Changes in deep abdominal muscle thickness during common trunk-strengthening exercises using ultrasound imaging.
Teyhen DS, Rieger JL, Westrick RB, Miller AC, Molloy JM, Childs JD. Changes in deep abdominal muscle thickness during common trunk-strengthening exercises using ultrasound imaging. J Orthop Sports Phys Ther. 2008 Oct; 38(10):596-605.