You saved the variable app.Pedobarography_Values in the file 'Pedobarography_Values.xslx' but by the documentation for xlswrite (which is, by the way, deprecated; use writetable or writematrix instead) the return value is simply the status of the write operation...1--> success, 0--> failure. So, the most you have done with the SAVE operation is write a single logical value to the location from the returned path into file named the result of evaluation of the string [selpath '.mat']. More than likely this is an invalid location.
At a minimum, use something like
selpath = uigetdir;