The performers in Circ du Soleil are aliens. I think that's the only possible explanation, and let's face it... if you were an alien on planet Earth, it would be the best cover imaginable. It's a place where borderline unnatural movement, superhuman strength, an unparalleled sense of balance, and futuristic neon clothes complete with matching cracked out headgear are just par for the course.
Whatever. I basically doubt that these people actually have bones. For real...that and they're impervious to gravity. Friction also has absolutely no effect on these people. Traction is just a concept.