Studying Fatigue on Ritalin: A repeated measures analysis. How do I ....

Hi,

I am studying fatigue in response to Ritalin. Subjects performed a fatiguing handgrip task of alternating grip and rest periods in a repeated measures design.

My research question: I would like to determine how Ritalin affected the generation of fatigue.
Analysis Question: I have created a fatigue, which is the inverse of the force over the experiment. Is there a way to compare force curves using Igor to investigate how fatigue changed over time between conditions? My initial reaction is to compare slopes in distinct portions of the curve but that limits my analysis to distinct periods, I think.

Is there another option to describe the difference between these curves?

Example: I have a attached a screen shot of two curves

Best,
Michael