Calculate area from a signal

Hi, would like to calculate area from this emg signal

There are three different channels. I've done RMS and snap the exact tiem I need to analyse but don't know how to calculate total area

My code is:

for c=2:2

A=strcat('S1_',num2str(c));

B=strcat(A,'.emt');

D=importdata(B,'\t',12);

[F, C]=size(D.data);

x=filter(Filtro_emg,D.data);

centro=(F-mod(F,2))/2;

x=x(((centro-4000)+242:(centro-4000)+3026),:);

RMS = Rms_emg (x,100)*1000;

S=smoothdata(RMS);

plot(S);

for b=3:5

Areatotal(b,c)=sum(S(:,b)); I've tried with this, but don't know if it's correct

Media(b,c)=mean(S(:,b));

Maximo(b,c)=max(S(:,b));

end

end

Please help, thanks!

Answer 1

[AndresVar]

You can use trapezoidal rule: see trapz: Trapezoidal numerical integration - MATLAB trapz (mathworks.com)

area = trapz(x,y) % i think for you trapz(S(:,b))  or just trapz(S(:,b)) if dx = 1

sum also works so you can compare your result. You must multiply the sum by dx, but it looks like dx=1 in your case.

[Julio Martín]

Thank you, I've compared both and result is the same

How could I also calculate the integral of this signal?

Thanks

[AndresVar]

for integral signal use 'cumtrapz' or 'cumsum'

btw beware of units when integrating and finding area. make sure its what you expected. dx is 1 but if you want to integrate with respect to time you need to find what is dt.

[Julio Martín]

Thank you. Exactly I have doubs about the result

With this code

for c=2:2

A=strcat('S1_',num2str(c));

B=strcat(A,'.emt');

D=importdata(B,'\t',12);

[F, C]=size(D.data);

x=filter(Filtro_emg,D.data);

centro=(F-mod(F,2))/2;

x=x((centro-4000)+133:(centro-4000)+483,:);

RMS = Rms_emg (x,100)*1000;

S=smoothdata(RMS);

figure

for b=3:3

plot(S(:,b));title('Tibial anterior');grid;xlabel('Tiempo mseg');ylabel('uV');

AreaGM1=sum(S(:,b));

end

end

I have a result of 42756.251 uV (I supose it's impossible in a time of 350 miliseconds). If x is time in miliseconds, how could I calculate it?

Thank you so much