Measure. Analyze. Learn.
Hi, I'm John Melville from Vernier Software & Technology.
I'm going to show you how to record an EMG.
An EMG is the electrical activity from a muscle.
One of the things we need to do though, if your going to
record an EMG, is we need to make sure that we don't have
other devices that are going to interfere with the recording.
Things that can interfere with this type of recording are
things that generate electric noise, like a cell phone,
or even, the power supply to a computer.
So, I'm going to disconnect the power supply to my computer.
We're going to be using the EKG Sensor.
Now, the EKG sensor is normally used to
record the electrical activity from the heart.
Now, the heart is a muscle. You have lots of other muscles
in your body, and they are also all electrically active.
We're also going to be using this Hand Dynamometer.
The Hand Dynamometer is going to be used to
measure the amount of force that's generated
by my hand, or my forearm.
So now, what I am going to do, is I'm just going to set up
the electrodes on my forearm for recording an EMG.
So, I'm going to take these electrode tabs,
and I am going to place them across the body of the muscle.
So, since we're looking at the forearm;
I'm going to place one here,
and another one here.
So, I'm going to be looking at the electrical activity of
this muscle, the forearm muscle.
So, when I squeeze the Hand Dynamometer, you can see
that that muscle contracts.
So, I'll be looking at the amount of force that I can generate
with my hand, and the amount of electrical activity
that's generated by this muscle.
I also need a ground. So, I'm going to actually place the ground,
I'll just place it over here.
And now, what I'm going to do is,
I'm going to actually take the EKG Sensor and apply the leads.
Now, in this case, it's important to understand that
the green lead and the red lead are
what I'm using to record from.
The black lead is actually used as what we just call a ground.
And, it doesn't matter what order they go in.
Just need to remember that you use the red and green lead to
record the muscle activity.
So, I'm going to take the red lead and put it here,
the green lead and put it here,
and the black lead here is just the ground,
and I'm going to place that back over here.
Then, I'm going to get these out of my way, a little bit, like that.
The other thing that I am going to do is that I need to
plug the sensor into the LabQuest Mini.
This is the LabQuest Mini interface.
I'm going to unwrap this wire, because normally if you're
recording from an EKG, it is important that this little box
also doesn't get any interference from electronic noise.
So, what I'm going to do, is I'm actually going to move that
little EKG Sensor over here, away from the monitor.
You could also put it in your pocket,
but I'm just going to move it over here.
The next thing I'm going to do is,
I'm going to plug in my Hand Dynamometer.
So now, I'm ready to start this experiment.
If you're using Logger Pro, you can just open an experiment file.
So, this experiment is actually part of
our Human Physiology Lab Book.
So, if you actually go to the "File" drop down menu,
and select "Open…", it will take you to the experiments folder.
If you go down to "_Human Physiology w Vernier",
you can just choose any of our EMG activities.
In this case, I'm looking at lab "18 EMG and Muscle Fatigue".
And, I'm going to open that file.
And, you can see that Logger Pro resets itself.
I have "Grip Strength" up top in this graph.
I'm going to have "EMG" activity down in this graph.
And now, I'm really just ready to start the experiment.
All that I have to do is zero the Hand Dynamometer.
And then, just hit the collect button.
Now, to zero the Hand Dynamometer, that's quite simple.
I just need to go to this button right here,
which is next to the data collection button.
This is just setting the zero point for the Hand Dynamometer.
And then, I can choose what one do I want to use,
and I'm just going to zero the Hand Dynamometer.
You could zero the EKG if you wanted to as well,
but it's not critical.
What you're about to see, is you're about to see
force being generated from the Hand Dynamometer,
and then the electrical activity from my muscle.
So, I'm going to show that to you, and then,
I'm going to explain to you a little bit about what that means,
and then, how we can actually analyze it.
And, this file is going to record for around 100 seconds.
We don't really need to record that long to analyze this data.
So, I'm going to change the duration of this experiment here,
by clicking on the data collection button.
And, I'm just going to record for 20 seconds.
So now, I'm going to hit collect.
I'm going to just not do anything for two seconds.
And then, I'm going to squeeze this Hand Dynamometer hard.
And then, I'm going to keep on squeezing it.
And, hopefully we'll see some fatigue.
Here we go: collect…
I'm going to squeeze…
[Strained voice] Keep squeezing…
[Loud exhale] Oh boy!
[Inhale] Now, I'm going to put this down.
Now, what you can see in this file, is that force went up.
And then, it stabilized. And then, it began to go down.
And then, I squeezed a little bit harder here.
And, the force continued to go down.
If you look, now, at the EMG trace, just take a look at
what we call the envelope of this EMG activity.
So, each one of these spikes that you see here,
is activity from my brain, telling my muscle to be active.
My muscles are electrically active.
So, the more spikes we see here,
the more muscle activity there is,
or the more electrically active the muscle is.
And what you can see is the envelope
of this activity is increasing even though
the strength is actually decreasing as a function of time.
What that means, is that my brain is
driving my muscle harder and harder,
but something is happening peripherally in the muscle to
actually make it weaker.
If you're teaching human anatomy and physiology,
what's happening is that the calcium is getting sequestered,
and I'm using up all my ATP.
And, that's actually a process that we call muscle fatigue.
So, there's a couple of different ways that
you can actually analyze fatigue in Logger Pro.
There's a couple other really interesting and
neat things you can show your students using an
EKG Sensor and a Hand Dynamometer.
So, what I would like to do next is
just show you how to overlay two graphs.
Because, what you can show is that
the muscle is electrically active before any
force is generated by the hand.
But, you have to do a special thing, and that's called
using a double axis on your graph.
The simplest way to do that is to take this graph,
and I'm just going to scroll it down here,
and then, I'm going to double click on the graph.
I double click on the graph,
you will see this graph options dialog.
And what I'm going to do is,
I'm going to select the "Axis Options" tab.
So, I'm just going to select here, on "Axis Options".
Now what you see;
this is all the choices that I have for the y-axis of my graph.
Right now it shows force.
But, if I select over here; on this little button, called
the "Right Y-Axis", I can actually have two axes on my graph.
I can have one displayed on the left,
and one displayed on the right.
So, I'm going to do that.
And remember, what I want to show in this case,
is I want to see force and muscle activity at the same time.
So, I'm going to select "Potential".
Which, in this case, is muscle activity.
If I then hit done.
Now, if you look at the graph: if you look right here;
I have force here; and potential here on this side.
But you see my muscle activity down here looks really small.
That's because I just haven't auto scaled this graph.
If I auto scale this graph, I'll be able to see
both axes maximized on the graph.
So, I'm going to go right over here, to "Auto Scale [Graph]".
There.
So now, what you should be able to see is force increases,
and then here's this wave of muscle activity.
And, you can really see it really nicely now that
this envelop gets bigger, and bigger, and bigger,
even though my grip strength is decreasing over time.
Now, if you want to show your students that the muscle
is definitely electrically active before force generation,
we can, once again, just zoom in on a given region.
So, let's zoom in right here on this area,
and take a look at the EMG and force.
So, I'm going to zoom in just on this area right here in the graph.
And, once again, I'm going to use the "Zoom In" button,
which is right here.
So, what you can see in this case,
I'm just going to point this out really quick.
Here is force in the red, and then it begins to go up, right here.
We can see that force begins to be generated right around here.
And, what you can see right here in this blue trace,
is the muscle is definitely active.
It begins to be active; if we just go down here;
right before force is being generated.
So, the muscle in this case is active before force is generated.
So, for more information on this activity,
which is lab "18 EMG and Muscle Activity" in our
"Human Physiology with Vernier" book,
just check out our web site, www.vernier.com.