Looping an animation smoothly

That’s true, the blue curve should be flat since it peaks at the point where the animation loops, but I don’t want that for all curves. I tried shift+e, but it just gave me two options: constant extrapolation and linear extrapolation.

And are you saying that I need to adjust the handles on the ends of each individual curve to get them to line up? There’s no way I’m going to do that for every bone in every action.