Area of Hysteresis Loop?

I need to find the area of a hysteresis loop for a set of dynamic data modeling a force-displacement relationship. I have obtained a figure of the loops, but what I need is just the area of the largest loop in the figure. Is there a way to isolate just this one loop through MATLAB? Also, what is the appropriate code to obtain the area of the loop?

Data file and figure can be found at:

http://www.4shared.com/file/Monww2RW/5_online.html http://www.4shared.com/office/XUBEa6nR/5_online.html

Thanks for any help.