The phrase "internal obliques" refers to a pair of muscles located inside the abdomen, along the sides of the waist. They help with bending, twisting, and stabilizing the torso. Full definition
Comparing different core isolation exercises, Youdas et al. (2008) measured internal oblique muscle activity during the roll out, bent leg curl up, supine double leg lowering, and side bride. (strengthandconditioningresearch.com)
The fibers of External and Internal Obliques run diagonally on the body, allowing for angled movement. (fitstep.com)
These other abdominal muscles lie over the top of our TA and include our right and left internal obliques, our right and left external obliques, and our rectus abdominus. (hab-it.com)