How can I get the maximum point coordinate of 5 curves?

Hi everyone,

I am on app designer and matlab 2016b. I am ploting 5 curves on UIAxes and I try to plot a 'o' on the maximum point of the 5 curves. The problem is that I can't find the abscissa x1 of the Ymax(y1). I tried to use the fonction max() as shown below but it just say me that the maximum is in the matrix WheelTorque_4.

[y1,x1] = max([max(WheelTorque_1) max(WheelTorque_2) max(WheelTorque_3) max(WheelTorque_4) max(WheelTorque_5)])
y1 =
   2.5798e+03
x1 =
     4

I don't know how to get the x1.

Does someone got a solution? thanks in advance