topic Re: electromyography EMG in Life Science

electromyography EMG

kmous — Fri, 06 Jun 2008 15:59:44 GMT

Has any one made a sort of VI to measure EMG signals ?

Electromyography (EMG) measures the response of muscles and nerves to electrical activity. It's used to help determine muscle conditions that might be causing muscle weakness, including muscular dystrophy and nerve disorders.

How Is an EMG Done?

Muscles are stimulated by signals from nerve cells called motor neurons. This stimulation causes electrical activity in the muscle, which in turn causes the muscle to contract or tighten. The muscle contraction itself produces electrical signals.

For the purpose of EMG, a needle electrode is inserted into the muscle (the insertion of the needle might feel similar to an injection). The signal from the muscle is then transmitted from the needle electrode through a wire (or more recently, wirelessly) to a receiver/amplifier, which is connected to a device that displays a readout.

any help ? just wanna know if someone did that before so that i can at least take some advices !!!

any examples on how to do that ?

Re: electromyography EMG

Steve.J — Fri, 06 Jun 2008 16:50:13 GMT

Hi there,

EMG signals are relatively small (microvolt to millivolt level, depending on electrodes and placement) and have energy up to about 1kHz or so. Typically EMG amplifiers have differential inputs (to reject the high common-mode noise typically due to AC line frequency interference), galvanic isolation (to protect the subject from shock), bandpass filtering (to reject DC electrode offsets and movement artifact), and a gain of about 1000. These amplifiers are commercially available from a number of suppliers in the US and around the world (try Google). Often the outputs of these amps are single-ended 0-5V or similar and ready to be acquired by a DAQ board. You cannot directly acquire EMG (or any biosignals) using a DAQ board for both technical and safety reasons.

For gross EMG (EMG recorded from a small region vs. a single motor neuron or motor unit) the signal "envelope" is what the researcher or clinician is interested in - basically, the signal power. The signal can be rectified (take absolute value), then integrated to get total area under the curve. If you do this, you need a way to reset the accumulated signal to zero (periodic reset or with a constant "decay" or time constant). Or you can use LabVIEW's frequency domain analysis functions (power spectrum, etc.) or Joint-Time-Frequency analysis tools for more quantititive analysis. It all depends on what your trying to accomplish. The bottom line is that NI's DAQ hardware and LabVIEW are great tools for acquiring and analyzing these signals.

Hope this helps!

Steve

Re: electromyography EMG

kmous — Fri, 06 Jun 2008 17:15:53 GMT

thank you for the info 🙂
I am new to labview (15-20 days ) only , do u have any small vi ready to start with ? how do i start with my VI ? from where ? i got all the equipement here and ready to start but i dunno how ...i found this and if u look at the bolck diagram i think that's what i need to do !!! do u have that VI ?
thank you

Re: electromyography EMG

Dennis_Knutson — Fri, 06 Jun 2008 18:15:51 GMT

As was already mentioned in this thread where you probably got that pdf, that VI is not available from NI. However, a lot of what that VI is doing, is just basic data acquisition. There is the DAQ Assistant and a large number of shipping examples that you can use to get started with acquiring some signals. That would be the firs\st step and any of the basic examples can be used for that. A very basic example such as Acq&Graph Voltage-Int Clk can be used to quickly acquire and display a voltage from multiple channels. Once you've done that, then you can add some of the other features such as filtering but you first need to get the signals into LabVIEW. Be sure to refer to Getting Started with DAQmx as well.

Re: electromyography EMG

kmous — Fri, 06 Jun 2008 19:35:55 GMT

do u think this example is the right one to start with my EMG ? .........will my signal be analog in this case ?

Re: electromyography EMG

Dennis_Knutson — Fri, 06 Jun 2008 20:12:30 GMT

If you have equipment similar to what Steve mentioned (i.e. the analog amplifiers), then your signals will be analog and other than the DAQ Assistant, is as basic as it gets. Frankly, I don't how your signals could be anything other than analog but since you have not provided a list of equipment, it's all just speculation.

Re: electromyography EMG

kmous — Sat, 07 Jun 2008 21:12:53 GMT

Yes they have everythink here so u think if i connect my EMG amplifier to my Ni 9205 module (because it is analog device) i can simulate the signal with that basic example ? thank you

Re: electromyography EMG

Dennis_Knutson — Sat, 07 Jun 2008 23:28:33 GMT

You want to simulate a signal now and not acquire an actual one? To simulate, you don't need any hardware at all. I don't know if there is a source for emg signals that you can input into your program. If you are familiar enough with what an emg signal is supposed to be, you can use the Simulate Arbitrary Signal Express VI.

Re: electromyography EMG

kmous — Sun, 08 Jun 2008 03:19:20 GMT

I am sorry i meant acquire an actual one by my word simulate !!! so what do u think ? is that VI a good one and maybe enough to acquire it ?

Re: electromyography EMG

Dennis_Knutson — Sun, 08 Jun 2008 04:16:56 GMT

As I've already said, the example is fine for you to get started.

Re: electromyography EMG

kmous — Mon, 09 Jun 2008 13:04:45 GMT

Good morning , this is an EMG program that i found at 3:00 pm this morning 🙂 I am trying to run it (did not connect the hardware) just to see what's going on !!! it gives me an error Duplicate Path , try to run it and see , is that my output file ? i saved it on my c:\ ...but did not work actually !!
thank you for ur help

Re: electromyography EMG

Dennis_Knutson — Mon, 09 Jun 2008 14:10:20 GMT

I can run the VI and not get that error. For a file name, I just used c:\emg.txt. You will need to determine which function is generating that error.

Re: electromyography EMG

kmous — Tue, 17 Jun 2008 16:39:05 GMT

I am running the VI and i am getting an error , i will attach the error !! is it something to do with the create function ?

Re: electromyography EMG

Dennis_Knutson — Tue, 17 Jun 2008 17:12:53 GMT

The error is pretty obvious. It would seem you have a cDAQ board that only supports a differential configuration and the Create Channel is specifying RSE. You can change the DAQmx Create Channel but I have no idea how you've done the wiring to the sensors or what type of sensors you have. I would recomend you review the section on field wiring in your user manual for the DAQ device.

Re: electromyography EMG

kmous — Wed, 18 Jun 2008 13:16:44 GMT

Hi , I found the problem , I was not connectiong to the right channel !!! :S
what do u know about EMG filter (lowpass/highpass/bandpass/bandstop, low cut-off, high cut-off).
what's the difference ?
and btw how can i display 2 channels at the same time on my graph ? let's say i am measuring 2 EMG signals !!! and i wanna set my channels bu default to be DaqMod2/ai0 and DaqMod2/ai1 and i choose one of them or both any idea ?
i will attach the VI's.

Re: electromyography EMG

Steve.J — Wed, 18 Jun 2008 13:46:39 GMT

Typically EMG is recorded using a bandpass filter with the low filter setting (high pass) at about 1Hz and the high filter (low-pass) setting at 100Hz or higher depending on what your sampling rate is and what you are trying to accomplish. For gross EMG activity, the settings are not critical.

Re: electromyography EMG

kmous — Wed, 18 Jun 2008 16:27:32 GMT

how can i display 2 channels at the same time on my graph ? let's say i am measuring 2 EMG signals !!! and i wanna set my channels bu default to be DaqMod2/ai0 and DaqMod2/ai1 and i choose one of them by true/false or both any idea ?
i will attach the VI's.

Re: electromyography EMG

Dennis_Knutson — Wed, 18 Jun 2008 18:39:31 GMT

The code you posted does have the physical channel control set for two channels. If you want to use different ones, click on the little arrow on the right side and then select 'Browse'.

Re: electromyography EMG

kmous — Wed, 18 Jun 2008 18:51:07 GMT

ya i know but i wanna use my channels like cDAQ3Mod2/ai0 and cDAQ3Mod2/ai1 !!!

Re: electromyography EMG

Dennis_Knutson — Wed, 18 Jun 2008 19:20:29 GMT

So what do you see when you select 'Browse'? You should see all available channels. Do you know that you can use Ctrl-Click or Shift-Click for multiple channels? Thats' the same thing you do in windows explorer to select multiple files.