(swelling music)
-: Now I'm gonna talk a little bit
about the physics of exercises.
So this is where it gets a little bit nerdy.
So get in, we're about to go do some science.
So if we look at movement,
we have basically two main terms we need to cover.
We have inertia, which is basically
an object resisting being moved.
So when an object is not moving, it's inertia,
basically, is what's keeping it from being moved.
And that's directly related to how much it weighs.
Momentum is what happens when things start moving.
So when something has momentum,
it's gonna resist being stopped.
So it's going at a certain speed, a certain velocity,
if you will, and it's going to take work to get
that object to then stop.
So if we look at it in its simplest form,
weights that are not moving resist being moved.
So that's inertia, which in this case,
represents the black car,
and weights that are moving resist being stopped,
which in this case, that's momentum
represented by the yellow car.
So when we look at say sports performance
and stuff like that, a lot of times,
it's the combination of this battle
between inertia and momentum,
or two opposing momentums, in terms of athletes,
or an athlete and an implement like a ball,
or whatever it may be.
All right, so, when we look at inertia,
one simple thing to look at is
if you have something that's not moving,
the more inertia it has, the harder it is to move.
But once you overcome that inertia, all the sudden,
it becomes easier to move, because the second
you overcome the inertia, you have momentum.
So if you were trying to push ball here,
and it just wouldn't move.
You push harder and harder and harder,
and the second that thing started to roll,
all of a sudden, it would be easier.
You would have momentum, and you would
be able to pick up speed.
So if there's a lot of inertia,
you're gonna need more initial force
to get that thing moving, but once it's moving,
you might be able to be able to keep it moving
with significantly less force.
So if we look at Newton's three laws,
which are basically the laws that
encompass movement and how these things interact,
an adequate amount of force is needed
to get something moving that's not moving,
and the same thing.
There needs to be an adequate force
to stop something that's moving.
So what we need to understand is what
are the things that are making something
either hard to move, hard to stop,
or easy to keep going?
Because those things are gonna affect
how much resistance the machine or the dumbbell
or whatever we're using in training is actually applying.
We just talked about resistance profiles.
Movement is going to complicate resistant profiles,
because when we look at a resistance curve,
and we just based it off the moment arm,
what we're looking at is how much would
that resistance we're getting,
when there's no movement?
The second we start moving weights,
if we create a significant amount of momentum,
that resistance profile is going to be altered.
So if you want an exercise to maintain
the resistance profile that it would have
just by looking at its momentum,
just by looking at the distance from the axis,
you would need to do that exercise
very slow and controlled.
If you want to manipulate that resistance profile,
then you could change the way in which you would
try and move that weight, whether you would try
and move that weight faster, whether you would try
and accelerate or explode into that load.
So if we look at this in a gym setting,
if we have a weight that's sitting on the ground,
it's a 50-pound weight.
Anything applied to that weight that's
more than 50 pounds of force
is gonna move that 50 pounds.
The second it starts to move,
it will take less than 50 pounds to keep it moving.
So if you started to lift something up,
it takes more than 50 pounds to get it
to come off the floor, but at that point,
if you generate a momentum,
it takes less than 50 pounds to keep lifting it
further off the floor.
It takes greater than 50 pounds to stop
that weight, if it was coming back down.
So as you're going to lower that weight,
if you wanted to stop it before it hit the ground,
now that weight has momentum.
So it's 50 pounds plus the momentum
that it's gained going down, because gravity
is pulling on it, all right?
So we have that weight coming down.
It takes more than 50 pounds to stop it.
So when we're lifting things up,
we're creating momentum against gravity.
The weight is getting easier,
lighter, lighter, lighter.
If that weight is going down,
and we're trying to create a force
that's in the opposite direction of the momentum,
it's gonna have to take more work
than what the actual weight of that dumbbell is.
So the important thing to understand is
that it takes more work to decelerate stuff,
and it takes less work to keep things moving
in the same direction once they have momentum.
So why does this matter?
So that momentum is changing the amount of tension,
the amount of work the muscle has to do.
If we generate momentum, on the concentric,
that's gonna be less work.
So if I create an initial movement,
and that weight is moving faster, concentrically,
there's gonna be less tension, let's work.
Now maybe I want that,
or maybe I want to avoid that,
depending on the stimulus of my training,
but it's important that I understand
what the appropriate application is.
On the way down, it's gonna be the opposite.
A huge thing when it comes to resistance profiles
is regardless of the resistance profile,
if there is enough momentum, essentially,
that tension could go all the way to zero,
where the muscle is having to do nothing.
So the equivalent is if I take pencil,
and I throw it up, at a certain point,
that pencil became weightless and floated.
So what tiny bit of tension that it was taking,
my muscle to move this, went to zero,
because I created so much momentum,
this essentially floated on its own.
The momentum that I created actually exceeded
the weight of this and the forces
that gravity was applying to it.
So if I create enough momentum,
I can take an exercise to where it's having
zero tension on the muscle.
So that's not good if I'm trying
to actually have tension there,
or if I'm trying to keep constant tension in the muscle
for a metabolic purpose or for hypertrophy purpose.
So the key to remember is that tempo is going
to be very, very important,
because tempo is, ultimately, the prescription
of not just long we want to stay in the different phases,
but also the prescription of how much momentum
we are or are not creating,
and the amount of deceleration and acceleration
that's going to happen.
So the faster that concentric,
the more acceleration and more momentum
I'm going to be generating, right?
The faster the eccentric, the more momentum
I'm gonna have to overcome and decelerate
to stop that load.
So very, very big differences.
The momentum is gonna make the concentric easier,
and it's gonna make the end of the eccentric harder,
where we actually have to really decelerate
and stop that load.
So to continue on this with the eccentric portion.
Because that weight gets heavier,
as we progress eccentrically,
and we get increasingly more and more load
and more and more speed, and also,
we need to stop that.
That creates a point where that decelerating,
or that aspect, could actually become dangerous,
because if we let that weight move really fast,
it's going to pick up momentum really fast,
and therefore, it's going to act
like a much, much heavier load.
So if we were using a weight that we could control,
and we start letting that weight go too fast,
it could potentially become like a weight
that is outside of what we could control,
a weight that's too heavy for us to control.
So when we look at injuries,
most injuries are gonna occur in some sort
of dynamic stopping position,
some sort of dynamic eccentric contraction
where either a person's trying to decelerate
their body weight from motion,
or they're trying to decelerate a load.
So most people get injured during the eccentric
of weight training exercises,
and they get injured during the stopping points
of performance exercises.
That's a huge thing, because when we look at
trying to prevent injury, controlling deceleration
is going to be huge, not just from a maximal tension,
but always making sure that you're staying
in the right range of motion,
and always making sure
that you're keeping joints integrity,
and you're not, all of a sudden, putting way more force
into that tissue than you intended,
simply because you weren't controlling the tempo.
So point-control the eccentric tempo,
especially the last part where you're like
getting bottom of the range.
So bouncing in the bottom of squat,
what do you think's happening?
If you fall down in a squat,
that squat, whatever weight you have on there,
is actually being magnified at the bottom,
when you have to stop that.
So the people that drop-down,
and they bounce that on their knee joints,
essentially, they're putting way more force
to their knee than what that actually weight
would have done if they were to come down
with a little bit of control.
So let me ask you a question now.
Is momentum good, or is momentum bad?
And the reality is, well, it depends.
There's gonna be times where momentum
might take an exercise that has
a really crappy resistance and now makes it beneficial.
There will be times where going
from using momentum not using momentum,
or vice versa, will allow me to one exercise,
and essentially, make it seem like two exercises,
because I can manipulate that resistance profile.
Take, for instance, a dumbbell lateral raise.
If I go slow, that dumbbell is gonna be really hard
to hold at the top, right?
But it's really easy to move at the bottom,
because if we look at my shoulder and the dumbbell,
the moment arm, the distance from that axis,
is really small here.
As I come up to here,
that moment arm is really long.
Now that makes the resistance profile really hard
at the top, really easy at the bottom.
Now what if I tried to fling the weight up?
So I try to move it up very, very fast.
Well, because I'm trying to accelerate,
my muscle's actually gonna be doing more work,
because it's trying to accelerate that weight.
So regardless of what the moment arm,
it's trying to overcome the inertia.
So the inertia that it has overcome
is gonna require more work to get it going,
but the momentum that I'm gonna gain
from doing that is gonna make the top easier.
So essentially, the resistance profile of doing
that exercise dynamically, versus slow and controlled,
could potentially flip.
So I could do an exercise
where I was going nice and controlled, slow,
maybe stopping, pausing at the top
and really overload, in the short position, that deltoid.
Then I could flip it up, and I could go more aggressive,
and now I'd be working the bottom position
a little more, de-loading the top position
a little bit more, and all of a sudden,
without even moving, I have picked an exercise
that complements the first exercise,
just by simply changing my tempo,
changing how I was going to use momentum
and overcome inertia.
All right, so in looking at how that helps momentum,
it takes unfavorable things,
and could make them more favorable.
We could take an exercise and add a variation to it
by simply just changing the speed.
We can manipulate the resistance profile.