The bottom line seems to be this:
By using cutting-edge motion-capture technology, we have been able to precisely break down and analyse specific motion patterns in male dancing that seem to influence women’s perceptions of dance quality. We find that the variability and amplitude of movements in the central body regions (head, neck and trunk) and speed of the right knee movements are especially important in signalling dance quality. A ‘good’ dancer thus displays larger and more variable movements in relation to bending and twisting movements of their head/neck and torso, and faster bending and twisting movements of their right knee. As 80 per cent of individuals are right-footed, greater movements of the right knee in comparison with the left are perhaps to be expected. In comparative research, there is extensive literature on the signalling capacities of movement…Researchers have suggested that females prefer vigorous and skilled males; such cues are derived from male motor performance that provides a signal of his physical condition.
The paper is here (pdf), via Samir Varma.