smart way of dealing with cyclic curves

Hi,

The image shows three plots that are cyclic in nature. I was wondering what is the best way I can get an average curve for each plot. My knowledge is limited to using polyfit, however this does not work in this case since there are repeating X values and it does not give me the elliptical shape that is characteristic of the plots.

any help or direction to good reading material is appreciated. Thanks

Lomas

http://imageshack.us/photo/my-images/801/25137034.jpg/

[Thorsten]

Please give some more details about the data, and how the are obtained, and please include an example.

[Lomas]

the plots are rotations of the scapula (three) with respect to the thorax vs upper arm elevation. So during upper arm circumduction the rotation of the scapula wrt thorax is measured. the subject performed this circumduction motion six times resulting in the multiple curves for each rotational degree of freedom of the scapula.