filter ECG and PPG signal with low pass filter

Hello guys.

I have ECG signal with 125 sampling frequency and i have to filter it with low pass filter. Which are the best "settings of filter?"

    [b, a] = fir1(%i need 2 arguments here
    , 'low');                          
    y = filtfilt(b, a, ECG);                                 
    [peaks, poloha] = findpeaks(y, 'MinPeakDistance', 320);  
    ECG_sprac = length(poloha);
  
    [b, a] = fir1(%i need 2 arguments here
     ,'low');                          
    y = filtfilt(b, a, PPG);                                 
    [peaks, poloha] = findpeaks(y, 'MinPeakDistance', 320);  
    PPG_sprac = length(poloha);
       
    
    
    breathVAL = (ECG_sprac + PPG_sprac)/2;

[Mathieu NOE]

hi

maybe you should first explain why the need for low pass filterning (noise ?) and also sharing the data would help

tx