I've discovered the photographer Paterakis and wonder how he managed to obtain the rendering of his series Shadow Life.
Obviously he uses a long-time exposure, but I can't guess much more...
In this below example from the site, you can see the effect: Pure white background, grey shapes from people in the very front and as subject a woman with movement-blur.
Just a simple white background, continuous light + flash with softboxes, slow shutter and flash heads synchronized on rear curtain.
When the face is visible: flash on the man + background. When body is black: flash only on background.
So you get the blur from the slow shutter (+ low continuous light), and you get the shape burned in from the flash. You can use multiple flashes for multiple burned in contours if necessary.
My best guess is that it is an extremely highly lit backdrop with people moving in shadow in front of it with a second or two exposure tops. It feels like there is likely some photo manipulation and masking as well, however it is possible that these could be a result of the well defined areas being in shadow the whole time and the partial exposures still bleeding in to clipping.
Alternately, some of it may have been achieved using masks for blending.
