Single frame, no compositing, no Photoshop or anything;
3 sec exposure, f/11, iso100 on a Nikon Z6 II with a Z 70-200mm
Most importantly for the long exposure to work, it's in a completely blacked-out studio with a black background and using the multiple flash feature on a couple of Godox studio strobes at 1 Hz. Through lots of trial and error, we found the best rhythm for posing in that 3 sec at 1 Hz tempo, but experimentation depending on the movement here was key.
This was done for a workshop I was teaching on capturing motion in different ways -- freezing it vs showing blur, etc. and this was the specialty shot I did to show off something a bit mind-boggling that can be done in-camera. I prefer doing effects even this dramatic naturally rather than in post.
P.S. my friend here is Kosta and he's an incredibly talented dancer, choreographer, and now director of dance films and performances.