hey guys dr goodin back again with a lecture about biomechanics as it relates to strength and conditioning this time we're talking about factors affecting human strength and [Music] power [Music] as i mentioned in the intro we are talking about factors affecting human strength and power from a biomechanical perspective now this comes from chapter two of the essentials of strength training and conditioning textbook put out by the nsca this chapter in particular was written by dr jeffrey mcbride okay let's get into the material so before we talk about factors affecting strength and power we have to know what strength and power are strength is the capacity to exert force at any given speed now that last bit at any given speed is important the reason why our strength is limited by speed is because down at the level of the muscle fiber there are certain contractile velocity components of muscle now what this means practically is that if you're trying to move very quickly very explosively very rapidly then your force is limited by that duration of time through which you can apply force so we're not going to be as strong during a vertical jump as we will be during a back squat i mean think about it how much can you back squat now could you jump very high with that weight on your back with that same load and the answer is no although you can exert a ton of force during a max back squat attempt you cannot hope to exert all of that force let alone more more than that during something that is time limited like a vertical jump so our strength is limited by time acceleration is the change in velocity per unit of time and this is associated with resistive force by newton's second law force equals max times acceleration and if you want to learn more about newton's second law click somewhere on the screen a little card will come up and you can check out some of my biomechanics videos now because force equals mass times acceleration we know that if strength is the ability to produce force then the amount that we can accelerate the object that we are moving will depend on that object's mass okay so a very massive object you are going to have a hard time accelerating it conversely a very light object you can accelerate it very very quickly because it doesn't require quite as much force power outside of the scientific realm is loosely defined as explosive strength so in athletics we would call somebody powerful if they can move another load very quickly or if they can move their own body very quickly they're they're explosive right if they have great jump height or they can knock someone down but it can also be defined as the rate of doing work so power is also equal to work divided by time another way to say this is power equals force times velocity and i really like that force times velocity definition because it reminds us that the greater the force you need to exert the lower the velocity of that exertion can be given a static amount of power available if the force requirement is lower then we can move at a much quicker velocity okay think about a medicine ball that weighs 6 pounds how high could you throw that versus a medicine ball that weighs 60 pounds there's a much greater force requirement for that 60 pound medicine ball so you will have a harder time accelerating it as quickly as you would the six pound medicine ball then we can define work as the product of force exerted on an object and the distance that the object moves in the direction that the force is exerted so for work equals force times displacement a practical example of this is a tall individual versus a short individual and the amount of work that they are completing with a 100 kilogram back squat so let's say you have a basketball player come in he's seven foot flat and he puts a bar on his back with a hundred kilos okay and then you have a five foot nothing individual come in and he puts a hundred kilogram bar on his back and they both squat who is going to be moving that bar farther well assuming they both squat to parallel the seven foot person is going to move that bar a much greater distance than the five foot tall person so the tall athlete will be completing more work it's actually physically harder for him or her to move that barbell even though it weighs the same amount as the one that the five foot tall person is moving and on top of that the biomechanical leverages for that shorter athlete are more likely better suited to squatting than that taller individual so a hundred kilos is not always a hundred kilos it doesn't feel the same across the board when you're considering athletes with different anthropometrics negative work is not work performed by the muscle it's now work performed on the muscle so we think of negative work as occurring during eccentric muscle actions two more definitions for you angular displacement this is the angle through which an object rotates okay so the amount of displacement would be measured in degrees all right and so maybe i'm starting my elbow at let's say 30 degrees or maybe that's 45 degrees and i extend all the way past 90 to 180 degrees and that would be 135 degrees of displacement of angular displacement rotational work is the amount of work done at the joint when you consider torque times angular displacement now i should probably have torque on here as well torque is equal to rotational force so torque is the rotational equivalent of force which is an object's tendency to want to rotate now torque times angular displacement equals rotational work and these definitions are important as we're considering movement from a biomechanical standpoint this is how we describe movement in biomechanical terms now the key takeaway here though for the strength and conditioning coach is that although the word strength is often associated with slow speeds and power is associated with high velocities of movement both variables actually reflect the ability to exert force at a given velocity now a specific example of this is seen when you compare the sports of olympic olympic-style weightlifting and powerlifting we use the word power for powerlifting when when in reality those athletes are exhibiting high levels of strength the ability to produce force period especially at slower speeds when in reality power should probably be reserved for olympic style weightlifting in which you have athletes moving heavy weights explosively very quickly in order to get them overhead right so they're heavy weights but they're not maximally heavy weights in the sense that power lifters are moving the most weight possible even if they get it there slowly the nature of olympic weightlifting is such that you have to move the weights explosively in order to get them up and racked on your shoulders or overhead of any sport olympic weightlifting has the highest power outputs particularly during the second pull of the snatch and the clean and during the jerk movement if you want to check out more about the power requirements and the power outputs of weight lifters check out some of dr garhammer's work so when we consider the differences between slow strength or your ability to produce force when you have unlimited time to do so and fast or explosive strength or power right which is a product of force times velocity when time is limited and you have to produce force quickly we can look at examples from power lifting from weight lifting and from track and field okay so this is ray williams squatting 183 kilograms 183.5 kilograms and this was from the ipf world classic powerlifting championships from 2018. check out how many spotters he has it's just unreal [Applause] crazy okay so he was red lighted on that meaning he didn't squat quite as low as he needed to by the judge's standards to make that a clean attempt however you can see how that back squad it seemed like he was in the hole for eternity and that was actually a fast squat for powerlifting sometimes those guys and girls really grind it out for a long time in the whole their ability to produce force in the back squat is not limited by the amount of time that they have to do it they could stay there for a long time if they had the muscular endurance for it okay let's look at an example from weightlifting okay so this is clarence kennedy he's an irish weightlifter he doesn't compete anymore but he's a super strong dude so let's watch him clean and jerk 222 and a half kilograms much less than a thousand pounds but watch how explosive it is all right here comes the jerk awesome so he is one explosive dude and you actually saw two different examples you saw him move a very heavy load explosively yes it wasn't as heavy as a world record back squat but it was very heavy it's more than i've ever squatted and then immediately after that he did a backflip which was which was just cool right so he moved a heavy load quickly right force times velocity and now let's see an example from everybody's favorite werner guntor werner gunthor is a world champion swiss shot putter back in the 70s or 80s i should know that and he's famous because his training techniques were evidence-based they're based on the latest science of this of the time and they're still really cutting edge and they were well documented okay so let's check out this plyometrics routine [Music] and he's going he's going that was awesome i mean imagine the explosiveness in this guy's quads and his glutes it's just phenomenal so here's the key point you guys strength and power they're biomechanical terms technically but we have to use them appropriately when we say somebody is strong what we're not saying is that there is some implied velocity component to that strength are they strong when time is unlimited and you can exhibit that force slowly or are they strong when time is limited like in those jumps that warner guntor just did or in the cleaning jerk that we see from weight lifters okay and so that would be called power and technically that is force times velocity whereas strength is force at a given velocity alright guys thanks for watching this video where we talked about the basic definitions of strength and power and some related definitions through the lens of biomechanics as it relates to strength and conditioning in the next video we are going to talk about some of the biomechanical determinants of strength to power in humans so stay tuned for that video it will appear somewhere on the screen if you guys have any questions ask them down below and until next time stay strong [Music] you