How do I generate a time base for a data set?

I have a file that contains EMG data. I need to generate a time base for the data set. The file is 5999 rows and 2 columns. This is what I currently have in the editor:

%Assignment 4 for SES 619 by Ethan Postans

Column1: EMG data for vastus lateralis muscle of the right leg.

Column2: EMG data for the vastus lateralis muscle of the left leg.

R_emg = data_set2(:,1);

L_emg = data_set2(:,2);

What is the line of code I should use to create a time base for this data set? And what is a time base?