There are four ab muscles: the rectus abdominis, external oblique, internal oblique, and transverse abdominis. Each has its own unique purpose in the body. The rectus abdominis is the six-pack muscle in the front of the abdomen. On its sides are the oblique muscles, and below all that is your transverse abdominis (you can’t see that muscle).
When you do a crunch, you’re flexing (or rounding) your spine. The rectus abdominis is primarily responsible for that motion. When you twist your spine, such as swinging a tennis racket or baseball bat, your obliques do most of the work. Most of the actions of your core are done by these few muscles.
Crunches are useful for building the rectus abdominis, but your core does much more than flex the spine. Think about all of the sports or activities you do in daily life that involve rotation. Even walking and running require strong obliques to turn your body with each stride.
Go to a boxing class or play a tennis match and you might wake up the next day with sore obliques. These muscles are important but often overlooked. It can be hard to mimic rotation in the gym, but doing crunches and sit-ups are easy.
One exercise we use to train the obliques is called a pallof press. You kneel on the ground and hold a resistance band in front of your body. The band tries to rotate your body, and you have to resist it. This exercise targets the obliques in the same way that a tennis swing does, except you’re preventing rotation rather than producing it.
You can also do this exercise standing or can add rotation as you get more advanced. We start with this more basic position–holding the band still, because we want to get you used to using your obliques first. Not everyone has done a rotational activity like tennis or golf before, and you may not be used to it.
Our goal is to build up your obliques slowly because rotational exercises can be dangerous. They require the spine to rotate, which could be dangerous if you’re not strong enough to keep your spine stable. Once you learn how to resist rotation, then you can produce it. Try going on the tennis court or hitting a golf ball after a few months of these oblique exercises and you’ll see what we mean!