Someone can be seen in the clip holding on to Efimova's feet so she doesn't fall off, so perhaps it's not quite as impressive as it seems at first glance. But it's still bloody difficult and requires a heck of a lot of strength to stay level as she feels the burn.
Efimova is a controversial figure in swimming, having served a 16-month ban across 2014-15 because of a positive drugs test for a banned steroid. Swimming's governing body FINA was also heavily criticised in 2016 when it lifted her provisional ban after she also tested positive to meldonium, allowing her to compete in the Rio Olympics.
Efimova was the target of attacks from fellow swimmers at the last Olympics, who didn't believe it was fair to be competing against her.
That explains why Scottish swimmer Michael Jamieson wasn't impressed with what he was seeing online. When Efimova's clip had a couple of million views he wrote on Twitter: "2 million views for a dope cheat, gtf."