How-to: Obliques with Small Ball is a variation of the original Pilates exercise “Obliques” (or “Criss-Cross” as it is sometimes called).  Adding the small ball under the back increases the instability of the exercise, thus increasing the challenge to the core. You’ll tone and strengthen the abdominal muscles, especially the internal and external obliques, and target the deep muscles that stabilize the spine. Spinal flexibility also increases as you engage the abdominal muscles through flexion and extension. Author: PilatesonFifth