Calculating max and minimum values between zero crossing points

I have a 23036 x 6 x 39 matrix which contains all of my data, from this i have calculated the zero crossing points for this data but i'm stuck on how i can use this information to calculate the maximum and minimum values between these points. I have attached the Zero crossing matrix and the code used however i couldn't attached the original as the file size is exceeded.

number=0;

for i=2561:size(Wavedata,1)-5118
    for j=1:size(Wavedata,2)
        for k=1:size(Wavedata,3)
            if (Wavedata(i,j,k)<0 && Wavedata(i+1,j,k)>0)
                number=number+1;% save index of zero-crossing
      A(number)=i;  
      B(number)=j;
      C(number)=k;
            end
        end
    end 
end
%A' is the timestep, dividing by the sampling frequency 128Hz gives the
%time value. 
z=[(A'/128) B' C'];