hello and welcome to this exam question video today what we're going to be talking about are
muscle contractions and in these two questions here 12.1 and 12.2 they're asking you to define
a type of contraction and also give a sporting example to back it up so before we go into
concentric and isometric we'll just talk about all of them and how different types of contraction can
be broken down and categorized so first of all a muscle contraction involves tension so it's when
the brain sends a signal through the body to a muscle and causes it to switch on to act against
a resistance of some sort this could be gravity it could be a force from an external person or object
and it might be to actually just move the body itself so whenever there is tension involved and
we can contract in two different ways when there's tension involved we can actually move the muscle
or we can hold the muscle so without movement so the muscle can be moving while under tension
or it can be static while under tension now these are called isotonic when there's movement
and isometric when there isn't movement so there are two different forms of contraction isotonic
and isometric the way that i have remembered it in the past and you know tell students to remember it
as well think of tonic water that has bubbles in and bubbles can move so whenever you hear isotonic
tonic water and the bubbles inside of it there's movement of those bubbles
so isotonic of moving while contracting muscle isometric aesthetic while contracting muscle
now within this movement category of isotonic muscle contractions or we can move a muscle
two ways we can lengthen it or we can shorten it and each of those have got a different name
for itself so when we lengthen the muscle and it's under tension it's elongating it's stretching out
so think elongating or eccentric elongates eccentric is when the muscle is under tension
and is lengthening the alternative is when it's shortening or it's coiling up it's getting shorter
in on itself and that's called concentric muscle contraction so concentric isotonic means that
the muscle is under tension and it's moving in on itself it's shortening it's coiling up
okay so we've got technically three different forms of muscle contraction we've got isometric
which is static contraction while under tension we've then got in the isotonic uh category we've
got eccentric which is the elongating the lengthening of a muscle while under tension
and then we've got the concentric contraction where the muscle is shortening or it's coiling up
in itself so if we jump back into the questions here define concentric contraction well we know
this is an isotonic contraction which involves tension and the muscle is going to be moving
how is it going to be moving it's going to be shortening so it's a muscle that shortens while
under tension using a sporting example in your answer define concentric contraction so this
is whenever a muscle is working against a force or resistance and it's getting shorter in the process
so this could be for example when you're running your quadriceps are causing flexion at the
knee because the quadriceps are contracting and shortening in the process as the as the quadriceps
shorten the tibia and fibula they extend the low and the quadriceps are extending the knee when
we continue to run the hamstrings at the back they contract concentrically so they shorten
to cause flexion at the knee to lift that tibia and fibula back up towards the pelvic region so
we've got quadricep contraction when running and hamstring contraction when we're running
we could also say the upward phase of a bicep curl so as we move away from by our waist and
we move the weight up towards our shoulders we're causing elbow flexion and the bicep is contracting
concentrically the bicep shortens and as a result it's bringing that radius of ulna our lower arm
up towards our shoulder causing elbow reflection if we jump down now to isometric contraction well
we now know that isometric contractions mean when a muscle is working it's under tension
but it's not moving it's not lengthening and it's not shortening so these are static
moves static moves that's a little bit of juxtaposition there but a static skill a
static action of the body so things like holding a headstand things like balancing on one leg
things like balancing on a beam while not moving perhaps performing pilate move or yoga moves where
you have to hold the position for three or four seconds perhaps in rugby when two scrum packs
come together and there's no movement the muscles in the player's legs they're trying to contract
concentrically but they can't because the opposing force is equal to the force that their muscles are
able to actually generate so there's no movement possible they stay fixed in that position they
don't move there's no flexion nor extension those joints stay fixed statically in that position
but the muscles are still working it might be if you jump onto a pull up bar and you pull up and
you hold your elbows at 90 degrees and you hold it there that would also be isometric contraction
our latissimus dorsis have contracted to pull our femur down into this extension phase so we've gone
from sort of flexion into extension and latissimus dorsis are contracting isometrically holding
our shoulder joints in position our biceps are contracting isometrically holding this
elbow in this 90 degree flexed position so the muscles are working but they're not lengthening
and they're not shortening if this question were to ask for eccentric contraction now we need to
think of a time when the body is controlling itself against gravity it's lowering something
or it's getting lower to the ground this is when gravity wins basically so if a person is
doing a squat for example as the bars on their back and they slowly lower themselves down and
gravity is pulling them down they're lowering themselves down to the floor they're gluteus
on the rear and is allowing the hip to go from extension into flexion and the glutes are actually
lengthening as that femur starts to lift up and the hips drop down the quadriceps they're also
stretching down because the leg goes from this extended position and it's gradually lowering
into that flexed position and the quadricep has to stretch itself out while under tension to allow
that movement to happen if there wasn't tension then that person with the squat bar would just
go straight down to the floor and there'd be no control so it could be for example a basketball
player who's just gone up for a layup or a dunk and they are landing after that basket attempt
so there's three different types of contraction we've got two categories isotonic and isometric
isotonic is when there's movement i think tonic bubbles they move in a glass of water
and movement can occur in two ways it can lengthen or it can shorten the length in england elongating
is eccentric isotonic and then the shortening the coiling up is the concentric isotonic and
that's that so i hope you found that useful and i'll see you again in the next one bye for now