“Little scientific attention has been paid to the complex task of hula hooping.” – explains a recent research paper from the Sensorimotor Neuroscience Laboratory at McMaster University, Hamilton, Canada.
To counter this lack of data, an investigative team set up motion-capture equipment to track in detail the gyratory movements of a set of  accomplished hula hoopists. Subsequent analysis of the results showed – for the first time – that various hoopists  utilise slightly different methods of invoking and sustaining the hoop oscillations :

“The abductor moments and powers were discovered to be paramount in maintaining hoop oscillations … However, hula hooping was demonstrated to be variable in terms of the involvement of flexor and extensor moments and powers of the ankle, knee and hip joints, resulting in the adoption of varying strategies by each of the three participants.”

The authors do point out though that “… the reader should exercise caution when interpreting the present results.” – primarily due to the relatively low number of participants in the experiment (3).
The lab’s research paper was published in the journal Human Movement Science, Volume 27, Issue 4, August 2008, and can be read in full here: