Almost every health club and college physical education program on the planet has a core training class, which specifically targets muscles in the thorax that support the spine. The basic concept behind these classes is that core stability is critical for maintaining spinal health, transferring force between the lower and upper body, and attaining an attractive-looking midsection (i.e., six-pack abs).
John Cissik from Texas Woman’s University, in a review of literature, concluded that there is little evidence for specifically targeting core muscles using exercise balls and unstable surfaces. Further, while many biomechanists, coaches, and therapists promote core-stabilization exercises, there is little evidence that they prevent injury. This is an extremely controversial topic that will require extensive study. (Strength Conditioning Journal, 33 (1): 10-14, 2011)