EMG Analysis

[Michela Persiani]

Hi all,

I've a question about the EMG analysis. I assessed an experiment about influence of vision on postural control. I recorded the muscle activation of soleus, tensor of fascia latae, tibialis anterior and gastrocnemius medialis of both legs. One of my collegue suggested me to combine the EMG signals of both legs for each muscles.
So far I couldn't find in the licterature if this method its correct.
I will appreciate if someone can helping me on that.

Regards

Michela

[Dan Robbins]

Re: EMG Analysis

Hi Michela,

I suppose it really depends on what your research question is, but I can't see a benefit to combining the signals.

Regards
Dan

[Matthew Tenan]

Re: EMG Analysis

Michela,
It may help if we know what exactly you mean by "combine the EMG signals". How would they be "combined"? As Dan alludes, it isn't a common procedure so it is hard to know the benefit without understanding how it would be implemented.

Matt

[Michela Persiani]

Re: EMG Analysis

Michela,
It may help if we know what exactly you mean by "combine the EMG signals". How would they be "combined"? As Dan alludes, it isn't a common procedure so it is hard to know the benefit without understanding how it would be implemented.

Matt

Hi,
firstly thanks for your reply. If I understood correctly to my colleague, combine the EMG signals means that he want to calculate the mean of the couple of muscles. In my mind this procedure is incorrect because one of the purpose of the study is to verify the muscles activation induced by the changes of visual environment. So we will lose a lot of information. The only benefit with this weird procedure is that we will reduce the variables so we can have an optimal statistical power.

thanks
Michela

[Dan Robbins]

Re: EMG Analysis

Hi Michela,

I agree that this is not an ideal approach. The only time I have seen EMG signals 'combined' was when a series of signals was added together to provide a total muscle activity, i.e. for all the body or upper/lower body analysis.

I don't see how average raw signal values would be of any use. Did you colleague indicate any other stages? For example normalising the signals first?

Regards
Dan

[Brad]

Re: EMG Analysis

Michela,


I assume when your colleague says "combine" the EMG signals he/she meant taking an average across all trials bilateraly for each instance in time. For example if you have tibialis activity of both the right and left legs sampling at 1000 Hz and your emg signal under investigation was exactly one second Then you would average each 1/1000 of a second across all trials of both legs. This would be done after rectification and normalization.
Personally I don't see this techniqu as adding anything to the analysis, unless you did not perform enough trials of each activity under investigation. EMG signals are highly variable so adequate sampling is necessary. If however you did perform a significant number of trials I have seen researches who only analyze data on one half of the body. The assumption here of course is that both sides responded to the stimulus the same. This would only work in a symmetric task such as an SOT task in the neurocom.


Hope this helped
-Brad-