Before revision: doi:10.1519/1533-4287(2003)017<0475:ECOTUA>2.0.CO;2 BOSU balls under back/gluteus can both increase and decrease abdominal muscle activation depending on the load, whereas placing a BOSU ball under the feet with the dome side down had little impact.
After revision: doi:10.1519/1533-4287(2003)017<0475:ECOTUA>2.0.CO;2