Asseyez-vous droit avec moins d'effort
From two studies with persons sitting upright without any backrest trying to keep a natural posture or doing a typing task, the conclusion was that the core muscles are less active when sitting on Backapp. Lumbar flexion was significantly reduced and so was activity of one of the main lumbar muscles. The conclusion is that sitting upright on Backapp is simpler than on an ordinary office chair. You can sit for a long time upright on Backapp without any back rest.
Manual Therapy (Volume 17, Issue 6) Pages 566-571
Ergonomics (Volume 55, Issue 12) pages 1586-1595
"Lumbar posture and trunk muscle activation during a typing task when sitting on a novel dynamic ergonomic chair". Kieran O'Sullivan, Raymond McCarthy, Alison White, Leonard O'Sullivan & Wim Dankaerts 2012.