- [Voiceover] When you start using your muscles
you can use them in different ways.
I know it sounds kind of weird,
like you know, your muscles contract they move something,
not always.
In the case of an isotonic contraction,
sure, the muscle is shortened in length
that means it's moving a physical force.
You're picking up a book, you're grabbing a glass of water
those are isotonic contractions.
You're physically shortening the muscle
and moving something.
Now there are also a type of isotonic
where the muscle elongates a little bit.
The key thing is isotonic, the muscle is moving,
while isometric the muscle doesn't move.
There's no movement, you're not moving an object
but in isometric contractions, you're still
putting force into it.
Think this way, you put 500 pounds on a barbell.
Try and pick it up,
what's the odds you're gonna pick up 500 pounds?
Probably for the vast majority of people in this world,
not gonna happen.
That would be an isometric contraction.
You're trying, your muscles are flexing,
you're trying to move them
but the weight is not moving.
The muscle's not shortening,
you're not moving that weight.
So you actually have these two different types,
isotonic, isometric.
Now the amount of nerves impulse,
the amount of nerve activation,
the amount of signals basically,
influences how much force.
The more signals you have, the more force you'll exert.
The fewer signals you have, the less force you'll exert.
All depends on what you're trying to move.
Now the way this is all broken down
is called a motor unit.
A motor unit is going to be a neuron,
so motor neuron, that's what carries the information
from your brain and spinal cord down to the muscle cell.
But the motor neuron can connect to several
if not dozens of muscle cells.
So that means every time this one neuron fires,
all the attached muscle cells are going to contract.
That's a motor unit.
And this motor unit really is the smallest
functional unit for muscle contraction.
You have to stimulate motor units,
you have to stimulate a group of cells
to get them to move.
And as they start to move,
or even if they're holding steady
they're generating some tensions,
we're talking about muscle tension.
Now, muscle tension is a mechanical force.
It's what your muscle can generate as it contracts.
That means as the muscle's larger
it could have more force, more tension.
Muscle's smaller, has less tension.
So this muscle tension, how much tension or force
is being generated is determined on the motor unit size.
How many muscle fibers are stimulated
for a particular neuron.
It's the number of active motor units.
The more motor units you have,
the more force you can generate.
And the frequency of stimulation.
If you can continuously, constantly
stimulate a motor unit, it will continuously and constantly
create force and create tension.
That's why you can vary the different amounts of tension
and force in your limbs, your body.
You can pick up a one pound book,
or you can pick up a 10 pound barbell.
You differ the amount of force you're using
to move those objects.
And when you do this, it's all or none.
Once a muscle cell is stimulated
it will contract fully.
Once it is not stimulated it will relax fully.
There's no half contraction for a cell.
Now obviously you can change how much force you exert
in a whole muscle, that's because you're adding
or subtracting motor units.
You cannot change the strength
of an individual muscle cell.
So what happens is as you have those muscle cells working,
they're generating your muscle tone.
Always your muscles have some tone.
Even when you lie in bed, even when
you're sitting down calmly,
muscles are maintaining a tone to maintain your posture.
They maintain a tone to keep you breathing.
They maintain a tone to make sure you're ready
to react to any situation.
So you always have some muscle tone.
But if you need more force than what that tone is providing,
then you have motor unit recruitment.
In the case of recruitment,
it's gonna bring more motor units in,
causing these motor units to stimulate more muscle fibers.
More muscle fibers means more force.
So pretty much you're recruiting more motor units,
recruiting more fibers to generate more force.
Here's an example of a neuromuscular junction,
you can see the motor neuron in the top figure is yellow,
coming down and meeting with a muscle cell.
In the bottom picture, which is actually a photograph
of actual muscle tissue, you can see the thick black line
coming from the top right and then kind of branching
down into the red muscle cells.
Those are the neurons coming down to meet
with the muscle.
That's gonna bring the electrical impulse down
and then transfer it into the muscle.
The term muscle twitch is referring to any complete cycle.
It's a complete cycle of contraction and then relaxation.
Therefore any stimuli that can cause
a contraction-relaxation is generating a twitch.
Most twitches are minute and small.
To create overall movements,
let's say taking your arm and flexing it,
showing muscle, that's multiple stimuli all in a row.
All this electrical impulse, all these muscle twitches
can be observed using a myogram.
A myogram is gonna be an electrical reading
showing these impulses.
So here's an example,
the first stimulus at time zero,
what does that do?
That is called the latent period.
Nothing moves, that's when the signal is being sent
from the brain or spinal cord down to the muscle.
Once the muscle receives the signal,
you go into the contraction,
it's generating force, generating tensions.
Once you generate enough force,
or you've had enough time based on this stimuli,
you go into relaxation.
That's one single muscle twitch.
But then if you notice, if you move into this
kind of more middle of the graph, in that middle tone,
you can see you have a stimulus,
goes up and doesn't fully relax.
You have another stimulus, and another stimulus,
and another and it keeps causing it to climb
higher and higher and higher.
That means it's caused it to have more and more force.
That's called summation.
But there's a limit.
There's a limit to how much you can go through summation.
You can only reach your maximum tension,
or maximum force.
Your muscles can only move so much weight.
Once you've reached that top,
the muscle's not really contracting or relaxing
it's just staying in the highly contracted phase.
It's referred to as tetanus.
I'm thinking tetanus as in tetanus shot,
yes they're related.
'Cause the tetanus shot
is meant to obviously prevent tetanus.
Tetanus is when a muscle freezes or locks up,
so the shot is to try to prevent any muscles
from freezing or locking up,
that's why it's the tetanus shot.
These muscle activities, we talked about different
types of movement, isotonic, isometric
but there's also different types of fibers.
So, it's called slow twitch
and that one's called fast twitch.
In the case of slow twitch
people that are working out for long periods of time,
jogging, biking, swimming, long, long durations
pretty much anything that needs endurance.
So these slow twitch muscles
are going to have a long phase of contraction.
They'll slowly contract over a longer period of time,
allowing each contraction to last longer.
While the fast twitch, think of sprinting,
weight lifting, tennis, very short quick
durations of signal.
Very short quick amounts of movements.
They're meant for more of the strength training,
more of the quick reaction training.
So it's all gonna be short duration, fast twitch.
Slow twitch, long duration.
Alright, strength training
now is this one of those things
where you go out and start doing a whole bunch of exercises?
No, no, no this is something where you have
to kind of think about what you're doing,
'cause very easily you could injure
or tear one of your muscles.
So when strength training one way is resistance training,
short very intense workouts.
Because they're short and intense
they're building more of the fast twitch muscle.
Aerobic training, well in aerobic training
you want to make sure you have plenty of oxygen
getting into your muscles.
And by doing that you're training your muscles,
you're training your heart to become more efficient,
to build endurance.
It helps to increase blood flow,
and usually once you hit that target heart rate
you want to hold it for 20 to 30 minutes.
And ideally that should be three times a week.
So, aerobic training, great for the heart,
great for the lungs, it really helps
increase blood supply to all your muscle cells.