Tariku Degefa, 25, and Yonas Alemu, 16, both from Ethiopia, have been performing together since Yonas was 10 years old, and are among only a handful of people in the world capable of the powerful form of foot juggling known as risley - where Tariku literally juggles Yonas using his feet.

The pair had left Spiegelworld's Empire show for a few weeks of training, but are now back for the final week of the Canberra tour, which production stage manager Terrence Williams said is a real boost to an already-acclaimed line-up.

"A risley act is quite a popular circus act but there are only so many groups in the world that do it because it's a very difficult training process. It takes a lot to be able to do a lot of those moves," he said.

"It's hard to describe … it's such precision and some of the moves are almost impossible to fathom until you see them.''

The performance, which runs close to six minutes, involves Tariku, the base, lying on a couch and pushing Yonas, the flyer, up in the air with his feet while Yonas twists, flips, and sometimes suddenly stops in a display of strength and balance.

It's a physically demanding routine which has only become harder as Yonas has grown - Mr Williams said he's shot up about 30 centimetres over the past 18 months.

"The routine has become more athletic as they've both conditioned and become stronger, so that is fantastic for us and for the audience," he said.

"To be the flyer your stomach has to have incredible muscles, your abs have to be quite strong, and then to be the base, you have to do a lot of work with your legs."

Mr Williams said the fact that there weren't many places you could go to see such an act added to the experience of working at Empire, where most of the routines defied belief.

"One of the fun parts of working here is that you get to watch people's reactions to something that most likely they've never seen," he said.

■ Spiegelworld's Empire is in Canberra in the Canberra Theatre Forecourt until November 3. Tickets are available via empireaustralia.com