Couldn't find anything on efficiency. It looks like everyone naturally sways, with women swaying more than men (duh), and that as fatigue sets in the amount of sway increases (although that may not be a bad thing).
Thorax and pelvis kinematics change during ... [Int J Sports Med. 2012] - PubMed - NCBI
Biodynamics. Influence of gender, power... [Med Sci Sports Exerc. 2007] - PubMed - NCBI
Came across this while searching... must be hard doing that kind of research. haha
The bar sinister: does handlebar level damage the ... [J Sex Med. 2012] - PubMed - NCBI