They are the only muscles in the abdominal cage that move in one plane. One of the most basic and easy to understand exercises to keep in your back garden is the oblique crunch.
I am sure the fact that most adults do not consider the oblique crunch a muscle exercise is because they are not aware of their oblique muscles. In fact, they don’t even know that the obliques (especially the more mobile external obliques) are active.
The muscles of the upper abdomen actually become active when you press on the obliques. But the oblique muscles are at the back, in the upper back, and so the oblique is not on the muscles of the waist in any sense other than from the chest down. The obliques have no function on the sides, under the arm pits, in the back, or in the front. What are the risks of carrying an extra stomach? Here, I am not referring to the risks of cancer which have been thoroughly investigated by large groups of scientists in all types of cancers. The body has three types of muscles in the abdominal wall. The external obliques (on the left side) and internal obliques (on the right ) are the only muscles that do not change in size with respiration, the ones we are concerned about here. The muscles of the waist and around the tummy (psoas muscles, lower rectus abdominis, and diaphragm) increase in size as the diaphragm works, which is why people with weak psoas muscles or diaphragm don’t get enough deep breathing.
The obliques work like springs: when you rest, both are relaxed. When you are breathing heavily, the external obliques become weak. This leads them to contract with less power, creating a very tight sensation in your own lower back, which makes you feel as if you’re trying to hold your breath (I know, I know, that’s like one more reason to get lots of deep abdominal breathing). This contraction in the oblique muscles can also come from the diaphragm (also known as the lower internal oblique, or LIO), which helps us keep the rib cage from collapsing. So, it must be a muscle. It has to be. Even if the “muscle” is just a bundle of fibers, it functions like a muscle, just like your heart muscle functions like a muscle.