifts off the ground and you swing it forward and typically we have 60 of a stance phase and 40 of That Swing phase so a big thing about data analyzes about healthy aging and and we raise this in class because this is one of the big issues is one of the U.N sustainability goals of of like how can we prevent Falls how can we have healthy aging and when you know there's the statistics 20 to 28 to 35 of the population over 64 experience at least one for every year and the four can be really really hard on someone who is who is a little bit older if your bones are a little bit weaker you can get hip fractures once you are bedridden then kind of you get these kind of secondary effects of not being able to move um and four related injuries are expected to increase as our aging population uh keeps keeps marching on about two percent a year and it's really expensive if you can imagine a hip fracture uh even really muscle soreness of a large four uh this is a huge kind of burden to to to the medical costs so in data analysis what we want to look at is kind of the stride length the speed and so you can kind of see those physics Concepts how is velocity going to be related here how is distance of movement going to be related here Force when you're pushing off the ground how much force are you being generated are you generating to create that movement of your foot as well as things like minimum foot clearance the distance between the bottom of your foot and the ground what is the minimum clearance that you're giving when you're walking and as you typically age you might start to drag your feet a little bit more which becomes dangerous because if there's uneven flaw or a step then you might hit that and trip so the main muscles that are involved in uh walking and running are the gastrocnemius which is on the on the back of your of your of your leg it's typically involved in running jumping these kind of uh large kind of explosive movements less involved in Walking um helps with what's called plantar flexion of of the foot you've got another muscle on the inside of that called the cilius and that's more used in Walking it's also used in running it's really important for balance uh it's got a skeletal muscle pump because it is used you know you can walk a long way without tiring so you can kind of think about the different types of muscles and you'll do this in a different class when you go on you can think about the different types of muscles based on whether it's kind of a short explosive movement that only needs to be used for a brief moment in time versus a muscle like the that's used for walking which needs to needs to go for long periods of time the slice muscle also as you're walking helps push blood back up into the heart so we kind of talked a little bit about this in one of the blood pressure classes and the the idea behind this is blood often pulls in your legs if you're not moving um so this muscle as you walk can kind of contract help create pressure in those vessels and that pressure pushes blood back into back hot so then if we're looking at gate what we want to see is things about abnormal gait okay and what are abnormal gait patterns so these can be due to physical injuries medical conditions or as well as they can be habitual and I wanted to talk kind of something about a habitual uh uh condition just because I thought it was a little bit more interesting and so this is about idiopathic toe walking in children which is a habitual um habitual problem uh there's no apparent reason for why kids toe walk and you can kind of have an image I think of what that might look like there's no neuromuscular issue there's no Orthopedic disorders uh kids can kind of walk on their heels if you ask them to it's just that um by by default if they're not really kind of actively thinking about it they'll walk on their toes another kind of issue is vestibular issues so we've got um we've got hair cells in our ear the other links that help us balance our our head our body and if you have balance issues then you that can lead to gait problems you can imagine if you can't feel that balance that Center of mass of your body when you start to walk that leads to issues as well we're talking about Center of mass and walking at the end of the slides today so what are the associations once you start uh having this idiopathic toe walking while you get shortened calf muscles tendinitis deformity of the hind foot and on large soleus muscle because you're on your toes so much and then abnormal gait patterns as well as um back problems when you you know these secondary issues and so what does this actually look like well so what it is is someone is just walking essentially on their toes uh how do we relate physics again to to gate analysis to the medical ideas so what we can do is we can put an accelerometer so we can measure the acceleration and the velocity of someone who is actually working in so in the clinics you might do this uh to characterize whether how bad it is or how fast they're moving and things like that and so when you have acceleration we've got acceleration on this axis in gravity in G's time in seconds on the other axis and this is what kind of a normal gate cycle will look like you've got a heel strike so when the heel hits you can imagine there's more acceleration right so there's more gravity that's what all I want you to take away from this that when you heel strike there's more acceleration when you've got this kind of normal stance the foot kind of sits and is just sitting on the ground so there's less acceleration it's flat and then when the foot starts to lift off again you get more acceleration again and then that heel strike big acceleration uh when you've got idiopathic toe Walkers unfortunately what happens is in that stance phase and that normal kind of stance phase where it should be steady they're on their toes so it's less supported and you start to get not get this kind of flat kind of normal stance but you get this kind of uh what's called a toe walking stance like kind of bumps in that acceleration okay so again this is just so you appreciate how physics again acceleration in this case here is used to characterize a a medical condition so what are the kind of kinematics that that's the general word that we use um to to Encompass uh the physics behind uh motion that we might be interested in well distance how far something's moving as I said the distance between the bottom of your foot to the top uh of how much on on the ground that you're leaving how far each one of your steps is is are your steps kind of getting shorter or is one side of your uh body like your left stride or your right stride shorter and that may uh tell something so distance tells us nothing about direction right it's just a metric of one meter let's say or two meters displacement uh becomes a vector and that also might mean well one meter in this direction so it may mean that your foot is moving straight or your right foot is moving straight where uh your left foot might be also doing one meter but going off on a slight angle we then have velocity which is also a vector a vector means that it has direction as well as uh magnitude so that would mean like one meter per second moving south or in this direction and velocity uh is best understood as the change in displacement vector or the change in um in in distance and Direction Over the change in time right so if I drive UH 60 kilometers in one hour then that velocity is assuming it's constant or the constant velocity there would be 60 kilometers divided by one hour so 60 kilometers in an hour so the idea of a velocity here is just that it's the the displacement over the time and it has a direction associated with it so then how is this used in sports medicine well contact Sports often Resort result in concussions we're seeing this a lot now um I mean it's always been there but with better science uh better understanding of what concussions are in terms of the Neuroscience behind it as well as the sports biomechanics side of it we've realized that what we call High acceleration events so you know two people running very very fast at each other uh accelerating into each other like in in rugby uh having a collision where that Collision uh causes a very abrupt uh stop very high acceleration if you're going at a high velocity and then you you go from that High Velocity to a complete stop or a backwards movement you need a large acceleration or a large Force to create that deceleration okay so we know from many many many studies uh that that high acceleration events can cause a risk of what's called now chronic traumatic encephalic encephalopathy takeoff and so typically we you know there are events like 10 G's right it's a very large events but if you're running straight at someone and someone's running the other way and you you you crash into each other then that can create those kind of uh those kind of accelerations those kind of forces from a biomechanics point of view it's it's really discussed as a failure of the body to be able to transfer energy safely if that makes sense right so you've got I'm I'm moving at a certain speed with a certain amount of energy uh someone hits me that's putting energy into my body and it's an inability of my body to crumple essentially my skull can't take that my brain can't take that if you think about cars and modern cars we have all these crumple zones uh all these kind of body all these protective areas that can kind of crumple down that we didn't used to have uh you know 40 50 years ago and the whole point of these crumple zones is that they can absorb energy safely so that the person in the car doesn't have to ex it doesn't have to absorb all that energy our bodies are designed to absorb some of this energies that's why we have skulls we have cushioning around our brain but above a certain point we can no longer uh we can no longer absorb that energy so in sports medicine uh often what is being done people will wear GPS packs they can use video now because you know the kind of speed of the video you know the distance that someone's running so if you know the distance you know the veloc you can calculate the velocity you can calculate the accelerations based on these video methods as well as these GPS sensors and people are doing some really amazing things about calculating risk profiles based on how much force they're being exerted on uh in in games another interesting place that I just kind of wanted to to raise because sport is not everyone's cup of tea is the idea of astronauts going into space and if you're a fan of late night TV this is called The Colbert you can kind of look up why it's called The Colbert um astronauts when they go into space without regular exercises has been known again for a long time uh in space we have what's called microgravity we don't have that same 9.8 meters per second that way we're kind of being exerted on uh down on Earth and so being in a kind of a small space shuttle as well as not having gravity so you know you float in in space so your bones and muscles begin to weaken begin to atrophy because again we'll talk about this in the second set of lectures if the bones don't have forces acting upon them they start to just atrophy down if you put more force on them they'll start to grow and strengthen much like your muscles if you put if you start doing weights go to the gym your muscles will start to grow when you stop doing that when you stop putting force on those muscles they'll start to weaken okay uh on Earth hopefully we all know this we experience a constant force due to gravity 9.8 meters per second you might not re you know you might not feel this all the time because you're just used to it really but if you went to space or if you went to someone with as higher gravity then you would start to notice that that change so in space bones and muscles don't have to support your body mass right and this concept of weight is mass times gravity so if you have a mass of your body and then in space there's very little gravity then the weight on your body is very minimal okay I'm in space my body now floats now my bones my muscles don't have to lift up my body uh every single day so in a 5 to 11 day space flight they found so this is from the NASA website uh they can you know have up to 20 muscle and bone loss that's a huge amount of bone loss and um I remember listening to one of the astronauts talk about how it took almost over a year just over a year to kind of regain that muscle mass and that's kind of how challenging it is it's similar to they they call it kind of similar to osteoporosis kind of bone degeneration or weakening uh that that can affect older people so what they do now is there's a strict kind of drug regime to ensure the muscles uh bones grow a strict diet as well as an exercise regime and this is what this kind of Cobra uh um exercise machine is which I thought was really really cool okay so then the last part of uh of of today's kind of lecture is going to be around talk moments of force center of masses and then kind of examples about how our body uses advantages in physics advantages and talk and moments of force to allow us to create more fine movement or stronger movements okay so Chris would have gone over some of this but um you know so there's we're just trying to have that overlap so that you can kind of see the physics and isolation and the physics with the medicine so what is talk okay so we we've talked about Force kind of force uh if you have an object you can just place a force on it and force equals the mass of the object multiplied by the acceleration we talk about talk now when we have rotation involved so it's not kind of a linear movement but a rotation uh around a pivot point so here we've got P this is just like a seesaw you've got a pivot point that seesaw will move like this around that Pivot Point okay and so talk sometimes it's also called moment of force is the application of a force that's causing a rotation now so again before we were looking at force in just one Movement Like left or right now we're talking about a rotation so a force on the end of here so like let's say the boy or the girl jumps up or down you're going to get a rotation around that Pivot Point and to calculate torque all we do is we think about the force that is is going up or down uh let's say at the the little girl to the force coming up this way and we multiply it by the distance from the pivot point so here L will be or X is this distance here to calculate the torque we just multiply it by the force and the force would be given let's say if there's only Gravity the mass times the gravity okay the Pivot Point here is at the center of mass but don't worry about that too much we'll talk about the center of mass in in uh in a few slides so L is often called the lever arm so the distance between here is the lever arm um and it's perpendicular so you know you've got actions like this perpendicular means it's 90 degrees to to the line of action so why is this important why are moments why is talk uh important well because it introduces this concept of uh Center of mass and for for biomechanics for medicine it's really important in terms of balance and balance is really important for healthy aging okay so if uh for typically um an object to be in balance or in equilibrium the forces acting on it must be zero however that's not enough in when we start to think about uh talk so if you just had two forces one going this way one going this way and the acting on the same way that's enough to balance out they'll you know if they're going in the same direction that might be an easier way to see they cancel out and there's no movement but in the if you have this ruler that you can kind of see here and we apply that same Force but now displaced you're going to cause rotation okay so what we're saying that um is now with equilibrium and and balance uh and talk to have equilibrium we have to have net talk not just net force so this would be net force zero this you know here because they're acting in different places now we've got talk right and that's going to cause movement so the example is when you've got working with a heavy bag you might lean your head to the other side why is that okay and that has to do with your center of mass and trying to locate your center of mass right above your feet or the best balance point okay so I guess the example here and I'm not sure if I can do it is if you can balance a pencil or a pen here uh the whole 20 minutes would just be me balancing this pen if you can balance this pen on a finger at a certain point that's typically where your center of mass is because gravity is acting on both sides or even if this has weight is acting down on it and those forces are creating those talks are balanced in each Direction so the point at which your balance is achieved is the center of mass my finger is acting as that Pivot Point okay and so the total torque once it's not moving is zero and so the center of gravity Center of mass is the point in an object at which the force of gravity may be taken to act so what that means is it's a simplification to say that if I can balance this then all I need to consider is that this Center of Mass is at this point here and all I need to worry about is simplifying this whole problem into having gravity acting at that Pivot Point so an example of this is like if you have a juggling ball or any a juggling pin and when you throw it up the dot here is the center of mass and what happens is whenever you have an object like this and you throw it up in the air the rotation will occur at the center of mass okay so this is just a nice physics properties of center of mass we'll keep talking about this in kind of a very general uh terms so the center of mass and movement why are we interested in the center of mass in these conditions well uh better balance if you know where your center of mass is what you want to do is have that over the most supportive base and typically that's your feet you don't want to if you lean over like I don't know if you can see me but if you can lean over like this and you start to walk your center of mass is now off your feet and you'll most likely fall over you might have also heard this idea of if you have the lower setting of gravity uh you'll have better of balance right think about really tall things heavy weights at high points that will topple over another really cool thing is things like tight War groupers or someone who's riding a bike on a on a rope you can use a counterbalance and what that means is let's say if you have heavy weights on your arms you can use those weights to to help balance out your center of mass as you walk okay so it's the same thing where now acting as a lever and we've got two weights here and we can move these weights up and down or add forces to them so that your center of mass is perfectly on this on this row so when we walk when we run we want to have a stable Center of mass over a stable or a center of mass over L stable um base right so what actually happens though is that our Center of mass kind of they call it this kind of inverted pendulum when we um when we walk and run so when we walk you you get kind of a point and your center of mass kind of pendulums from this this point here okay um it reaches the highest point mid-stance uh when you're running it the center of mass Falls after heel strike and it reaches the lowest point uh at midst stance and then Springs back up okay so really here it's just to say you know when we're walking when we're running when we're looking at how there may be difficulties in people's uh and if it was walking style cellular mass is an interesting one because we know how well hopefully we can we can appreciate how the center of mass should be placed over the the most stable base and when it's not when people have deficits that can cause people to trip to four so as I said when we walk it's similar to like an inverted pendulum so like my foot is here and as I leave a forward uh my center of mass if it's the dot here is is moving forward as we get older or as we have injuries um we can get stiff leg Gates so it's less compliant uh less maneuverability the the the muscles and tendons that support our walking uh kind of allow us to have that pivot movement when we run though our legs work more like pogo sticks so they're more compliant they bounce they kind of do this so you kind of they kind of uh model it more like a a little pogo stick and so you can see that you have a lower Center of rest typically when you run you kind of get down a little bit lower as your legs bounce um to allow you to have that that balanced movement okay so the loss kind of part of the lecture today it's been a long one today uh is talking about levers and in the body so uh Chris would have talked a little bit about first second and third class levers this is a challenging Concept in in physics and so I wanted to kind of just go over it again and then talk and show examples of them in the body so what are levers and why is there a first second and third class it really just has to do about where you're putting the force and where the fulcrum or the pivot point is okay so for a first class lever it's like a seesaw the pivot point is in between where the force and the resistance are okay exactly like a seesaw when you have a second class lever both the force and the the resistance are on one side of the pivot point for a second class lever the resistance is closer to the Pivot Point as a as opposed to the force and for a third class lever the force is closer to the pivot point then the the resistance an example of a second class lever is a wheelbarrow right there's a pivot point at the wheel you put weight inside the wheelbarrow and then you grab the the the the far end of that okay an example of a third class lever will have some in the body as well is like a rowing uh boat okay and we'll talk about the advantages of each one of these uh different class leaks each one has its own advantage in either expanding a movement uh leveraging force and things like that so that's why they're all used in the body so there's a concept called mechanical advantage okay and so much like the the the idea of um uh the Cecil or the the the wheelbarrow we use these because a small amount of force can be used to generate a large much larger amount of force on on an object and so why is this important well it allows us to create bigger movements or stronger movements and our body can take advantage of this so the example here is that this if we put 10 Newtons of force down here and 20 newtons of resistance here and that's one meter away and two meters away this is in balance so how is this imbalance right so we know that torque is the distance two meters times the force 10. so 10 times 2 is 20. this is now one meter away from this so it's one meter times 20 and we're getting the same number 20 newtons okay so by being further away from the pivot point then the the the resistance a small amount of force can be used to create the same amount of torque okay and so this is what's called mechanical advantage the mechanical advantage formula is the moment arm of the force that in this case is 10 over the moment are um resistance right so by being twice as far away from the pivot point I can use half the amount of force to create that same movement okay and the body takes advantage of this in different situations so the first is that first class levers in the body okay we can produce a mechanical advantage which means more output force or we can create a large much larger movement using a shorter action okay so we can do the opposite we can make a small movement and by having it further away it creates a bigger movement so the example here and I don't have a picture of it I think is the so I have to do it myself Atlanta occipital joint uh in the back of the back of the neck muscles and the front of your skull so there's a pivot point here right I've got muscles here and we want to look at the movement of my head like this so if the pivot point is here my muscles move up and down on the back of my neck and my head moves a long distance up and down okay so if my Pivot Point is here is a short distance to the back of my neck muscle and when I move a small distance on the back of my neck muscle my head moves a big distance so it's just kind of amplifying the movement on the front of my head can you think about another one I'm kind of just going to leave it open so you can pop it on on Moodle this is the opposite example right a long distance from the muscle now and a short distance to the load so this is what we had before the torque is the lever arm multiplied by the force here and because there's such a large distance there's a large mechanical advantage so you can move a large load with a small amount of effort a second class lever in the body again is like the wheelbarrow example okay so now the load is in between the effort so the effort is here on the outside and the fulcrum or the Pivot Point an example of this is your toes you can lit the the pivot point is here in your ankle oh sorry the pivot point is is is um on your toes uh and you can kind of lever up or down uh on the on the back of your of your ankles okay as the load is closer to the Pivot Point there's always a mechanical advantage because you're always further away from the pivot point so the torque that's been created right so the distance between a and F Will Always by the definition of a second class lever be longer than the distance between A and R right and because that distance is longer there's always going to be a mechanical advantage of using this type of lever right you can use a smaller movement or a smaller Force to create create a much larger Force active that's what's so cool about second class things so the third class lever is really really common in the body okay so here again what's the difference between a third and second class both the force and the resistance are on one side of the pivot point but now the force is being closer to the pivotal Point than the resistance examples here are your arm right you've got fulcrum Pivot Point at your elbow the force is being generated by your bicep muscle and the resistance is let's say you know putting some weight on your hand here so why would we do this well because now our our our our Force point is much closer to the Pivot Point what we have actually a mechanical disadvantage right so we have to apply a larger Force here to get that same range of movement here but what's the what's the benefit here if I make a small movement here right and that could just be like one centimeter you can see that this will move much much larger range okay so the the benefit of the class maneuver is that we can use a a output force will be applied over you know a much bigger distance and what does that allow us to do it allows us to make you know I can make a small movement here and I can do a big movement on my arm out here I can do really fine control things using that same kind of movement okay so it's really important and really big in our body because it allows us to to take one bicep movement or one muscle movement and amplify the the the external control okay so in the next kind of uh set of videos we'll actually talk about the skeletal system so that's the backbone or the bones not backbones the bones of the the body which allows these levers to occur