"Invisible chairs"

YouTube link. 

The two most reasonable explanations are:

1) A support inside their pants which flexes 90 degrees only.  It would have to interface with some anchoring point on the floor.

2) Wire supports from above connecting to a body harness.  Other "flying" performers raise this possibility.

Any other ideas?  It seems to have been filmed at a live performance, so presumably there is no green screen video editing.

Via Nothing To Do With Arbroath.