import numpy as np
x, y = np.loadtxt("MotionData.txt", skiprows=1 ,usecols = (0,1), unpack=True)

If you don't want to read all the columns of your data file you can specify which columns to read with usecols. In this case you will read the first and the second columns and you will not read the third column. Note that there are only two arrays to the left of the equal sign here which are x and y.