EMG Amplitude Analysis -Mean, Peak, Integral EMG-

Hello everyone,

I hope you enjoyed my previous posts about EMG pre-processing and timing analysis.

EMG on Nordic Hamstring Curl - Filtering, Rectifying, Enveloping -

https://ryuugaku-abc.site/emg-on-hamstring

Hello everyone, Have you ever imagined visualizing muscle forces ?? There are many ways, but electromyography aka EMG is just one way. It detects action potentials on muscles and shows signal waves as an output. As a simple example, the bigger waves, the more muscle force. In this blog, I will show you how to collect and analyze EMG data. What does EMG look like ??You can watch the video applying EMG on hamstring. On the video, 2 small poles detect action potentials, and 1 blue box...

Takashi's Study Abroad

EMG Timing Analysis -Muscle on, Muscle off, Duration-

https://ryuugaku-abc.site/emg-timing-analysis

Hello everyone, In the last blog, I explained how to pre-process EMG data (If you haven't checked it out, please go to my previous blog and YouTube video below). The envelope we created last time is nice to see, but people may think "so what ?" Therefore, this time I would like to go further ... Then, why do not we find when muscles activated, when they dropped out, and how long they activated ?? Procedure1, Pre-process EMG dataWe did this last time, so ple...

In this time, we go a bit further in EMG analysis, so we will conduct EMG amplitude analysis. By very simple definition, EMG amplitude is a parameter on y-axis of EMG plot. I know it is too simple, but it is easy to remember. The amplitude represents how big or small action potential on muscle is. Obviously, the bigger amplitude, the bigger muscle activation.

Procedure

1, Pre-process data

I am explaining how to pre-process EMG data on my blog and YouTube video, so please check it out !!

Takashi's Study Abroad

EMG on Nordic Hamstring Curl - Filtering, Rectifying, Enveloping -

https://ryuugaku-abc.site/emg-on-hamstring

2, Find muscle activation duration

I am explaining how to find muscle on, off, and activation duration on my blog and YouTube video, so please check it out !!

Takashi's Study Abroad

EMG Timing Analysis -Muscle on, Muscle off, Duration-

https://ryuugaku-abc.site/emg-timing-analysis

3, Mean EMG analysis

Mean EMG analysis is finding an average EMG value in each muscle. We can just use enveloped EMG data and find its average. The mean EMG looks like …

If we normalize data (I will show you how to do it in another time), we can compare mean EMG amplitude in one muscle with another muscle. To normalize our data, we have to have a reference trial such as a maximum voluntary contraction (MVC) trial. Unfortunately, we do not have the trial… Technically, we can normalize the data by using the maximum EMG value in our trials, but we can only compare the same muscle among different trials. For example, we can compare the right bicep femoris in trial 1 with trial 2. Without normalization, we can only observe EMG pattern. I can only see the fourth trial is the highest EMG amplitude among other trials so far …

4, Peak EMG analysis

It is the maximum version of mean EMG analysis. Instead of average, we find the maximum value of enveloped EMG data in each muscle. The peak EMG looks like this …

As I mentioned in mean EMG analysis section, we can take one of peak values (the maximum value) from here and normalize the enveloped EMG data to compare the same muscle in one trial with another trial. Normalization procedure is kind of simple. You just need to divide all EMG values by the peak value, so you can get % of the EMG values respect to the peak value.

5, Integral EMG analysis

It is like impulse. The formula is amplitude * Δtime. Don’t worry about the formula. A programming language does the job for you. Basically, we find a value in area under the curve by using the formula. A plot below shows you what I mean …

The blue line is enveloped EMG data, and colored areas are integral parts of EMG. I defined the integral part of 1 second around 20, 50, and 80% of muscle activation. Integral values of all other trials are below …

As you guessed, the integral EMG value is increasing from 20% to 80% of muscle activation. Also, the increment is observable across all trials.

My YouTube video

I am explaining all procedures of how to do EMG amplitude analysis on my YouTube video, so please check it out !!

MATLAB code and EMG data

Enjoy!!